Metal-Oxide Based Nanomaterials: Synthesis, Characterization and Their Applications in Electrical and Electrochemical Sensors

Synthesis of nickel-sphere coated Ni-Mn layer for efficient electrochemical detection of urea

Using a trustworthy electrochemical sensor in the detection of urea in real blood samples received a great attention these days. A thin layer of nickel-coated nickel-manganese (Ni@NiMn) is electrodeposited on a glassy carbon electrode (GC) (Ni@NiMn/GC) surface and used to construct the electrochemical sensor for urea detection. Whereas, electrodeposition is considered as strong technique for the controllable synthesis of nanoparticles. Thus, X-ray diffraction (XRD), atomic force microscope (AFM), and scanning electron microscope (SEM) techniques were used to characterize the produced electrode. AFM and SEM pictures revealed additional details about the surface morphology, which revealed a homogenous and smooth coating. Furthermore, electrochemical research was carried out in alkaline medium utilizing various electrochemical methods, including cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The electrochemical investigations showed that the electrode had good performance, high stability and effective charge transfer capabilities. The structural, morphological, and electrochemical characteristics of Ni@NiMn/GC electrodes were well understood using the analytical and electrochemical techniques. The electrode showed a limit of detection (LOD) equal to 0.0187 µM and a linear range of detection of 1.0-10 mM of urea. Furthermore, real blood samples were used to examine the efficiency of the prepared sensor. Otherwise, the anti-interfering ability of the modified catalyst was examined toward various interfering species.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

Gold nanowires-based sensor for quantification of H2O2 released by human airway epithelial cells

Hydrogen peroxide (H2O2) is a biomarker relevant for oxidative stress monitoring. Most chronic airway diseases are characterized by increased oxidative stress. To date, the main methods for the detection of this analyte are expensive and time-consuming laboratory techniques such as fluorometric and colorimetric assays. There is a growing interest in the development of electrochemical sensors for H2O2 detection due to their low cost, ease of use, sensitivity and rapid response. In this work, an electrochemical sensor based on gold nanowire arrays has been developed. Thanks to the catalytic activity of gold against hydrogen peroxide reduction and the high surface area of nanowires, this sensor allows the quantification of this analyte in a fast, efficient and selective way. The sensor was obtained by template electrodeposition and consists of gold nanowires about 5 μm high and with an average diameter of about 200 nm. The high active surface area of this electrode, about 7 times larger than a planar gold electrode, ensured a high sensitivity of the sensor (0.98 μA μM-1cm-2). The sensor allows the quantification of hydrogen peroxide in the range from 10 μM to 10 mM with a limit of detection of 3.2 μM. The sensor has excellent properties in terms of reproducibility, repeatability and selectivity. The sensor was validated by quantifying the hydrogen peroxide released by human airways A549 cells exposed or not to the pro-oxidant compound rotenone. The obtained results were validated by comparing them with those obtained by flow cytometry after staining the cells with the fluorescent superoxide-sensitive Mitosox Red probe giving a very good concordance.

Recent advances in sensing toxic nerve agents through DMMP model simulant using diverse nanomaterials-based chemical sensors

Recent terrorist assaults have demonstrated the need for the exploration and design of sustainable and stable chemical sensors with quick reaction times combined with great sensitivity. Among several classes of chemical warfare agents, nerve agents have been proven to be the most hazardous. Even short-term exposure to them can result in severe toxic effects. Human beings inadvertently face the after-effects of these chemicals even several years after these chemicals were used. Due to the extreme toxicity and difficulty in handling, dimethyl methylphosphonate (DMMP), a simulant of nerve agents with much lesser toxicity, is frequently used in laboratories as a substitute. Having a chemical structure almost identical to those of nerve agents, DMMP can mimic the properties of nerve agents. Through this paper, authors have attempted to introduce the evolution of several chemical sensors used to detect DMMP in recent years, including field-effect transistors, chemicapacitors, chemiresistors, and mass-sensitive sensors. A detailed discussion of the role of nanomaterials as chemical sensors in the detection of DMMP has been the main focus of the work through a comprehensive overview of the research on gas sensors that have been reported making use of the properties of a wide range of nanomaterials.

Powders to Thin Films: Advances in Conjugated Microporous Polymer Chemical Sensors

Chemical sensing of harmful species released either from natural or anthropogenic activities is critical to ensuring human safety and health. Over the last decade, conjugated microporous polymers (CMPs) have been proven to be potential sensor materials with the possibility of realizing sensing devices for practical applications. CMPs found to be unique among other porous materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) due to their high chemical/thermal stability, high surface area, microporosity, efficient host-guest interactions with the analyte, efficient exciton migration along the π-conjugated chains, and tailorable structure to target specific analytes. Several CMP-based optical, electrochemical, colorimetric, and ratiometric sensors with excellent selectivity and sensing performance were reported. This review comprehensively discusses the advances in CMP chemical sensors (powders and thin films) in the detection of nitroaromatic explosives, chemical warfare agents, anions, metal ions, biomolecules, iodine, and volatile organic compounds (VOCs), with simultaneous delineation of design strategy principles guiding the selectivity and sensitivity of CMP. Preceding this, various photophysical mechanisms responsible for chemical sensing are discussed in detail for convenience. Finally, future challenges to be addressed in the field of CMP chemical sensors are discussed.

