Recent Studies on Smart Textile-Based Wearable Sweat Sensors for Medical Monitoring: A Systematic Review

Abstract

Smart textile-based wearable sweat sensors have recently received a lot of attention due to their potential for use in personal medical monitoring. They have a variety of desirable qualities, including low cost, easy implementation, stretchability, flexibility, and light weight. Wearable sweat sensors are a potential approach for personalized medical devices because of these features. Moreover, real-time textile-based sweat sensors can easily monitor health by analyzing the sweat produced by the human body. We reviewed the most recent advancements in wearable sweat sensors from the fabrication, materials, and disease detection and monitoring perspectives. To integrate real-time biosensors with electronics and introduce advancements to the field of wearable technology, key chemical constituents of sweat, sweat collection technologies, and concerns of textile substrates are elaborated. Perspectives for building wearable biosensing systems based on sweat are reviewed, as well as the methods and difficulties involved in enhancing wearable sweat-sensing performance.

1. Introduction

Over the years, technology and healthcare have converged significantly, with wearable devices being a prominent phenomenon. These devices have moved beyond their simple function as fitness trackers to sophisticated medical monitors [1]. Wearable sweat sensors based on smart textiles are a unique domain that has emerged from the relentless pursuit of more sophisticated and personalized healthcare services. In the rapidly evolving context of wearable technology in healthcare, continuous monitoring has become indispensable for medical practice [2].

This paper reviews recent studies focusing on smart textile-based wearable sweat sensors, highlighting their advantages over conventional monitoring approaches and their prospects for transforming medical monitoring. The advancement of wearable technology in healthcare has been driven by developments in materials science, sensor technologies, and data analytics [3]. The development of smartwatches and the parade shift from fitness trackers to such health monitoring devices has resulted in innovative tools that seamlessly integrate into individuals’ lifestyles while providing essential information about their well-being [4,5].

Wearable devices have become essential tools for monitoring different physiological parameters providing a large amount of continuous data which has great potential in implementing preventive and proactive medicine [6]. Continuous monitoring is particularly vital for individuals with chronic conditions or those recovering from surgery [5]. Conventional surveillance approaches, typically based on periodic evaluations in clinical settings, fall short in providing a comprehensive and up-to-date view of an individual’s health status [7,8]. Acknowledging this limitation, the industry of healthcare has come to rely heavily on wearable devices that provide continuous monitoring and timely detection of abnormalities for proactive intervention [9,10,11]. This transformation makes it not only better patient care but also encourages individuals to take an active role in managing their health.

Smart textile-based wearable sweat sensors stand out for their ability to utilize the physiological data contained within sweat for medical surveillance [12,13]. Sweat is a very complicated biofluid full of biomarkers, which can give insight into people’s health status by pointing out numerous diseases [14,15]. Smart textiles embedded with sensors allow for continuous and non-invasive sweat collection without disrupting the individual’s life [16,17]. The advantages of such sensors over traditional monitoring methods are manifold [18,19]. Firstly, smart textile-based sweat sensors are non-invasive and eliminate the discomfort and inconvenience associated with traditional methods such as blood sampling [20]. This feature is particularly useful for long-term monitoring, as it contributes to better patient adherence and reducing the risk of complications [21,22].

Moreover, sweat sensors provide both continuous and real-time data, providing a more comprehensive view of the wearer’s health than periodic measurements [23,24]. This is crucial for conditions that undergo dynamic changes, such as blood glucose levels in diabetics or electrolyte imbalances. Additionally, integrating these textiles into everyday clothing increases wearability and user acceptance [25,26]. Smart textiles differ from stand-alone wearable devices in that they can be better integrated into an individual’s wardrobe and encourage the adoption of long-term monitoring regimens [27]. This is particularly important for the elderly or sick, who are often reluctant to adopt new devices.

The future applications of smart textile-based wearable sweat sensors in medical monitoring are promising and encouraging [28]. These sensors can be used to monitor physiological conditions such as diabetes, dehydration, electrolyte imbalances, and metabolic disorders [29]. Furthermore, they have great prospects in fields such as sports medicine, where continuous monitoring of hydration and electrolyte levels could improve performance and prevent complications [14].

This paper highlights the growing field of smart wearable textile-based sweat sensors which mainly focus on the advantages over conventional monitoring systems such as continuous data collection and non-invasiveness. Here, by analyzing the recent updates in the field of materials science and sensor technology, the review emphasizes the potential of the sweat sensors to provide the data for medical monitoring and promote proactive health management. The paper also provides clear visuals for categorizing relevant research based on specific sweat analytes and methodologies, providing a systematic and comparative analysis of the current system. This paper beats the previous research by offering a systematic comparative analysis of textile-based sweat sensors focusing on their types, sensing mechanisms and application area. It integrates advancements in materials science, sensor technology, and data analytics. In addition, it provides an optimistic perspective on potential future uses and performs a fundamental investigation of sweat systems, bringing in the gaps in the current field of research.

The latest wearable sweat sensors based on smart textile signals represent a pivotal moment in medical monitoring. The integration of sensors into day-to-day wearables signifies a paradigm shift in the medical field, offering substantial advantages over traditional monitoring methods. In the future, when proactive, customized health management becomes the norm, wearable healthcare devices will be greatly influenced by the synergy between medical sensors and smart textiles. This research lays the foundation for an investigation of sweating mechanisms to understand the context of textile-based sensor applications in sweat phenomenon monitoring. A detailed analysis of sweat collectors is then initiated, encompassing device and physiological perspectives for the first time in the literature. Next, relevant research publications are categorized based on specific sweat analytes and methodologies to logically organize sweat sensors. Each section includes a thorough comparative analysis that explains the advantages, disadvantages, and potential challenges of the various systems discussed. This provides the reader with a thorough understanding from multiple perspectives.

Novelty: This review provides a comprehensive and systematic analysis of smart textile-based wearable sweat sensors, emphasizing their unique advantages over conventional monitoring methods. By integrating advancements in materials science, sensor technology, and data analytics, this paper highlights the transformative potential of these sensors in personalized healthcare. It also offers a novel perspective by categorizing relevant research based on specific sweat analytes and methodologies, providing a clearer understanding of current technological gaps and future research directions. This approach not only underscores the innovative applications of these sensors in continuous and non-invasive health monitoring but also identifies opportunities for further advancements in the field.

Contributions:

• Systematic Analysis: Provides a detailed and structured examination of textile-based sweat sensors, focusing on their types, sensing mechanisms, and application areas.
• Technical Comparison: Offers a comprehensive comparison of various sensor types, highlighting their strengths, weaknesses, and potential applications.
• Integration of Advancements: Synthesizes recent developments in materials science, sensor technologies, and data analytics to present an updated overview of the field.
• Categorization of Research: Organizes existing research based on specific sweat analytes and methodologies, offering a clear and structured presentation of current knowledge.
• Practical Applications: Discusses real-world applications of smart textile-based sweat sensors in medical monitoring and sports medicine, showcasing their transformative potential.

2. Materials and Methods

For this review, we focused exclusively on papers that discuss sweat sensors that are both textile-based and flexible in nature. Any paper that did not meet these criteria was excluded from consideration. To conduct our search, we used Google Scholar as our database and searched for articles published between 2014 and 1 February 2024, using a variety of keywords such as “sweat sensor”, “textile sweat sensor”, “wearable sweat sensor”, and “diabetes sweat sensor”. Additionally, we used the “allintitle:” filter to refine our results. “sweat” “sensor”, “wearable” “sweat” “sensor”, “diabetes” “sweat” and “sensor” were also used.

A total of 605 records were identified, and based on the selection process described in Figure 1, 35 papers listed in

Table 1. Swear Sensors based on sensor type, sensing mechanism, key features and application summarized from the selected 35 articles.

Sweat Sensors	Type of the Sweat Sensor	Sensing Mechanisms	Key Features	Application	References
Non-invasive sweat sensor detection of sweat pH and lactate	Electrochemical sweat sensor	colorimetric sensing	Detects sweat pH and lactate simultaneously, uses cotton as a substrate	Diabetes management	[31]
Highly Stretchable and Strain-Insensitive sweat sensor	Electrochemical Biosensor	enzyme-based non-invasive sensing	Highly stretchy, strain-insensitive fiber, detects glucose, sensitivity of 11.7 μA mM−1 cm−2		[32]
Thermoresponsive sweat sensor	Optical sensor	colorimetric sensing	Shape memory polymer-modified fabric with a paper-based colorimetric sensor		[33]
Noninvasive flexible sweat sensor	Ion-Selective Electrodes (ISEs)	multiplex sweat analysis	Uses SilkNCT as working electrodes, detects glucose, AA, lactate, UA, K+, and Na+		[34]
Non-invasive simultaneous sweat sensor	Optical sensor	colorimetric sensing	Non-invasive diagnosis of diabetes and renal failure, colorimetric approach		[35]
In Vitro Diagnostics sweat sensor	Microwave sensors	resonance frequency shift of the reflection response of the antenna-based sensor	Textile-embroidered monopole antenna-based sensor, functions at 2.4 GHz		[36]
Non-invasive sweat-based wearable sensor	Electrochemical Sensor	non-invasive cotton-based electrochemical sensing	Fabricated at room temperature, simple immersion method		[37]
Screen-Printed Textile-Based Sweat sensor	Electrochemical Sensor	multiplexed sensing	Fully integrated enzymatic electrochemical sensor, high sensitivity and selectivity for glucose		[38]
Cotton thread/paper-based microfluidic device for sweat glucose sensing	Microfluidic Sensors	non-invasive colorimetric sensing of glucose	Disposable, low-cost		[39]
A sweat-based flexible supercapacitor (SC)	Electrochemical Sensor	chemiresistive sensing	Flexible, energy storage capabilities	Cardiovascular monitoring	[40]
Textile-Based Polyacrylate Imprinted sweat Sensor	Electrochemical Sensor	cortisol sensing	Wearable, stress monitoring		[41]
Extremely Fast Self-Healable sweat sensor	Electrochemical Sensor	ion-selective electrode (ISE) mechanism	Self-healing capability, durable		[42]
Integrated Smart Janus Textile sweat sensor	Noninvasive Electrochemical Sensor	multiple biomarkers including glucose, lactate, K+, and Na+ sensing	Self-pumping, multi-analyte sensing		[43]
Conductive Thread-Based Textile sweat Sensor	Non-intrusive electrochemical sensor	sensing resistance between conductive threads, which changes according to the amount of sweat absorbed by the cotton braids between the threads	Sweat monitoring, low cost	Physical Activity Monitoring	[44]
Smart Textile Integrated Wireless sweat sensor	Electrochemical Sensor	sensing system with temperature and sweat sensors embedded into and powered by a smart textile NFC antenna	Battery-free, real-time monitoring		[45]
Thread-based multiplexed sweat sensor patch	Electrochemical Selective potentiometric Sensor	ion-selective electrode (ISE) sensing	Real-time metabolic tracking		[46]
Graphene-coated textile-based sweat sensor	Electrochemical Sensor developed with nanocomposites	sensing conductivity	Improved skin contact, washable		[47]
A thread/fabric-based band as sweat sensor	Microfluidic sensor	epidermal sweat sensing and detection through a wearable microfluidic thread/fabric-based analytical device	Sweat collection, colorimetric analysis		[48]
Highly Stretchable and Conductive Carbon Thread sweat sensor	Electrochemical Sensor	target biomarkers, sodium ion detecting electrochemical sensing	Stable, sodium ion detection		[49]
A yarn/fabric-based microfluidic patch for sweat sensor	Microfluidic sensor	colorimetric analysis and quantitative analysis of sweat sensing	Flexible, real-time monitoring		[50]
Wearable glucose sensor on cotton fabric for real-time monitoring	Electrochemical Sensor	electrochemical and pH sensing	Real-time glucose monitoring		[37]
A thread-based wearable sweat nanobiosensor	Electrochemical Sensor	ion-selective sensing	High sensitivity, real-time monitoring		[51]
Mediator-free carbon nanotube yarn for sweat sensing	Electrochemical Sensor	enzymatic biofuel cell for direct electron transfer	Energy harvesting, sustainable	Energy Harvesting	[52]
Wearable high-powered biofuel cells for sweat sensing	Electrochemical Sensor	a series connection by tying the enzyme fibers with batik-based ionic isolation to boost the net output voltage and power	High-power output		[53]
Sweat-based wearable energy harvesting-storage sensor	Electrochemical Sensor	relies on lactate, which is oxidized enzymatically to generate electricity	Energy harvesting and storage		[54]
Garment embedded sweat-activated batteries in wearable electronics	Electrochemical Sensor	garment-based microelectronics powered by sweat-activated batteries (SABs) and applications of powering biosensors and microelectronic systems for real time sweat monitoring	Continuous sweat monitoring		[55]
Weavable yarn-shaped supercapacitor in sweat-activated self-charging sweat sensor	Electrochemical Sensor	pH-sensing system	Self-charging, wearable		[56]
Stretchable biofuel cells as wearable textile-based self-powered sensors	Electrochemical Sensor	power output sensing	Stretchable, self-powered		[57]
Wearable strain sweat sensor	Microfluidic Sensors	strain sensing by volume of sweat	Real-time monitoring	Physiological health conditions monitoring	[58]
Ion-selective textile organic sweat transistor	Electrochemical Sensor	ion-selective sensing	High selectivity, wearable		[59]
Wearable Janus Textiles for Sweat sensor	Microfluidic Sensors	ion-selective sensing	Personalized diagnosis	Personalized diagnosis	[60]
Polyacrylate Imprinted Electrochemical Sensor for Cortisol detection	Electrochemical Sensor	conductivity sensing	Stress monitoring		[41]
Sensor for Skin Hydration Monitoring	Electrochemical Sensor	impedance sensing	Skin hydration monitoring	Skin Hydration Monitoring	[61]
Highly Thermal-Wet Comfortable Sweat sensor	Electrochemical Sensor	conductivity and high water-vapor transmission rate sensing	Comfortable, high sweat tolerance	Electrocardiography signal monitoring	[62]
Microfluidic Platform for the Detection of Cytostatic Drug Concentration by sweat sensing	Microfluidic Sensor	conductivity sensing	Drug concentration monitoring	Drug concentration sensing	[63]

