Chemosensors, Volume 10, Issue 8 (August 2022) – 55 articles

Biochar is a pyrolytic material with several environmental benefits such as reducing greenhouse gas emissions, sequestering atmospheric carbon and contrasting global warming. However, nowadays, it has moved to the forefront for its conductivity and electron transfer properties, finding applications in the fabrication of electrochemical platforms. In this field, researchers have focused on low-cost biomass capable of replacing more popular and expensive carbonaceous nanomaterials (i.e., graphene, nanotubes and quantum dots) in the realization of sensitive cost-effectiveness and eco-friendly electrochemical tools. This review discusses recent developments of biochar-modified screen-printed electrodes (SPEs). Special attention has been paid to biochar’s manufacturing processes, electron-donating capabilities and sensing applications. Examples of representative works are introduced to explain the distinct roles of biochar in several electro-bioanalytical strategies. Full article

A novel donor-π-acceptor fluorescent dye as a chemosensor for Cu²⁺ ions is herein presented. The fluorophoric core consists of a 3,5-diphenyl-dicyanomethylene-4H-pyran (DCM), with extended styryl chains on positions 2 and 6, bearing terminal di-(2-picolyl)amine (DPA) groups for metal coordination. Optical characterization of the chemosensor dye reveals an absorption maximum at ca. 500 nm and a strong bathochromic shift in the emission, reaching ca. 750 nm in polar solvents. This solvatochromic behavior, which yields very large Stokes shifts (up to ~6700 cm⁻¹), is characteristic of the strong intramolecular Charge Transfer (CT) nature of this chromophoric system. While the chemosensor has demonstrated no changes in its optical properties over a wide pH range (2–12), a strong quenching effect was observed upon Cu²⁺ coordination, with a 1:1 binding stoichiometry, indicating that only one DPA unit is capable of effectively chelating Cu²⁺, rendering the second DPA motif inactive. The binding constant was determined to be 7.5 × 10⁷ M⁻¹, indicating a very high sensitivity, and an LOD of 90.1 nM. Competition assays have demonstrated that the chemosensor is highly selective towards Cu²⁺, even in the presence of excesses of other mono- and di-valent cations. Co²⁺ and Ni²⁺ proved to be the strongest interferents, particularly in the luminescent response. Paper test-strips prepared with the embedded sensor showed a fluorometric response in the presence of different copper (II) concentrations, which attested to the potential of this chemosensor to be used in the determination of Cu²⁺ content in aqueous media, for in-field applications. Full article

This research is focused on the development of pH indicators based on the quinoxaline signaling group for acidic aqueous solutions (pH 1–5). A push–pull quinoxaline QC1 in which two electron-donating (3-aminopropyl)amino substituents are attached to positions 6 and 7 of the electron-deficient quinoxaline moiety was prepared using the palladium-catalyzed C–N cross-coupling reaction. The 3-aminopropyl residues are mostly protonated in aqueous solutions below pH 8, thus serving as hydrophilizing substituents that render quinoxaline derivative QC1 water-soluble in this range of acidities and useful for measurements in the pH range of 1–5. This chromophore is a dual optical chemosensor that exhibits shifts of both absorption and emission bands in response to external stimuli. The presence of naturally relevant metal cations (13 ions) does not interfere with spectrophotometric and fluorescence measurements of the optical response of aminoquinoxaline in the visible region. Moreover, these spectral changes are easily observed by the naked eye, allowing for rapid semi-quantitative analyses under “in-field” conditions. Full article

