High-performance sensor based on copper oxide nanoparticles for dual detection of phenolic compounds and a pesticide

Exploring the diverse applications of sol-gel synthesized CaO:MgAl2O4 nanocomposite: morphological, photocatalytic, and electrochemical perspectives

A nanocomposite of CaO:MgAl2O4 was synthesized through a straightforward and cost-effective sol-gel method. The investigation of the novel CaO:MgAl2O4 nanocomposite encompassed an examination of its morphological and structural alterations, as well as an exploration of its photocatalytic activities and electrochemical characteristics. XRD analysis revealed a nanocomposite size of 24.15 nm. The band gap, determined through UV studies, was found to be 3.83 eV, and scanning electron microscopy (SEM) illustrated flake-like morphological changes in the CaO:MgAl2O4 samples. TEM, HRTEM, and SAED studies of a CaO:MgAl2O4 nanocomposite would reveal important details about its morphology, crystallography, and nanostructure. Photocatalytic activity was quantified by studying the degradation of Acid Red-88 (AR-88) dye in a deionized solution, achieving a 70% dye degradation under UV irradiation in 120 min. Plant growth examinations were carried out using dye degraded water to test its suitability for agriculture. The electrochemical energy storage and sensing applications of the prepared nanocomposite were examined using CaO:MgAl2O4 modified carbon paste electrode through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In conclusion, the synthesized CaO:MgAl2O4 nanocomposite demonstrated promising morphological and structural characteristics, efficient photocatalytic activity, and potential applications in electrochemical energy storage, highlighting its versatility for various technological and environmental applications.

Joule Heating in Controlled Atmospheres to Process Nanocarbon/Transition Metal Oxide Composites and Electrodes

Composites of nanocarbons and transition metal oxides combine excellent mechanical properties and high electrical conductivity with high capacitive active sites. These composites are promising for applications such as electrochemical energy conversion and storage, catalysis, and sensing. Here, we show that Joule heating can be used as a rapid out-of-oven thermal processing technique to crystallize the inorganic metal oxide matrix within a carbon nanotube fabric (CNTf) composite. We choose manganese oxide and vanadium oxide as model metal oxides and show that the Joule heating process is rapid and enables accurate control over the temperature and phase transitions. Next, we use thermogravimetric analysis and Joule heating experiments in controlled atmospheres to show that metal oxides can actually catalyze thermal degradation and reduce the thermal stability of the CNTs, which could limit processing of many oxides. We solve this by using a reducing hydrogen atmosphere to successfully extend the Joule processing window and thermal stability of the CNTf/metal oxide composite to ∼1000 °C.

Pesticides monitoring in biological fluids: Mapping the gaps in analytical strategies

Pesticides play a key-role in the development of the agrifood sector allowing controlling pest growth and, thus, improving the production rates. Pesticides chemical stability is responsible of their persistency in environmental matrices leading to bioaccumulation in animal tissues and hazardous several effects on living organisms. The studies regarding long-term effects of pesticides exposure and their toxicity are still limited to few studies focusing on over-exposed populations, but no extensive dataset is currently available. Pesticides biomonitoring relies mainly on chromatographic techniques coupled with mass spectrometry, whose large-scale application is often limited by feasibility constraints (costs, time, etc.). On the contrary, chemical sensors allow rapid, in-situ screening. Several sensors were designed for the detection of pesticides in environmental matrices, but their application in biological fluids needs to be further explored. Aiming at contributing to the implementation of pesticides biomonitoring methods, we mapped the main gaps between screening and chromatographic methods. Our overview focuses on the recent advances (2016-2021) in analytical methods for the determination of commercial pesticides in human biological fluids and provides guidelines for their application.