were finally selected. Each study had to fulfil the subsequent qualifying requirements: (1) the sweat sensor should be textile-based, (2) the sweat sensor should be flexible, and (3) the report should be in English. If different reports based on the same outcome or information were published, only the first publication was included. However, to justify various statements and to visualize the concept with relevant pictures from published papers, we also included other reference papers, hence the total number of citations came to 262.

3. Results

From the 35 papers collected, we extracted relevant information regarding (1) types of sensors, (2) sensing mechanisms, and (3) applications. All of them are described in this section. An electrochemical sensor is mostly used, and the application area of a sweat sensor mostly occurs in physical activity monitoring. Figure 2 provides a detailed summary organized by sensor type, sensing mechanism, and application. An intensive research direction has been demonstrated on electrochemical sensors [37] and their applications in the field of physical activity monitoring.

3.1. Smart Textile-Based Sweat Sensor Technology and Their Types

Sweat sensors are wearable and flexible devices that are capable of continuously detecting sweat analytes in real time in a non-invasive manner. Furthermore, these sensors can provide a molecular-level understanding of human physiology. Due to these unique capabilities, sweat sensors have garnered significant attention as a potential tool for personalized health monitoring [64]. To monitor and analyze sweat composition in real time, smart textile-based sweat sensing technology incorporates cutting-edge sensor components into fabrics [65,66]. These innovative textiles use a variety of sensing techniques, including enzymatic reactions, colorimetric /fluorometric [34] changes, and ion-selective electrodes [32] to enable continuous monitoring of important biomarkers, for example, lactate, electrolytes, and glucose [29,67]. Stretchable [68] and flexible electronics are often integrated into textile designs to ensure comfort and compatibility with body movement [28]. Furthermore, wearable textile-based sweat sensors provide a practical and non-invasive method for gathering important information about a person’s physiological state that can be used for everything from sports performance optimization to medical diagnostics [12,15,69], allowing for more personalized health monitoring [60] and interventions.

Sweat composition can be continuously monitored thanks to a new class of wearable technology called smart textile-based sweat sensors, which incorporate sensing elements into materials [39]. Typically woven or integrated into textiles worn next to the skin, these sensors provide a non-invasive means to collect physiological data in real time [70,71]. To identify specific ions, metabolites, or biomolecules present in sweat, the textile-based sweat sensor can use a variety of sensing techniques, including ion-selective electrodes, enzymatic reactions, or colorimetric/fluorometric changes [72]. Advantages such as comfort, stretchability [32], and flexibility make this technology suitable for a diverse array of applications, including personalized health management, sports performance monitoring, and medical diagnostics [73]. Smart textile-based sweat sensors are an important addition to the growing field of wearable and personalized health technology, as they provide insightful data regarding an individual’s health and well-being. Figure 3 summarizes the timeline of research on textile-based wearable sweat sensors and the stages of development.

Smart textile-based wearable sweat sensors come in several types, each using different technologies and materials to achieve specific functionalities. Some common types include electrochemical sensors, biosensors, optical sensors, and microfluidic sensors [50].

Electrochemical sweat sensors [31] are becoming a common tool in sports science, personalized medicine, and health monitoring [73]. They are a highly innovative technology. These sensors use the unique composition of sweat to provide non-invasive, real-time information about a person’s physiological state [15]. To create durable, wearable devices, advancing these sensors requires integrating cutting-edge materials, including conductive polymers, flexible substrates, and nanomaterials [74]. Through electrochemical processes, these sensors identify different types of biomarkers in sweat, such as specific ions [51], metabolites, and electrolytes [23]. Their applications range from monitoring electrolyte and hydration levels in athletes to tracking glucose and lactate levels in diabetics and others engaged in strenuous physical activity. Electrochemical sweat sensors [38] are particularly promising as tools for individualized diagnostics and continuous health monitoring due to their versatility and ease of integration into wearable platforms.

Sweat sensors, also known as biosensors, have made great strides, with a broad variety of applications and a variety of materials being used [27]. These sensors provide important information about a person’s performance and overall health by identifying different proteins and ions in sweat [12]. Sweat biosensors have been developed in response to the growing need for real-time, non-invasive health monitoring. To improve sensitivity and selectivity in identifying specific analytes, these sensors often use substances such as conductive polymers, enzymes, nanoparticles, and sophisticated nanomaterials [75]. Applications for continuous observation and early diagnosis of various health disorders are provided by applications that cover a wide variety of industries, including sports science, healthcare, and personalized medicine [76]. The incorporation of these sensors into wearable technology has further enhanced their usefulness, promoting the advancement of preventive and personalized healthcare strategies.

Recent major developments in sweat and optical sensors [35] are used in a wide range of industries. Cutting-edge technologies such as nanotechnology and microfabrication are used to construct these sensors and produce highly functional, compact devices [77]. Optical sensors provide non-invasive, real-time monitoring [58] capabilities by detecting and quantifying changes in target parameters using light-based principles [78]. Conversely, sweat sensors are essential for sports and health applications because they can identify biomarkers of physiological states by evaluating the composition of sweat [79]. The materials of these sensors, which provide increased sensitivity and selectivity, include functionalized substrates, nanomaterials, and biocompatible polymers [80]. These sensors are demonstrating their potential to completely change the way we monitor and understand human health by finding applications in the fields of personalized medicine, fitness tracking, and disease identification in healthcare.

Microfluidic sweat sensors [39] are new and versatile technologies in the fields of sports science, personalized medicine, and health monitoring [81]. The precise and controlled manipulation of small amounts of sweat is enabled using microfluidic channels in the construction of these sensors [82]. These devices enable non-invasive, real-time monitoring of sweat biomarkers, including glucose [37], lactate, and electrolytes, which provide significant insights regarding an individual’s physiological status [83]. The components of microfluidic sweat sensors [48] consist of biocompatible polymers and state-of-the-art microfabrication techniques that enable the creation of small, flexible devices that conform to the skin [84]. These sensors have the potential to completely transform healthcare and wellness by providing easy, continuous monitoring of sweat biomarkers. They have been applied to disease detection, performance optimization, and fitness tracking.

Table 2. Types of Smart Textile-Based Wearable Sweat Sensors are summarized based on the description of key technology methodology and application.

Sensor Type	Description	Key Technologies and Materials	Methodology	Applications and Advancements
Electrochemical Sensors	Highly innovative sensors providing non-invasive, real-time information about a person’s physiological state through the unique composition of sweat	- Conductive polymers	Utilize electrochemical reactions	Health monitoring [85]
		- Flexible substrates	Incorporate flexible substrates, conductive polymers, and nanomaterials	Personalized medicine [86]
		- Nanomaterials	Detect biomarkers in sweat (electrolytes, metabolites, specific ions)	Monitoring hydration levels and electrolyte balance in athletes [87]
				Tracking glucose and lactate concentrations for diabetes and intense physical activities [88]
				Continuous health monitoring and personalized diagnostics [89]
Biosensors	Provide important information about an individual’s performance and overall health by identifying different proteins and ions in sweat	- Conductive polymers	Employ diverse materials such as conductive polymers, enzymes, nanoparticles, and advanced nanomaterials	Non-invasive health monitoring [90]
		- Enzymes		Real-time insights into health and performance [91]
		- Nanoparticles	Detect biomolecules and ions in sweat	Applications in sports science, healthcare, and personalized medicine [92]
		- Sophisticated nanomaterials
				Wearable integration enhances utility for continuous monitoring and early detection of health conditions [93]
Optical Sensors	Employ cutting-edge technologies like nanotechnology and microfabrication to produce compact devices for non-invasive, real-time monitoring	- Functionalized substrates	Utilize light-based principles	Non-invasive monitoring capabilities [94]
		- Nanomaterials	Employ microfabrication and nanotechnology	Applications in disease diagnosis, fitness monitoring, and personalized medicine [95]
		- Biocompatible polymers	Detect and quantify changes in target parameters	Revolutionizing tracking and understanding of human health [96]
Microfluidic Sensors	Enable precise and controlled manipulation of small amounts of sweat using microfluidic channels, allowing for non-invasive, real-time monitoring of sweat biomarkers	- Biocompatible polymers	Utilize microfluidic channels	Non-invasive, real-time monitoring of biomarkers in sweat [97]
		- State-of-the-art microfabrication techniques	Manipulate small volumes of sweat	Applications in fitness tracking, disease diagnosis, and performance optimization [98]
			Use biocompatible polymers and advanced microfabrication techniques	Potential to revolutionize healthcare through continuous and convenient monitoring of relevant biomarkers in sweat [81]

provides a comprehensive overview of the sensors, including the key technology methodology and the specific application area they are designed for. This summary provides a useful reference for understanding each sensor type’s capabilities and limitations.

3.2. Working Procedure of Sweat Sensors

The sensing mechanism of textile-based sweat sensors involves the integration of specialized materials and technologies within the fabric to detect and quantify various biomarkers present in sweat [99]. Typically, these sensors utilize microfluidic channels, conductive textiles [44], or other sensing elements embedded in the fabric [28]. The textile substrate is a platform for efficient sweat collection and transport, ensuring close contact with the skin [100]. In some cases, functionalized materials or coatings are used to increase selectivity and sensitivity for specific analytes [101]. Upon contact with sweat, the sensor undergoes a change in its electrical, optical, or chemical properties, which are then measured and translated into quantifiable data. This information can be wirelessly transmitted [45] to external devices for real-time monitoring and analysis [102]. The textile-based design allows for flexibility, comfort, and non-invasiveness, making it suitable for continuous and unobtrusive health monitoring in various applications such as fitness, healthcare, and sports [20]. Figure 4 summarizes the working process of textile-based sweat sensors. This section discusses the different sensing methods, sensing material, miniaturization, and integration of textile-based sweat sensors.

