An interference-free new xanthine biosensor based on immobilized enzyme-nanogold conjugate on carbon nanotube doped poly(3,4-Ethylenedioxythiophene) composite film

Noble metal/metal-organic framework nanoparticle-based electrochemical sensors for evaluating fish quality: a comprehensive review

Fish quality is a big-picture issue because of the possible presence of many chemical and biological pollutants, that may affect fish leading to environmental and health hazards. In this regard, researchers focus on developing efficient strategies for evaluating fish quality in terms of safety and freshness. Fish safety is determined based on assessing various pollutants, such as heavy metals, pesticides, dyes, and drugs, in fish tissue. Additionally, fish freshness evaluation is based on assessing some indicators including xanthine, hypoxanthine, uric acid, and histamine. Many chromatographic methods can assess all of these chemical indicators to evaluate the fish quality. However, these methods are expensive and often require sophisticated steps. Thus, electrochemical methods based on noble metal nanoparticles (NMNPs), metal-organic frameworks (MOFs) NPs, and their composites as electrode modifiers were investigated as potential replacements for the chromatographic ones. These materials showed high catalytic activity and electrical conductivity compared to the other electrode modifiers. In this review, we spotlight the role of NMNPs and MOF NPs in evaluating the quality of fish samples as a food source. Overall, NMNPs and MOF NPs are considered promising electrode materials for the electrochemical monitoring of fish quality.

Impedance nanobiosensor based on enzyme-conjugated biosynthesized gold nanoparticles for the detection of Gram-positive bacteria

In this report, gold nanoparticles (GNPS) were synthesized using cell-free extracts of seven different isolates, namely, Pseudomonas aerogenosa CEBP2, Pseudomonas sp. CEBP1, Pseudomonas pseudoalcaligenes CEB1G, Acinetobactor baumani CEBS1, Cuprividus sp. CEB3, Micrococcus luteus CUB12, and Pandoraea sp. CUB2S. The spectroscopic (UV-vis, FTIR, DLS, XRD, EDS) and microscopic (FESEM, TEM) results confirm the reduction of Au3+ to Au0 in the presence of biomolecules having reducing as well as self-stabilizing activity. In this green synthesis approach, the average particle size of biosynthesized GNPS might vary (4-60 nm) depending on the bacterial species, pH of the media, incubation time, and temperature. In this study, GSH-modified BSGNPs (Au-GSH) have shown antimicrobial activity with better stability against Gram-positive bacteria. After conjugation of lysozyme with Au-GSH (lyso@Au-GSH), the zone of inhibition was enhanced from 12 to 23 mm (Au-GSH). The TEM study shows the spherical GNP (16.65 ± 2.84) turns into a flower-shaped GNP (22.22 ± 3.12) after conjugation with lysozyme due to the formation of the protein corona. Furthermore, the nanobioconjugate (lyso@Au-GSH) was immobilized with Nafion on a glassy carbon electrode to fabricate a label-free impedance biosensor that is highly sensitive to monitor changes in the transducer surface due to biomolecular interactions. The uniquely designed biosensor could selectively detect Gram-positive bacteria in the linear range of 3.0 × 101-3 × 1010 cfu mL-1 with RE <5%. The proposed simplest biosensor exhibited good reproducibility (RSD = 3.1%) and excellent correlation (R2 = 0.999) with the standard plate count method, making it suitable for monitoring Gram-positive bacterial contamination in biofluids, food, and environmental samples.

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

Novel Enzymatic Biosensor Utilizing a MoS2/MoO3 Nanohybrid for the Electrochemical Detection of Xanthine in Fish Meat

A rapid, reliable, and user-friendly electrochemical sensor was developed for the detection of xanthine (Xn), an important biomarker of food quality. The developed sensor is based on a nanocomposite comprised of molybdenum disulfide-molybdenum trioxide (MoS2/MoO3) and synthesized using a single-pot hydrothermal method. Structural analysis of the MoS2/MoO3 nanocomposite was conducted using X-ray diffraction (XRD) and Raman spectroscopy, while its compositional properties were evaluated through X-ray photoelectron spectroscopy (XPS). Morphological features were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Two-dimensional (2D) MoS2 offers advantages such as a high surface-to-volume ratio, biocompatibility, and strong light-matter interaction, whereas MoO3 serves as an effective electron transfer mediator and exhibits excellent stability in aqueous environments. The enzymatic biosensor derived from this nanocomposite demonstrates remarkable cyclic stability and a low limit of detection of 64 nM. It enables rapid, reproducible, specific, and reproducible detection over 10 cycles while maintaining a shelf life of more than 5 weeks. These findings highlight the potential of our proposed approach for the development of early detection devices for Xn.