Excessive ethanol gas is a huge safety hazard, and people will experience extreme discomfort after inhalation, so efficient ethanol sensors are of great importance. This article reports on ethanol gas sensors that use NiO hollow spheres assembled from nanoparticles, nanoneedles, and nanosheets prepared by the hydrothermal method. All of the samples were characterized for performance evaluation. The sensors based on the NiO hollow spheres showed a good response to ethanol, and the hollow spheres assembled from nanosheets (NiO-S) obtained the best ethanol gas-sensing performance. NiO-S provided a larger response value (38.4) at 350 °C to 200 ppm ethanol, and it had good stability and reproducibility. The nanosheet structure and the fluffy surface of NiO-S obtained the largest specific surface area (55.20 m²/g), and this structure was beneficial for the sensor to adsorb more gas molecules in an ethanol atmosphere. In addition, the excellent sensing performance could ascribe to the larger Ni³⁺/Ni²⁺ of NiO-S, which achieved better electronic properties. Furthermore, in terms of commercial production, the template-free preparation of NiO-S eliminated one step, saving time and cost. Therefore, the sensors based on NiO-S will serve as candidates for ethanol sensing. Full article

Lipophilicity is one of many parameters involved in the biological activity of drugs, as it affects their pharmacokinetic and pharmacodynamic behavior. Generally, lipophilicity is assessed by the partition coefficient of a compound between a nonpolar phase (n-octanol) and an aqueous phase (water), expressed as P (partition coefficient) or as its decimal logarithm (Log P). The gold standard method for the experimental determination of Log P is the shake-flask method. In this context, chromatographic methods enable the direct and simple quantification of the partitioned compound between the two phases. This review discusses the use of liquid chromatography (LC) for direct and indirect determination of lipophilicity. Beyond the classical isotropic log P determination, methods for assessing anisotropic lipophilicity are also reviewed. Several examples are discussed that highlight the versatility of LC technique and current trends. The last section of this review focuses on a case study describing an experience of our group and emphasizing the dual role of LC in determining Log P. Full article

This work presents the development of a MIP-based screen-printed potentiometric cell for sensing the pesticide atrazine. The cell comprises three screen-printed electrodes; the working and the counter are obtained by graphite-ink and the pseudo-reference by silver/silver chloride-ink. All electrodes are printed on the support of polyester. Obviously, only the working and the pseudo-reference electrodes are connected for potentiometric measurements. The prepolymeric mixture was composed of the reagents at the following molar ratio: 1 atrazine (ATZ):5 methacrylic acids (MAA):4 ethylene glycol dimethacrylate (EGDMA). An amount of 7 µL of the prepolymeric solution was drop coated on the graphite working electrode of the cell, and the polymerization was carried out in an oven at 70 °C overnight. The specific sites obtained after polymerization and template elution can be viewed as the ionophore of a usual ISE membrane. The active ion is the atrazine in its protonated form, positively charged, so the determination was carried out in aqueous solutions at pHs1.5. At these conditions, the potential increases linearly with atrazine concentration ranging from 5 × 10⁻⁷ to 5 × 10⁻⁶ M; the limit of detection obtained is 4 × 10⁻⁷ M. The slope of the calibration curve E vs. log c (obtained as an average value of the slope of different standardization performed with several electrodes) is 40(6) mV/dec; the sub-Nernstian behavior can be ascribed to the interference of the anions present in the solution media. Full article

The rapid development of the human population has created demand for an increase in the production of food in various fields, such as vegetal, animal, aquaculture, and food processing. This causes an increment in the use of technology related to food production. An example of this technology is the use of gases in the many steps of food treatment, preservation, processing, and ripening. Additionally, gases are used across the value chain from production and packaging to storage and transportation in the food and beverage industry. Here, we focus on the long-standing and recent advances in gas-based food production. Although many studies have been conducted to identify chemicals and biological contaminants in foodstuffs, the use of gas sensors in food technology has a vital role. The development of sensors capable of detecting the presence of target gases such as ethylene (C₂H₄), ammonia (NH₃), carbon dioxide (CO₂), sulfur dioxide (SO₂), and ethanol (C₂H₅OH) has received significant interest from researchers, as gases are not only used in food production but are also a vital indicator of the quality of food. Therefore, we also discuss the latest practical studies focused on these gases in terms of the sensor response, sensitivity, working temperatures, and limit of detection (LOD) to assess the relationship between the gases emitted from or used in foods and gas sensors. Greater interest has been given to heterostructured sensors working at low temperatures and flexible layers. Future perspectives on the use of sensing technology in food production and monitoring are eventually stated. We believe that this review article gathers valuable knowledge for researchers interested in food sciences and sensing development. Full article

