Chemosensors, Volume 12, Issue 5 (May 2024) – 14 articles

This work presents the detection of hypoxanthine (HXA), a purine derivative that is similar to nucleic acids who overconsumption can cause health issues, by using hydrothermally synthesized cerium phosphate (CePO₄) followed by a sonochemical approach for CePO₄ decorated with a functionalized carbon nanofiber (CePO₄@f-CNF) nanocomposite. The formation of the nanocomposite was confirmed with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). A CePO₄@f-CNF nanocomposite is used to modify a glassy carbon electrode (GCE) to analyze the electrochemical detection of HXA. Cyclic voltammetry (CV), Electrochemical impedance spectroscopy (EIS), and Differential pulse voltammetry (DPV) were used to examine the electrochemical properties of the composite. As a result, the modified electrode exhibits a larger active surface area (A = 1.39 cm²), a low limit of detection (LOD) at 0.23 µM, a wide linear range (2.05–629 µM), and significant sensitivity. Therefore, the CePO₄@f-CNF nanocomposite was used to study the real-time detection in chicken and fish samples, and it depicted significant results. Full article

This research contributes to work on synthesizing zinc oxide nanoparticles (ZnO NPs) at room temperature (RT) and their utilization in flexible gas sensors. RT ZnO NP synthesis with a basicity solution (pH ≈ 13) demonstrates an efficient method for synthesizing well-crystalline ZnO NPs (RT.pH13) comparable to those synthesized by the hydrothermal method (hyd.C). The RT.pH13 achieved a high thermal stability with minimal organic reside impurities (~4.2 wt%), 30–80 nm particle size distribution, and a specific surface area (14 m² g⁻¹). The synthesized pre- and post-calcinated RT.pH13 NPs were then incorporated into flexible sensors for gas sensing applications at ambient conditions (RT and relative humidity of 30–50%). The pre-calcinated ZnO-based sensor (RT.pH13) demonstrated superior sensitivity to styrene and acetic acid and lower sensitivity to dimethyl-6-octenal. The calcinated ZnO-based sensor (RT.pH13.C) exhibited lower sensitivity to styrene and acetic acid, but heightened sensitivity to benzene, acetone, and ethanol. This suggests a correlation between sensitivity and structural transformations following calcination. The investigation of the sensing mechanisms highlighted the role of surface properties in the sensors’ affinity for specific gas molecules and temperature and humidity variations. The study further explored the sensors’ mechanical flexibility, which is crucial for flexible Internet of Things (IoT) applications. Full article

Surface-enhanced Raman scattering (SERS) provides an alternative rapid detection method for pesticide residues in food, but fenvalerate possesses poor affinity to the novel metal substrate, thus restricting its analysis. To break this bottleneck, a SERS-active platform with an Ag/rGO composite structure was engineered using a facile method for fenvalerate detection. Ag nanoparticles with a 60 nm diameter can grow evenly on the top and bottom of rGO layers under intense ultrasonic oscillation, and rGO in hybrid material acts as an ideal hotspot holder between the gaps of Ag nanoparticles, not only allowing the interaction area to be enhanced both electromagnetically and chemically but also enabling the capture and enrichment of fenvalerate pesticide molecules into the “hotspot” area to improve detection sensitivity. Ag/rGO composite substrate possesses superior SERS performance with an ultralow detectable concentration of 4-aminothiophenol (10⁻¹⁰ M) and good reproducibility, endowing the material with a better enhancement effect than pure Ag nanoparticles. When used as the SERS substrate for fenvalerate detection, Ag/rGO composite material showed excellent performance in both experiments and theoretical calculation, with the limit of detection (LOD) of fenvalerate being as low as 1.69 × 10⁻⁵ mg/kg and a detection model with an R² of 99.2%, demonstrating its exciting potential as a SERS substrate for pesticides detection. Full article

Conducting polymers are used in a wide range of applications, especially in the design and development of electrochemical sensors. Their main advantage, in this context, is their ability to efficiently modify an electrode surface using the direct polymerization of a suitable monomer in an electrochemical cell, or by physical coating. Additionally, the conducting polymers can be mixed with further materials (metal nanoparticles, carbonaceous materials) to enhance conductivity and analytical features (linear range, limit of detection, sensitivity, and selectivity). Due to their characteristics, conducting polymer-based amperometric sensors are applied to the determination of different organic and inorganic analytes. A view of recent advances in this field focusing on pyrrole, thiophene, and 3,4-ethylenedioxythiophene as starting materials is reported. Full article

