Chemosensors, Volume 10, Issue 9 (September 2022) – 31 articles

Driving safety issues, such as drunk driving, have drawn a lot of attention since the advent of shared automobiles. We used an electronic nose (EN) detection device as an onboard system for shared automobiles to identify drunk driving. The sensors in the EN, however, can stray in cold winter temperatures. We suggested an independent component analysis (ICA) correction model to handle the data collected from the EN in order to lessen the impact of low temperature on the device. Additionally, it was contrasted with both the mixed temperature correction model and the single temperature model. As samples, alcohol mixed with concentrations of 0.1 mg/L and 0.5 mg/L were tested at (20 ± 2) °C, (−10 ± 2) °C, and (−20 ± 2) °C. The results showed that the ICA correction model outperformed the other models with an accuracy of 1, precision of 1, recall of 1, and specificity of 1. As a result, this model can be utilized to lessen the impact of low temperature on the EN’s ability to detect the presence of alcohol in the driver’s inhaled gas, strongly supporting its use in car-sharing drink driving. Other ENs that need to function in frigid conditions can also use this technique. Full article

In order to rationally apply potassium fertilizer, it is very important to realize the rapid and accurate evaluation of soil available potassium (K). Conventional methods are time-consuming, consumables-consuming and laborious. A high-efficiency method was proposed in this study to meet the demand for rapid evaluation, including rapid extraction, uniform evaporation and LIBS detection. To shorten the extraction time, we increased the oscillation frequency and removed the operation of dry filtration. Compared with the conventional extraction method of the Chinese national standard (CNS), the extraction time was reduced from 30 min to 2 min. In addition, we developed a uniform evaporation method for liquid–solid transformation on the batch-detection fixed area aluminum substrate. This method reduced the moisture interference. At the same time, increasing the liquid viscosity and restricting the liquid area and shape could reduce the coffee ring effect (CRE). The determination coefficient of the calibration curve by our method was 0.99, and the limit of quantitation reached 0.8 mg/kg. Real soil samples were taken as validation, and the average relative error between our method and the CNS method was 3.58%. The results indicate that our method combined with LIBS technology could provide a fast and accurate evaluation of soil available K. Full article

The preparation and self-assembling of monodisperse gold nanoparticles (Au NPs) is of great significance for its SERS application. According to the oleylamine-reduced method, oleylamine (OAm) serves as the reducing agent and stabilizing agent, and the effects of different reaction parameters such as solvent and temperature on the size and dispersity of Au NPs have been evaluated. The Au NPs synthesized with toluene as the solvent have the best dispersity and narrowest particle size distribution with adjustable sizes. The particle size gradually increases with the increase in reaction temperature. The highly ordered self-assembly film of Au NPs was employed as surface-enhanced Raman scattering (SERS) substrate for the probing molecule of rhodamine 6G. The Au substrate exhibits excellent spatial uniformity and SERS reproducibility, which indicates its practicability as a substrate. This study provides a simple synthesis strategy of highly ordered monodispersed Au NPs, which can serve as a SERS substrate with excellent spatial uniformity and SERS re-producibility. Full article

Two-dimensional (2D) or ultrathin metal sulfides have been emerging candidates in developing high-performance gas sensors given their physisorption-dominated interaction with target gas molecules. Their oxysulfide derivatives, as intermediates between oxides and sulfides, were recently demonstrated to have fully reversible responses at room temperature and long-term device stability. In this work, we explored the micro-scale self-assembly of ultrathin nickel oxysulfide through the calcination of nickel sulfide in a controllable air environment. The thermal treatment resulted in the replacement of most S atoms in the Ni-S frameworks by O atoms, leading to the crystal phase transition from original hexagonal to orthorhombic coordination. In addition, the corresponding bandgap was slightly expanded by ~0.15 eV compared to that of pure nickel sulfide. Nickel oxysulfide exhibited a fully reversible response towards H₂ at room temperature for concentrations ranging from 0.25% and 1%, without the implementation of external stimuli such as light excitation and voltage biasing. The maximum response factor of ~3.24% was obtained at 1% H₂, which is at least one order larger than those of common industrial gases including CH₄, CO₂, and NO₂. Such an impressive response was also highly stable for at least four consecutive cycles. This work further demonstrates the great potential of metal oxysulfides in room-temperature gas sensing. Full article

