Chemosensors, Volume 12, Issue 2 (February 2024) – 13 articles

The Raman spectroscopy analysis technique has found extensive applications across various disciplines due to its exceptional convenience and efficiency, facilitating the analysis and identification of diverse substances. In recent years, owing to the escalating demand for high-efficiency analytical methods, deep learning models have progressively been introduced into the realm of Raman spectroscopy. However, the application of these models to portable Raman spectrometers has posed a series of challenges due to the computational intensity inherent to deep learning approaches. This paper proposes a lightweight classification model, named RepDwNet, for identifying 28 different types of biological blood. The model integrates advanced techniques such as multi-scale convolutional kernels, depth-wise separable convolutions, and residual connections. These innovations enable the model to capture features at different scales while preserving the coherence of feature data to the maximum extent. The experimental results demonstrate that the average recognition accuracy of the model on the reflective Raman blood dataset and the transmissive Raman blood dataset are 97.31% and 97.10%, respectively. Furthermore, by applying structural reparameterization to compress the well-trained model, it maintains high classification accuracy while significantly reducing the parameter size, thereby enhancing the speed of classification inference. This makes the model more suitable for deployment in portable and mobile devices. Additionally, the proposed model can be extended to various Raman spectroscopy classification scenarios. Full article

ZnO nanoparticles (NPs) were prepared by green synthesis using plant leaf extraction of Ochradenus baccatus and characterized by XRD, FESEM, HRTEM, and Raman spectroscopy techniques. Since elevated CO levels have been associated with inflammatory conditions, cardiovascular diseases, and respiratory disorders and the methane gas primarily produced by gut microbiota and linked to gastrointestinal disorders and other abnormal methane levels in breath samples, the nanoparticles were applied for gas sensor fabrication. Thus, the gas sensors fabricated using ZnO nanoparticles were investigated for CH₄, H₂, CO, and NO₂ gases. The gas sensing was performed for the fabricated sensors at various operating temperatures and gas concentrations. Interestingly, leaf-extracted green synthesized ZnO NPs were more sensitive to CH₄, CO, and NO₂ gases than to H₂. The results of sensing studies revealed that the nanoparticles exhibit a selectivity toward gas depending on the gas type. The sensor response was also studied against the humidity. These findings bridge between the laboratory and industry sectors for future gas sensors development, which can be used for exhaled breath analysis and serve as potential diagnostic tools for highly sensitive contagious diseases. Full article

The Amperometric Gas Sensor (AGS) uses an electrode as the transducer element which converts its signal into a current from the electrochemical reaction of analytes taking place at the electrode surface. Many attempts to improve AGS performance, such as modifying the working electrode, applying a particular gas-permeable membrane, and selecting the proper electrolyte, etc., have been reported in the scientific literature. On the other hand, in the materials community, atomic gold has gained much attention because its physicochemical properties dramatically differ from those of gold nanoparticles. This paper provides an overview of the use of atomic gold in AGSs, both in a bulky AGS and a miniaturized AGS. In the miniaturized AGS, the system must be redesigned; for example, the aqueous electrolyte commonly used in a bulky AGS cannot be used due to volatility and fluidity issues. A Room Temperature Ionic Liquid (RTIL) can be used to replace the aqueous electrolyte since it has negligible vapor pressure; thus, a thin film of RTIL can be realized in a miniaturized AGS. In this paper, we also explain the possibility of using RTIL for a miniaturized AGS by incorporating a quartz crystal microbalance sensor. Several RTILs coated onto modified electrodes used for isomeric gas measurement are presented. Based on the results, the bulky and miniaturized AGS with atomic gold exhibited a higher sensor response than the AGS without atomic gold. Full article

The present work describes the synthesis of an electroactive nanocomposite consisting of carbon black (CB) and polyaniline (PANI) obtained by in situ oxidative polymerization. Monomer P1 was used as a polyaniline precursor. P1 has surfactant properties that allow obtaining core–shell structures dispersed in an aqueous medium. The nanocomposite, together with silver nanoparticles (AgNPs) as an electrocatalytic element, was used to modify the surface of a glassy carbon electrode (GCE) for glucose detection. Electroactive areas were calculated using the Randles–Sevick equation. The results showed that the CB-PANI.1-1/AgNP nanocomposite exhibited a larger electroactive surface area (0.3451 cm²) compared to AgNP alone (0.0973 cm²) or the CB-PANI.1-1 composite (0.2989 cm²). Characterization of CB-PANI.1-1/AgNP, by cyclic voltammetry in the presence of glucose, showed a new oxidation peak with a maximum current close to 0.7 V due to the oxidation of glucose to gluconolactone. The amperometry test at 0.7 V showed a linear response with R² of 0.999 as a function of the analyte concentration. The glucose sensor presented a linear detection range of 1 to 10 mM, a sensitivity of 41 µA mM⁻¹ cm⁻², and a limit of detection (LOD) of 520 µM. Full article