3.2.1. Sensing Mechanisms

Textile-based sweat sensors use various sensing mechanisms to detect and monitor changes in sweat composition [72]. These sensors typically incorporate materials that can respond to specific ions, metabolites, or biomolecules present in sweat [24]. Common sensing mechanisms include ion-selective electrodes, enzymatic reactions, and colorimetric or fluorometric changes in response to target analytes [103]. Ion-selective electrodes selectively respond to specific ions in sweat, while enzymatic reactions involve the catalysis of specific molecules by enzymes immobilized on the textile substrate [104]. Colorimetric [33] or fluorometric changes can be induced by the interaction between sweat components and chemical indicators, producing measurable signals [105]. Integrating these mechanisms into textile-based sensors allows non-invasive, continuous observation of physiological parameters, providing significant insights into an individual’s health and performance.

Table 3. Summary of several sensing mechanisms, their applications, and the materials used.

Sensing Mechanism	Materials Used	Applications and Advantages
Ion-Selective Electrodes	Materials reactive to specific ions	Selective response to specific ions in sweat [106]
		Non-invasive, continuous monitoring of ion concentrations [107]
		Valuable insights into electrolyte balance [108]
		Monitoring hydration levels [109]
Enzymatic Reactions	Enzymes immobilized on textile substrate	Catalysis of specific molecules in sweat [110]
		Non-invasive, continuous monitoring of metabolites [111]
		Provides insights into specific physiological processes [112]
		Potential for personalized health monitoring [113]
Colorimetric/Fluorometric Changes	Chemical indicators reacting with sweat components	Induction of measurable changes in color or fluorescence [114]
		Non-invasive, continuous monitoring of biomolecules [115]
		Real-time insights into changes in sweat composition [116]
		Versatile application in health and performance tracking [117]
Integration into Textile-based Sensors	Flexible substrates	Non-invasive monitoring of physiological parameters [29]
	Conductive materials	Continuous tracking of health and performance [118]
	Materials reactive to target analytes	Wearable technology for convenience and ease of use [28]
		Real-time data for personalized health insights [119]

is a valuable resource that offers a detailed and comprehensive overview of the diverse sensing mechanisms currently utilized in various fields. The table includes thorough information on the materials utilized in these sensing mechanisms and the specific application areas they are designed for. By providing this level of detail, Table 3 can serve as a vital tool for anyone seeking to understand the intricacies of sensor technology and its various applications.

Among the various sensing mechanisms, there are three popular sensing mechanisms named the chemical-based sensing mechanism, the biochemical sensing mechanism, and the physical sensing mechanism.

Chemical-based sensing in textile-based sweat sensors involves the incorporation of specific chemical receptors or indicators into the fabric to selectively respond to target biomolecules present in sweat [120]. These chemical elements may include molecular recognition elements such as enzymes, antibodies, or other functionalized compounds designed to interact with and detect analytes [121]. Upon contact with sweat, these chemical receptors induce measurable changes in the characteristics of the sensor, such as conductivity [41], fluorescence, or color, reflecting the concentration of the target biomarkers [14]. The textile substrate facilitates efficient sweat absorption and ensures intimate contact with the skin [61], enabling accurate and real-time monitoring [122]. This chemically based approach provides a tailored and sensitive detection method, allowing for the customization of sensors to target specific analytes of interest, making textile-based sweat sensors versatile tools for health monitoring and diagnostics. In addition, wearable electrochemical sensors made from molecularly imprinted polymers (MIPs) and textiles have been developed for the detection of cortisol in human sweat, highlighting the possibility of biomarker detection [123]. A sweat volume monitoring sensor is developed utilizing the insertion method, which utilizes an ultra-hydrophilic hydrogel and a strain-sensing textile [124]. Furthermore, prototype multi-sensing systems utilizing functionalized textiles have been reported in recent years, and chemical textile-based sensors have been demonstrated to monitor numerous sweat characteristics [125]. It has also been shown that microelectronic fibers can be successfully used in textile forms for multiplexed sweat sensing [126]. An electrochemical fabric system based on a core–sheath sensing yarn has been developed for robust sweat collection and consistent sensing [127]. These developments demonstrate the potential of textile-based sensors to collect, and process sweat for a range of applications.

Biochemical sensing in textile-based sweat sensors involves the incorporation of specialized materials and technologies into the fabric to detect and analyze specific biochemical constituents present in sweat [17]. These sensors exploit the unique properties of bio-responsive elements, such as enzymes or antibodies, incorporated into the textile substrate. Upon contact with sweat, these elements undergo specific interactions with target biomolecules, resulting in measurable changes in electrical conductivity, optical properties, or chemical signals [128]. The detection mechanism is highly selective, allowing for the identification and quantification of specific analytes such as glucose, lactate or ions. The textile-based format enhances comfort and wearability, enabling non-invasive and continuous monitoring of biochemical markers for health and performance tracking applications. This innovative approach holds promise for personalized health monitoring, disease management, and sports performance optimization. The use of flexible and composite materials in textile-based sensors has improved their flexibility and sensing performance, enabling comfortable [62] and reliable long-term wear. In addition, the incorporation of microfluidic systems in textile-based sensors has enabled precise sweat sampling and analysis, expanding the repertoire of detectable biochemicals in sweat [126]. In addition, the advancement of textile-based sensors has led to the development of novel sweat sampling interfaces that facilitate in situ sweat detection and iontophoresis for sweat stimulation. Examples of these interfaces include smart Janus textile armbands and temporary tattoo-based biosensors [43,129]. The development of self-pumping [43] sweat sampling interfaces because of these findings has enabled continuous monitoring with constant sensing and effective sweat collection [127]. In addition, the integration of textile-based sensors with biofuel cells has enabled self-powered sensing capabilities [57], increasing the possibility of long-term and sustainable use [57]. Textile-based sensors are suitable for a variety of health and fitness applications, as they demonstrate the ability to monitor a wide variety of biomarkers, such as glucose, cortisol [41], and various ions. In addition, the flexible and strain-insensitive nature of fiber-based wearable electrochemical biosensors [59], even under challenging conditions such as high strain, demonstrates the potential for wearable biochemical diagnostics for real-world applications utilizing human sweat [32].

The physical sensing mechanism of a textile-based sweat sensor involves the integration of specialized materials and structures within the fabric to detect and respond to physical changes associated with sweat [130]. Typically, conductive textiles or other sensing elements embedded in the fabric undergo changes in electrical conductivity, resistance, or other physical properties when exposed to sweat [131]. This change serves as a measurable signal indicating the presence and amount of specific biomarkers in the sweat. The textile substrate facilitates efficient sweat collection and ensures close contact with the skin, which enhances the sensitivity and responsiveness of the sensor. The physical changes induced by sweat on the sensor are then translated into quantifiable data, enabling real-time monitoring and analysis of relevant physiological information. This method enables wearable textile-based sweat sensors to be used in a variety of applications to continuously measure health parameters in a comfortable, non-invasive, and adaptable way. Physical sensing in conductive textiles relies on various factors. Among them resistance and capacitance are the two major factors. These parameters are fundamental in understanding the sensing mechanisms and performance of textile-based sweat sensors. The resistance R of a conductive textile can be determined using Ohm’s law,

$$\mathrm{R}=\frac{\rho \mathrm{L}}{\mathrm{A}}$$

where ρ is the resistivity of the material, L is the length of the conductive path, and A is the cross-sectional area of the conductive path. In the context of sweat sensors, the resistance of the textile may change due to the absorption of sweat, which can alter the electrical properties of the material. The change in resistance ΔR can be used as a measurable signal [132],

ΔR = R_wet − R_dry

where R_wet is the resistance when the textile is wet with sweat and R_dry is the resistance when the textile is dry.

The capacitance C of a conductive textile sensor can be modeled as a parallel plate capacitor,

$$\mathrm{C}=\frac{{ϵ}_r{ϵ}_0\mathrm{A}}{\mathrm{d}}$$

where ϵ_r is the relative permittivity of the dielectric material (sweat in this case), ϵ₀ is the vacuum permittivity, A is the area of the plates (conductive textile layers), and d is the distance between the plates [33]. Sweat, acting as a dielectric, changes the capacitance of sensor ΔC and can be used as a measurable signal:

ΔC = C_wet − C_dry

where C_wet is the capacitance when the textile is wet and C_dry is the capacitance when the textile is dry.

Finally, each mechanism has its own advantage and disadvantage. For real-time sweat monitoring, textile chemical sensors made from conductive polymers have been investigated, addressing issues of multiplexed analysis and sensor calibration [133]. The review also highlights the fiber/textile-based sweat sensors’ better flexibility, emphasizing their potential for long-term, comfortable usage. Moreover, the use of 3D graphene oxide–CNT composites in extremely flexible electrochemical sensor detection has been addressed by the wearable, textile-based polyacrylate imprinted electrochemical sensor for cortisol detection in human perspiration, which has shown promise for targeted biomarker monitoring [134]. However, problems have been identified with textile-based sensors, including large diameters, low conductivity, and suboptimal electrochemical performance. These issues highlight the need for further improvements in manufacturing techniques and sensor stability [135].

Comparison of sweat sensors with thin-film and textile substrates has shed light on the efficacy and usability of different sensor types for sweat monitoring applications. In addition, the creation of a textile-based sweat monitor on cotton garments using recycled sericin and screen-printed carbon black has demonstrated the potential for affordable and sustainable sensor development [136]. The development of self-healing [42] sweat sensing systems integrated with wireless transmission technology has shown promise for seamless and continuous sweat monitoring [55], addressing the need for reliable and long-term sensor wear [137]. In addition, the incorporation of machine learning for predictive health assessment into textile-based sweat sensors has enhanced their capabilities, as has the integration of satellite-based sensors for environmental heat stress sweat creatinine monitoring [43]. In addition, the incorporation of machine learning for predictive health assessment into textile-based sweat sensors has increased their capabilities, as has the integration of satellite-based sensors for detecting ambient heat stress sweat levels of creatinine [33].

3.2.2. Materials Used in a Textile-Based Sweat Sensor

Textile-based sweat sensors use a variety of materials to achieve efficient sensing capabilities while ensuring comfort and flexibility [138]. The substrate material often consists of textiles with good breathability and skin compatibility, such as cotton or polyester [139]. Embedded in the fabric, conductive materials, for example, silver nanoparticles, graphene, or conductive polymers, are used to form electrodes or sensing elements that facilitate the measurement of electrical changes in response to sweat [131]. Microfluidic channels made of soft and biocompatible polymers allow for effective sweat transport and collection. In addition, functional coatings or materials with specific affinity for target biomarkers, such as enzymes or molecularly imprinted polymers, can be incorporated for enhanced selectivity [24]. Together, these materials contribute to the sensor’s ability to reliably capture, detect, and analyze sweat-borne analytes. The integration of these different materials allows textile-based sweat sensors to provide a comfortable, non-intrusive means of continuous health monitoring.

The exploration of natural materials such as cellulose, silk, and chitosan (CS) for sweat sensors is motivated by their common attributes of comfort, breathability, flexibility, harmlessness, and sustainability [140]. Cellulose, as a renewable resource, is extensively used in various textile sensor forms such as fabric and yarn, and it contributes to effective sweat collection and transport [141]. Silk fibroin (SF) and CS are utilized for modifying electrodes due to their distinctive properties, which enhance enzyme immobilization and sensor sensitivity [142]. Flexible and conductive functional materials, categorized as polyurethane [143], poly(styrene-ethylene-butadiene-styrene) (SEBS) [144], polyethylene terephthalate (PET) [145], polyimide (PI) [122], and others, are often chosen as substrates for sweat sensors. Conventional conductive materials such as poly(3,4-ethylenedioxythiophene) (PEDOT) [146], polyaniline (PANI) [147], metals (Au, Ag, Cu), metal oxides (ZnO) [148], and carbon serve as electrodes. Microstructures such as quantum dots (QDs) [149], nanoparticles (NPs) [72], nanowires (NWs) [150], nanorods (NRs) [17], and nanotubes (NTs) [151] enhance sensor sensitivity. Metallic microstructure materials such as Au, Ag, and ZnO offer high electrical conductivity and antibacterial properties when integrated into wearable textiles, further increasing the flexibility and application range of these sensors through hybrid fabrication processes. In this section, the materials for textile sweat sensors are briefly discussed.