Two methods were proposed and implemented for the fabrication of channel waveguides in an Er-doped Tellurite glass. In the first method, channel waveguides were fabricated by implanting 1.5 MeV and 3.5 MeV energy N⁺ ions through a special silicon mask to the glass sample at various fluences. Those waveguides implanted at a fluence of 1.0 × 10¹⁶ ions/cm² operated up to 980 nm, and showed green upconversion of the Erbium ions. In the second method, channel waveguides were directly written in the Er³⁺: TeO₂W₂O₃ glass using an 11 MeV C⁴⁺ ion microbeam with fluences in the range of 1 · 10¹⁴–5 · 10¹⁶ ions/cm². The waveguides worked in single mode regime up to the 1540 nm telecom wavelength. Propagation losses were reduced from the 14 dB/cm of the as-irradiated waveguides by stepwise thermal annealing to 1.5 dB/cm at λ = 1400 nm. Full article

In this study, Ni–Co–Te nanocomposites with multi-dimensional hierarchical structure were successfully prepared using a hydrothermal method. Ni–Co–Te nanocomposites used as electrode materials afford enhanced electroactive properties for electrochemical acetaminophen sensing. Field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were used to characterize the morphological and structural properties to boost their further promotion in acetaminophen sensing. The electrochemical performance of Ni–Co–Te nanocomposites was characterized by electrochemical measurements (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)). The lower electronegativity of the telluride atom and unique structural features of Ni–Co–Te nanocomposites endow the materials with promising performance in acetaminophen sensing (including linear range from 2.5 to 1000 μM, sensitivity of 0.5 μAμM⁻¹cm⁻², limit of detection of 0.92 μM, and excellent selectivity). The results indicated that Ni–Co–Te nanocomposites can serve as promising electrode materials for practical application in electrochemical acetaminophen sensing. Full article

In this study, a paper-based sensor was developed for the detection of hydrogen-peroxide-related biomarkers, with glucose oxidase catalyzing as an example. Potassium iodide can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of hydrogen peroxide to colorize the paper-based biosensor detection area, which was imaged by a scanner, and the color intensity was analyzed by the Adobe Photoshop. Under the optimal conditions, the color intensity shows a good linear relationship with hydrogen peroxide and glucose concentrations in the ranges of 0.1–5.0 mM and 0.5–6.0 mM, respectively. The detection limit of hydrogen peroxide is 0.03 mM and the limit of quantification of glucose is 0.5 mM. Besides, the method was employed in measuring glucose concentration in fruit samples, and the spiked recoveries are in the range of 95.4–106.1%. This method is cost-effective, environmentally friendly, and easy to be operated, which is expected to realize the point-of-care testing of more hydrogen-peroxide-related biomarkers. Full article

The carbon quantum dot (CQD) paper-based analytical device (PAD) has drawn great attention and is being intensively explored. However, the construction of a continuous flow CQD synthesis device remains challenging. In this work, a continuous flow reaction apparatus was constructed to synthesize nitrogen-doped CQDs using a mixed-solvent system of tetraethylene glycol and water. The optical properties of the CQDs were characterized. The CQDs were found to be quenched by phenolics such as chlorogenic acid, salvianolic acid B, and rutin. The CQD PAD was prepared for the determination of the total phenolic content of honeysuckle extracts. A smartphone was used to test the analytical performance of the CQD PAD. The results demonstrated that the degree of fluorescence quenching of the CQDs showed a linear relationship with the concentration of the added chlorogenic acid solution. This method was compared with the total phenolic assay in the Chinese Pharmacopoeia, and the statistical test showed no significant difference between their results. With aqueous tetraethylene glycol as the solvent for the synthesis, the continuous flow reactor for CQD preparation could be easily set up. The CQD PAD is convenient, cheap, and expected to be used for the rapid quality detection of traditional Chinese medicines. Full article