The equivalency of pH measurements between aqueous and non-aqueous or viscous solutions is of great interest in biomedical applications as well for processing food and pharmaceuticals. Commercial glass-type electrodes have practical limitations, such as bulky sizes and membrane clogging in viscous environments. In this study, planar and flexible electrochemical pH sensors with iridium oxide as the sensing film have been developed by sol-gel and oxidation processes. A reference electrode was prepared by screen printing Ag/AgCl ink on the same polyimide substrate. The small form factors of the planar flexible electrodes provide an advantage in small volume or conformal surface measurements. Cyclic voltammetry was performed in different pH solutions. The electrode originally produced a response of −70.1 mV/pH at room temperature in aqueous solutions. The sensitivities were reduced when salt was added into the buffer solutions, although output potentials were increased. Sensing performances in a wide range of viscous conditions with various concentrations of added salt have been analyzed to study their effects on pH-sensing responses. Suitable calibration techniques using aqueous buffer solutions were studied for output potentials and their respective pH readings in viscous salt-added solutions. The mechanisms affecting output potentials are explained and results matched well for two different thickening agents. Specificity to pH changes measured by the planar IrO_x-Ag/AgCl pH electrodes showed how the potential-pH calibration should consider the interference effect of salt. The viscosity effects on pH reading errors became more pronounced as solution viscosity increased. Comparisons of pH readings to those from a commercial glass-bodied pH meter indicated that the planar electrodes provided predictable pH deviations that were confined to a limited range. The planar IrO_x-Ag/AgCl electrodes on flexible polyimide substrates have mostly been demonstrated with aqueous solutions in various diagnostic and environmental monitoring applications. This work provides more insights into pH sensing performance when the fluid is viscous and contains salt, which often is the case in biomedical and food-processing applications. Full article

Femtosecond laser ablation spark-induced breakdown spectroscopy (fs LA-SIBS) was developed to quantitatively analyze vanadium, molybdenum, chromium, manganese, aluminum, nickel, and copper in a steel alloy. In the experiment, a femtosecond laser operating at a repetition rate of 1 kHz was used as the laser ablation source, and spark discharge was utilized to re-excite the plasma and enhance the atomic intensity. A compact fiber spectrometer was used to record and analyze the plasma emission spectra in a nongated signal-recording mode. The calibration curves of V, Mo, Cr, Mn, Al, Ni, and Cu elements in steel alloy samples were established, and the detection limits of these elements were determined to be 10.9, 12.6, 4.0, 5.7, 8.7, 7.9, and 3.1 ppm with fs LA-SIBS, respectively, which were 4–12-fold better than those achieved with femtosecond laser-induced breakdown spectroscopy (fs LIBS). Compared with conventional LIBS, the fs LA-SIBS technique provided a rapid and high spatial resolution approach to quantitative elemental analysis, with better analytical sensitivity. Full article

Inorganic lead-halide perovskite, cesium lead bromide (CsPbBr₃), shows outstanding optoelectronic properties. Both solution- and melt-based methods have been proposed for CsPbBr₃ crystal growth. The solution-based growth was done at low-temperature, whereas the melt-based growth was done at high-temperature. However, the comparison of optical, physical, and defect states using these two different growth conditions has been scarcely studied. Here, we have compared the thermal and optical properties of solution-grown and melt-grown single crystals of CsPbBr₃. Positron Annihilation Lifetime Spectroscopy (PALS) analysis showed that melt-grown crystal has a relatively smaller number of defects than the chemical synthesis method. In addition, crystals grown using the chemical method showed a higher fluorescence lifetime than melt-grown CsPbBr₃. Full article