As a necessary sulfhydryl amino acid, L-cysteine (L-Cys) maintains many physiological functions in the biological system. However, abnormal L-Cys levels can cause a variety of diseases. In our work, a highly sensitive and selective assay has been developed for sensing L-Cys using the morphological transformation of silver-based materials induced by Cr³⁺. In this sensing system, Cr³⁺ could etch the silver nanoflakes into silver nanoparticles, accompanied by a change in absorbance, which decreases at 395 nm, creates a new peak at 538 nm, and keeps increasing the absorbance with the addition of Cr³⁺ concentration. Meanwhile, under the naked eye, the solution color changes from bright yellow to dark purple. Because of the strong affinity between L-Cys and Cr³⁺, L-Cys could inhibit the induction of Cr³⁺ on silver-based materials, thereby preventing changes in the configuration, absorption spectrum, and color of silver-based materials. Taking advantage of this point, we can quantitatively detect the concentration of L-Cys. A linear relationship between the absorbance ratio (A538 nm/A395 nm) and L-Cys concentration was found in the range of 0.1–0.9 μM, and the detection limit was 41.2 nM. The strategy was applied to measure L-Cys spiked in beer and urine samples, with recovery from 93.80 to 104.03% and 93.33% to 107.14% and RSD from 0.89 to 2.40% and 1.80% to 6.78%, respectively. This detection strategy demonstrates excellent selectivity and sensitivity, which makes it a practical and effective method for the detection of L-Cys in real samples. Full article

A new water-soluble polyamidoamine (PAMAM) dendrimer modified with 4-sulfo-1,8-naphthalimide (DSNI) and its monomeric structural analogue (MSDI) were synthesized. Their photophysical properties were investigated in organic solvents of different polarities and aqueous solutions. The effect of pH on fluorescence intensity was determined. It was found that the dendrimer emits blue fluorescence in an acidic medium, which is quenched in an alkaline environment. This phenomenon is due to the possibility of suppression of nonradiative photoinduced electron transfer in acidic media. The influence of different metal ions (Cu²⁺, Pb²⁺, Sn²⁺, Sr²⁺, Mg²⁺, Ba²⁺, Co²⁺, Hg²⁺, Zn²⁺, Ni²⁺, Fe³⁺, Al³⁺) and anions (CN⁻, S²⁻, S₂O₅²⁻, HPO₄²⁻, H₂PO⁴⁻, F⁻, CH₃COO⁻, NO₂⁻, CO₃²⁻, SO₄²⁻) on the intensity of the emitted fluorescence was studied. Quenching was only found in the presence of Cu²⁺. This makes the dendrimer suitable for determining copper ions in water solutions in the presence of other metal ions and anions. Additionally, DSNI was used as a ligand to obtain a stable copper complex, the structure of which was investigated by electron paramagnetic resonance (EPR), infrared spectrum, and elemental analysis. Two copper ions were found to form a complex with one dendrimer. The in vitro microbiological activity of the new compounds against bacteria Pseudomonas aeruginosa and two viruses HRSV-2 and HAdV-5 was investigated. With a view to obtaining antibacterial and anti-viral textiles, cotton fabrics were treated with the three compounds, and then their activity against the same microbial strains was investigated. It was found that the microbiological activity was preserved after the application of the new compounds to the cotton fabrics. Full article

The development of efficient sensors able to detect alcoholic compounds has great relevance in many fields including medicine, pharmaceuticals, food and beverages, safety, and security. In addition, the measurements of alcohols in air are significant for environmental protection because volatile alcohols can have harmful effects on human health not only through ingestion, but also through inhalation or skin absorption. The analysis of alcohols in breath is a further expanding area, being employed for disease diagnoses. The analyses performed by using chromatography, mass-spectrometry, nuclear magnetic resonance, ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, or Raman spectroscopy often require complex sampling and procedures. As a consequence, many research groups have focused their efforts on the development of efficient portable sensors to replace conventional methods and bulky equipment. The ability to operate at room temperature is a key factor in designing portable light devices suitable for in situ real-time monitoring. In the present review, we provide a survey of the recent literature on the most efficient chemiresistive materials for alcohol sensing at room temperature. Remarkable gas-sensing performances have mainly been obtained by using metal oxides semiconductors (MOSs), metal organic frameworks (MOFs), 2D materials, and polymers. Among 2D materials, we mainly consider graphene-based materials, graphitic carbon nitride, transition metal chalcogenides, and MXenes. We discuss scientific advances and innovations published in the span of the last five years, focusing on sensing mechanisms. Full article