MoO3/WO3/rGO as electrode material for supercapacitor and catalyst for methanol and ethanol electrooxidation

The potential of metal oxides in electrochemical energy storage encouraged our research team to synthesize molybdenum oxide/tungsten oxide nanocomposites (MoO3/WO3) and their hybrid with reduced graphene oxide (rGO), in the form of MoO3/WO3/rGO as a substrate with relatively good electrical conductivity and suitable electrochemical active surface. In this context, we presented the electrochemical behavior of these nanocomposites as an electrode for supercapacitors and as a catalyst in the oxidation process of methanol/ethanol. Our engineered samples were characterized by X-ray diffraction pattern and scanning electron microscopy. As a result, MoO3/WO3 and MoO3/WO3/rGO indicated specific capacitances of 452 and 583 F/g and stability of 88.9% and 92.6% after 2000 consecutive GCD cycles, respectively. Also, MoO3/WO3 and MoO3/WO3/rGO nanocatalysts showed oxidation current densities of 117 and 170 mA/cm2 at scan rate of 50 mV/s, and stability of 71 and 89%, respectively in chronoamperometry analysis, in the MOR process. Interestingly, in the ethanol oxidation process, corresponding oxidation current densities of 42 and 106 mA/cm2 and stability values of 70 and 82% were achieved. MoO3/WO3 and MoO3/WO3/rGO can be attractive options paving the way for prospective alcohol-based fuel cells.

Synthesis and Sensing Response of Magnesium Antimoniate Oxide (MgSb2O6) in the Presence of Propane Atmospheres at Different Operating Voltages

Nanoparticles of MgSb2O6 were synthesized using a microwave-assisted wet chemistry method, followed by calcination at 700 °C. Their ability to detect different concentrations of propane gas (C3H8) at various operating voltages was evaluated. The material's crystalline phase was identified using X-ray powder diffraction (XRD). The morphology was analyzed by scanning electron microscopy (SEM), finding bar- and polyhedron-type geometries. Through transmission electron microscopy (TEM), we found particle sizes of 8.87-99.85 nm with an average of ~27.63 nm. Employing ultraviolet-visible (UV-Vis) spectroscopy, we found a band gap value of ~3.86 eV. Thick films made with MgSb2O6 powders were exposed to atmospheres containing 150, 300, 400, and 600 ppm of propane gas for dynamic testing. The time-dependent sensitivities were ~61.09, ~88.80, ~97.65, and ~112.81%. In addition, tests were carried out at different operating voltages (5-50 V), finding very short response and recovery times (~57.25 and ~18.45 s, respectively) at 50 V. The excellent dynamic response of the MgSb2O6 is attributed mainly to the synthesis method because it was possible to obtain nanometric-sized particles. Our results show that the trirutile-type oxide MgSb2O6 possesses the ability, efficiency, and thermal stability to be applied as a gas sensor for propane.

A rapid and reliable electrochemical determination of 5- hydroxymethylfurfural in honey exploiting nickel oxide nanoparticles modified electrode

This study presents a novel approach for the rapid and reliable electrochemical determination of 5-hydroxymethylfurfural (5-HMF) in honey using a screen-printed carbon electrode modified with nickel oxide nanoparticles (NiONPs/SPCE). The NiONPs were synthesized using a simple method and characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The NiONPs/SPCE demonstrated enhanced sensitivity and selectivity for 5-HMF detection. The electrochemical behavior of 5-HMF on the NiONPs/SPCE was investigated using techniques such as cyclic voltammetry (CV) and square wave voltammetry (SWV). The optimum experimental conditions were obtained including a 5 μL of 5.0 mg/mL NiONPs modifier, the voltammetric response of step potential 15 mV, amplitude 50 mV and frequency 50 Hz in 0.1 M BR buffer pH 13 as supporting electrolyte. The proposed method exhibited a linear relationship between the cathodic peak current and the concentration of 5-HMF in the concentration ranges of 0.5-5.0 ppm, with a limit of detection (LOD) of 0.24 ppm. The selectivity of the NiONPs/SPCE was evaluated by studying potential interferences commonly found in honey samples, and the results demonstrated excellent selectivity for 5-HMF detection. The reproducibility and stability of the NiONPs/SPCE were also assessed, with low relative standard deviations (RSD) obtained for both the cathodic peak current (2.94 %) and long-term stability (3.14 %). The developed NiONPs/SPCE method was successfully applied to the determination of 5-HMF in real honey samples, yielding comparable results to the standard HPLC method. This work showcases the potential of the NiONPs/SPCE as a practical and cost-effective electrochemical sensor for the accurate analysis of 5-HMF in honey samples.