Mo₂C is a two-dimensional material with high electrical conductivity, low power consumption, and catalytic effect, which has promising applications in the field of microfluidic gas detection. First principles were used to study the adsorption characteristics of Mo₂C monolayer on four typical decomposition gases of SF₆ (H₂S, SO₂, SOF₂, and SO₂F₂), and to explore the feasibility of its application in the detection of SF₆ decomposition components. The results showed that Mo₂C chemisorbed all four gases, and the adsorption capacity was H₂S < SO₂ < SOF₂ < SO₂F₂. The adsorption mechanism of Mo₂C as a microfluidic sensor was analyzed in combination with its charge-density difference and density of states. On the other hand, the different work-function change trends after adsorbing gases provide the possibility for Mo₂C to selectively detect gases as a low-power field-effect transistor sensor. All content can be used as theoretical guidance in the realization of Mo₂C as a gas-sensitive material for the detection of SF₆ decomposition components. Full article

Carbon-based quantum dots and their nanocomposites have sparked immense interest for researchers as sensors due to their attractive physico-chemical properties caused by edge effects and quantum confinement. In this review article, we have discussed the synthesis and application of nanocomposites of graphene quantum dots (GQDs) and carbon quantum dots (CQDs). Different synthetic strategies for CQDs, GQDs, and their nanocomposites, are categorized as top-down and bottom-up approaches which include laser ablation, arc-discharge, chemical oxidation, ultrasonication, oxidative cleavage, microwave synthesis, thermal decomposition, solvothermal or hydrothermal method, stepwise organic synthesis, carbonization from small molecules or polymers, and impregnation. A comparison of methodologies is presented. The environmental application of nanocomposites of CQDs/GQDs and pristine quantum dots as sensors are presented in detail. Their applications envisage important domains dealing with the sensing of pollutant molecules. Recent advances and future perspective in the use of CQDs, GQDs, and their nanocomposites as sensors are also explored. Full article

The sensitive and selective detection of nitroaromatic explosives is of great significance to national security and human health. Herein, the novel linear polymer l-PAnTPE and cross-linked polymer PAnTPE nanoparticles based on anthracene and tetraphenylethene groups were designed and successfully synthesized via Suzuki-miniemulsion polymerization. The particle sizes of the polymers are around 73 nm, making them well dispersible in water. The cross-linked polymer PAnTPE exhibits porous structure, which is beneficial for the diffusion/adsorption of analytes. The fluorescence sensing towards nitroaromatics was performed in the aqueous phase, and l-PAnTPE and PAnTPE nanoparticles showed different quenching degree towards different nitroaromatics. Among them, the quenching constant K_SV values of l-PAnTPE and PAnTPE towards 2,4,6-trinitrophenol (TNP) reach 1.8 × 10⁴ M⁻¹ and 4.0 × 10⁴ M⁻¹, respectively, which are 1–2 orders of magnitude higher than other nitroaromatic explosives, thus demonstrating the high sensitivity and selectivity of TNP detection in the aqueous phase. The sensing mechanism was further discussed to clarify this phenomenon by analyzing UV–Vis absorption, excitation, fluorescence spectra, cyclic voltammograms and fluorescence decay measurements. In addition, the paper strips tests exhibit that l-PAnTPE and PAnTPE have great potential in the application of fast, low-cost and on-site nitroaromatics detection. Full article

Serotonin is a biogenic amine that has multiple roles in the human body and is mainly known as the happiness hormone. A new laccase (Lac)-based biosensor has been developed for the qualitative and quantitative determination of serotonin in three dietary supplements from three different manufacturers. The enzyme was immobilized on an organized mesoporous carbon-modified carbon screen-printed electrode (OMC-SPE) by the drop-and-dry method, the active surface being pretreated with glutaraldehyde. With the new biosensor, serotonin was selectively detected from different solutions. Square-wave voltammetry was the technique used for the quantitative determination of serotonin, obtaining a detection limit value of 316 nM and a quantification limit value of 948 nM in the linearity range of 0.1–1.2 µM. The pH for the determinations was 5.2; at this value, the biocatalytic activity of the laccase was optimal. At the same time, the electrochemical performance of the OMC-SPE/Lac biosensor was compared with that of the unmodified sensor, a performance that highlighted the superiority of the biosensor and the very important role of the enzyme in electrodetection. The results obtained from the quantitative determination of serotonin by square-wave voltammetry were compared with those from the FTIR method, revealing a very good correlation between the results obtained by the two quantitative determination methods. Full article