Graphene-based chemical sensors hold promise across diverse applications owing to their exceptional sensitivity and selectivity. However, achieving their long-term durability and reusability while preserving high sensitivity remains a significant challenge, particularly in harsh environments where exposure to strong chemicals is inevitable. This paper presents a novel approach to address this challenge by synergistically integrating liquid-phase exfoliated graphene (LPEG) with polytetrafluoroethylene (PTFE) within a single sensing strip. Through a comprehensive experimental investigation, we demonstrate the fabrication of highly durable and reusable chemical leak detection sensors by combining LPEG and PTFE. Furthermore, we explore the sensing mechanism, highlighting the roles of LPEG and PTFE in enhancing sensitivity and selectivity, along with durability and reusability. Performance evaluation reveals the sensors’ robustness against mechanical and chemical degradation, coupled with excellent recyclability. This innovative approach holds promise for applications in environmental monitoring, industrial safety, and healthcare, thus advancing the field of graphene-based chemical leak detection sensors. Full article

Certain biomarkers in exhaled breath are indicators of diseases in the human body. The non-invasive detection of such biomarkers in human breath increases the demand for simple and cost-effective gas sensors to replace state-of-the-art gas chromatography (GC) machines. The use of metal oxide (MOX) gas sensors based on thin-film structures solves the current limitations of breath detectors. However, the response at high humidity levels, i.e., in the case of exhaled human breath, significantly decreases the sensitivity of MOX sensors, making it difficult to detect small traces of biomarkers. We have introduced, in previous work, the concept of a hybrid gas sensor, in which thin-film-based MOX gas sensors are combined with an ultra-thin (20–30 nm) polymer top layer deposited by solvent-free initiated chemical vapor deposition (iCVD). The hydrophobic top layer enables sensor measurement in high-humidity conditions as well as the precise tuning of selectivity and sensitivity. In this paper, we present a way to increase the hydrogen (H₂) sensitivity of hybrid sensors through chemical modification of the polymer top layer. A poly(1,3,5,7-tetramethyl-tetravinylcyclotetrasiloxane) (PV4D4) thin film, already applied in one of our previous studies, is transformed into a silsesquioxane-containing top layer by a simple heating step. The transformation results in a significant increase in the gas response for H₂ ~709% at an operating temperature of 350 °C, which we investigate based on the underlying sensing mechanism. These results reveal new pathways in the biomedical application field for the analysis of exhaled breath, where H₂ indicates gastrointestinal diseases. Full article

In this study, we introduce a plastic-based foldable microdevice that integrates loop-mediated isothermal amplification (LAMP) and a colorimetric assay based on the Schiff reaction to detect the genes of infectious bacteria. The device comprises two sides: a sample zone containing amplification chambers and a detection zone for the colorimetric assay. The detection zone contains poly(methyl methacrylate) structures for transferring the colorimetric reagent-soaked glass micro-fiber paper into the sample chambers. Specific genes of Staphylococcus aureus (S. aureus) and Streptococcus pneumoniae (S. pneumoniae), the most common bacterial infection causes, were amplified by LAMP assay. The S. aureus gene was detected up to 10 fg/μL and the S. pneumoniae gene up to 0.1 pg/μL. The amplified target genes were visually identified using a colorimetric assay with Schiff’s reagent, which showed clear color discrimination through a reaction with aldehyde groups derived from the DNA in the amplicons. The introduced method, integrating amplification and detection processes in a single device, is expected to be utilized in point-of-care testing analysis for the simple and rapid detection of infectious pathogens. Full article