The role of MOF based nanocomposites in the detection of phenolic compounds for environmental remediation- A review

Phenolic compounds would be the emerging pollutant by 2050, because of their wide spread applicability in daily life and therefore the adoption of suitable detection methods in which identification and separation of isomers is highly desirable. Owing to the fascinating features, Metal-organic framework (MOF), a class of reticular materials holds a large surface area with tunable shape and adjustable porosity will provide strong interaction with analytes through abundant functional groups resulting in high selectivity towards electrochemical determination of phenolic isomers. Nevertheless, the sensing performance can still be further improved by building MOF network (intrinsic resistance) with functional (conducting) materials, resulting in MOF based nanocomposite. Herein, this review provides the summary of MOF based nanocomposites for electrochemical sensing of phenolic compounds developed from 2015. In this review, we discussed the demerits of pristine MOF as electrode materials, and the requirement of new class of MOF with functional materials such as nanomaterials, carbon nanotubes, graphene and MXene. The history and evolution of MOF nanocomposite-based materials are discussed and also featured the impressive physical and chemical properties. Besides this review discusses the factors influencing the conducting pathway and mass transport of MOF based nanocomposite for enhanced sensing performance of phenolic compounds with suitable mechanistic illustrations. Finally, the major challenges governing the determination of phenolic compounds and the future advancements required for the development of MOF based electrodes for various applications are highlighted.

A Review of Nanocomposite-Modified Electrochemical Sensors for Water Quality Monitoring

Electrochemical sensors play a significant role in detecting chemical ions, molecules, and pathogens in water and other applications. These sensors are sensitive, portable, fast, inexpensive, and suitable for online and in-situ measurements compared to other methods. They can provide the detection for any compound that can undergo certain transformations within a potential window. It enables applications in multiple ion detection, mainly since these sensors are primarily non-specific. In this paper, we provide a survey of electrochemical sensors for the detection of water contaminants, i.e., pesticides, nitrate, nitrite, phosphorus, water hardeners, disinfectant, and other emergent contaminants (phenol, estrogen, gallic acid etc.). We focus on the influence of surface modification of the working electrodes by carbon nanomaterials, metallic nanostructures, imprinted polymers and evaluate the corresponding sensing performance. Especially for pesticides, which are challenging and need special care, we highlight biosensors, such as enzymatic sensors, immunobiosensor, aptasensors, and biomimetic sensors. We discuss the sensors' overall performance, especially concerning real-sample performance and the capability for actual field application.

Electrochemical (Bio)Sensors for Pesticides Detection Using Screen-Printed Electrodes

Pesticides are among the most important contaminants in food, leading to important global health problems. While conventional techniques such as high-performance liquid chromatography (HPLC) and mass spectrometry (MS) have traditionally been utilized for the detection of such food contaminants, they are relatively expensive, time-consuming and labor intensive, limiting their use for point-of-care (POC) applications. Electrochemical (bio)sensors are emerging devices meeting such expectations, since they represent reliable, simple, cheap, portable, selective and easy to use analytical tools that can be used outside the laboratories by non-specialized personnel. Screen-printed electrodes (SPEs) stand out from the variety of transducers used in electrochemical (bio)sensing because of their small size, high integration, low cost and ability to measure in few microliters of sample. In this context, in this review article, we summarize and discuss about the use of SPEs as analytical tools in the development of (bio)sensors for pesticides of interest for food control. Finally, aspects related to the analytical performance of the developed (bio)sensors together with prospects for future improvements are discussed.

Detection of phenol by incorporation of gold modified-enzyme based graphene oxide thin film with surface plasmon resonance technique

In this study, the incorporation between gold modified-tyrosinase (Tyr) enzyme based graphene oxide (GO) thin film with surface plasmon resonance (SPR) technique has been developed for the detection of phenol. SPR signal for the thin film contacted with phenol solution was monitored using SPR technique. From the SPR curve, sensitivity, full width at half maximum (FWHM), detection accuracy (DA) and signal-to-noise ratio (SNR) have been analyzed. The sensor produces a linear response for phenol up to 100 µM with sensitivity of 0.00193° µM^-1. Next, it can be observed that deionized water has the lowest FWHM, with a value of 1.87° and also the highest value of DA. Besides, the SNR of the SPR signal was proportional to the phenol concentrations. Furthermore, the surface morphology of the modified thin film after exposed with phenol solution observed using atomic force microscopy showed a lot of sharp peaks compared to the image before in contact with phenol proved the interaction between the thin film and phenol.