Despite potential advantages of metal oxide semiconductors (MOSs)-based gas sensors, the limitation of very high baseline resistance is still unsatisfactory for practical application. By means of element doping, the performance of metal oxide materials used as gas sensors can be optimized. Herein, different cations (Al³⁺, Sn⁴⁺, and Sb⁵⁺) doped ZnO nanoparticles were synthesized and used as the acetone sensing materials. Results show that the resistance of sensors based on Sn⁴⁺ doped ZnO was significantly reduced (from 5.18 to 0.28 MΩ) at 270 °C without sacrificing the acetone sensing responses. In addition, the gas sensor also exhibited the fast response/recovery time (1/10 s) and great long-term stability. The electron compensation and improved adsorbing oxygen ability for the Sn⁴⁺ doped ZnO nanoparticles contributed to the relatively low resistance and enhanced acetone sensing performances. Full article

The world of sensors is diverse and is advancing at a rapid pace due to the fact of its high demand and constant technological improvements. Electrochemical sensors provide a low-cost and convenient solution for the detection of variable analytes and are widely utilized in agriculture, food, and oil industries as well as in environmental and biomedical applications. The popularity of electrochemical sensing stems from two main advantages: the variability of the reporting signals, such as the voltage, current, overall power output, or electrochemical impedance, and the low theoretical detection limits that originate from the differences in the Faradaic and nonFaradaic currents. This review article attempts to cover the latest advances and applications of electrochemical sensors in different industries. The role of nanomaterials in electrochemical sensor research and advancements is also examined. We believe the information presented here will encourage further efforts on the understanding and progress of electrochemical sensors. Full article

Nitrogen-doped carbon quantum dots are easily obtainable nanomaterials endowed with remarkable fluorescence properties for the detection of contaminations by heavy metals. In this report, we show that nanometric particles with high specificity for silver cations can be prepared by hydrothermal synthesis starting from citric and folic acid solutions. Solutions of these N-CQDs give a strong fluorescence emission in the violet region (385 nm) when excited at 330 nm, which can be quenched selectively by silver (I) cations at sub-nanomolar concentrations, while other cations do not give any effect. This remarkable feature was tentatively correlated with the stronger interactions between silver ion and small portions of the nanomaterial surface by comparing Ag⁺ and the isoelectronic Cd²⁺. Full article

Herein, we describe the facile synthesis of spinel MgFe₂O₄ ferrite and its potential use as a gas sensor using a straightforward and reliable sol–gel approach, i.e., the glycine-assisted auto-combustion route. The novelty in obtaining the sensing material via the auto-combustion route is its inherent simplicity and capability to produce the material at an industry scale. The said cost-effective process makes use of simple metal salts (Mg and Fe-nitrates) and glycine in an aqueous solution, which leads to the formation of spinel MgFe₂O₄ ferrite. A single-phase crystallinity with crystallite sizes ranging between 36 and 41 nm was observed for the synthesized materials using the X-ray diffraction (XRD) technique. The porous morphologies of the synthesized materials caused by auto-ignition during the combustion process were validated by the microscopic investigations. The EDS analysis confirmed the constituted elements such as Mg, Fe, and O, without any impurity peaks. The gas-sensing ability of the synthesized ferrites was examined to detect various reducing gases such as LPG, ethanol, acetone, and ammonia. The ferrite showed the highest response (>80%) toward LPG with the response and recovery times of 15 s and 23 s, respectively. Though the sensor responded low toward ammonia (~30%), its response and recovery times were very quick, i.e., 7 s and 9 s, respectively. The present investigation revealed that the synthesized ferrite materials are good candidates for fabricating high-performance sensors for reducing gases in real-world applications. Full article