New cosmetic formulations are continuously requested by the market and the ingredients are constantly evolving. Recently the use of antioxidants has gained success and, in this context, analytical methods able to quickly and easily assess the antioxidant activity of cosmetics would make it possible to carry out analyses on new formulations even within the manufacturing process without the need for specialized laboratories and personnel, thus evaluating directly on-site the effectiveness and the shelf life of products. In this work, a chemiluminescent inhibition assay was developed for determining the total antioxidant activity in cosmetic products. The method was based on the luminol/enhancers/hydrogen peroxide/horseradish peroxidase chemiluminescent system, which generates light signals measurable through simple and compact instrumentation. The formation of the chemiluminescent signal is inhibited by the presence of antioxidant substances while it is restored once all the antioxidant molecules have been oxidized. The time of appearance of the light signal is related to the total antioxidant activity. The assay was carried out exploiting an integrated device comprising a microwell plate coupled with an array of amorphous silicon hydrogenated photosensors enclosed in a mini-dark box. The method was optimized in terms of concentrations and volumes of the required reagents and sample pre-treatment. A calibration curve was generated taking as a reference the antioxidant activity of ascorbic acid obtaining a detection limit of 10 µM. The developed method was applied to cosmetic products currently on the market as well as on spiked samples in order to evaluate the performance of the methods in terms of sensitivity, accuracy, and reproducibility. Full article

This paper presents the impact of the decoration of reduced graphene oxide (rGO) with metallic nanoparticles to detect sulfur dioxide (SO₂). Copper and platinum were employed to produce metal nanoparticles (NPs) for the chemical and physical decoration of rGO to form the nanocomposites (rGO/NPs). We optimized NP loading by varying the concentrations of metal ions and deposition times for chemical and physical decoration, respectively. The chemical decoration presents a random nanoparticle distribution on the rGO surface with a broad particle size distribution (1 to 100 nm with a majority less than 40 nm). In comparison, the physical decoration presents uniformly distributed nanoparticles with particles of a size between 1 and 20 nm, with a majority less than 10 nm. The chemically decorated structures present the best gas responses and show that lower NP loading provides better responses. The nanocomposites present responses owing to a better synergy between NPs and the rGO surface, combined with the catalytic action of the NPs on the rGO. The physical decoration allows higher NP surface coverage than the chemical one but implies a lower remaining rGO naked surface for gaseous molecule interaction. These results illustrate that the NPs’ surface and the uncovered rGO contribute to the gas response. Full article

The aim of this work was to explore the possibility of using a Cu-exchanged zeolitic volcanic tuff (which is natural and easy to prepare and apply) for the preparation of a new low-cost carbon paste amperometric sensor for H₂O₂ detection. The properties of the zeolitic volcanic tuff were determined using chemical analysis, energy-dispersive X-ray spectroscopy, the specific surface area, electron microscopy, X-ray diffraction spectroscopy, and Fourier-transform infrared spectroscopy. The sensor was successfully built and operates at pH 7, at an applied potential of −150 mV Ag/AgCl/KCl_sat, presenting a sensitivity of 0.87 mA M⁻¹, a detection limit of 10 µM and a linear domain up to 30 mM H₂O₂. These good electroanalytic parameters for H₂O₂ detection (a low detection limit and high sensitivity) support the possibility of using these sensors for the detection of many analytes in environmental, food and medical applications. Full article

In this study, a method was developed for the rapid online measurement of sodium nitrite solutions using near-infrared spectroscopy. A series of standard solutions of sodium nitrite at different concentrations were prepared, and the samples were measured in cuvettes and flow cells. Following the preprocessing of raw spectra and band selection, partial least squares were used to establish a prediction model, and the coefficient of determination (R²) of the validation set and the root mean square error of prediction (RMSEP) of the model were 0.9989 and 0.0338. The results demonstrate that the established model can meet the demands of online measurement and perform the rapid, nondestructive detection of sodium nitrite solutions, which provides some basis for the automated formulation of feedstock in spent fuel reprocessing. Full article