A novel two-dimensional nanocomposite Pt/Ti₃C₂T_x-CNT was synthesized for the non-invasive rapid detection of toluene, a lung cancer biomarker, via cataluminescence (CTL). Pt/Ti₃C₂T_x-CNT exhibited a good catalytic performance toward toluene. The CTL sensor based on Pt/Ti₃C₂T_x-CNT has the advantage of rapid response: The average response time was about 1 s, and the average recovery time was about 30 s. Moreover, the material has a wide scope of detection for toluene, and the limit of detection defined as 3 S/N was about 2 ppm. The optimal working temperature (150 °C) is lower than common sensors, so it has a broad prospect in the actual detection process. Aside from its weak response to formaldehyde, the sensor only exerted a strong response signal to toluene, and no response was observed to other VOCs, indicating that this CTL sensor has good selectivity for toluene. The possible sensing mechanism of CTL showed that toluene was oxidized to generate excited-state CO₂*, which emitted a luminescent signal when it returned to the ground state. Full article

A novel voltammetric electronic tongue (VE-tongue) system based on three nanocomposites modified working electrodes was used for the discrimination of red wine from different geographical origins. The three types of modified working electrodes were fabricated to detect glucose (Glu), tartaric acid (TA), and non-specific flavor information in a red wine sample, respectively. The electrochemical properties of three electrodes were tested by cyclic voltammetric method, and pH, accumulation time, and scan rates were optimized for Glu and TA sensors. Scanning electron microscopy (SEM), X-ray proton spectrum (XPS), and X-ray diffraction (XRD) were used for the characterization of modified materials. This sensor array was then applied to identify four kinds of red wines from different geographical origins, and the multi-frequency and potential steps (STEP) method was used to obtain flavor information regarding rice wines. The classification ability of this VE-tongue system was evaluated by using partial least squares (PLS) regression and principal component analysis (PCA), while back propagation neural network (BPNN), random forest (RF), support vector machines (SVM), deep neural network (DNN), and K-nearest neighbor (KNN) were used for the prediction. The results showed that PCA could explain about the 95.7% of the total variance, and BPNN performed best in the prediction work (the prediction accuracy was 95.8%). Therefore, the VE-tongue system with BPNN was chosen to effectively discriminate red wines from different geographical origins, and the novel VE-tongue aiming at red wine discrimination with high accuracy and lower cost was established. Full article

A porphyrin derivative functionalized with the L-enantiomer of proline amino acid was characterized at the air–pure water interface of the Langmuir trough. The porphyrin derivative was dissolved in dichloromethane solution, spread at the air–subphase interface and investigated by acquiring the surface pressure vs. area per molecule Langmuir curves. It is worth observing that the behavior of the molecules of the porphyrin derivative floating film was substantially influenced by the presence of L-proline amino acid dissolved in the subphase (10⁻⁵ M); on the contrary, the physical chemical features of the floating molecules were only slightly influenced by the D-proline dissolved in the subphase. Such an interesting chirality-driven selection was preserved when the floating film was transferred onto solid supports by means of the Langmuir–Schaefer method, but it did not emerge when a spin-coating technique was used for the layering of the tetrapyrrolic derivatives. The obtained results represent proof of concept for the realization of active molecular layers for chiral discrimination: porphyrin derivatives, due to their intriguing spectroscopic and supramolecular properties, can be functionalized with the chiral molecule that should be detected. Moreover, the results emphasize the crucial role of the deposition technique on the features of the sensing layers. Full article