Flexible and stretchable strain sensors can be applied for human health monitoring and disease diagnoses via the output of multiple biophysical signals. However, it is still a challenge to fabricate short-peptide-based strain sensors. Here, we prepared a novel polymer-dipeptide double-network hydrogel with excellent stretchability, responsiveness, and stability. The poly(acrylic acid) (PAA) gel, by cross-linking, maintains mechanical and flexible properties, and the fluorenyl methoxycarbonyl-diphenylalanine (Fmoc-FF) network, by non-covalent interactions, is helpful for energy dissipation. With increasing tensile or compression strains, the PAA/Fmoc-FF hydrogel exhibited a high mechanical strength and fast recovery. Moreover, as the presence of KCl improves the electronic conductivity, the hybrid gel exhibited a cyclic strain-stress performance, which is the foundation of a strain sensor. Based on that, its application as a motion sensor was demonstrated by monitoring the movements of human joints, such as the forefinger, wrist, elbow, and knee. Consequently, the hybrid polymer-peptide gel could be an ideal candidate for wearable sensors in the future. Full article

Colorimetric enzyme-linked immunosorbent assay (ELISA) has been widely applied as the gold-standard method for cytokine detection for decades. However, it has become a critical challenge to further improve the detection sensitivity of ELISA, as it is limited by the catalytic activity of enzymes. Herein, we report an enhanced colorimetric ELISA for ultrasensitive detection of interleukin-6 (IL-6, as a model cytokine for demonstration) using Pd@Pt core@shell nanodendrites (Pd@Pt NDs) as peroxidase nanomimics (named “Pd@Pt ND ELISA”), pushing the sensitivity up to femtomolar level. Specifically, the Pd@Pt NDs are rationally engineered by depositing Pt atoms on Pd nanocubes (NCs) to generate rough dendrite-like Pt skins on the Pd surfaces via Volmer–Weber growth mode. They can be produced on a large scale with highly uniform size, shape, composition, and structure. They exhibit significantly enhanced peroxidase-like catalytic activity with catalytic constants (Kcat) more than 2000-fold higher than those of horseradish peroxidase (HRP, an enzyme commonly used in ELISA). Using Pd@Pt NDs as the signal labels, the Pd@Pt ND ELISA presents strong colorimetric signals for the quantitative determination of IL-6 with a wide dynamic range of 0.05–100 pg mL⁻¹ and an ultralow detection limit of 0.044 pg mL⁻¹ (1.7 fM). This detection limit is 21-fold lower than that of conventional HRP-based ELISA. The reproducibility and specificity of the Pd@Pt ND ELISA are excellent. More significantly, the Pd@Pt ND ELISA was validated for analyzing IL-6 in human serum samples with high accuracy and reliability through recovery tests. Our results demonstrate that the colorimetric Pd@Pt ND ELISA is a promising biosensing tool for ultrasensitive determination of cytokines and thus is expected to be applied in a variety of clinical diagnoses and fundamental biomedical studies. Full article

In the proposed method, microwave-assist heating and AgNO3/trisodium citrate were used to create the polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs) sensor. This sensor had a peroxidase-like activity that could catalytically oxidize O-phenylenediamine (OPD, colourless) into 2,3-diaminophenazine (ox-OPD, greenish-yellow colour) in the presence of H₂O₂, otherwise, in the presence of Hg²⁺, this pass has been effectively inhibited. The degree of colour fading was directly correlated with Hg²⁺ concentration. These results indicated the selectivity of Hg²⁺ ions toward PVP-AgNPs after establishing the PVP-AgNPs/OPD/H₂O₂ system. This selectivity was proved by the negative results obtained from other mon-, di-, and trivalent ions such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Ba²⁺, Co²⁺, Ni²⁺, Cd²⁺, and Cr³⁺, instead of Hg²⁺. Consequently, a reliable, selective, and eco-effective spectrophotometric approach was designed for the detection of Hg²⁺ in various types of water samples. LOD was extended to lower than 0.1 µM, and a fading in the obtained colour was shown by the naked eye at a concentration higher than 1.5 µM of Hg²⁺. The elemental details for preparing the used PVP-AgNPs, such as particle size, morphology, polydispersity index (PdI), and their UV-visible spectrum, were identified by SEM technique, TEM, UV-visible spectrophotometer, and zeta-sizer device. Thus, the peroxidase mimicking the activity of OPD/H₂O₂ was confirmed by a fluorescence technique. The greenness profile of this work was confirmed after applying a reported assessment tool. Full article