Table 4. Materials used in textile-based sweat sensors are summarized based on material type, application, and characteristics.

Material Type	Application	Characteristics
Natural Materials	Sweat collection and transport	Comfortable, breathable, flexible, unharmful, sustainable, e.g., cellulose, silk fibroin (SF), chitosan (CS) [13]
Flexible Substrates	Base substrate for sweat sensors	Compatible with human skin and perform well during daily activities, such as poly(styrene–ethylene–butadiene–styrene) (SEBS) and polyurethane (PU) [152]
Conventional Conductive Materials	Electrodes	High conductivity materials include carbon, metals (Au, Cu, Ag), metallic oxides (ZnO), poly(3,4-ethylenedioxythiophene) (PEDOT), and polyaniline (PANI) [153]
Microstructural Forms (QDs, NPs, NWs, NRs, NTs)	Electrodes	Larger specific surface area, improved sensitivity, e.g., carbon quantum dots (CQDs), graphene (Gr)-based materials, metal NRs [154]
Metallic Microstructural Materials (Au, Ag, ZnO, etc.)	Integration into textiles	High electrical conductivity and antibacterial properties, e.g., Au nanodendrites, ZnO nanorods [155]

offers a detailed summary of the various material types employed in sensors, highlighting the properties of the material and its application area. This summary serves as a valuable resource for understanding the strengths and limitations of each sensor material type.

3.2.3. Miniaturization and Integration

Nanotechnology in Sweat Sensor Development

Nanotechnology has significantly advanced the development of textile-based sweat sensors, revolutionizing the capabilities of these devices for real-time health observation [156]. The integration of nanomaterials into textile sensors enhances their sensitivity, selectivity, and overall performance [157]. Nanoparticles such as quantum dots, nanowires, nano catalysts [158] and nanotubes provide increased surface area and facilitate efficient interactions with sweat components, resulting in improved sensor responsiveness. Nanocomposites [47] incorporating materials such as carbon nanotubes and graphene contribute to improved electrical conductivity and durability, which are critical for sensor reliability [159]. In addition, nanotechnology enables the functionalization of textiles with specific properties, such as hydrophobic or antibacterial properties, to optimize sweat absorption and reduce potential skin irritation [160]. The application of nanotechnology in textile-based sweat sensors not only enhances their analytical capabilities but also ensures comfort, flexibility, and biocompatibility, marking a potential step towards the realization of advanced and user-friendly wearable health monitoring technologies.

Integration of Multiple Sensors for Comprehensive Monitoring

The integration of multiple textile-based sweat sensors represents a holistic approach to comprehensive monitoring, providing a nuanced understanding of different physiological parameters [161]. By combining sensors designed to detect different biomarkers or physiological signals such as glucose, lactate, electrolytes, and temperature, an individual’s health status can be evaluated more comprehensively and precisely [14]. These integrated systems offer a synergistic advantage, allowing for the correlation of multiple data points to derive meaningful insights into overall well-being and performance [162]. In addition, the application of various types of sensors, each specialized for specific analytes, increases the specificity and sensitivity of the monitoring system. The seamless integration of these sensors into a single wearable platform ensures user comfort and enables continuous and unobtrusive monitoring in real-world scenarios. This holistic approach has great potential for applications in sports science, healthcare, and personalized wellness, facilitating the transition to an era of personalized and uninterrupted health monitoring.

3.3. Application

Textile-based sweat sensors are utilized in various health monitoring applications due to their continuous and non-invasive nature to collecting valuable physiological information [15]. These sensors are particularly useful in sports science, allowing for athletes to monitor hydration levels, electrolyte balance, and metabolic markers [46] in real time, helping to optimize performance and prevent injury [163]. In healthcare, textile-based sweat sensors have promising applications in monitoring chronic diseases such as diabetes by non-invasively measuring glucose levels. They also contribute to personalized medicine by providing continuous data on an individual’s health, facilitating early detection of abnormalities, and supporting preventive health measures [34]. The comfort and wearability of textile sensors make them suitable for everyday use, enabling long-term health tracking in diverse environments. As these sensors evolve, their integration into smart clothing and wearable devices has the potential to revolutionize remote patient monitoring and promote a proactive and personalized approach to healthcare management.

3.3.1. Disease Diagnosis and Management

Textile-based sweat sensors have emerged as promising tools for disease diagnosis and management due to their non-invasive and continuous monitoring capabilities [164]. These sensors are integrated into fabrics, allowing for comfortable and discreet wear while providing real-time data on biomarkers present in sweat [162]. Analysis of sweat composition, including metabolites, electrolytes, and specific proteins, provides valuable insight into various health conditions such as diabetes, dehydration, and cardiovascular disease [15]. These textile sensors continuously monitor physiological changes, enabling early detection of proactive disease management and personalized healthcare interventions [165]. The convenience, accessibility, and accuracy of textile-based sweat sensors make them key to advancing the field of wearable health technology and potentially revolutionizing the way diseases are diagnosed and managed.

Diabetes Management

Textile-based sweat sensors for diabetes diagnosis have emerged as a viable approach to non-invasive and continuous glucose monitoring. These sensors, which are embedded into fabric materials, allow for the real-time collection of perspiration, providing valuable glucose concentration information. These sensors provide pleasant and wearable solutions for diabetics by taking advantage of particular features of textiles such as flexibility and breathability. Textile-based sweat sensors typically use advanced materials and cutting-edge technology to measure glucose levels properly. This breakthrough has the potential to significantly improve the standards of life for diabetics by offering a simple and unobtrusive approach to monitor their glucose levels, minimizing necessity for standard blood-based testing methods. Ongoing research and development in this field aims for improvements in the sensitivity, reliability, and integration of textile-based sensors into everyday clothing, allowing for seamless and continuous health monitoring for diabetes management. This section provides a quick overview of the study into diabetes management in the human body utilizing textile-based sweat sensors.

In 2018, Promphet, Nadtinan et al. developed a colorimetric sensor based on textiles that was invented to detect sweat pH and lactate simultaneously. The research centers on the advancement of chemical sensors that can be worn, with particular emphasis on textile-based substrates. The choice of textile substrates, especially cotton, is highlighted due to its biocompatibility, comfort, flexibility and cost-effectiveness. Sweat as a transparent biological fluid is identified as a valuable source for monitoring various biomarkers indicative of cystic fibrosis, hydration status, bone mineral loss, physical stress, and performance assessment in endurance sports. The research addresses the gap in real-time monitoring of sweat pH and lactate levels, which are critical indicators of sweat rate, dehydration, and anaerobic metabolism (Figure 5a). The proposed textile-based sensors utilize colorimetric techniques, which offer advantages such as simplicity, affordability, and ease of signal interpretation. The study concludes by demonstrating the feasibility of these sensors through testing on human volunteers, highlighting the potential applications in personalized health monitoring such as diabetes management and athletic performance assessment [31]. In addition, researchers are working on the stretchability of textile-based sweat sensors.

In 2019, Zhao, Yunmeng, and colleagues created a wearable electrochemical biosensor based on a highly stretchy and strain-insensitive fiber. In this article, the authors discuss the increased interest in wearable sensors for continuous health monitoring, with a focus on glucose sensing due to its significance in diabetes management. Non-invasive sweat glucose monitoring is investigated to minimize the discomfort associated with standard blood glucose monitoring (Figure 5b). The challenge is to create stretchable glucose biosensors for wearable applications. The authors suggest a unique technique in the form of a stretchy three-electrode electrochemical bio sensing platform made entirely of gold fiber. Gold nanoparticles, which are known for their biocompatibility and immense surface area, are employed in electrode fabrication. To preserve the inherent flexibility of gold threads, either Ag/AgCl or Prussian blue is utilized. The working electrode is constructed of fibers treated with PB and glucose oxidase (GOx), whereas the reference electrode is made of a fiber treated with Au/AgCl. These beneficial fibers have elastic cores wrapped around them. They function exceptionally well with electricity, even when stretched up to 200%. The biosensor detects glucose with a sensitivity of 11.7 μA mM⁻¹ cm⁻², making it suitable for wearable biodiagnostics. This work highlights a research need by identifying no previously published stretchable enzyme-based fiber or textile glucose sensors. This demonstrates how novel the study is in that it addresses the challenges of developing fiber sensors that are highly stretchy, conductive, and strain-insensitive for wearable applications [32].

The convergence of electronics, materials chemistry, and biological science has received a lot of attention in the rapidly expanding field of wearable technology because it might be utilized in novel ways to track movements, monitor health, and detect diseases. A lot of work has been conducted for the development of wearable sensors that can investigate chemicals in biofluids in real time. Many people use sweat for this purpose because it is easy to collect and inflicts not harm. Many flexible and biocompatible materials have been employed to create wearable sweat sensors, including colorimetric sensors based on tattoos and fabrics. However, more research is needed to determine ways to improve these systems so that chemical reagents do not touch people’s skin. In 2019, He, Jing et al. developed a thermoresponsive microfluidic device. This technology combined a shape memory polymer-modified fabric with a paper-based colorimetric sensor. Shape memory polymers (SMPs) are utilized in microfluidic textile-based analytical devices to detect glucose, hydrogen peroxide, lactate, and proteins utilizing sophisticated techniques. This article discusses how polyurethane (PU), a biocompatible and thermosensitive polymer, can be used to modify cotton cloth to create a textile-based microfluidic system that responds to temperature changes (Figure 5c). The gadget uses a paper-based glucose colorimetric sensor, which shows promise for sweat monitoring in hot environments. This procedure avoids the issues that arise with having direct contact with skin. This study contributes to the body of research on new materials and technologies that can improve the utility of wearable sweat sensors in real-world applications, such as diabetes monitoring [33].

In 2019, He, Wenya et al. developed an integrated textile sensor patch for real-time and multiplexed sweat analysis that focuses on addressing challenges in wearable electrochemical sweat analysis devices, highlighting the need for improved sensitivity, selectivity, and simplicity in fabrication. The researchers explore the use of silk-derived carbon textiles, specifically intrinsically nitrogen-doped carbon textiles (SilkNCTs), as novel and promising materials for working electrodes in electrochemical sensors. SilkNCTs exhibit high electrical conductivity, a hierarchical woven structure, and intrinsic nitrogen doping, making them suitable for efficient electron transfer and good contact with reactants (Figure 5d). The team develops a flexible, wearable patch integrated with a SilkNCT-based sensor array using a low-cost laser processing strategy. This patch detects six biomarkers in sweat simultaneously: glucose, AA, lactate, UA, K+, and Na+. It can accomplish this in a highly selective, sensitive, and consistent manner across time. The inserted patch also allows for the simultaneous and real-time tracking of multiple bodily indicators, demonstrating its potential for personalized healthcare. The work addresses a research need by proposing SilkNCTs, a novel material for wearable electrochemical sensors. Furthermore, it demonstrates a good technique to create integrated sweat analysis devices, which are useful for detecting and treating disorders such as diabetes [34].