MIL-101(Cr) molecular cage anchored on 2D Ti3C2TX MXene nanosheets as high-performance electrochemical sensing platform for detection of xanthine

A new electrochemical sensing material based on the MIL-101(Cr) molecular cage anchored on 2D Ti₃C₂T_X-MXene nanosheets was prepared by using the in situ growth molecular engineering strategy. The sensing material was characterized by using different methods such as SEM, XRD, and XPS. The electrochemical sensing performance of MIL-101(Cr)/Ti₃C₂T_x-MXene was studied by DPV, CV, EIS, and other techniques. The electrochemical tests showed that the linear range of the modified electrode for xanthine (XA) detection was 1.5-73.0 μM and 73.0-133.0 μM, the detection limit was 0.45 μM (working potential of + 0.71 V vs. Ag/AgCl), and the performance is superior compared with the reported enzyme-free modified electrodes for detecting XA. The fabricated sensor has high selectivity and stability. It has good practicability in serum analysis with recoveries of 96.58-103.27% and a relative standard deviation (RSD) of 3.58-4.32%.

Graphitic Carbon Nitride-Wrapped Metal-free PoPD-Based Biosensor for Xanthine Detection

A metal-free, enzymatic biosensor was developed using graphitic carbon nitride (g-C₃N₄)-wrapped poly-ortho-phenylenediamine (PoPD) for the determination of xanthine (Xn). Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction confirmed the successful formation of the PoPD, g-C₃N₄ nanosheets and PoPD@g-C₃N₄ nanocomposite. Furthermore, the electrochemical behavior of the biosensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The prepared enzyme electrode exhibited maximum response at pH 7.5 with a response time of 5 s, and its sensitivity was 5.798 μAM^-1. The nanocomposite shows exceptional sensing capabilities for detecting Xn, having a wide linear range from 1 nM to 1 μM with a relatively low detection limit of 0.001 nM. The biosensor shows good stability (4 weeks) and reproducibility and can detect the presence of Xn from other interfering analytes. Validation of the biosensor with real samples obtained from Rohu (Labeo rohita) fish shows that the fabricated biosensor has the requisite potential to be used for Xn detection in meat samples.

A nonenzymatic reduced graphene oxide-based nanosensor for parathion

Organophosphate-based pesticides (e.g., parathion (PT)) have toxic effects on human health through their residues. Therefore, cost-effective and rapid detection strategies need to be developed to ensure the consuming food is free of any organophosphate-residue. This work proposed the fabrication of a robust, nonenzymatic electrochemical-sensing electrode modified with electrochemically reduced graphene oxide (ERGO) to detect PT residues in environmental samples (e.g., soil, water) as well as in vegetables and cereals. The ERGO sensor shows a significantly affected electrocatalytic reduction peak at -0.58 V (vs Ag/AgCl) for rapid quantification of PT due to the amplified electroactive surface area of the modified electrode. At optimized experimental conditions, square-wave voltammetric analysis exhibits higher sensitivity (50.5 μA·μM-1·cm-2), excellent selectivity, excellent stability (≈180 days), good reproducibility, and repeatability for interference-free detection of PT residues in actual samples. This electrochemical nanosensor is suitable for point-of-care detection of PT in a wide dynamic range of 3 × 10-11-11 × 10-6 M with a lower detection limit of 10.9 pM. The performance of the nanosensor was validated by adding PT to natural samples and comparing the data via absorption spectroscopy. PT detection results encourage the design of easy-to-use nanosensor-based analytical tools for rapidly monitoring other environmental samples.