An electrochemical sensor based on carbon paste modified with polyethyleneimine was developed and employed for the determination of caffeic acid in aromatic herbs. The sensor was prepared by mixing polyethylenimine (1.5% v/v), graphite powder, and mineral oil. The polyethylenimine-based electrode showed an enhancement of charge transfer at the electrode–solution interface and a higher current intensity for the electrochemical reaction of caffeic acid, in comparison to the unmodified electrode. The calibration plot of caffeic acid constructed in 0.1 mol L⁻¹ acetate buffer (pH 5.0) by square wave voltammetry was linear in the range of 1.25 to 19.9 μmol L⁻¹ with a limit of detection of 0.13 μmol L⁻¹, respectively. Finally, the proposed sensor was employed to monitor the caffeic acid with accuracy in dried Thymus vulgaris and Salvia officinalis samples, with recovery results from 93 to 105%. Full article

We report on the optical characterization of very high-efficiency and high-resolution holographic volume phase transmission gratings. The gratings are recorded in a new photo-polymerizable mixture made by epoxy-resin and multi-acrylate. The epoxy-resin used is known to make tenacious acrylate-based films. The holographic mixture contains two photo-initiators, the synergic effect of which enables a reliable photo-polymerization process in the visible region of the electromagnetic spectrum. The recorded holograms are mechanically stable, show long-term temporal stability and very high values of diffraction efficiency, coupled with good angular selectivity due to a relatively narrow band of wavelengths. We measured the intensity of the transmitted beam and calculated the intensity of the diffracted beam at different wavelengths, deriving the refractive index modulation and the grating pitch by fitting the experimental data with a slightly modified theoretical approach. These kind of mixtures can be used in several fields of application, such as chemical or bio-sensors, high resolution optical sensors, high-density optical data storage, encryption and security. Full article

The employment of graphene for multifunctional uses has been a cornerstone in sensing technology. Due to its excellent electrochemical properties, graphene has been used in its pure and composite forms to detect target molecules over a wide range of surfaces. The adsorption process on the graphene-based sensors has been studied in terms of the change in resistance and capacitance values for various industrial and environmental applications. This paper highlights the performance of graphene-based sensors for detecting different kinds of domestic and industrial gases. These graphene-based gas sensors have achieved enhanced output in terms of sensitivity and working range due to specific experimental parameters, such as elevated temperature, presence of particular gas-specific layers and integration with specific nanomaterials that assist with the adsorption of gases. The presented research work has been classified based on the physical nature of graphene used in conjugation with other processed materials. The detection of five different types of gases, including carbon dioxide (CO₂), ammonia (NH₃), hydrogen sulphide (H₂S), nitrogen dioxide (NO₂) and ethanol (C₂H₅OH) has been shown in the paper. The challenges of the current graphene-based gas sensors and their possible remedies have also been showcased in the paper. Full article

Determination of pH values has a vital influence in many chemical and biological processes. To accurately determine pH values, we fabricated a highly photostable ratiometric fluorescent pH−sensitive nanosensor by staining the core of mesoporous silica nanoparticle with a rhodol dye and chemically labelling its outer shell with a rhodamine derivative dye. The two dyes possess opposite pH−responding directions, which increases the band of the signal change. There is a nine−fold change in fluorescence intensity ratios when the solution pH changes from 3.0 and 9.0. Meanwhile, the nanosensors displayed yellowish emission in low pH value, orange emission in mid pH value, and reddish emission in high pH value, which can be readily inspected by bare eyes. Last but not least, excellent photostability and reversibility features make the nanosensors useful for the continuous measuring of pH with high accuracy. Full article