Fluorescence-based microarray offers great potential in clinical diagnostics due to its high-throughput capability, multiplex capabilities, and requirement for a minimal volume of precious clinical samples. However, the technique relies on expensive and complex imaging systems for the analysis of signals. In the present study, we developed a smartphone-based application to analyze signals from protein microarrays to quantify disease biomarkers. The application adopted Android Studio open platform for its wide access to smartphones, and Python was used to design a graphical user interface with fast data processing. The application provides multiple user functions such as “Read”, “Analyze”, “Calculate” and “Report”. For rapid and accurate results, we used ImageJ, Otsu thresholding, and local thresholding to quantify the fluorescent intensity of spots on the microarray. To verify the efficacy of the application, three antigens each with over 110 fluorescent spots were tested. Particularly, a positive correlation of over 0.97 was achieved when using this analytical tool compared to a standard test for detecting a potential biomarker in lupus nephritis. Collectively, this smartphone application tool shows promise for cheap, efficient, and portable on-site detection in point-of-care diagnostics. Full article

Methane detection is important for the safety of production and life. Metal oxide semiconductor (MOS) methane detection is a mature and widely used technology but still experiences problems such as unsatisfying low-temperature sensing performances. In this study, ZnO/Pd with Pd nanoparticles of different diameters was prepared to study the influence of Pd dispersion on CH₄ sensing properties. Results showed that CH₄ sensing enhancements were positively correlated with the dispersity of Pd. Moreover, by galvanic replacement using Ag as the sacrificial template, a highly dispersive loading of Pd on ZnO was realized, and the CH₄ sensing performance was further enhanced while the amount of Pd reduced from 1.35 wt% to 0.26 wt%. Experiments and DFT calculation indicated that improved CH₄ sensing performance resulted from abundant catalytic sites induced by highly dispersed Pd NPs and the enhanced CH₄ adsorption on positively charged Pds caused by electrons transferred from Pd to Ag. This study provides a strategy to achieve high dispersion of Pd to maximize the utilization of noble metal, which is promising for lowering the cost of the MOS-based CH₄ sensors. Full article

Pesticides are commonly used in agriculture and are an important factor of food security for humankind. However, the overuse of pesticides can harm non-target organisms, and, thus, it is vital to comprehensively study their effects on the different metabolic pathways of living organisms. In the present study, enzyme-inhibition-based assays have been used to investigate the effects of commercial pesticide formulations on the key enzymes of the organisms, which catalyze a wide variety of metabolic reactions (protein catabolism, lactic acid fermentation, alcohol metabolism, the conduction of nerve impulses, etc.). Assay conditions have been optimized, and the limitations of the methods used in the study, which are related to the choice of the solvent for commercial pesticide formulations and optical effects occurring when commercial pesticide formulations are mixed with solutions of enzymes and substrates of assay systems, have been revealed. The effects of commercial pesticide formulations on simple chemoenzymatic assay systems (single-enzyme reactions) have been compared to their effects on complex multicomponent molecular systems (multi-enzyme reactions) and organisms (luminescent bacterium). The in vitro assay systems have shown higher sensitivity to pesticide exposure than the in vivo assay system. The sensitivity of the in vitro assay systems increases with the elongation of the chain of conjugated chemoenzymatic reactions. The effects exerted by commercial pesticide formulations with the same active ingredient but produced by different manufacturers on assay system functions have been found to differ from each other. Full article

As a volatile organic compound, toluene is extremely harmful to the environment and human health. In this work, through a simple one-step solvothermal method, Ni-doped ZnO sensitive materials (0.5, 1, and 2 at% Ni-doped ZnO) with a core-shell morphology were synthesized for the first time for toluene gas detection. The sensing test results showed that the sensor based on 1 at% Ni-doped ZnO exhibited the best toluene sensing performance. The response was up to 210 to 100 ppm toluene at 325 °C. The sensor exhibited high selectivity, fast response/recovery characteristics (2/77 s), and low detection limit (500 ppb, 3.5). Furthermore, we carried out molecular-level research on the sensitive material prepared in this experiment by various characterization methods. The SEM characterization results showed that ZnO and Ni-doped ZnO possessed the core-shell morphology, and the average grain size decreased with the increase in the Ni doping content. The UV–Vis test showed that the band gap of ZnO became smaller with the increase in the Ni doping amount. The enhanced toluene sensing performance of 1 at% Ni-doped ZnO could be ascribed to the structural sensitization and Ni doping sensitization, which are discussed in detail in the sensing mechanism section. Full article