Voltammetric Sensor Based on the Combination of Tin and Cerium Dioxide Nanoparticles with Surfactants for Quantification of Sunset Yellow FCF

Sunset Yellow FCF (SY FCF) is one of the widely used synthetic azo dyes in the food industry whose content has to be controlled for safety reasons. Electrochemical sensors are a promising tool for this type of task. A voltammetric sensor based on a combination of tin and cerium dioxide nanoparticles (SnO2-CeO2 NPs) with surfactants has been developed for SY FCF determination. The synergetic effect of both types of NPs has been confirmed. Surfactants of various natures (sodium lauryl sulfate (SLS), Brij® 35, and hexadecylpyridinium bromide (HDPB)) have been tested as dispersive media. The best effects, i.e., the highest oxidation currents of SY FCF, have been observed in the case of HDPB. The sensor demonstrates a 4.5-fold-higher electroactive surface area and a 38-fold-higher electron transfer rate compared to the bare glassy carbon electrode (GCE). The electrooxidation of SY FCF is an irreversible, two-electron, diffusion-driven process involving proton transfer. In differential pulse mode in Britton-Robinson buffer (BRB) pH 2.0, the sensor gives a linear response to SY FCF from 0.010 to 1.0 μM and from 1.0 to 100 μM with an 8.0 nM detection limit. The absence of an interferent effect from other typical food components and colorants has been shown. The sensor has been tested on soft drinks and validated with the standard chromatographic method.

Sense and Shoot: Unveiling the Electro-/Photocatalytic Potential of 2D White Graphene-Supported Perovskite Strontium Cobaltite from Detection to Remediation of Oxidative Stress Herbicide (Mesotrione)

In this research, we employed a strategy akin to "Feeding Two Birds with One Stone" aiming for the dual objectives of highly selective electrochemical detection and photocatalytic degradation of the environmentally hazardous herbicide mesotrione (MTN). We achieved this by utilizing hexagonal boron nitride (BN)-supported strontium cobaltite perovskite nanocomposites (SrCoO3/BN). The fabrication of the innovative bifunctional SrCoO3/BN nanocomposites involved a straightforward process of precipitation, followed by an annealing treatment and ultrasonication. The successful formation of these nanocomposites was corroborated through the application of diverse spectroscopic tools. Notably, as-prepared SrCoO3/BN nanocomposites exhibited a remarkable sensing platform for MTN, characterized by a notably low detection limit (11 nm), considerable sensitivity (3.782 μA μM-1 cm-2), and outstanding selectivity, alongside remarkable stability. Concurrently, these SrCoO3/BN nanocomposites demonstrated exceptional visible-light-driven photocatalytic efficacy for MTN degradation (99%) and complete mineralization. Our investigation systematically delved into the influence of operational parameters, including catalyst loading and the involvement of reactive oxidative species, in both the electrocatalytic and photocatalytic reactions. Drawing from these comprehensive studies, we have proposed plausible mechanisms for detecting and degrading MTN. Our findings pave the way for catalyst development, offering a unified solution for detecting and eliminating toxic organic compounds from the environment.

A highly efficient NiCo2O4 decorated g-C3N4 nanocomposite for screen-printed carbon electrode based electrochemical sensing and adsorptive removal of fast green dye

Herein, we demonstrate the preparation and application of NiCo2O4 decorated over a g-C3N4-based novel nanocomposite (NiCo2O4@g-C3N4). The prepared material was well characterized through several physicochemical techniques, including FT-IR, XRD, SEM, and TEM. The electrochemical characterizations via electrochemical impedance spectroscopy show the low electron transfer resistance of NiCo2O4@g-C3N4 owing to the successful incorporation of NiCo2O4 nanoparticles on the sheets of g-C3N4. NiCo2O4@g-C3N4 nanocomposite was employed in the fabrication of a screen-printed carbon electrode-based innovative electrochemical sensing platform and the adsorptive removal of a food dye, i.e., fast green FCF dye (FGD). The electrochemical oxidation of FGD at the developed NiCo2O4@g-C3N4 nanocomposite modified screen-printed carbon electrode (NiCo2O4@g-C3N4/SPCE) was observed at an oxidation potential of 0.65 V. A wide dual calibration range for electrochemical determination of FGD was successfully established at the prepared sensing platform, showing an excellent LOD of 0.13 µM and sensitivity of 0.6912 µA.µM-1.cm-2 through differential pulse voltammetry. Further, adsorbent dose, pH, contact time, and temperature were optimized to study the adsorption phenomena. The adsorption thermodynamics, isotherm, and kinetics were also investigated for efficient removal of FGD at NiCo2O4@g-C3N4-based adsorbents. The adsorption phenomenon of FGD on NiCo2O4@g-C3N4 was best fitted (R2 = 0.99) with the Langmuir and Henry model, and the corresponding value of Langmuir adsorption efficiency (qm) was 3.72 mg/g for the removal of FGD. The reaction kinetics for adsorption phenomenon were observed to be pseudo-second order. The sensitive analysis of FGD in a real sample was also studied.

