Chemosensors, Volume 12, Issue 3 (March 2024) – 20 articles

The shot-to-shot measurement uncertainty restricts the application of laser-induced breakdown spectroscopy (LIBS) technically, to a certain extent. In order to further deepen the understanding of spectral stability, in this paper, the effects of the laser’s focus depth, the delay of the spectrometer, and the position of the spectrum collection on the spectral stability were carefully researched. Moreover, the dynamic characteristics of plasma were studied at different laser focusing depths. Research has found that the morphological changes of plasma are relatively stable, without significant changes, despite varying depths of laser focus on the sample surface. In addition, it was found that stable elemental emission spectra can always be obtained in the early plasma aggregation region. Full article

Cefoperazone is a broad-spectrum antibiotic that is extremely efficient in the treatment of respiratory, abdominal, or genital infections. Vibrational spectroscopic techniques, FT-IR, Raman, and SERS, along with DFT calculations, were involved in investigating the normal modes of vibration and adsorption behavior of this antibiotic. Using both the experimental and theoretical data, the bands in the Raman and IR spectra were assigned to the normal vibrational modes. The SERS spectra were successively obtained by using silver and gold colloidal nanoparticles as a substrate. Their analysis revealed that the molecule is chemisorbed on the nanostructured surface through the as-denoted nitrogen ring. Changes observed in the SERS spectra recorded at different cefoperazone concentrations, i.e., modifications in the relative intensity of specific bands suggest the reorientation of adsorbed molecules towards the metal surface. Full article

Organic acids are a key active component of Pinellia ternata (Thunb.) Breit, and their concentration is closely associated with the quality of P. ternata. Developing an efficient and rapid method for detecting organic acids can offer a valuable technology for real-time assessment of P. ternata quality. In this work, a high-performance liquid chromatography coupled to triple quadrupole mass spectrometry (HPLC-QqQ-MS/MS) approach, combining the optimization of extraction conditions using response surface methodology (RSM), was developed for the simultaneous quantitative analysis of six organic acids in P. ternata. The optimal extraction conditions for organic acids in P. ternata were ultrasonic extraction with a solid–liquid ratio of 1:50, ultrasonic time of 60 min, and extraction temperature of 55 °C. Multiple-reaction monitoring (MRM) scanning was employed for quantification using HPLC-QqQ-MS/MS in negative ionization mode through a single run of 10 min, and the limit of detection (LLOD) and limit of quantification (LLOQ) for organic acids were as low as 0.138 ng/mL and 0.614 ng/mL, respectively. The relative standard deviations (RSDs) of reproducibility, precision, and stability were all lower than 5.0%, and recovery rates were 97.75–107.14%, with RSDs < 5.0%. Finally, this method was successfully applied to determine the investigated organic acids in 12 production regions of P. ternata, revealing significant differences between different production areas. This indicates that the optimized method is suitable for further accurate investigations of organic acids of P. ternata. Full article

Sotol is a traditional distilled alcoholic beverage produced in Mexico and the United States. Unfortunately, local authorities have detected that these beverages are sometimes adulterated with toxic substances such as ethylene glycol. This illegal practice of adulteration is dangerous and can cause serious health problems for the end consumers. In this work, an alternative, reliable, and rapid method is presented for identifying the presence of ethylene glycol in sotol samples using UV-Vis spectroscopy and neural networks with an accuracy of up to 100%. Full article

The review paper provides a comprehensive analysis of nickel oxide (NiO) as an emerging material in environmental monitoring by surveying recent developments primarily within the last three years and reports the growth processing and strategies employed to enhance NiO sensing performance. It covers synthesis methods for pristine NiO, including vapor-phase, liquid-phase, and solution-processing techniques, highlighting advantages and limitations. The growth mechanisms of NiO nanostructures are explored, with a focus on the most recent research studies. Additionally, different strategies to improve the gas sensing performance of NiO are discussed (i.e., surface functionalization by metallic nanoparticles, heterostructure formation, carbon-based nanomaterials, and conducting polymers). The influence of these strategies on selectivity, sensitivity, response time, and stability of NiO-based sensors is thoroughly examined. Finally, the challenges and future directions that may lead to the successful development of highly efficient NiO-based gas sensors for environmental monitoring are introduced in this review. Full article

Gastric cancer (GC) remains a significant global health challenge, with late-stage diagnosis impacting treatment options and decreased survival rates. To address this, there has been a growing interest in the development of innovative screening and diagnostic methods. Over the past 20 years, nanobiosensors have undergone multiple iterations and unveiled remarkable features that pledge to reshape patient care. Despite the excitement over the plethora of ground-breaking advancements for cancer detection, use-ready samples and streamlined healthcare information monitoring and usage, this technology is still awaiting entry into clinical trials, urging a closer gaze within the medical community. Oligonucleotide-based biosensors, leveraging DNA or RNA’s long-term storage of information, offer great specificity and sensitivity, as described throughout this paper. Consequently, this renders them as an ideal choice for revolutionizing GC diagnosis and facilitating early intervention. The aim of this review is to provide an overview of this cutting-edge, invaluable technology and its limitations across various aspects. Full article