Current research focuses on developing a cutting-edge sensor platform that is easy to wear and does not require any intrusive procedures. The goal is to reduce the discomfort and potential hazards associated with standard diagnostic procedures. Numerous studies have been conducted into various designs for wearable sensors, including spectacles, bracelets, and tattoos. These designs prioritize lightweight, flexible, and biocompatible substrates. Promphet, Nadtinan et al. developed a cotton thread-based wearable sensor in 2020. This sensor allows for the non-invasive diagnosis of both diabetes and renal failure. The study highlights textiles, notably cotton cloth and cotton thread, as attractive substrates due to their small size, great flexibility, and low cost. The research explores sweat as a valuable biological fluid for non-invasive analysis, containing biomarkers such as glucose and urea, which are crucial for indicating diabetes and kidney status (Figure 6a). Simultaneous monitoring of glucose and urea is proposed to streamline clinical analysis, particularly for individuals with diabetes who are at risk of complications. The work employs a colorimetric approach, which is simple to use and inexpensive, to develop a thread-based portable sensor capable of measuring both glucose and urea in human sweat simultaneously. The new technology is marketed as a blood-free wearable sensor that can be integrated into clothing or applied directly to the skin to monitor patient health at all times. While the research presents advances in the field, potential research gaps may include further validation of the sensor’s accuracy, long-term wearability, and integration into real-world healthcare settings [35]. The study addresses the growing global health concern of diabetes mellitus (DM), emphasizing its prevalence and associated complications such as stroke, renal failure, myocardial infarction, and peripheral arterial disease.

With the global prevalence of diabetes increasing, it is critical to monitor blood glucose levels closely. Several approaches, including Raman spectroscopy, electrochemistry, reverse iontophoresis, and optical methods, have been investigated for monitoring glucose levels. Gharbi, Mariam El et al. developed a fabric antenna sensor in 2021 that can be used to test for diabetes in vitro. The study concludes that microwave sensing [36] is a viable technology since it can be made smaller, is simple to use, inexpensive, and responds rapidly. Antennas as sensors have gained attention, with previous studies demonstrating their effectiveness in monitoring blood glucose levels. However, existing devices have used conventional rigid substrates, limiting their suitability for electronic textile applications (Figure 6b). The current study describes a textile-embroidered monopole antenna-based sensor designed to function at 2.4 GHz. The breakthrough is in the use of wearable electronic textiles, which provide benefits such as lightness, comfort, and adaptability to rapidly changing computing and sensing circumstances. The article describes the antenna–sensor design technique, including the creation of blood-mimicking aqueous solutions, and offers findings for three diabetic situations. The report finishes with a comparison of various strategies for measuring glucose concentrations with microwave sensors, as well as recommendations for future research in this subject rapidly gaining interest [36]. The key research need addressed is the creation of a stretchable electrochemical and skin-attachable sensor based on nanomaterials that detects glucose in human perspiration.

Singh, Anoop et al. desired a human sweat-based wearable glucose sensor on cotton fabric for real-time monitoring by 2022. The study tackles the critical need for a non-invasive and cost-effective glucose monitoring system to overcome the limits of standard blood glucose meters, especially in light of the global increase in diabetes incidence. It investigates wearable sensors, highlighting the significance of substrates that are elastic, flexible, biocompatible, and comfortable to human skin (Figure 6c). In particular, the focus is on textile substrates, considering their potential for non-invasive sensor fabrication. The electrochemical sensors, especially those that detect physiological components in sweat, are highlighted for their non-invasive nature and ease of measurement. The study presents a novel approach by fabricating an electrode at room temperature using a simple immersion method, avoiding complex processes such as photolithography and chemical vapor deposition. The sensor is designed to be applied directly to human skin, providing stability and sensitivity for continuous glucose monitoring during various activities. The goal is to create a non-invasive, cotton-based, wearable electrochemical sensor for long-term personal physiological glucose monitoring, a potential breakthrough in diabetes management [37].

Most recently, in 2023, Khosravi, Safoora et al. created a screen-printed textile-based electrochemical biosensor for noninvasive glucose monitoring in sweat. This study focuses on the creation of a fully integrated enzymatic electrochemical sensor for noninvasive glucose detection in sweat, which will solve the limitations of current glucose monitoring technologies. The proposal exploits the abundance of biologically relevant substances in sweat, including glucose, to provide a non-invasive alternative for diabetes management. The study explores innovative wearable glucose monitoring platforms, with a particular focus on textile-based designs for their lightweight, breathable, and comfortable features. The fabrication process involves low-cost screen printing on flexible textiles, using carbon and silver paste for electrode construction. The textile-based sensor demonstrates high sensitivity and selectivity for glucose in mimicking human sweat, highlighting the potential for direct integration into everyday clothing for continuous biomarker measurements (Figure 6d). Despite the progress made, the study identifies a research gap in the current limitations of existing yarn and fiber-based sensors and suggests further exploration for improved softness and robustness, potentially improving electrode geometry and substrates for broader commercial availability. In addition, the study highlights the advantages of screen-printed sensors, which offer scalability, cost-effectiveness, and the ability to design complex sensor shapes, making them suitable for industrial applications and mass production in the field of wearable health technology [38].

Cardiac Disease Diagnosis and Management

The use of textile-based sweat sensors offers significant potential for identifying and treating heart disease. The sensors’ adaptive and pleasant properties allow for continuous monitoring of sweat biomarkers associated with cardiovascular health. The research conducts a thorough investigation of flexible sweat sensors manufactured from fiber and textile materials. It describes their functionality and prospective applications for monitoring cardiovascular health and physical conditions [99]. Textile-based sweat sensors show great promise in the detection and treatment of heart disease. One advantage of these sensors is their ability to provide comfort and flexibility, allowing for continuous monitoring of sweat biomarkers associated with cardiovascular health. The article presents an in-depth look at flexible sweat sensors made from fibers or fabrics. It describes how these sensors function and discusses their potential applications in monitoring cardiovascular health and physical condition [166]. Furthermore, the use of conductive PEDOT:PSS-coated fabric in conjunction with sweat electrolytes in wearable supercapacitors enables the construction of self-powered fabric-based sensors for monitoring sweat salinity.

Figure 7a [40] shows how this technology could be used to monitor cardiovascular health. Furthermore, the ability to monitor stress-related biomarkers linked with cardiovascular health is demonstrated by the invention of textile-based wearable sensors for detecting cortisol in sweat (Figure 7b) [41]. Furthermore, the proposed combination of a shape memory polymer-modified textile, a temperature-responsive microfluidic system, and a paper-based colourimetric sensor has the ability to detect glucose in human sweat in real time. This is critical for efficiently controlling cardiovascular health [33]. Furthermore, research into bio-based, self-healing supramolecular polymers for wearable sensors that monitor sweat in real time has shown promise for consistent and continuous monitoring of sweat biomarkers, particularly those linked with cardiovascular health (Figure 7c) [42]. An effective method for collecting sweat biomarkers, namely those linked with cardiovascular health monitoring, is to construct integrated smart Janus textile bands that can self-pump sweat for sampling and analysis, as demonstrated in Figure 7d [43]. Textile-based sweat sensors offer a promising technique for identifying and treating heart disease. They provide continuous and non-invasive monitoring of biomarkers relevant to cardiovascular health.

Overall, diabetes management seems to be a promising applied area for disease diagnosis and management. Table 1 provides a comprehensive overview of diabetes management, including the researchers, sensor types, and key features.

3.3.2. Continuous Health Tracking

Textile-based sweat sensors offer a breakthrough approach to continuous health tracking by seamlessly integrating into clothing, providing a non-intrusive and comfortable monitoring solution [166]. These textile-embedded sensors can analyze sweat composition in real time, enabling continuous assessment of key biomarkers such as glucose, electrolytes, and lactate [33]. This innovative technology has immense potential for personalized health monitoring, providing individuals with valuable insights into their physiological status for proactive health management.

Physical Activity Monitoring

The potential of textile-based sweat sensors to monitor physiological parameters in real time and non-invasively during physical activity has attracted much interest [167]. One advantage of these sensors is that they can be easily incorporated into clothing, providing comfortable, continuous monitoring that does not interfere with the user’s movements. A textile sensor based on conductive thread was developed by Jia, Ji et al. in 2018 to continuously detect sweat levels. The importance of sweat as a physiological indicator of comfort, emotional state, health, and exercise intensity is the main topic of this study. Sweat detection has been studied in the past, but there have been concerns with studies of sedentary individuals, sensor attachment pain, and sensors that only measure the components of sweat rather than its quantity (Figure 8a). The current work addresses these challenges by providing a textile-based sensor design that monitors sweat volume while ensuring comfort, robustness against body motion, and cost-effectiveness. To keep the sensor stable during movement, conductive threads are woven into cotton braids and covered with a structured cotton cover. This design provides stable measurements, usability benefits, and low-cost manufacturing. The study advances the field by providing a viable solution for continuous sweat monitoring, filling the gaps in current methods, and providing applications for physical activity monitoring in healthcare, fitness assessment, and other areas [44].

In 2019, Jiang, Yutong et al. developed a sophisticated textile that monitors body temperature and perspiration levels using wireless power and near field communication. This work presents battery-free smart textile NFC antennas that are integrated with external temperature and humidity sensors. This integration provides real-time monitoring of body temperature and sweat levels. The NFC antennas serve as both communication interfaces and wireless power harvesters, outperforming battery-powered sensors. The proposed sensing device is made of conductive threads coated in silver and a cotton substrate. It includes a rectifier to raise voltage for wireless power transmission, as well as an Android app for smartphone data access (Figure 8b). Applications range from systemic hyperthermia monitoring to wound healing and general healthcare. To address issues related to the conformal structure of textiles during body movement, one method is to reduce the size of the circuit and carefully select body locations that are less affected for inserting the devices. The paper provides an in-depth look into the textile sensing circuit’s development, design, fabrication, and testing. It also examines experimental findings and their uses in everyday and medical settings [45]. This study contributes significantly to the field by establishing battery-free real-time monitoring of body temperature and perspiration loss via the use of new textile NFC technology.

In 2020, Terse-Thakoor, Trupti et al. designed a thread-based multiplexed sensor patch for real-time sweat detection. The research focuses on the development of minimally invasive wearable devices for health monitoring, namely the real-time tracking of metabolic indicators in sweat for accurate athletic performance assessment, clinical diagnosis, and emergency alarms. The study emphasizes sweat’s usefulness as a diagnostic fluid due to its accessibility and high concentration of physiological indicators (Figure 8c). Despite earlier difficulties in integrating electronics with flexible sweat sensors, textile-based techniques are developing as adaptable alternatives that can be seamlessly integrated into current clothes. The study describes a revolutionary completely integrated thread-based technology for detecting salt, ammonium, pH, and lactate directly from sweat while also offering a wireless electronic display for real-time monitoring. The chosen biomarker panel provides a comprehensive physiological assessment of athletic performance, and the fabrication process employs polyester and stainless steel threads covered with conductive inks for selective potentiometric and amperometric sensing. The resulting wearable patch, fitted into a band-aid style, displays continuous sweat evaporation for fresh sample collection, overcoming previous problems and demonstrating the adaptability of textile-based sensors for personalized use cases [46].

In 2020, Shathi, Mahmuda Akter et al. developed an extremely flexible and washable sports bra. The bra is coated with graphene and is intended to monitor human health. This study was published in the journal “Materials & Design” (number 193, pages 1087–1092). The study intends to address the limitations of standard metal electrodes, such as restricted flexibility, breathability, and skin irritation, in health monitoring devices used to detect arrhythmia. The study proposes a unique approach for covering textile-based electrodes with graphene oxide (GO) and reduced graphene oxide (rGO) using a large-scale dyeing process (Figure 9a). This graphene-coated textile electrode is intended to improve skin contact, boost washability, and ensure long-term stability, thereby eliminating the constraints commonly associated with metal electrodes. The study also looks into the use of highly conductive polymers, notably 3,4-polyethylenedioxy:polystyrene sulfonate (PEDOT:PSS), to improve the flexibility, washability, and breathability of textile electrodes. This research focuses on creating textile electrodes that are flexible, washable, and breathable. These electrodes are designed for use in biomedical and health monitoring systems, specifically to detect arrhythmia. The primary goal is to reduce electrical signal distortion during the diagnostic process. The suggested method uses a layer-by-layer (LbL) drop casting process to achieve the necessary properties for effective real-time health monitoring [47].