The artificial olfactory image was proposed by Lundström et al. in 1991 as a new strategy for an electronic nose system which generated a two-dimensional mapping to be interpreted as a fingerprint of the detected gas species. The potential distribution generated by the catalytic metals integrated into a semiconductor field-effect structure was read as a photocurrent signal generated by scanning light pulses. The impact of the proposed technology spread beyond gas sensing, inspiring the development of various imaging modalities based on the light addressing of field-effect structures to obtain spatial maps of pH distribution, ions, molecules, and impedance, and these modalities have been applied in both biological and non-biological systems. These light-addressing technologies have been further developed to realize the position control of a faradaic current on the electrode surface for localized electrochemical reactions and amperometric measurements, as well as the actuation of liquids in microfluidic devices. Full article

The nutritional properties of Pleurotus mushrooms were studied to select the varieties with the most favourable properties. These mushrooms have high nutritional value; they are rich in carbohydrates, protein, minerals, vitamins, chitin and reducing compounds, such as phenols and polyphenols. In this study, the polyphenol profiles of thirteen Pleurotus ostreatus cultivars were established by the UHPLC-ESI-MS/MS technique. The results showed that 4-hydroxibenzoic acid, caffeic acid, p-coumaric acid and vanillic acid were the most abundant polyphenolic components in the samples. In addition, the Fourier-transformed near infrared (FT-NIR) spectra of the samples were recorded and evaluated. The correlation between the differences in NIR spectra and the differences in polyphenol patterns of the samples was investigated. The polyphenol results were subjected to several statistical evaluations (Kruskal–Wallis test, Principal Component Analysis (PCA), Spearman correlation analysis, cluster analysis) to detect possible differences between the samples. Relationships between the polyphenol profile and antioxidant capacity (FRAP), total polyphenol content (TPC), free amino acid content (fAA) and the values of each polyphenol component were examined. Based on the results, an effort was made to group the varieties according to the attributes tested. Full article

Leaves of yerba mate plant (Ilex paraguariensis) have a wealth of nutrients, ingested by people who drink them in the hot water infusion popularly known as mate. In the present work, the laser-induced breakdown spectroscopy (LIBS) technique was applied for the first time to analysis of the extractability of macronutrients, including Mg, Ca, Na, and K, in commercial samples of yerba mate. Powdered samples from leaves’ material were used to simulate the infusion process in the laboratory. To carry out LIBS analysis, the emission spectra were measured before and after the infusion from the samples prepared in pellets. The spectral data were processed and analyzed by a specially designed algorithm. A coefficient of extractability was calculated for each of the investigated macronutrients in the range 34–76%, showing a good correlation with the corresponding elemental concentrations leached into the water infusion, determined by Atomic Absorption Spectroscopy. The obtained results demonstrated the feasibility of our approach for the rapid analysis of extractable macronutrients present in yerba mate leaves. Full article

This study reports, for the first time, the utilization of two-dimensional (2D) tellurium (Te) nanosheets for the efficient nonenzymatic detection of hydrogen peroxide (H₂O₂). H₂O₂ acts as a pivotal biomarker with widespread applications across environmental, biological, industrial, and food processing domains. However, an excessive accumulation of H₂O₂ in the body poses a severe threat to human life. Consequently, the imperative need for a selective, sensitive, and cost-effective sensing platform for H₂O₂ detection has gained paramount significance. Employing a low-cost and straightforward hydrothermal method, Te nanosheets were synthesized to address the escalating demand for a reliable detection platform. The as-synthesized Te nanosheets are characterized through Raman spectroscopy and atomic force microscopy techniques. The electrochemical performance of the Te nanosheets integrated onto a glassy carbon (Te-GC) electrode was thoroughly investigated using cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. The experiments were designed to evaluate the response of the Te-GC electrode in the presence and absence of H₂O₂, alongside its performance in the detection of other pertinent interfering analytes. The sensor shows a limit of detection of 0.47 µM and a sensitivity of 27.2 µA µM⁻¹ cm⁻² towards H₂O₂. The outcomes of this study demonstrate the efficacy of Te nanosheets as a promising material for nonenzymatic H₂O₂ detection in urine samples. The simplicity and cost-effectiveness of the hydrothermal synthesis process, coupled with the notable electrochemical performance of the Te/GC electrode, highlight the potential of Te nanosheets in the development of a robust sensing platform. This research contributes to the ongoing efforts to enhance our capabilities in monitoring and detecting H₂O₂, fostering advancements in environmental, biomedical, and industrial applications. Full article