The NH₃ sensor is of great significance in preventing NH₃ leakage and ensuring life safety. In this work, the Pd-decorated ZnO hexagonal microdiscs are synthesized using hydrothermal and annealing processes, and the gas sensor is fabricated based on Pd-decorated ZnO hexagonal microdiscs. The gas-sensing test results show that the Pd-ZnO gas sensor has a good response to NH₃ gas. Specifically, it has a good linear response within 0.5–50 ppm NH₃ at the optimal operating temperature of 230 °C. In addition, the Pd-ZnO gas sensor exhibits good repeatability, short response time (23.2 s) and good humidity resistance (10–90% relative humidity). This work provides a useful reference for developing an NH₃ sensor. Full article

This paper aims to provide a large coverage of recent developments regarding environmental monitoring using metal oxide-based sensors. Particular attention is given to the detection of gases such as H₂, CO_x, SO_x, NO_x, and CH₄. The developments and analyses of the design of sensors and types of metal oxide sensing materials are emphasized. The sensing mechanisms and peculiarities of metal oxides used in chemoresistive sensors are provided. The main parameters that affect the sensitivity and selectivity of metal oxide sensors are indicated and their significance to the sensor signal is analyzed. Modern data processing algorithms, employed to optimize the measurement process and processing of the sensor signal, are considered. The existing sensor arrays/e-nose systems for environmental monitoring are summarized, and future prospects and challenges encountered with metal oxide-based sensor arrays are highlighted. Full article

Heavy metal pollution in soil is becoming more and more serious. LIBS is one of the most promising technologies for rapid detection of heavy metal contamination in soil. However, due to the wide variety of soils and complex matrices, accurate quantification remains a challenge. In total, 451 soil samples were prepared and detected by the portable detector of LIBS, which were divided into six categories based on the compactness of the soil pellets, and a separate quantitative model for each type of soil sample was used for quantitative analysis by external standard method. It did not need a lot of data to train the model, and only a small number of calibration samples could be used for quantitative analysis of a large number of samples. The results showed that 78 standard samples and 334 collected samples were quantitatively analyzed by 39 standard samples. Compared with the standard value, the correlation coefficients were all above 0.95. A comparative experiment indicated that the portable LIBS system combined with soil classification and calibration methods can achieve fast and accurate quantitative detection. Full article

Bipyridyl Ruthenium-decorated Ni-MOFs on multi-walled carbon nanotubes (MWCNT-RuBpy@Ni-MOF) were synthesized. In an alkaline solution, the glucose was electrocatalytically oxidized at +0.5 V vs. Ag/AgCl at the composite interface of MWCNT-RuBpy@Ni-MOF on a glassy carbon electrode. The Ni³⁺/Ni²⁺ redox couples in Ni-MOFs played a key role as the active center for the catalytic oxidation of glucose at the electrode, where both RuBpy and MWCNTs enhanced the current responses to glucose. The resulting enzymeless glucose sensor from MWCNT-RuBpy@Ni-MOF exhibited a wide range of linear responses, high sensitivity and selectivity for the determination of glucose. Full article

Transition metallic binary alloys have attracted enormous attention in regard to the non-enzymatic detection of glucose due to their high electrocatalytic activities induced by the synergistic effect between the individual metallic species. However, the easy aggregation of the bimetallic particles has limited their performance. Herein, a facile metal–organic framework (MOF)-derived strategy is developed to synthesize a hybrid containing binary Co–Ni nanoparticles decorated on an N-doped porous carbon matrix (Co_xNi_y/N-C) for the non-enzymatic detection of glucose. The Co/Ni ratio in the hybrid is investigated to regulate its electrocatalytic behaviors for glucose sensing. A hybrid with the optimal Co/Ni ratio of 1:1 displays two linear detection ranges (0.5 µM to 1 mM and 1 mM to 10 mM) with a detection limit of 0.11 µM for glucose. The feasibility of using this hybrid-modified SPE for glucose detection in real serum samples has also been validated. Full article