An insight of light-enhanced electrochemical kinetic behaviors and interfacial charge transfer of CuInS2/MoS2-based sensing nanoplatform for ultra-sensitive detection of chloramphenicol

Owing to the effective combination between MoS₂ sheets with CuInS₂ nanoparticles (NPs), a direct Z-scheme heterojunction was successfully constructed and proved as a promising structure to modify the working electrode surface with the aim of enhancing overall sensing performance towards CAP detection. Herein, MoS₂ was employed as a high mobility carrier transport channel with a strong photo-response, large specific surface area, and high in-plane electron mobility, while CuInS₂ acted as an efficient light absorber. This not only offered a stable nanocomposite structure but also created impressive synergistic effects of high electron conductivity, large surface area, highlight exposure interface, as well as favorable electron transfer process. Moreover, the possible mechanism and hypothesis of the transfer pathway of photo-induced electron-hole pairs on the CuInS₂-MoS₂/SPE as well as their impacts on the redox reaction of K₃/K₄ probes and CAP were proposed and investigated in detail via a series of calculated kinetic parameters, demonstrating the high practical applicability of light-assisted electrodes. Indeed, the detection concentration range of the proposed electrode was widened from 0.1 to 50 μM, compared with that of 1-50 μM without irradiation. Also, the LOD and sensitivity values were calculated to be approximately 0.06 μM and 0.4623 μA μM^-1, which is better than that of 0.3 μM and 0.095 μA μM^-1 without irradiation.

Artificial intelligence enhanced sensors - enabling technologies to next-generation healthcare and biomedical platform

The fourth industrial revolution has led to the development and application of health monitoring sensors that are characterized by digitalization and intelligence. These sensors have extensive applications in medical care, personal health management, elderly care, sports, and other fields, providing people with more convenient and real-time health services. However, these sensors face limitations such as noise and drift, difficulty in extracting useful information from large amounts of data, and lack of feedback or control signals. The development of artificial intelligence has provided powerful tools and algorithms for data processing and analysis, enabling intelligent health monitoring, and achieving high-precision predictions and decisions. By integrating the Internet of Things, artificial intelligence, and health monitoring sensors, it becomes possible to realize a closed-loop system with the functions of real-time monitoring, data collection, online analysis, diagnosis, and treatment recommendations. This review focuses on the development of healthcare artificial sensors enhanced by intelligent technologies from the aspects of materials, device structure, system integration, and application scenarios. Specifically, this review first introduces the great advances in wearable sensors for monitoring respiration rate, heart rate, pulse, sweat, and tears; implantable sensors for cardiovascular care, nerve signal acquisition, and neurotransmitter monitoring; soft wearable electronics for precise therapy. Then, the recent advances in volatile organic compound detection are highlighted. Next, the current developments of human-machine interfaces, AI-enhanced multimode sensors, and AI-enhanced self-sustainable systems are reviewed. Last, a perspective on future directions for further research development is also provided. In summary, the fusion of artificial intelligence and artificial sensors will provide more intelligent, convenient, and secure services for next-generation healthcare and biomedical applications.

Effects of Plasma Treatment on the Surface and Photocatalytic Properties of Nanostructured SnO2-SiO2 Films

In this work, we study the effects of treating nanostructured SnO₂-SiO₂ films derived by a sol-gel method with nitrogen and oxygen plasma. The structural and chemical properties of the films are closely investigated. To quantify surface site activity in the films following treatment, we employed a photocatalytic UV degradation test with brilliant green. Using X-ray photoelectron spectroscopy, it was found that treatment with oxygen plasma led to a high deviation in the stoichiometry of the SnO₂ surface and even the appearance of a tin monoxide phase. These samples also exhibited a maximum photocatalytic activity. In contrast, treatment with nitrogen plasma did not lead to any noticeable changes in the material. However, increasing the power of the plasma source from 250 W to 500 W led to the appearance of an SnO fraction on the surface and a reduction in the photocatalytic activity. In general, all the types of plasma treatment tested led to amorphization in the SnO₂-SiO₂ samples.

Review on Surface-Modified Electrodes for the Enhanced Electrochemical Detection of Selective Serotonin Reuptake Inhibitors (SSRIs)

Selective serotonin re-uptake inhibitors (SSRIs) are one of the most commonly prescribed classes of antidepressants used for the treatment of moderate to severe depressive disorder, personality disorders and various phobias. This class of antidepressants was created with improved margins of safety. However, genetic polymorphism may be responsible for the high variability in patients' responses to treatment, ranging from failure to delayed therapeutic responses to severe adverse effects of treatment. It is crucial that the appropriate amount of SSRI drugs is administered to ensure the optimum therapeutic efficacy and intervention to minimise severe and toxic effects in patients, which may be the result of accidental and deliberate cases of poisoning. Determining SSRI concentration in human fluids and the environment with high sensitivity, specificity and reproducibility, and at a low cost and real-time monitoring, is imperative. Electrochemical sensors with advanced functional materials have drawn the attention of researchers as a result of these advantages over conventional techniques. This review article aims to present functional materials such as polymers, carbon nanomaterials, metal nanomaterials as well as composites for surface modification of electrodes for sensitive detection and quantification of SSRIs, including fluoxetine, citalopram, paroxetine, fluvoxamine and sertraline. Sensor fabrication, sensor/analyte interactions, design rationale and properties of functional material and the electrocatalytic effect of the modified electrode on SSRI detection are discussed.