Then, in 2020, Zhao, Zhiqi, and colleagues created a thread/fabric-based band as a flexible and wearable microfluidic device for sweat sensing and monitoring. The study tackles the constraints of standard biomarker analysis approaches, such as invasive procedures and complicated gear, by offering a new way to continuous health monitoring based on textile-based sweat sensors. The study emphasizes the significance of sweat as a biofluid rich in different indicators, highlighting the potential of skin-mounted wearable sensors as a non-invasive alternative (Figure 9b). Textile-based materials, such as fabric and yarn, are investigated for their adaptability, low cost, and appropriateness as substrates for wearable sweat sensors. The designed microfluidic band combines hydrophobic fabric with hydrophilic thread to collect and transfer sweat, allowing for on-site monitoring of electrolytes, metabolites, and local sweat loss. The colorimetric assay, which is backed by a smartphone app, improves detection accuracy and provides a simple, cost-effective, and wearable platform for point-of-care diagnostics and health monitoring [48].

Furthermore, Kim et al. [49] show the practical use of textile-based sweat sensors in physical activity monitoring by incorporating highly stretchable and conductive carbon threads into elastic rubber for wearable real-time sweat monitoring during stretching exercise [49]. The study investigates the use of wearable sensor technologies in human health monitoring and customized treatment, highlighting the importance of continuous and non-invasive biomarker collecting. While present wearable sensors largely measure physical activity and vital signs, there is a research void in the collection of chemical health data. The research describes textile-based sweat sensors and emphasizes its utility in obtaining sweat biomarkers during various activities (Figure 9c). The incorporation of carbon fiber into an elastomeric substrate via 3D printed molds with a serpentine pattern is offered as a promising platform for real-time sweat detection. The resulting wave-shaped CT/Ecoflex (w-CT/Eco) sensors have extraordinary stretchability and stability, allowing for accurate detection of sodium ion concentrations [49] in sweat. Finally, the paper describes the successful real-time on-body monitoring of sodium ion concentrations during various physical activities with the designed wearable sensor platform.

In 2023, Yu, Wenze et al. developed a yarn/fabric-based microfluidic patch for sweat sensing and monitoring. Sweat, which is rich in biomarkers that reflect human health and performance, provides an ideal alternative for monitoring various conditions such as cystic fibrosis, muscle fatigue, stress, and diabetes. The critical need for a non-invasive, real-time sweat sensor capable of quantitatively detecting multiple biomarkers has led to research using electrochemical and colorimetric methods (Figure 9d). Electrochemical methods offer high sensitivity and stability, while colorimetry, with its simplicity and cost-effectiveness, is gaining traction, particularly in textile-based platforms that offer comfort and breathability for natural sweating. The reported wearable sweat-sensing patch, which integrates yarn and fabric in a microfluidic system, enhances wearability and comfort by allowing direct skin contact. The hydrophilic microfluidic platform transfers sweat through yarn microchannels to detection sites on the fabric, enabling colorimetric analysis to determine biomarker concentrations and offering a promising approach for continuous and non-invasive health monitoring [50].

Overall, the reviewed studies provide comprehensive insights into the development, challenges, and applications of textile-based sweat sensors for physical activity monitoring, highlighting their potential to revolutionize real-time and non-invasive monitoring of physiological parameters during various activities.

Mental State Monitoring

The invention of textile-based sweat sensors has created new opportunities for monitoring a variety of physiological and psychological conditions. These sensors have several advantages, including flexibility, comfort, and the capacity to constantly monitor sweat vapor with high sensitivity and rapid response [34]. They have been utilized to detect sweat pH, lactate, and other biomarkers, making them useful for a variety of applications, including mental state monitoring [168,169]. Furthermore, wearable sensors have been utilized to detect patients’ mental states, suggesting the potential for mental health monitoring through ubiquitous sensors and machine learning [83,134]. Furthermore, research has established the feasibility of monitoring mental states using EEG and proposed effective mental workload estimation using task-independent EEG features [14,170]. These developments in sensor technology and data analysis have the potential to transform mental state monitoring by providing real-time insights into an individual’s mental health.

The use of textile sensors for real-time and multiplexed sweat analysis has allowed for the simultaneous detection of various health-related biomarkers, resulting in a comprehensive picture of an individual’s physiological and mental condition [14]. In addition, the development of microfluidic sensing patches has facilitated regional and correlative sweat analysis, removing the critical bottleneck for temporal and regional sweat analysis, and paving the way for sweat decoding [171]. These technological advances not only enable the monitoring of physiological parameters but also hold promise for understanding an individual’s mental state through the analysis of sweat biomarkers. In addition to sensor technologies, there is an increasing interest in exploiting smartphone ownership and mobile applications to track mental health symptoms [172]. This suggests a move toward employing ordinary technologies for mental health monitoring, which could enable widespread and continuous monitoring of mental states. Furthermore, the ability to identify and anticipate affective states of employees at work has the potential to improve mental health and productivity, emphasizing the larger implications of mental state monitoring beyond individual healthcare [173]. In summary, the combination of textile-based sweat sensors, microfluidic sensing patches, EEG-based monitoring, and smartphone technology has considerably expanded the field of mental state monitoring. These technology advancements have the potential to provide real-time, continuous, and complete monitoring of an individual’s mental health, with implications for individualized treatment, workplace well-being, and larger social effect.

Drug Monitoring

The creation of a textile-based sweat sensor for medication delivery systems is a potential field of study. Textile-based sensors have been investigated for real-time sweat monitoring, with an emphasis on interfaces, wearable computing, and personalized health management [174]. These sensors have been developed to be flexible and self-powered, making them ideal for incorporation into smart textiles and wearable systems [175,176]. Furthermore, textile-based sensors can monitor chemicals and analyze perspiration for drug administration [166,177]. The detection of glucose and other indicators in human sweat has also been investigated using textile-based sensors combined with microfluidic devices and paper-based colorimetric sensors [33,40]. Furthermore, the use of conductive thread-based textile sensors for continuous sweat level monitoring has been studied, emphasizing the potential for drug administration [63]. Furthermore, the development of biosensing textile-based patches with integrated optical detection systems, as well as thread-based multiplexed sensor patches for real-time sweat monitoring, reveals the wide range of textile-based sensing techniques [41,44]. In addition, innovative materials such as silk-based electrodes and laser-induced graphene/polymer hybrid fibers have been investigated to increase the performance and comfort of textile-based sensors for on-skin drug delivery applications [137]. These developments aim to improve the sweat tolerance and conformability of textile-based sensors, making them appropriate for long-term drug delivery monitoring.

The use of textile-based sweat sensors in drug delivery systems has significant potential for individualized healthcare management. The development of flexible, self-powered, and extremely sensitive textile-based sensors, as well as the research into new materials marks a significant step toward implementing textile-based drug delivery systems.

Table 5. Continuous Health Tracking is summarized below based on Researchers, Sensor Types, Key Features, and Applications.

Publication Year	Researchers	Sensor Type	Key Features	Applications	Reference
2018	Jia, Ji, et al.	Conductive thread	Sweat monitoring, low-cost	Activity monitoring, healthcare	[43]
2019	Jiang, Yutong, et al.	NFC-enabled textile	Battery-free, real-time monitoring	Systemic hyperthermia, wound healing	[44]
2020	Terse-Thakoor, Trupti, et al.	Thread-based multiplexed	Real-time metabolic tracking	Athletic assessment, clinical diagnosis	[45]
2020	Shathi, Mahmuda Akter, et al.	Graphene-coated bra	Improved skin contact, washable	Detecting arrhythmia	[46]
2020	Zhao, Zhiqi, et al.	Thread/fabric microfluidic	Sweat collection, colorimetric analysis	Point-of-care diagnostics	[47]
2022	Kim et al.	Stretchable carbon threads	Stable, sodium ion detection	Activity monitoring	[48]
2023	Yu, Wenze, et al.	Yarn/fabric microfluidic	Real-time sweat sensing	Cystic fibrosis, diabetes monitoring	[178]

provides a detailed summary of the Continuous Health Tracking scientists involved in the research. It observes the types of sensors used and the essential features that are noteworthy. It provides a comprehensive overview of the research conducted in this field, including key information that can be useful for gaining insights into Continuous Health Tracking.

3.3.3. Personalized Monitoring

Personalized monitoring through textile-based sweat sensors represents a cutting-edge approach in healthcare [179]. These sensors, seamlessly integrated into clothing, enable continuous and non-invasive tracking of individual biomarkers present in sweat. By analyzing real-time data on electrolytes, metabolites and other vital indicators, a personalized profile of the wearer’s health is created [180]. This dynamic monitoring allows for tailored interventions, including medication adjustments, lifestyle changes, or targeted therapies, based on each individual’s unique needs [181]. Textile-based sweat sensing technology thus paves the way for a new era of personalized healthcare, where treatment strategies are fine-tuned to optimize outcomes based on real-time physiological data.

Tailoring Treatment Plans Based on Real-Time Data

The integration of textile-based sweat sensors into healthcare allows for customized treatment plans based on real-time data [12,156]. As users perform daily activities, the sweat sensor continuously monitors physiological parameters by analyzing biomarkers such as electrolytes, heavy metals, and metabolites [23]. The collected data are processed through algorithms to provide immediate insights into the individual’s health status. This real-time information enables healthcare professionals to dynamically adjust and personalize treatment plans to address specific needs and optimize therapeutic interventions [182,183]. The ability to tailor treatments based on immediate and continuous feedback from the textile-based sweat sensor represents a significant advancement in precision medicine and patient-centered care.

Improving Patient Outcomes through Personalized Interventions

Textile-based sweat sensors represent a promising avenue for improving patient outcomes through personalized interventions [27]. Seamlessly integrated into everyday clothing, these sensors continuously monitor key biomarkers in real time, providing dynamic insights into an individual’s physiological state [29]. By analyzing sweat composition, healthcare providers can tailor interventions based on the specific needs and variations in a patient’s health, leading to more precise and personalized treatment strategies [12]. This proactive approach allows for timely adjustments to medications, lifestyle recommendations, or therapeutic interventions, ultimately optimizing patient care and contributing to improved overall health outcomes [184,185]. Thus, textile-based sweat sensing technology plays a key role in advancing personalized medicine and increasing the effectiveness of healthcare interventions.

3.3.4. Energy Harvesting

Energy harvesting by textile-based sweat sensors [52] adds an innovative dimension to wearable health monitoring [54,186]. These sensors, seamlessly integrated into clothing, not only collect real-time data from sweat biomarkers but also harvest the energy generated during the monitoring process [180]. The energy harvesting [53] mechanism could use the wearer’s body heat or motion to generate power, reducing or eliminating the need for external power sources. This self-sustaining approach increases the overall efficiency and sustainability of the wearable system, ensuring continuous and uninterrupted monitoring [187,188]. By harvesting energy from the wearer’s activities, textile-based sweat sensors represent a potential breakthrough in powering wearable health technologies, contributing to improved user comfort and device longevity. Recent research has focused on harnessing biochemical and biomechanical energy from sweat by integrating textile-based sensors with energy harvesting technologies [189,190]. These devices use textile qualities to construct wearable energy microgrids capable of generating and storing energy from human activities [54]. This includes technology such as sweat-based biofuel cells and triboelectric generators, which can extract energy from movement and perspiration. The gathered energy is subsequently stored in supercapacitors [40], resulting in high power output [191,192,193].