Immunoassays are analytical tools that attract growing research attention in the field of sensors. Among the different analytical methods, the immunoassays based on optical readout have an important role due to the high sensitivity reached in past years by the instrumentation as well as by the preparation of new labels. This review aims to give an overview in term of basic concepts and practical examples of the most used optical immunoassays techniques, in order to help readers to choose the most useful techniques for their analyses. Particular emphasis is dedicated to the application of the presented immunoassays on the detection of the SARS-CoV-2 virus. Full article

This study investigated the electrochemical synthesis of Prussian blue (PB) nanocrystals on a screen-printed carbon electrode (SPCE) modified with a thin film of magnetite nanoparticles (nano-Fe₃O₄) in aqueous mixture solutions of potassium hexacyanoferrate(III) and different kinds of acids. The generated PB nanocrystals exhibited varied voltammetric responses that are highly related to the characteristics and properties of acids in the mixture solution. Interestingly, in the presence of glyphosate as an organic acid, surface magnetite nanoparticles were occluded within electrogenerated Prussian blue nanocubes (PBNC), which are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), and cyclic voltammetry (CV). Furthermore, the possible reaction mechanism for the formation of PBNC is proposed in this study. The obtained PBNC was also evaluated as an electrocatalyst of hydrogen peroxide and applied to the detection of glyphosate. Full article

This review presents numerous studies in which mass spectrometry has been used to assist forensic investigation. Due to its unique capabilities, mainly high-resolution mass data and structural information, high sensitivity, and cooperation with separation techniques, this method provides access to many tools streamlining and accelerating sample analysis. Low analyte consumption, advanced derivatization procedures and availability of isotopically labeled standards offer opportunities to study materials previously not considered viable evidence, opening new avenues in forensic investigations. Full article

An increase in interest in the use of sensing technologies (e.g., electrochemistry, fluorescence, thermal, surface plasmon resonance, piezo, reflectometry, chemo or bioluminescence, and optics) as analytical methods to be implemented in a wide range of fields, including agriculture and food has been witnessed in recent years. Most of these applications have been evaluated and developed targeting a wide range of samples (e.g., raw materials, commodities, soils, water, food ingredients, natural products). Sensing technologies must be integrated with different data analytical techniques (e.g., pattern recognition, modelling techniques, calibration development) to develop a target application. The increasing availability of modern and inexpensive sensors, together with access to easy-to-use software is determining a steady growth in the number of applications and uses of these technologies. This short review underlined and briefly discussed practical considerations that support the robust development and implementation of applications that combine the use of sensing technologies with chemometrics. Full article

The meat industry requires prompt and effective control measures to guarantee the quality and safety of its products and to avert the incidence of foodborne illnesses and disease outbreaks. Although standard microbiological methods and conventional analytical techniques are employed to monitor the quality and safety, these procedures are tedious and time-consuming, require skilled technicians, and sophisticated instruments. Therefore, there is an urgent need to develop simple, fast, and user-friendly hand-held devices for real-time monitoring of the quality of meat and meat products in the supply chain. Biosensors and chemical indicators, due to their high sensitivity, specificity, reproducibility, and stability, are emerging as promising tools and have the potential for monitoring and controlling the quality (freshness and sensory traits such as tenderness) and safety (metabolites, contaminants, pathogens, drug residues, etc.) of muscle foods. In this review, the application of biosensors in the meat industry and their emerging role in the quantification of key meat quality components are discussed. Furthermore, the role of different biosensors to identify and detect contaminants, adulterants, pathogens, antibiotics, and drug residues in meat and meat products is also summarized. Full article