Chemical recycling of polyester textile wastes using silver-doped zinc oxide nanoparticles: an economical solution for circular economy

The waste management of polyethylene terephthalate (PET)-derived polyester (PES) textile is a global issue, and material recovery through chemical recycling can restore a circular economy. In our investigation, microwave-induced catalytic aminolysis and glycolysis of PES textile wastes using Ag-doped ZnO nanoparticles have been proposed. Ag-doped ZnO is prepared by the sol-gel method and characterised by XRD, FT-IR, UV-Vis, SEM-EDX and TEM. The reaction parameters such as PET-to-catalyst ratio, microwave power and irradiation time, temperature and catalyst recycling have been optimised. The catalyst was found to be more stable and could be recycled up to six times without losing its activity. Both the aminolysis and glycolysis of PES showed 100% conversion and afforded of bis (2-hydroxy ethylene) terephthalamide (BHETA) and bis (2-hydroxy ethylene) terephthalate (BHET), respectively. The depolymerisation of PES wastes using Ag-doped ZnO afforded BHETA and BHET for about 95 and 90%, respectively. The monomers BHET and BHETA confirmed by FT-IR, ¹H NMR and mass spectroscopy. According to the findings, 2 mol% Ag-doped ZnO has higher catalytic activity.

Metal Oxides Nanomaterials and Nanocomposite-Based Electrochemical Sensors for Healthcare Applications

Wide-ranging research efforts have been directed to prioritize scientific and technological inventions for healthcare monitoring. In recent years, the effective utilization of functional nanomaterials in various electroanalytical measurements realized a rapid, sensitive, and selective detection and monitoring of a wide range of biomarkers in body fluids. Owing to good biocompatibility, high organic capturing ability, strong electrocatalytic activity, and high robustness, transition metal oxide-derived nanocomposites have led to enhancements in sensing performances. The aim of the present review is to describe key advancements of transition metal oxide nanomaterials and nanocomposites-based electrochemical sensors, along with current challenges and prospects towards the development of a highly durable and reliable detection of biomarkers. Moreover, the preparation of nanomaterials, electrode fabrication, sensing mechanism, electrode-bio interface, and performance of metal oxides nanomaterials and nanocomposite-based sensor platforms will be described.

On-Site Detection of Volatile Organic Compounds (VOCs)

Volatile organic compounds (VOCs) are of interest in many different fields. Among them are food and fragrance analysis, environmental and atmospheric research, industrial applications, security or medical and life science. In the past, the characterization of these compounds was mostly performed via sample collection and off-site analysis with gas chromatography coupled to mass spectrometry (GC-MS) as the gold standard. While powerful, this method also has several drawbacks such as being slow, expensive, and demanding on the user. For decades, intense research has been dedicated to find methods for fast VOC analysis on-site with time and spatial resolution. We present the working principles of the most important, utilized, and researched technologies for this purpose and highlight important publications from the last five years. In this overview, non-selective gas sensors, electronic noses, spectroscopic methods, miniaturized gas chromatography, ion mobility spectrometry and direct injection mass spectrometry are covered. The advantages and limitations of the different methods are compared. Finally, we give our outlook into the future progression of this field of research.

Hydrothermal synthesis of ZnZrO2/chitosan (ZnZrO2/CS) nanocomposite for highly sensitive detection of glucose and hydrogen peroxide

In this work, pure ZnZrO₂ and chitosan supported (ZnZrO₂/CS) nanocomposite have been synthesized at low coast by hydrothermal method. FT-IR, Micro Raman, PXRD, HR-SEM-EDAX, HR-TEM, AFM, BET and XPS were used to analyze the structural and morphological properties of the fabricated nanocomposites. The fabricated ZnZrO₂ and ZnZrO₂/CS nanocomposites were measured for their electrocatalytic activity towards glucose and hydrogen peroxide determinations. The ZnZrO₂/CS sensor exhibited wide detection range (5 μM to 5.85 mM), high sensitivity (6.78 μA mM^-1 cm^-2), LOD (2.31 μM), and long-term stability for glucose detection in alkaline solution. Also, as a multifunctional electrochemical sensor, ZnZrO₂/CS sensor exhibits excellent sensing ability towards hydrogen peroxide, with a wide dynamic range (20 μM to 6.85 mM), a high sensitivity (2.22 μA mM^-1 cm^-2), and a LOD (2.08 μM) (S/N = 3). The electrochemical measurement shows that the ZnZrO₂/CS sensor has excellent catalytic activity and a much LOD than ZnZrO₂. The modified electrode showed excellent anti interference nature. Furthermore, this ZnZrO₂/CS electrode was used to detection of glucose and H₂O₂ in human blood serum and HeLa cells respectively.

