Chemosensors

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

The quantitative determination of proteins is an important parameter in biochemistry, biotechnology and immunodiagnostics, and the importance of serum albumin in clinical diagnosis should be highlighted, given that alterations in its concentration are generally associated with certain diseases. As possible probes for this purpose, squaraine dyes have been arousing the interest of many researchers due to their unique properties, such as absorption in the visible spectra, moderate relative fluorescence quantum yields and increased fluorescence intensity after non-covalent binding to specific ligands. In this work, five squaraine dyes, four of which have never been reported in the literature, were characterized and evaluated in vitro and in silico concerning their potential application as fluorescent probes for human serum albumin detection. After interaction with the protein, the fluorescence intensity increased from 12 to 41 times, depending on the dye under study. High sensitivity (1.0 × 10⁵ − 5.4 × 10⁵ nM), low detection limits (168–352 nM) and moderate quantitation limits (560–1172 nM) were obtained, proving the efficiency of the method. In addition, moderate-to-excellent selectivity was observed compared to γ-globulin proteins. Molecular docking suggests that the dyes interact more effectively with the Sudlow site I, and binding energies have been markedly higher than those of warfarin, a molecule known to bind to this site specifically. Full article

Thin copper selenide films were synthesized on polyamide sheets using the successive ionic layer adsorption and reaction (SILAR) method at three different temperatures. It was found that elevating the temperature of the solution led to the creation of copper selenide films with different features. X-ray diffraction characterization revealed that all films crystallized into a cubic Cu_2−xSe, but with different crystallinity parameters. With elevating the temperature, grain size increased (6.61–14.33 and 15.81 for 40, 60 and 80 °C, respectively), while dislocation density and the strain decreased. Surface topology was investigated with Scanning Electron Microscopy and Atomic Force Microscopy, which revealed that the grains combined into agglomerates of up to 100 nm (80 °C) to 1 μm (40 °C). The value of the direct band gap of the copper selenide thin films, obtained with UV/VIS spectroscopy, varied in the range of 2.28–1.98 eV. The formation of Cu_2−xSe was confirmed by Raman analysis; the most prominent Raman peak is located at 260 cm⁻¹, which is attributed to binary copper selenides. The thin Cu_2−xSe films deposited on polyamide showed p-type conductivity, and the electrical resistivity varied in the range of 20–50 Ω. Our results suggest that elevated temperatures prevent large agglomeration, leading to higher resistance behavior. Full article

This paper proposes a method based on key parameter monitoring and a backpropagation neural network to standardize LIBS spectra, named KPBP. By monitoring the laser output energy and the plasma flame morphology and using the backpropagation neural network algorithm to fit the spectral intensity, KPBP standardizes spectral segments containing characteristic lines. This study first conducted KPBP experiments on the spectra of pure aluminium, monocrystalline silicon, and pure zinc to optimize the KPBP model and then performed KPBP standardization on the characteristic spectral lines of a GSS-8 standard soil sample. The spectral intensity relative standard deviations (RSDs) of Al 257.51 nm, Si 298.76 nm, and Fe 406.33 nm dropped from 12.57%, 16.60%, and 14.10% to 3.40%, 3.20%, and 4.07%, respectively. Compared with the internal standard method and the standard normal variate method, KPBP obtained the smallest RSD. The study also used a GSS-23 standard soil sample and a Beijing farmland soil sample to conduct KPBP optimization experiments. The RSD of spectral intensity was still significantly reduced, proving that the KPBP method has stable effects and wide applicability to improve the repeatability of LIBS soil analysis. Full article