As a new form of energy, hydrogen (H₂) has clean and green features, and the detection of H₂ has been a hot topic in recent years. However, the lack of suitable laser sources and the weak optical absorption of H₂ limit the research concerning its detection. In this study, a continuous-wave distributed feedback (CW-DFB) diode laser was employed for sensing H₂. Tunable diode laser absorption spectroscopy (TDLAS) was adopted as the detection technique. The strongest H₂ absorption line, located at 4712.90 cm⁻¹ (2121.83 nm, line strength: 3.19 × 10⁻²⁶ cm⁻¹/cm⁻² × molec), was selected. We propose a H₂-TDLAS sensor based on the wavelength modulation spectroscopy (WMS) technique and a Herriott multipass gas cell (HMPC) with an optical length of 10.13 m to achieve a sensitive detection. The WMS technique and second harmonic (2f) demodulation technique were utilized to suppress system noise and simplify the data processing. The 2f signal of the H₂-TDLAS sensor, with respect to different H₂ concentrations, was measured when the laser wavelength modulation depth was at the optimal value of 0.016 cm⁻¹. The system’s signal-to-noise ratio (SNR) and minimum detection limit (MDL) were improved from 248.02 and 0.40% to 509.55 and 0.20%, respectively, by applying Daubechies (DB) wavelet denoising, resulting in 10 vanishing moments. The Allan variance was calculated, and the optimum MDL of 522.02 ppm was obtained when the integration time of the system was 36 s. Full article

In this series of two papers, the humidity sensing of a carbon nanotube (CNT) network-based material is transduced and studied through quartz crystal microbalance (QCM) measurements. To this aim, quartzes functionalized with different amounts of sensing material were realized, exposed to different humidity levels, and characterized. In this second paper, the experimental results are presented and discussed. The sensing mechanisms are elucidated exploiting the theory presented in the first paper of this series. The presented results show that the investigated material functionalization induces a large response of QCM to humidity in terms of resonant frequency even at low RH levels, with a sensitivity of about 12 Hz/%RH (at RH < 30% and room temperature and 10 ug of deposited SWCNT solution) and an increase in sensitivity in the high RH range typical of nanostructured film. Regarding the response in terms of motional resistance, a large response is obtained only at intermediate and high humidity levels, confirming that condensation of water in the film plays an important role in the sensing mechanism of nanostructured materials. Full article

Compared with traditional two-dimensional culture, a three-dimensional (3D) culture platform can not only provide more reliable prediction results, but also provide a simple, inexpensive and less time-consuming method compared with animal models. A direct in vitro model of the patient’s tumor can help to achieve individualized and precise treatment. However, the existing 3D culture system based on microwell arrays has disadvantages, such as poor controllability, an uneven spheroid size, a long spheroid formation time, low-throughput and complicated operation, resulting in the need for considerable labor, etc. Here, we developed a new type of microdevice based on a 384-well plate/96-well plate microarray design. With our design, cells can quickly aggregate into clusters to form cell spheroids with better roundness. This design has the advantage of high throughput; the throughput is 33 times that of a 384-well plate. This novel microdevice is simple to process and convenient to detect without transferring the cell spheroid. The results show that the new microdevice can aggregate cells into spheroids within 24 h and can support drug and radiation sensitivity analyses in situ in approximately one week. In summary, our microdevices are fast, efficient, high-throughput, simple to process and easy to detect, providing a feasible tool for the clinical validation of individualized drug/radiation responses in patients. Full article

Microwave dielectric sensing offers a rapid, label-free, and non-invasive way of characterization and sensing of biological materials at the microfluidic scale. In this work, a dielectric sensing is achieved with a microwave interferometric setup that is applied to cytometric applications. A fast way to analyze and design an interferometric system at microwave frequencies in software tools is proposed together with a novel manufacturing and assembly process, which enables a short recovery time and avoids extensive microwave-microfluidic chip fabrication. The simulation and measurement results of the interferometric setup are in agreement with an excellent match at levels below S₂₁ = −60 dB. The sensitive microwave setup is evaluated on measurements of 3 µm polystyrene spheres and finally applied for characterization of a widely used laboratory Saccharomyces cerevisiae strain, the S288C, in a frequency range from 4 to 18 GHz. Full article