Textile-based energy-harvesting technologies have been explored in the context of wearable and large-area energy-harvesting textiles, demonstrating their potential for next-generation wearable functional electronics [194,195]. The success of conductive polymers (CPs) in textile devices, including energy harvesting devices and sensors, highlights the versatility and applicability of textile-based energy harvesting systems [196]. In addition, the integration of sweat-based energy harvesters with other energy harvesting technologies has been proposed to address the challenges associated with limited sweat availability, thereby enhancing power generation [56] and storage capabilities [54]. The development of textile-based triboelectric nanogenerators (T-TENGs) has attracted a lot of attention because of its potential for energy harvesting and self-powered sensing, as well as their breathability and flexibility for smart textiles [197]. Furthermore, the importance of textile-based energy harvesting systems for biomedical applications has been emphasized, showing the connection of textile-based energy harvesters to existing models of biomedical sensors [198].

In addition, the integration of sweat-based supercapacitors with wearable systems demonstrates the potential for self-powered smart textiles, enabling the storage of harvested energy for various applications [54,199,200]. The review of available solutions and techniques for physiological monitoring through smart textiles highlights the importance of advanced textile implementations for sweat sensing, demonstrating the potential for energy harvesting from this biofluid [187]. The integration of textile-based sweat sensors with energy harvesting technologies represents a promising avenue for the development of self-sustaining and wearable energy microgrid systems. These advances hold significant potential for powering the next generation of wearable electronics and personalized health monitoring by harnessing biochemical and biomechanical energy from sweat.

3.4. Selection and Comparative Analysis of Sensor Types

We conducted a detailed comparative analysis of various sensor types discussed in our study, focusing on their unique technical characteristics and potential applications. This table provides a succinct summary of the comparative technical features of each sensor type, aiding in understanding their capabilities and suitability for different applications in health monitoring and diagnostics. The following technical characteristics of the sensors are compared in

Table 6. Comparative Technical Characteristics of Sensor Types.

Sensor Type	Sensitivity (Units)	Selectivity (%)	Response Time (s)	Accuracy (%)	Durability (Cycles)	Applications
Conductive Threads	High	Medium	Low	Medium	High	Physical activity monitoring, healthcare
NFC-enabled Textiles	Medium	High	Very Low	High	Medium	Systemic hyperthermia, wound healing
Thread-based Microfluidics	High	High	Medium	High	High	Point-of-care diagnostics, health monitoring
Graphene-coated Textiles	High	High	Medium	High	High	Arrhythmia detection, long-term monitoring
Carbon Fiber-based Sensors	High	High	Low	High	High	Real-time sodium ion detection, sports monitoring
Yarn/Fabric-based Microfluidics	High	High	Medium	High	High	Continuous health monitoring, disease management

.

• Sensitivity: Indicates the sensor’s ability to detect minute changes in biomarker concentration.
• Selectivity: Measures the sensor’s ability to distinguish target analytes from interfering substances.
• Response Time: Refers to the time taken by the sensor to produce a measurable signal after exposure to the analyte.
• Accuracy: Represents how closely the sensor’s measurements align with the true values of the analyte concentration.
• Durability: Indicates the number of cycles or duration the sensor can maintain its performance under typical usage conditions.

To provide a comprehensive understanding of the various sensor types discussed in our study, we conducted a detailed comparative analysis highlighting their respective strengths, weaknesses, and potential applications. This analysis aims to clarify how each sensor type addresses specific technological gaps and offers comparative advantages in different practical applications.

Table 7. Comparative Analysis of Sensor Types.

Sensor Type	Strengths	Weaknesses	Potential Applications
Conductive Thread	Flexibility, low cost	Limited sensitivity, durability	Activity monitoring, healthcare
NFC-enabled Textile	Battery-free, real-time monitoring	Range limitation, cost	Systemic hyperthermia, wound healing
Thread-based Multiplexed	Real-time metabolic tracking	Limited biomarker panel, integration	Athletic assessment, clinical diagnosis
Graphene-coated Textile	Improved skin contact, washable	High cost, complex fabrication	Detecting arrhythmia
Thread/Fabric Microfluidic	Sweat collection, colorimetric analysis	Integration complexity, calibration	Point-of-care diagnostics
Stretchable Carbon Threads	Stable, sodium ion detection	Fabrication complexity, cost	Activity monitoring
Yarn/Fabric Microfluidic	Real-time sweat sensing	Sensor integration, scalability	Cystic fibrosis, diabetes monitoring

summarizes these key points succinctly.

The selection of specific sensor groups in our review is justified by their unique capabilities and advantages over other sensor types. For instance, conductive thread sensors offer excellent flexibility and affordability, making them suitable for continuous activity monitoring and healthcare applications. In contrast, graphene-coated textiles provide improved skin contact and washability, addressing concerns of skin irritation and long-term wearability associated with traditional metal electrodes. Each sensor type contributes uniquely to overcoming critical limitations in current sensor technologies, thereby advancing the field towards more effective and practical applications.

4. Discussion

Textile-based sweat sensors have great potential for continuous health monitoring, but there are several challenges to their implementation [72]. Finding a balance between the stretchability and flexibility of the sensor and the durability required for daily use is a major challenge [201]. Textiles are less elastic than elastomers, making them less useful for physically demanding activities [202]. In addition, there are engineering problems in integrating complicated sensor components into fabrics without compromising wearability and comfort. There are also scalability and manufacturing cost issues, as the manufacturing process often involves labor-intensive processes such as cleanroom-based coating and printing, which increase production costs [28]. For textile-based sweat sensors to be widely adopted, these barriers must be overcome to enable seamless integration into regular clothing and to ensure their continued affordability and reliability for widespread use in healthcare and individualized monitoring applications.

4.1. Technical Challenges

In order for textile-based sweat sensors to be successfully implemented, several technological issues need to be addressed. The incorporation of sensor components can affect the feel and wearability of the fabric, so striking a careful balance between sensor functionality and textile comfort is a major concern [203]. Another technical challenge is to ensure the robustness and durability of the sensors while maintaining their stretchability and suppleness, which are essential to accommodate body movements [159,204]. In addition, it is still difficult to collect data consistently and reliably over a wide range of user actions, requiring sophisticated sensor design and calibration [205]. Technical barriers also arise in the selection and integration of appropriate materials, such as conductive electrodes and substrates, into textiles. Careful consideration of manufacturing feasibility and sensor performance is required [206]. To improve the accuracy, reliability, and usability of textile-based sweat sensors and to facilitate their widespread use in wearable technology and health monitoring applications, these technological barriers must be overcome.

4.1.1. Sensor Accuracy and Reliability

The development of textile-based sweat sensors involves numerous technical problems, particularly in terms of sensor accuracy and dependability. These problems include the requirement for innovative solutions to overcome traditional sensor constraints, such as the capacity to monitor numerous analytes at the same time, on-site signal processing, and sensor calibration procedures for reliable physiological analysis [207]. Furthermore, the fluidity, volatility, and ultralow volume of sweat make proper sampling procedures difficult, increasing the risk of contamination from the skin surface [1,3]. Furthermore, wearable electrochemical sweat analysis devices present significant problems due to the complexity of fabrication techniques as well as the relatively low sensitivity and selectivity in measuring numerous biomarkers simultaneously [34,134]. To address these challenges, researchers have proposed novel solutions, such as the creation of superhydrophobic sweat sensors made of composite materials sandwiched between superhydrophobic textile layers, which enable continuous measurement of sweat vapor with high sensitivity and rapid response. Furthermore, the application of flexible fiber/textile-based sweat sensors has been investigated, with an emphasis on the opportunities and constraints connected with their implementation [208,209]. Furthermore, the creation of self-pumping sweat sampling and analysis systems has been proposed to solve the issues related with sweat sample methodologies [210].

When considering the accuracy and dependability of sensors, it is crucial to take into account various factors including battery limitations, environmental noise, and sensor drift. These elements can pose challenges to achieving dependable sensing with wearable and implantable sensors [211]. In addition, the electrical behavior of sensors can be highly dependent on temperature gradients, leading to reliability degradation and reduced measurement accuracy [212]. Furthermore, the accuracy of individual sensors can be affected by several factors, including instrument malfunction and inherent measurement errors [213]. Therefore, the development of reliable sensing systems requires addressing these challenges by integrating data redundancy, source credibility, and dynamic sensor reliability considerations [214]. In summary, several technical obstacles must be addressed to overcome the shortcomings of conventional sensors and develop reliable sensing systems that account for temperature gradients, environmental perturbations, and sensor drift. These challenges affect the development of textile-based sweat sensors and their accuracy and reliability. For textile-based sweat sensors to be successfully implemented in physiological monitoring applications, these issues must be fixed.

4.1.2. Power Consumption and Energy Efficiency

To address the technical challenges of power consumption and energy efficiency in textile-based sweat sensors, for multiplexed in situ sweat analysis, the integration of sensor arrays must be carefully considered. The necessity of this integration arises from the fact that it permits the concurrent observation of numerous analytes, including electrolytes and glucose while ensuring precision medicine and physiological monitoring [215]. In addition, the use of conductive polymers in textile chemical sensors offers promising biocompatibility for effective interface with the human body, which is essential for wearable sensor applications [216]. In addition, the advancement of smart textiles and sensorized apparel intended for physiological monitoring presents possibilities for overcoming the obstacles associated with energy efficiency and power consumption in sweat sensors [20].

In the context of power consumption and energy efficiency, the challenges associated with the bulky and stiff devices used in sweat sensors highlight the need for innovative solutions to enable long-term wearable use [134]. Furthermore, the fabrication of self-sustaining wearable electronics activated by human sweat, such as weavable and scalable cotton yarn-based batteries, provides an opportunity to address the energy requirements of textile-based sensors. Furthermore, the creation of a self-sustaining wearable multimodular e-textile bioenergy microgrid system presents a viable way to increasing the energy efficiency of wearable sensor applications [190]. Furthermore, the combination of strain-insensitive fiber-based wearable electrochemical biosensors and highly elastic fiber-based potentiometric ion sensors offers opportunities to address the challenges of maintaining analytical performance and conductivity in stretchable states, contributing to energy-efficient sensor designs [32,217]. Furthermore, capillary-driven and pre-programmed sweat flow can be used to improve energy efficiency and address power consumption issues by developing vertical textile epifluidics for integrated real-time electrochemical sweat sensing [218]. Addressing the technical challenges of power consumption and energy efficiency in textile-based sweat sensors requires the integration of sensor arrays for multiplexed analysis, the development of biocompatible conductive polymers, and the exploration of smart textiles and sensor-equipped clothing for physiological tracking. In addition, the advancement of self-powered wearable electronics, highly stretchable fiber-based sensors, and vertical textile epifluidics offer promising opportunities to improve energy efficiency in sweat-sensing applications.

4.1.3. Practical Considerations of Textile-Based Sweat Sensors

Long-term wearable sweat sensors can only perform if the sensors are performing as estimated in terms of their sensitivity [219]. Glucose and electrolytes are a few biomarkers that need to be quantified over a long time to inform clients’ health management and intervention [102]. Greater sensor sensitivity is the ability to record small alterations in an individual’s physiological state that demonstrate disease progression and treatment outcomes [140]. Routine sensor calibration and testing allow for maintaining the accuracy of measurements for use in tracking patient trends and outcomes. Therefore, enhancements to sensor accuracy, sensitivity, and dependability are crucial for wearable sweat sensor usage in constant health monitoring.

• Washability:

The durability of textile-based sweat sensors hinges on several critical properties: The functional requirements are mechanical properties for breathability [220], durability, washability for garments to be functional after being washed many times, ease and reliability of contact with the skin and resistance to chemicals/environment [219]. It is for these properties that these sensors can be made longer-lasting and more accurate in real-life usage, making their use in healthcare and monitoring of individuals efficient. The textile-based sweat sensors were subjected to standard washing tests to evaluate their durability. The sensors were tested under room temperature, e.g., in 30 °C machine wash with mild detergent for up to 10–20 washing cycles. Results showed that the sensors retained 10–15% of their initial sensing performance after 10–20 cycles, demonstrating their robustness in regular washing conditions [56]. In addition to sensing performance, there are other important parameters that define the applicability as well as stability of sweat-sensing textile platforms [64]. Here, the main requirement is that these sensors must be able to resist several washing cycles without compromising their sensing and structural properties. It is crucial to determine how many times a washing machine may be utilized before it becomes ineffective and how often it will require repair or other treatments [56,221,222].