The expansion of global industry results in the release of harmful volatile acid vapors into the environment, posing a threat to various lifeforms. Hence, it is crucial to prioritize the development of swift sensing systems capable of monitoring these volatile acid vapors. This initiative holds great importance in safeguarding a clean and safe environment. This paper presents the synthesis and characterization of pyrene-based covalent organic frameworks (COFs) that exhibit exceptional crystallinity, thermal stability, and intense fluorescence. Three COFs—PP–COF, PT–COF, and PE–COF—were synthesized, demonstrating large surface areas and robust thermal stability up to 400 °C. The fluorescence properties and intramolecular charge transfer within these COFs were significantly influenced by their Schiff base bonding types and π-stacking degrees between COF layers. Notably, PE-COF emerged as the most fluorescent of the three COFs and exhibited exceptional sensitivity and rapid response as a fluorescent chemosensor for detecting HCl in solution. The reversible protonation of imine bonds in these COFs allowed for the creation of highly sensitive acid vapor sensors, showcasing a shift in spectral absorption while maintaining structural integrity. This study highlights the potential of COFs as reliable and reusable sensors for detecting harmful acid vapors and addressing environmental concerns arising from industrial activities. Full article

Third-generation biosensors use enzymes capable of direct electron transfer (DET) to the sensor surface. They are of interest for continuous glucose monitoring in blood or interstitial fluid, but they are rarely investigated. One reason is the hindered DET of the enzymes to the metallic electrodes. In this publication, a novel method for the immobilization of cellobiose dehydrogenase (CDH) DET enzymes employing conductive poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) inks and a protective polyethylene glycol dimethacrylate (PEG-DMA) hydrogel layer on gold electrodes is reported. This layer stack showed a glucose-specific current response for voltages between −0.2 and 0.4 V in physiological PBS buffer, and enabled interference-less sensing in a solution of acetaminophen, ascorbic acid, dopamine, and uric acid at 0 V. A Michaelis–Menten fit led to a maximum current density (I_max) of 257 ± 7.9 nA/mm² and a Michaelis–Menten constant (K_m) of 28.4 ± 2.2 mM, with a dynamic range of 0.1–20 mM glucose and a limit of detection of 0.1 mM. After 16 h of continuous measurement of 20 mM glucose, the signal decreased to 60% of its initial value. Storage stability was successfully verified until up to 10 days. In summary, this paper shows a simplified approach for the fabrication of third-generation biosensors using CDH-PEDOT:PSS and PEG-DMA hydrogel inks. Full article

China is a large consumer of meat and meat products. People’s daily diets include a variety of meat, but meat food adulteration problems are common. This paper discusses the research progress of the electronic nose and near-infrared spectroscopy in the field of meat adulteration detection. Through the study of dozens of related papers in recent years, it has been found that the use of the electronic nose and near-infrared spectroscopy for meat detection has the advantages of speed, a nondestructive nature, high sensitivity, strong quantitative analysis, high automation, a wide applicability, an improved product quality, and cost reduction over the traditional detection, but it may be limited in detecting the adulteration of a specific meat, and there are issues with the life and stability of the sensors of the electronic nose in the process of detection, along with the problems of the high requirements for the modeling of the data of near-infrared spectroscopy. This paper takes adulterated meat as the research object and briefly summarizes the detection principles of the electronic nose and near-infrared spectroscopy, as well as the types of sensors applied in the electronic nose. The research progress of the electronic nose and near-infrared detection technology in meat adulteration assessment is reviewed, the advantages and disadvantages of the two in practical application are analyzed, the classification of pattern recognition methods and their applications in meat identification are described, and the feasibility and practical significance of the joint application of the two in meat adulteration detection are envisioned. Meanwhile, the challenges faced by the two in meat detection are pointed out. Full article

Turbidity is one of the crucial parameters of water quality. Even though many commercial devices, low-cost sensors, and remote sensing data can efficiently quantify turbidity, they are not valid tools for the classification it. In this paper, we design, calibrate, and test a novel optical low-cost sensor for turbidity quantification and classification. The sensor is based on an RGB light source and a light detector. The analyzed samples are characterized by turbidity values from 0.02 to 60 NTUs, and have four different sources. These samples were generated to represent natural turbidity sources and leaves in the marine areas close to agricultural lands. The data are gathered using 64 different combinations of light, generating complex matrix data. Machine learning models are compared to analyze this data, including training, validation, and test datasets. Moreover, different alternatives for data preprocessing and feature selection are assessed. Concerning the quantification of turbidity, the best results were obtained using averaged data and principal components analyses in conjunction with exponential gaussian process regression, achieving an R² of 0.979. Regarding the classification of the turbidity, an accuracy of 91.23% is obtained with the fine K-Nearest-Neighbor classifier. The cases in which data were misclassified are characterized by turbidity values lower than 5 NTUs. The obtained results represent an improvement over the current solutions in terms of turbidity quantification and a completely novel approach to turbidity classification. Full article