Selective Voltammetric Sensor for the Simultaneous Quantification of Tartrazine and Brilliant Blue FCF

Tartrazine and brilliant blue FCF are synthetic dyes used in the food, cosmetic and pharmaceutical industries. The individual and/or simultaneous control of their concentrations is required due to dose-dependent negative health effects. Therefore, the paper presents experimental results related to the development of a sensing platform for the electrochemical detection of tartrazine and brilliant blue FCF based on a glassy carbon electrode (GCE) modified with MnO₂ nanorods, using anodic differential pulse voltammetry. Homogeneous and stable suspensions of MnO₂ nanorods have been obtained involving cetylpyridinium bromide solution as a cationic surfactant. The MnO₂ nanorods-modified electrode showed a 7.9-fold increase in the electroactive surface area and a 72-fold decrease in the electron transfer resistance. The developed sensor allowed the simultaneous quantification of dyes for two linear domains: in the ranges of 0.10-2.5 and 2.5-15 μM for tartrazine and 0.25-2.5 and 2.5-15 μM for brilliant blue FCF with detection limits of 43 and 41 nM, respectively. High selectivity of the sensor response in the presence of typical interference agents (inorganic ions, saccharides, ascorbic and sorbic acids), other food dyes (riboflavin, indigo carmine, and sunset yellow), and vanillin has been achieved. The sensor has been tested by analyzing soft and isotonic sports drinks and the determined concentrations were close to those obtained involving the chromatography technique.

Comparative pulmonary toxicity assessment of tungsten trioxide and tungsten trioxide hydrate nanoparticles

Tungsten trioxide (WO₃)-based nanoparticles (NPs) are gaining popularity because of their exciting potential for photocatalytic applications; however, the toxic potential of WO₃-based NPs remains a concern. In this study, we evaluated the toxic risk of WO₃ NPs and hydrated WO₃ NPs (WO₃·H₂O NPs) using lung cells and explored the underlying mechanism. WO₃ NPs and WO₃·H₂O NPs significantly decreased the number of viable cells (59.5 %-85.8 % of control) and promoted apoptosis in human alveolar basal epithelial A549 cells after a 24-h exposure. Both WO₃ NPs and WO₃·H₂O NPs reduced the expression of heme oxygenase-1 (0.15-0.33 folds of control) and superoxide dismutase 2 (0.31-0.66 folds of control) and increased reactive oxygen species production (1.4-2.6 folds of control) and 8-hydroxy-2'-deoxyguanosine accumulation (1.22-1.43 folds of control). The results showed that WO₃ NPs have higher cytotoxicity and oxidative potential than WO₃·H₂O NPs. In addition, the WO₃ NP cellular uptake rate was significantly higher than the WO₃·H₂O NPs uptake rate in pulmonary cells. The greater extent of oxidative adverse effects induced by WO₃-based NPs appears to be related to the enhanced particle uptake. WO₃ NPs and WO₃·H₂O NPs exposure led to the secretion of inflammatory factor interleukin 6 (1.63-3.42 folds of control). Decreases in serpin family A member 1 gene expression (0.28-0.58 folds of control) and increases in the oxidation of neutrophil elastase inhibitor (1.34-1.62 folds of control) in pulmonary cells also suggest that exposure to WO₃ NPs and WO₃·H₂O NPs raises the risk of developing chronic obstructive pulmonary disease. Taken together, our findings indicate that the toxic risk of WO₃ NPs and WO₃·H₂O NPs must be considered when manufacturing and applying WO₃-based NPs.

Artificial olfactory sensor technology that mimics the olfactory mechanism: a comprehensive review

Artificial olfactory sensors that recognize patterns transmitted by olfactory receptors are emerging as a technology for monitoring volatile organic compounds. Advances in statistical processing methods and data processing technology have made it possible to classify patterns in sensor arrays. Moreover, biomimetic olfactory recognition sensors in the form of pattern recognition have been developed. Deep learning and artificial intelligence technologies have enabled the classification of pattern data from more sensor arrays, and improved artificial olfactory sensor technology is being developed with the introduction of artificial neural networks. An example of an artificial olfactory sensor is the electronic nose. It is an array of various types of sensors, such as metal oxides, electrochemical sensors, surface acoustic waves, quartz crystal microbalances, organic dyes, colorimetric sensors, conductive polymers, and mass spectrometers. It can be tailored depending on the operating environment and the performance requirements of the artificial olfactory sensor. This review compiles artificial olfactory sensor technology based on olfactory mechanisms. We introduce the mechanisms of artificial olfactory sensors and examples used in food quality and stability assessment, environmental monitoring, and diagnostics. Although current artificial olfactory sensor technology has several limitations and there is limited commercialization owing to reliability and standardization issues, there is considerable potential for developing this technology. Artificial olfactory sensors are expected to be widely used in advanced pattern recognition and learning technologies, along with advanced sensor technology in the future.

Laser-assisted surface activation for fabrication of flexible non-enzymatic Cu-based sensors

A rapid and effective technique has been develped for the fabrication of sensor-active copper-based materials on the surface of such flexible polymers as terephthalate, polyethylene naphthalate, and polyimide using the method of laser surface modification. For this purpose, we optimized the polymer surface activation parameters using laser sources with a picosecond pulse duration for subsequent selective metallization within the activated region. Furthermore, the fabricated copper structures were modified with gold nanostructures and by electrochemical passivation to produce copper-gold and oxide-containing copper species, respectively. As a result, in comparison with pure copper electrodes, these composite materials exhibit much better electrocatalytic performance concerning the non-enzymatic identification of biologically important disease markers such as glucose, hydrogen peroxide, and dopamine.