In this study, we report a straightforward and reproducible hydrothermal synthesis of copper oxide nanowires, their morphological and chemical characterization, and their application in gas sensing. Results show that the hydrothermal process is mainly influenced by the reaction time and the concentration of the reducing agent, demonstrating the synthesis of fine and long nanowires (diameter of 50–200 nm and length of 25 µm) after 10 h of reaction with 0.1 M of pyrrole. Two different annealing temperatures were tested (205 and 450 °C) and their effect on the morphology, chemical composition, and crystal size of the nanowires was analyzed by SEM, XPS, and XRD techniques, respectively. The analysis shows that the Cu²⁺ oxidation state is mainly obtained at the higher annealing temperature, and the nanowires’ shape suffers a transformation due to the formation of agglomerated crystallites. The gas sensing tests for acetone, ethanol, toluene, and carbon monoxide show preferential response and sensitivity to acetone and ethanol over the other analytes. The annealing temperature proves to have a higher influence on the stability of the nanowires than on their gas sensitivity and selectivity, showing better medium-term stability for the nanowires annealed at 450 °C. Full article

The growing bioeconomic demand for lightweight materials with combined sustainability, large-scale production, ease in functionalization and competitive mechanical properties has seen the revival of cellulose as a scaffold for several applications. In particular, due to its multifunctional features, cellulose has found application in sensor and biosensor fabrication. Nonetheless, the great variety of cellulose properties and formulations makes the choice of the best suited cellulose-based material for a specific sensing strategy a difficult task. This review offers a critical discussion and guide for the reader towards the understanding of which of the multiple cellulose derivatives and properties can be exploited for the optimal performance of the desired sensing device. We introduce the unique molecular structure, nanoarchitecture and main properties of cellulose and its derivatives. The different functionalization approaches for anchoring receptors on cellulose derivatives and the processing methodologies for fabricating cellulose-based sensors are explored. As far as the use and performance of cellulose-based functional materials in sensors is concerned, we discuss the recent advances of optical and electrochemical sensors and biosensors for biomedical and environmental monitoring. Full article

Free metal ion concentrations of amalgamating elements such as Zn, Cd, In, or Pb can be determined with absence of gradients and Nernstian equilibrium stripping(AGNES) in a variety of matrices, ranging from seawater to wine or dissolving nanoparticles. In this hands-on paper, we review the fundamental concepts and provide the practical steps to implement AGNES, including ready-to-run files for the software controlling the potentiostat, computation spreadsheets, step-by-step laboratory protocols, etc. Two case studies with a free Zn concentration determination are discussed: (i) a synthetic solution with the ligand oxalate and (ii) a natural sample of the Segre river (Catalonia, Spain). Suggestions for the extension of AGNES to other systems are indicated. Full article

The increasing demand for rare earth elements (REE) requires faster analysis techniques for their rapid exploration. Laser-induced breakdown spectroscopy (LIBS) has on-site and real time analysis capability. However, interference and the weaker emission of minor REEs are key challenges for the complex REE emission spectra. Using simulations and experimental results, we presented essential principles for improved line identification in the transient spectra of complicated samples, such as those of REE ores (e.g., monazite). Knowledge of plasma conditions, spectral collection setup, and capability of the spectral system are key parameters to consider for the identification of an emission line in such spectra. Furthermore, emission intensity dependence on laser wavelength was analyzed for major and minor REEs using IR (1064 nm), visible (532 nm) and UV (266 nm) irradiation. A higher plasma temperature was found with the IR laser, while stronger material ablation was observed by UV irradiation. Higher particle density by UV laser ablation was the key factor in the higher signal intensity of the minor elements, and this laser can improve the emission signals for LIBS use as an REE analyzer. Full article