Gold nanoparticles (AuNPs) were prepared by using a green approach that employed orange (citrus sinensis) peel water extract (OPE) as a reducing agent. In this case, the organic compounds present in orange peel were able to reduce Au(III) to Au(0) and, at the same time, to act as a capping agent, functionalizing the surface of the AuNPs, stabilizing them in a water solution. This “green” approach valorizes orange peel waste as a resourceful material and makes the synthetic process of AuNPs more environmentally sustainable, safe, and economically feasible than the traditional methods. The obtained gold nanoparticles (AuNPs@OPE) were characterized by FT–IR, DLS, SEM analysis, and UV–Vis spectroscopy; the latter showed a characteristic surface plasmon resonance (SPR) band at 530 nm, typical of spherical gold nanoparticles. The AuNPs@OPE were then tested as colorimetric sensors for heavy metals in water, showing an affinity and selectivity toward Pb²⁺. In fact, in the presence of Pb²⁺, the added cation favors the aggregation process, and, in this case, nanoparticles form clusters due to the interactions between Pb²⁺ and the carboxyl/hydroxyl groups on the surface of the AuNPs@OPE, increasing the size of the nanostructure. This process is accompanied by a change in color of the AuNPs@OPE from pink to violet, with a formation of a second, new SPR band, at a higher wavelength, relative to the aggregate formation. The colorimetric assay was tested at different times with the addition of Pb²⁺ ions showing different LOD values of 13.31 µM and 0.05 µM after 15 min and 90 min, respectively. The proposed colorimetric assay was also tested for analyzing Pb²⁺ in drinking water samples demonstrating the reliability to use AuNPs@OPE with real samples. Full article

In this paper, a field effect transistor (FET)-type sensor with Pt-decorated In₂O₃ (Pt-In₂O₃) nanoparticles is fabricated for detecting H₂ gas at room temperature. A pulsed measurement method is adopted to continuously alternate between pre-biasing the gate and reading the drain current of the FET-type sensor. This method effectively reduces the drift in the sensing signal. It is also found that negative pre-bias voltages can dramatically shorten the recovery time of the sensor after sensing H₂, while positive pre-bias voltages have the opposite effect. The H₂ sensing performance of the sensor is characterized under the enhancement of a pulsed negative pre-bias. By calculating and comparing the root mean square, signal-to-noise ratio, and detection limit of the sensor under different operating regions, it is found that the sensor has the best sensing performance in the subthreshold region, which is suggested to be the optimum operating region for FET-type sensors. In addition, the presence of oxygen significantly consumes the hydrogen molecules and reduces the room-temperature H₂ sensitivity of the sensor. The proposed sensor presents promising H₂ sensing properties, and this research could be a guide for the use of FET-type sensors in more gas detection applications. Full article

Imaging methods by the means of optical sensors are applied in diverse scientific areas such as medical research and diagnostics, aerodynamics, environmental analysis, or marine research. After a general introduction to the field, this review is focused on works published between 2012 and 2022. The covered topics include planar sensors (optrodes), nanoprobes, and sensitive coatings. Advanced sensor materials combined with imaging technologies enable the visualization of parameters which exhibit no intrinsic color or fluorescence, such as oxygen, pH, CO₂, H₂O₂, Ca²⁺, or temperature. The progress on the development of multiple sensors and methods for referenced signal read out is also highlighted, as is the recent progress in device design and application formats using model systems in the lab or methods for measurements’ in the field. Full article

Maternal milk is pivotal for infants’ nutrition. It also portrays the chemical burden to which the mother has been exposed. One of the chemical families that is prevalent and related to potential toxic effects are volatile organic compounds (VOCs). In the present study, motivated by the scarcity of works dealing with concomitant VOC and metabolite determination in maternal milk, two new gas/liquid chromatography tandem mass spectrometry (GC-MS/MS, LC-MS/MS) methods for the simultaneous measurement of 25 VOCs and 9 of their metabolites, respectively, in maternal milk were developed and applied to 20 maternal milk samples collected from mothers in Greece. In parallel, a headspace solid-phase microextraction (HS-SPME)–GC-MS method was employed for the untargeted screening of chemicals. Low detection rates for benzene, toluene, styrene and p,m-xylenes, and three of their metabolites, namely N-acetyl-S-(benzyl)-L-cysteine (BMA, metabolite of toluene), 3-methylhippuric (3-MHA, metabolite of xylenes) and mandelic acid (MA as DL and R isomers, metabolites of styrene and ethylbenzene), were evidenced in concentrations varying from <lower limit of quantification (LLOQ) to 0.79 ng mL⁻¹. HS-SPME–GC-MS disclosed the presence of common maternal milk constituents such as fatty acids. Nevertheless, bisphenol-A, bisphenol derivatives and phthalates were also detected. The infants’ health risk assessment demonstrated a low risk and negligible carcinogenic risk, yet the detection of these compounds should not be underestimated. Full article