Photoinduced Electron Transfer in Organized Assemblies—Case Studies

In this review, photoinduced electron transfer processes in specifically designed assembled architectures have been discussed in the light of recent results reported from our laboratories. A convenient and useful way to study these systems is described to understand the rules that drive a light-induced charge-separated states and its subsequent decay to the ground state, also with the aim of offering a tutorial for young researchers. Assembled systems of covalent or supramolecular nature have been presented, and some functional multicomponent systems for the conversion of light energy into chemical energy have been discussed.

Advanced Functionalized CeO2/Al2O3 Nanocomposite Sensor for Determination of Opioid Medication Tramadol Hydrochloride in Pharmaceutical Formulations

BACKGROUND

The exceptional characteristics of cerium oxide (CeO₂) and aluminum oxide (Al₂O₃) nanoscales have inspired significant attention to those nanocomposites as possible electroactive resources for applications of sensing and biosensing.

METHODS

In this research, an innovative new factionalized CeO₂/Al₂O₃ nanocomposite membrane sensor was presented to assess tramadol hydrochloride (TRD) in marketable products.

RESULTS

Tramadol-phosphomolybdate (TRD-PM) was formed by mixing tramadol hydrochloride and phosphomolybdic acid (PMA) in the attendance of polymeric matrix and o-nitrophenyloctyl ether solvent mediator. With 1.0 × 10^-10-1.0 × 10^-2 mol L^-1 as a range of linearity and E_mV = (57.567 ± 0.2) log [TRD] + 676.29 as a regression equation, the functionalized sensor using TRD-PM-CeO₂/Al₂O₃ nanocomposite showed great selectivity and sensitivity for the discriminating and measurement of TRD. Using the regression equation E_mV = (52.143 ± 0.4) log [TRD] + 431.45, the unmodified coated wire sensor of TRD-PM, on the other hand, showed a Nernstian response between 1.0 × 10^-6 and 1.0 × 10^-2 mol L^-1, Using the methodology's specified guidelines, the proposed improved potentiometric system was validated against several criteria.

CONCLUSION

The suggested method is suitable for the determination of TRD in its products.

Reagentless electrochemical biosensors through incorporation of unnatural amino acids on the protein structure

Typical protein biosensors employ chemical or genetic labeling of the protein, thus introducing an extraneous molecule to the wild-type parent protein, often changing the overall structure and properties of the protein. While these labeling methods have proven successful in many cases, they also have a series of disadvantages associated with their preparation and function. An alternative route for labeling proteins is the incorporation of unnatural amino acid (UAA) analogues, capable of acting as a label, into the structure of a protein. Such an approach, while changing the local microenvironment, poses less of a burden on the overall structure of the protein. L-DOPA is an analog of phenylalanine and contains a catechol moiety that participates in a quasi-reversible, two-electron redox process, thus making it suitable as an electrochemical label/reporter. The periplasmic glucose/galactose binding protein (GBP) was chosen to demonstrate this detection principle. Upon glucose binding, GBP undergoes a significant conformational change that is manifested as a change in the electrochemistry of L-DOPA. The electroactive GBP was immobilized onto gold nanoparticle-modified, polymerized caffeic acid, screen-printed carbon electrodes (GBP-LDOPA/AuNP/PCA/SPCE) for the purpose of direct measurement of glucose levels and serves as a proof-of-concept of the use of electrochemically-active unnatural amino acids as the label. The resulting reagentless GBP biosensors exhibited a highly selective and sensitive binding affinity for glucose in the micromolar range, laying the foundation for a new biosensing methodology based on global incorporation of an electroactive amino acid into the protein's primary sequence for highly selective electrochemical detection of compounds of interest.

Paving the Way for a Green Transition in the Design of Sensors and Biosensors for the Detection of Volatile Organic Compounds (VOCs)

The efficient and selective detection of volatile organic compounds (VOCs) provides key information for various purposes ranging from the toxicological analysis of indoor/outdoor environments to the diagnosis of diseases or to the investigation of biological processes. In the last decade, different sensors and biosensors providing reliable, rapid, and economic responses in the detection of VOCs have been successfully conceived and applied in numerous practical cases; however, the global necessity of a sustainable development, has driven the design of devices for the detection of VOCs to greener methods. In this review, the most recent and innovative VOC sensors and biosensors with sustainable features are presented. The sensors are grouped into three of the main industrial sectors of daily life, including environmental analysis, highly important for toxicity issues, food packaging tools, especially aimed at avoiding the spoilage of meat and fish, and the diagnosis of diseases, crucial for the early detection of relevant pathological conditions such as cancer and diabetes. The research outcomes presented in the review underly the necessity of preparing sensors with higher efficiency, lower detection limits, improved selectivity, and enhanced sustainable characteristics to fully address the sustainable manufacturing of VOC sensors and biosensors.

Acrylate and Methacrylate Polymers' Applications: Second Life with Inexpensive and Sustainable Recycling Approaches

Polymers are widely employed in several fields thanks to their wide versatility and the easy derivatization routes. However, a wide range of commercial polymers suffer from limited use on a large scale due to their inert nature. Nowadays, acrylate and methacrylate polymers, which are respectively derivatives of acrylic or methacrylic acid, are among the most proposed materials for their useful characteristics like good biocompatibility, capping ability toward metal clusters, low price, potentially recyclability and reusability. Here, we discuss the advantages and challenges of this class of smart polymers focusing our attention on their current technological applications in medical, electronic, food packaging and environmental remediation fields. Furthermore, we deal with the main issue of their recyclability, considering that the current commercial bioplastics are not yet able to meet the global needs as much as to totally replace fossil-fuel-based products. Finally, the most accredited strategies to reach recyclable composites based on acrylic polymers are described.