Surface-enhanced Raman scattering (SERS) has received increasing attention from researchers since it was first discovered on rough silver electrode surfaces in 1974 and has promising applications in life sciences, food safety, and environmental monitoring. The discovery of graphene has stirred considerable waves in the scientific community, attracting widespread attention in theoretical research and applications. Graphene exhibits the properties of a semi-metallic material and has also been found to have Raman enhancement effects such as in metals. At the same time, it quenches the fluorescence background and improves the ratio of a Raman signal to a fluorescence signal. However, graphene single-component substrates exhibit only limited SERS effects and are difficult to use for trace detection applications. The common SERS substrates based on noble metals such as Au and Ag can produce strong electromagnetic enhancement, which results in strong SERS signals from molecules adsorbed on the surface. However, these substrates are less stable and face the challenge of long-term use. The combination of noble metals and graphene to obtain composite structures was an effective solution to the problem of poor stability and sensitivity of SERS substrates. Therefore, graphene-based SERS has been a popular topic within the last decade. This review presents a statistically based analysis of graphene-based SERS using bibliometrics. Journal and category analysis were used to understand the historical progress of the topic. Geographical distribution was used to understand the contribution of different countries and institutions to the topic. In addition, this review describes the different directions under this topic based on keyword analysis and keyword co-occurrence. The studies on this topic do not show a significant divergence. The researchers’ attention has gradually shifted from investigating materials science and chemistry to practical sensing applications. At the end of the review, we summarize the main contents of this topic. In addition, several perspectives are presented based on bibliometric analysis. Full article

In this work, a screening of Sonogel-Carbon (SNGC) electrodes modified with nanomaterials (carbon nanotubes and gold nanoparticles) and the study of their effect on the electrochemical performance of sinusoidal voltage (SV) and current (SC)-based biosensors are reported. Surface modification was achieved by drop-casting and electrodeposition methodologies. Within the strategies used, SV and SC, recently exploited procedures, were used to electrodeposit simultaneously a poly 3,4-ethylenedioxythiophene (PEDOT)-tyrosinase layer and the corresponding nanostructured material. Dopamine was selected as a benchmark analyte to evaluate the analytical performance of the different (bio)sensors obtained in terms of relevant figures of merit, such as sensitivity, limits of detection and quantitation, and accuracy, among others. A discussion about the pros and cons between the type of modification and the methods employed is also presented. Briefly, SC based sensors offered excellent quality analytical parameters and lower dispersion of the results. They were employed for more specific electrochemical studies, including interferences assays and the determination of DA in real samples, obtaining good recoveries (101–110.6%). The biosensor modified with gold nanoparticles (AuNPs) (drop-casting method) and SC-electrodeposited showed the best figures of merit: R² = 0.999; sensitivity = −4.92 × 10⁻⁹ A·µM⁻¹; RSD_sensitivity = 1.60%; LOD = 5.56 µM; RSD_LOD = 6.10%; and LOQ = 18.53 µM. Full article

In this series of two papers, the humidity sensing of a carbon nanotube’s (CNTs) network-based material is studied through quartz crystal microbalance (QCM) sensors. To this aim, quartzes functionalized with different amounts of sensing material were realized, exposed to different humidity levels, and characterized. In this first paper, the theoretical framework is presented, whereas the second one presents the experimental study. This paper discusses at first the water adsorption and desorption on single-wall carbon nanotube (SWCNT) networks, and subsequently deeply investigates the behavior of QCM-based measurements. Numerical simulations based on the equivalent electrical model of the quartz were used for predicting the vibrational behavior of functionalized QCMs when exposed to different humidity levels, accounting for the effect of the different water adsorption mechanisms: chemisorption, physisorption, and capillary condensation. Full article