We report the effects of thermal oxidation on the sensing properties of porous silicon. Porous silicon substrates were prepared by electrochemical etching and thermally oxidized at different temperatures. A comparative EDS analysis shows that porous surfaces oxidized at higher temperatures have higher oxygen-to-silicon ratios. Our results indicate that the chemoresistive response due to the presence of isopropanol vapors at room temperature also increases with an increasing oxidation temperature. The presence of oxygen atoms in the PS layer could both protect the sensor from further atmospheric oxidation and increase its sensitivity. Full article

Malachite green (MG) is a triphenylmethane cationic dye used in aquaculture practice, although it has been banned in several countries. The illegal use by fish producers, however, persists due to its effectiveness, and ready and cheap supply. To prevent indiscriminate applications, strict control measures with simple analytical approaches are therefore necessary. With this purpose, a novel, cheap and simple method applying electrospun polyimide nanofibers was developed and validated for MG control in water by color image analysis. For detection, a simple apparatus and ImageJ^® software to treat images captured by common smartphones were used. A detection limit of 0.013 mg/L with a linear analytical response range within the concentration of 0.05 to 0.3 mg/ L of malachite green (MG) with a correlation coefficient of 0.997 and standard deviation (n = 9) varying from 1.01 to 3.92% was achieved with the proposed method. Accuracy was assessed by recovery assays in water samples and percentages of 96.6 to 102.0% were obtained. The method is robust and suitable for the rapid and reliable monitoring of MG in water. Full article

In this study, thin-film thermocouples (TFTCs) were combined with a smart bolt to design a smart bolt that can directly test high temperature in service monitoring and parameter calculation for gas turbine structure design. The first-principles calculation was used to analyze the design of the surface properties of nickel-based alloys and insulating layers, and finite element analysis was used to optimize dimension parameters by controlling the thermal stress matching of insulating layers and sensitive layers. The effect of the glass powder with different particle sizes on the microstructure of the ITO and In₂O₃ films was studied via SEM. The preferred particle size of the additive glass powder is 400 nm. The XRD pattern shows the (222) peak has the highest intensity. The intensities of the (222) and (622) peaks increase after the heat treatment. The calibration results show that the average Seebeck coefficient of the TFTCs can reach 64.9 μV/°C at 1100 °C with a maximum voltage of 71.4 mV. The repeatability error of the cycles of the sensor after heat treatment is ±1.05%. The repeatability of the sensor is up to 98.95%. The smart bolts were tested for application in small aero engines. It can be seen that under the impact of 1000 °C, the thermal response of the prepared smart bolt is better than that of the K-type armored thermocouple, and the thermal balance is achieved faster. The intelligent bolt sensor proposed in this work has better engineering application prospects owing to its convenience of installation in harsh environments. Full article

Exploring novel sensing materials to rapidly identify CH₄ at low temperatures is crucial for various practical applications. Herein, a novel ZnO-xBa/Pd with Ba of cocatalyst loading from 0 to 2.0 wt% was facilely prepared using a two-step impregnation method to improve the sensitivity of the CH₄ gas sensor. The microstructure, chemical states of the elements, and surface properties of ZnO-Ba/Pd were characterized, and the gas-sensitive performance of ZnO-Ba/Pd sensors was investigated. Compared to methane sensors based on other inorganic and organic material sensors, the sensor based on ZnO-1.0Ba/Pd exhibited a faster response/recovery time (1.4 s/8.3 s) and higher response (368.2%) for 5000 ppm CH₄ at a lower temperature (170 °C). Moreover, the ZnO-1.0Ba/Pd sensor exhibited full reversibility and long-term stability, as well as excellent selectivity at 170 °C. The excellent performance of the ZnO-Ba/Pd sensor was attributed to the electron donation by Ba, which increases the electron density around Pd, thus enhancing the catalytic activity of Pd and promoting oxygen adsorption on the ZnO surface. The present work provides a method for the rational design and synthesis of sensitive materials in practical CH₄ detection. Full article