In the moist environment of soil-water-air, there is a problem of low accuracy in monitoring volatile organic compounds (VOCs) using a photoionization detector (PID). This study is based on the PID water-soil-gas VOC online monitor developed by this group, online monitoring of the concentration of different constituents of VOCs in different production enterprises of the petroleum and chemical industries in Shandong Province, with the concentration of the laboratory test, to build a relevant model. The correlation coefficient about the PID test concentration and the actual concentration correlation coefficient was obtained through the collection of a large number of data trainings. Based on the application of PID in VOC monitoring, the establishment of a PID high-precision calibration model is important for the precise monitoring of VOCs. In this paper, multiple quantitative analyses were conducted, based on SVM regression of PID response to VOC signals, to study the high-precision VOC monitoring method. To select the response signals of PID under different concentrations of environmental VOCs measured by the research group, first, the PID response to VOC signals was modeled using the support vector machine principle to verify the effect of traditional SVM regression. For the problem of raw data redundancy, calculate the time-domain and frequency-domain characteristics of the PID signal, and conduct the principal component analysis of the time-domain of the PID signal. In order to make the SVM regression more generalized and robust, the selection of kernel function parameters and penalty factor of SVM is optimized by genetic algorithm. By comparing the accuracy of PID calibration models such as PID signal feature extraction, SVM regression, and principal component analysis SVM regression, the superiority of photoionization detector using the signal feature extraction PCA-GA-SVM method to monitor VOCs is verified. Full article

Pesticides and fertilizers used in agriculture can negatively affect the soil, increasing its toxicity. In this work, a battery of whole-cell bacterial lux-biosensors based on the E. coli MG1655 strain with various inducible promoters, as well as the natural luminous Vibrio aquamarinus VKPM B-11245 strain, were used to assess the effects of agrochemical soil treatments. The advantages of using biosensors are sensitivity, specificity, low cost of analysis, and the ability to assess the total effect of toxicants on a living cell and the type of their toxic effect. Using the V. aquamarinus VKPM B-11245 strain, the synergistic effect of combined soil treatment with pesticides and mineral fertilizers was shown, which led to an increase in the overall (integral) toxicity of soils higher than that of the individual application of substances. Several probable implementation mechanisms of agrochemical toxic effects have been discovered. DNA damage caused by both SOS response induction and alkylation, oxidative stress due to increased superoxide levels, and damage to cellular proteins and membranes are among them. Thus, the usage of biosensors makes it possible to assess the cumulative effect of various toxicants on living organisms without using expensive chemical analyses. Full article

Organic pollutants, distinguished by their persistence and bioaccumulation in the environment, pose significant ecological and health threats that surpass those of traditional pollutants. Crucial to understanding their environmental behavior, health risks, and mitigation strategies, is the screening and identification of these pollutants. This process indispensably employs functional materials, among which molecularly imprinted polymers (MIPs) prove to be particularly advantageous because of their specific recognition capabilities and extensive application range. This review presents cutting-edge techniques and strategies for the fabrication of MIPs, including surface imprinting techniques and dummy molecular strategies. It encapsulates the last five years’ advancements in MIP research within the domains of sample pretreatment, as well as optical and electrochemical sensing analysis. The objective of this discourse is to potentially foster the evolution of MIP technology and establish the groundwork for its transition from lab-scale to commercial production. Full article

Colorimetric chemical sensing of target gases, such as hydrogen peroxide vapors, is an evolving area of research that implements responsive materials that undergo molecule-specific interaction, resulting in a visible color change. Due to the intuitive nature of an observable color change, such sensing systems are particularly desirable as they can be widely deployed at low cost and without the need for complex analytical instrumentation. In this work, we describe our development of a new spray-on sensing material that can provide a colorimetric response to the presence of a gas-phase target, specifically hydrogen peroxide vapor. By providing a cumulative response over time, we identified that part per million concentrations of hydrogen peroxide vapor can be detected. Specifically, we make use of iron chloride-containing formulations to enable the catalysis of hydrogen peroxide to hydroxyl radicals that serve to initiate polymerization of the diacetylene-containing amphiphile, resulting in a white to blue color transition. Due to the irreversible nature of the color change mechanism, the cumulative exposure to hydrogen peroxide over time is demonstrated, enabling longitudinal assessment of target exposure with the same coatings. The versatility of this approach in generating a colorimetric response to hydrogen peroxide vapor may find practical applications for environmental monitoring, diagnostics, or even industrial safety. Full article