• Strain–stress and stretch test:

Stress–strain and stretch tests were performed using standard tensile testing machines or dynamic mechanical analyzers (DMAs) to assess the mechanical properties. The sensors exhibited high elasticity with a tensile strength of [value] and maintained functionality after 10–20 stretching cycles to 80–90% of their original length. This indicates their suitability for applications requiring flexibility and repeated motion [13,223]. Stress–strain and stretch tests are equally important for determining the sensors’ resistance to mechanical loads, which include bending, stretching [224], and twisting that mimic common movements in daily activities [225,226]. These tests ensure that the sensors are consistently in good contact with the skin, which is important for reliable and continuous tracking of sweat biomarkers.

• Flexibility:

Flexibility tests, including bending and twisting, were conducted to determine the sensors’ ability to withstand mechanical deformation. The sensors were bent to angles of up to 90 degrees and twisted 2500 cycles of repeated strain of 100% without significant performance loss, highlighting their adaptability to various body movements [13]. Further, a flexibility check indicates the extent to which the sensors are pleasant to the body shapes and movement variety which is crucial in guaranteeing the user’s compliance [227]. By incorporating the above practical aspects, the textile-based sweat sensors can provide optimal performance and extend beyond the criterion of stability and practicality [13,48,99]. This is important to spur their use across healthcare and other personal monitoring markets.

4.2. User Acceptance and Privacy Concerns

The potential of textile-based sweat sensors to monitor physiological indicators and sweat composition in real time has drawn a lot of interest to their development. Because of their non-invasiveness and capacity for continuous monitoring, textile-based sensors are well suited for a range of uses, such as fitness, healthcare, and personalized medicine. These sensors are made to overcome the drawbacks of conventional sensors, namely their incapacity to track several analytes at once and their absence of on-site signal processing equipment for precise physiological state analysis [29,46]. Furthermore, textile-based sensors provide the skin with its natural breathability, which encourages sweating and evaporative cooling naturally. This is necessary for precise sweat analysis [46].

The integration of conductive polymers (CPs) into textile electrochemical sensors has been a focus of research to overcome challenges associated with real-time sweat monitoring, such as low conductivity, large diameters, expensive manufacturing processes, and poor electrochemical performance [153,228,229]. In addition, the development of textile-based molecularly imprinted polymer (MIP) wearable electrochemical sensors has demonstrated the potential to detect specific biomarkers, such as cortisol, in human sweat [213]. These technological advancements in sensors have enabled the creation of malleable and printable arrays of potentiometric sensors based on textiles. These arrays are designed to analyze simultaneous multi-ions of perspiration and have applications in the field of health and fitness [165].

In addition, recent research has focused on addressing the practical challenges associated with textile-based sensors, such as the impact of external factors such as dirt, oil, and wetness on sensor performance [230]. Superhydrophobic textiles have been developed to allow sweat vapor permeation while preventing interference from external water droplets and internal sensitive sweat, ensuring accurate and reliable sensor operation [134]. In addition, the use of microfluidics-based wearable sweat sensors has been proposed to minimize contamination and evaporation and provide superior usability compared to hand-held point-of-care devices [231].

4.2.1. Cultural and Social Factors Influencing Adoption

Social and cultural factors play an important role in the adoption of technology, especially textile-based sweat sensors [232]. The related variables that highlight the importance of understanding the sociocultural factors that influence the adoption of solar energy technology illuminate how social and cultural factors influence the decision-making processes involved in deciding whether to purchase a hybrid vehicle [233]. This matter demonstrated how many cultural factors can influence educators’ use of free educational resources in different ways [234]. In addition, the researchers demonstrated how cultural characteristics influence the use of social media, highlighting the importance of cultural differences in technology adoption [235]. These studies all emphasize the importance of considering social and cultural factors when choosing which technology to use. Therefore, in the context of textile-based sweat sensors, it is imperative to understand how cultural and social conventions, preferences, and attitudes affect the acceptance and use of these cutting-edge sensing technologies [236,237]. Understanding these factors can help develop tailored strategies to promote the adoption of textile-based sweat sensors in different social and cultural contexts [12]. The combination of these cases highlights the importance of considering social and cultural factors when studying the adoption of technologies such as textile-based sweat sensors. By identifying and addressing these factors, it is possible to develop more effective adoption strategies and promote the widespread acceptance of textile-based sweat sensors in a range of social and cultural situations [238,239].

4.2.2. Data Security and Privacy in Medical Monitoring

The incorporation of textile-based sweat sensors into medical monitoring systems signifies a potentially fruitful pathway towards the continuous, non-intrusive surveillance of diverse sweat biomarkers [240]. These sensors are highly suitable for sweat composition analysis due to their non-invasive nature and ability to monitor the epidermis continuously in real time [24]. A recent study documented the creation of a flexible perspiration analysis patch that utilizes a carbon textile derived from silk. This patch enables the concurrent detection of six health-related indicators [241,242]. In addition, the use of superhydrophobic textile layers in sweat sensors has been shown to enable continuous measurement of sweat vapor that reacts quickly and with high sensitivity, contributing to the advancement of sweat sensing technology [134,243].

However, the implementation of these sensors in medical monitoring systems requires a comprehensive consideration of data security and privacy. Since the data collected by these sensors are sensitive and personal, ensuring the security and privacy of this information is critical. This is particularly important in the context of remote health monitoring applications, where sensor nodes are deployed in potentially hostile environments [244]. In addition, secure transmission and storage of medical data, including sweat biomarker information, is essential to protect patient privacy and maintain data integrity [245].

Various techniques and technologies have been proposed to address the challenges of ensuring the privacy and integrity of medical information in medical data security [245,246]. In addition, the use of blockchain-based systems and fuzzy-based bio-key management schemes has been explored to enhance the security and privacy of medical data, including information obtained from wearable sensors.

4.3. Future Research Directions

Prospective avenues of investigation for textile-based sweat sensors present a variety of obstacles as well as opportunities [247]. Future research on graphene-based textile strain sensors appears to be very promising and provides important direction and guidance for the development of this technology [248,249]. Furthermore, there are many opportunities and challenges for future research in the field of the function of conductive polymers in the creation of textile electrochemical sensors for sweat monitoring in real time [12,129]. Future studies in this area are now possible thanks to advances in wearable sweat sensors, which have overcome previous challenges and provided new approaches to understanding body dynamics at the molecular level [250]. Further research into self-powered cloth-based sensors is made exciting by the successful demonstration of a wearable supercapacitor for sweat salt monitoring based on conductive PEDOT: PSS-coated fabric [40,251].

While commercially available sensors exist for perspiration drug monitoring, the advancement of sensors based on textiles is still in its preliminary stages of development. This indicates the need for additional research to develop the field and fill this void [252,253]. The considerable potential for developing advanced and efficient perspiration analyte identification sensors using graphene promotes further investigation in this area. Additional research is necessary to incorporate these remarks and advance the field. This paper also presents recommendations and future directions for wearable sweat sensors based on current research trends. Furthermore, the examination of textile-based perspiration sensors in contrast to alternative substrates and materials underscores the need for ongoing research to optimize the performance capabilities of such sensors. The advancement of textile-based sensors for moisture measurement and the BIOTEX project’s focus on developing a textile-based perspiration collection and analysis system [138] facilitate further investigation in this field. Furthermore, an intriguing avenue for additional investigation in personalized health monitoring involves the integration of intelligent Janus textile armbands that enable self-pumping perspiration collection and analysis.

4.3.1. Advancements in Sensor Technology

In recent years, considerable breakthroughs have been made in the development of sensor technology for cloth-based perspiration sensors. Numerous issues that had previously hampered wearable sweat sensors have been resolved. Currently, novel ways are being explored to obtain molecular-level understanding of the complexities of physiological dynamics [186,254]. In contrast to traditional sensor approaches, significant work has been dedicated to overcoming technical challenges and implementing new perspiration monitoring solutions [255]. The creation of conductive polymer-based textile chemical sensors built specifically for real-time perspiration monitoring demonstrates the key challenges in this sector [256]. Furthermore, by overcoming hurdles in the design and manufacture of stretchable/flexible wearable sensors made from carbon and textile materials for health monitoring, the potential of textile-based multi-ion perspiration sensor arrays has been demonstrated [257].

The creation of incredibly rapid self-healing supramolecular bio-based polymers for wearable, in-the-moment sweat monitoring sensors has also been facilitated by recent technological developments. These polymers integrate wireless transmission technology using a Bluetooth module. In addition, flexible sweat sensors based on fibers or fabrics have shown potential but need to be improved compared to similar tag-based sweat sensors [258]. Wearable textile sensors have advanced significantly through the integration of smart textiles, providing new interfaces for detecting physical movements in everyday life. Furthermore, the potential for textile-based sensors to track specific biomarkers has been established via a textile-based wearable molecularly imprinted polymer (MIP) electrochemical sensor to detect cortisol in human perspiration [259]. The most adaptable method for sweat monitoring is the incorporation of textile-based sensors into currently available clothing, underscoring the potential for broad acceptance and daily integration. Furthermore, the development of smart Janus textile bands with integrated technology for sweat analysis and self-pumping sweat sampling has demonstrated the possibility of direct sampling interfaces between the sweating epidermis and the sensor element, which could lead to in situ sweat detection [260]. These advancements have considerably accelerated the development of textile-based sweat sensors, which have a wide range of applications in personalized biometrics and health monitoring.

4.3.2. Collaborations between Textile and Medical Research Communities

In recent years, medical and textile research teams have collaborated on textile-based sweat sensors, which has garnered interest. To overcome the significant problems in this field, conductive polymer-based textile chemical sensors have been created specifically for real-time sweat monitoring [166]. Furthermore, the advancement of wearable sweat sensors has led to the resolution of several old problems and the creation of new perspectives for understanding the molecular dynamics of our body [17,261]. The European BIOTEX project in the 2000s is credited with kick-starting sweat sensor research. A large research team focused on biosensing textiles for personal health management, indicating the first attempts at collaboration between the two communities. In addition, the review of flexible sweat sensors based on textiles and fibers explains the advantages of using textile substrates for sweat sensors, in addition to their applications in various industries. A wearable textile-based electrochemical sensor imprinted with polyacrylate for sweat cortisol detection serves as an example of the successful fusion of materials science and biosensors for tailored health management. The development of a textile-based sweat collection and analysis tool was also facilitated by the BIOTEX project, highlighting the successful collaboration between the textile and medical research sectors [262]. The importance of multidisciplinary research, the need for innovative approaches to tailored health management, and the development of textile-based sweat sensors are all evident from these examples, which also highlight the need for collaboration between textile and medical research groups.

5. Conclusions

Sweat sensors in textile materials are vital for monitoring body parameters and can be integrated into everyday clothing to expand healthcare possibilities. They improve user comfort, provide continuous data, and can detect movement, sports activities, and training. These sensors are also helpful in managing chronic conditions like cardiovascular issues and diabetes. Smart textile-based wearable sweat sensors offer a cost-effective and easy-to-implement solution with physical attributes like stretchability, flexibility, and lightweight design while enabling real-time health monitoring through sweat analysis. Our review highlights significant advancements in the field, encompassing fabrication techniques, material innovations, and applications in disease detection and monitoring. Additionally, we discuss the integration of biosensors with electronics, the critical chemical components of sweat, and the challenges associated with sweat collection technologies and textile substrates. Moving forward, overcoming the identified challenges and enhancing sensor performance is crucial for the continued development and widespread adoption of wearable sweat-sensing systems. In conclusion, textile-based sweat sensors are applicable for altering the type of preventive and personalized healthcare that could change existing ideas of health monitoring and healthcare in the future.