Direct competitive immunosensor for Imidacloprid pesticide detection on gold nanoparticle-modified electrodes

A direct competitive immunosensor for the electrochemical determination of Imidacloprid (IMD) pesticide on gold nanoparticle-modified screen-printed carbon electrodes (AuNP-SPCE) is here reported for the first time. Self-obtained specific monoclonal antibodies are immobilized on the AuNP-SPCE taking advantage of the AuNPs biofunctionalization abilities. In our biosensor design, free IMD in the sample competes with IMD conjugated with horseradish peroxidase (IMD-HRP) for the recognition by the antibodies. After that, 3,3',5,5'-Tetramethylbenzidine (TMB) is enzymatically oxidized by HRP, followed by the oxidized TMB reduction back at the surface of the SPCE. This process gives an associated catalytic current (analytical signal) that is inversely proportional to the IMD amount. The main parameters affecting the analytical signal have been optimized, reaching a good precision (repeatability with a RSD of 6%), accuracy (relative error of 6%), stability (up to one month), selectivity and an excellent limit of detection (LOD of 22 pmol L^-1), below the maximum levels allowed by the legislation, with a wide response range (50-10000 pmol L^-1). The detection through antibodies also allows to have an excellent selectivity against other pesticides potentially present in real samples. Low matrix effects were found when analysing IMD in tap water and watermelon samples. The electrochemical immunosensor was also validated with HPLC-MS/MS, the reference method used in official laboratories for IMD analysis, through statistical tests. Our findings make the electrochemical immunosensor as an outstanding method for the rapid and sensitive determination of IMD at the point-of-use.

High surface area 3D-MgO flowers as the modifier for the working electrode for efficient detection of 4-chlorophenol

We report for the first time, magnesium oxide (MgO) 3D-flowers, synthesized by a simple reflux method. The synthesized MgO 3D-flowers were characterized by powder X-ray diffraction (PXRD), ultra-violet visible (UV-vis) spectroscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) mapping to confirm their purity, morphology and elemental composition. The synthesized MgO 3D-flowers had a very high specific surface area of 218 m2 g-1 as confirmed by the N2 adsorption-desorption isotherm. These MgO 3D-flowers were employed as an electrode modifier for the construction of an electrochemical sensor to detect 4-chlorophenol (4-CP). The active surface area of the glassy carbon electrode (GCE) was modified with MgO 3D-flowers with the assistance of 0.1% Nafion (MgO 3D-flowers/GCE) and the MgO 3D-flowers/GCE sensor shows an excellent electrocatalytic behavior towards 4-CP. The constructed MgO 3D-flowers/GCE sensor exhibits the limits of detection (LOD) of 45 nM, 68 nM, and 52 nM, and sensitivities of 2.84 μA μM-1 cm-2, 5.94 μA μM-1 cm-2, and 10.67 μA μM-1 cm-2 in cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) techniques, respectively. The modified MgO 3D-flowers/GCE sensor displays excellent performance in terms of sensitivity, selectivity, repeatability and reproducibility. The excellent electrocatalytic activity of the proposed MgO 3D-flowers/GCE sensor was attributed to the high specific surface area, surface electron transfer ability and the presence of the edges/corner defects of MgO 3D-flowers.

Fabrication of 4-aminophenol sensor based on hydrothermally prepared ZnO/Yb2O3nanosheets

A facile hydrothermal process was used to prepare nanostructures of ZnO/Yb₂O₃in alkaline medium, which were applied for efficient chemical sensor development. The sensor fabricated with ZnO/Yb₂O₃nanostructures may be a promising sensitive chemical sensor for the effective detection of environmental effluents.