Machine learning-assisted ammonium detection using zinc oxide/multi-walled carbon nanotube composite based impedance sensors

We report a machine learning approach to accurately correlate the impedance variations in zinc oxide/multi walled carbon nanotube nanocomposite (F-MWCNT/ZnO-NFs) to NH4+ ions concentrations. Impedance response of F-MWCNT/ZnO-NFs nanocomposites with varying ZnO:MWCNT compositions were evaluated for its sensitivity and selectivity to NH4+ ions in the presence of structurally similar analytes. A decision-making model was built, trained and tested using important features of the impedance response of F-MWCNT/ZnO-NF to varying NH4+ concentrations. Different algorithms such as kNN, random forest, neural network, Naïve Bayes and logistic regression are compared and discussed. ML analysis have led to identify the most prominent features of an impedance spectrum that can be used as the ML predictors to estimate the real concentration of NH4+ ion levels. The proposed NH4+ sensor along with the decision-making model can identify and operate at specific operating frequencies to continuously collect the most relevant information from a system.

Cerium(IV) and Iron(III) Oxides Nanoparticles Based Voltammetric Sensor for the Sensitive and Selective Determination of Lipoic Acid

A novel voltammetric sensor based on CeO2·Fe2O3 nanoparticles (NPs) has been developed for the determination of lipoic acid, playing an essential role in aerobic metabolism in the living organism. Sensor surface modification provides a 5.6-fold increase of the lipoic acid oxidation currents and a 20 mV anodic shift of the oxidation potential. The best voltammetric parameters have been obtained for the 0.5 mg mL-1 dispersion of CeO2·Fe2O3 NPs. Scanning electron microscopy (SEM) confirms the presence of spherical NPs of 25-60 nm, and their aggregates evenly distributed on the electrode surface and formed porous coverage. This leads to the 4.4-fold increase of the effective surface area vs. bare glassy carbon electrode (GCE). The sensor shows a significantly higher electron transfer rate. Electrooxidation of lipoic acid on CeO2·Fe2O3 NPs modified GCE is an irreversible diffusion-controlled pH-independent process occurring with the participation of two electrons. The sensor gives a linear response to lipoic acid in the ranges of 0.075-7.5 and 7.5-100 μM with the detection limit of 0.053 μM. The sensor is selective towards lipoic acid in the presence of inorganic ions, ascorbic acid, saccharides, and other S-containing compounds. The sensor developed has been tested on the pharmaceutical dosage forms of lipoic acid.

Effect of Al and Mg Doping on Reducing Gases Detection of ZnO Nanoparticles

In this work, the main objective is to enhance the gas sensing capability through investigating the effect of Al and Mg doping on ZnO based sensors. ZnO, Mg1% doped ZnO, Al5% doped ZnO and (Al5%, Mg1%) co-doped ZnO nanoparticles (NPs) were synthesized by a modified sol-gel method. The structural characterization showed the hexagonal crystalline structure of the prepared samples. Morphological characterizations confirmed the nanometric sizes of the NPs (27–57 nm) and elemental composition investigation proved the existence of Al and Mg with low concentrations. The optical characterization showed the high absorbance of the synthesized samples in the UV range. The gas sensing performances of the synthesized samples, prepared in the form of thick films, were investigated. Sensing tests demonstrated the high influence of the Al and Mg on the sensing performances towards H2 and CO gas, respectively. The 5A1MZO-based sensor exhibits high sensitivity and low detection limits to H2 (<2 ppm) and CO (<1 ppm). It showed a response around 70 (at 250 °C) towards 2000 ppm H2 and 2 (at 250 °C) towards CO.

On the Use of Pulsed UV or Visible Light Activated Gas Sensing of Reducing and Oxidising Species with WO3 and WS2 Nanomaterials

This paper presents a methodology to quantify oxidizing and reducing gases using n-type and p-type chemiresistive sensors, respectively. Low temperature sensor heating with pulsed UV or visible light modulation is used together with the application of the fast Fourier transform (FFT) to extract sensor response features. These features are further processed via principal component analysis (PCA) and principal component regression (PCR) for achieving gas discrimination and building concentration prediction models with R² values up to 98% and RMSE values as low as 5% for the total gas concentration range studied. UV and visible light were used to study the influence of the light wavelength in the prediction model performance. We demonstrate that n-type and p-type sensors need to be used together for achieving good quantification of oxidizing and reducing species, respectively, since the semiconductor type defines the prediction model’s effectiveness towards an oxidizing or reducing gas. The presented method reduces considerably the total time needed to quantify the gas concentration compared with the results obtained in a previous work. The use of visible light LEDs for performing pulsed light modulation enhances system performance and considerably reduces cost in comparison to previously reported UV light-based approaches.