Ag-modified CuO cavity arrays as a SERS-electrochemical dual signal platform for thiram detection

Rapid and sensitive determination of pesticide residues in fruits and vegetables is critical for human health and ecosystems. This paper used an Ag-modified CuO sphere-cavity array (CuO@Ag) electrode as a thiram SERS/electrochemical dual readout detection platform. Numerous Raman "hotspots" generated by uniformly distributed silver nanoparticles, charge transfer at the CuO@Ag interface, and the formation of Ag-thiram complexes contribute to the significant enhancement of this SERS substrate, which results in excellent SERS performance with an enhancement factor up to 1.42 × 106. When using SERS as the readout technique, the linear range of the substrate for thiram detection was 0.05-20 nM with a detection limit (LOD) of up to 0.0067 nM. Meanwhile, a correlation between the value of change in current density and thiram concentration was established due to the formation of stable complexes of thiram with Cu2+ generated at specific potentials. The linear range of electrochemical detection was 0.05-20.0 μM, and the detection limit was 0.0167 μM. The newly devised dual-readout sensor offers notable sensitivity and stability. The two signal readout methods complement each other in terms of linear range and detection limit, making it a convenient tool for assessing thiram residue levels in agro-food. At the same time, the combination of commercially available portable equipment makes on-site monitoring possible.

Complexes of Ag and ZnO nanoparticles with BBR for enhancement of gastrointestinal antibacterial activity through the impacts of size and composition

This study introduces the bioformulations of Ag/BBR and ZnO/BBR complexes against pathogenic bacteria in the gastrointestinal tract. Without the use of toxic reduction agents, Ag and ZnO NPs were prepared using an electrochemical method and then facially mixed with BBR solution to form Ag/BBR and ZnO/BBR complexes. BBR molecules are strongly conjugated with Ag and ZnO NPs through coordinated bonding and electrostatic interaction. As a result, the presence of BBR significantly influenced the nanoparticle growth, resulting in the formation of core/shell structured Ag/BBR and ZnO/BBR NPs with small particle sizes. The antibacterial test showed that BBR, Ag, or ZnO components all contributed to the increase of antibacterial ability of Ag/BBR and ZnO/BBR NPs against both methicillin-resistant Staphylococcus aureus (MRSA) and Salmonella enteritidis (S. enteritidis). The bactericidal ability of Ag/BBR and ZnO/BBR complexes against MRSA was exhibited even at a concentration of four-fold dilution (corresponding to 1.25 g L^-1 of BBR and 46.25 mg L^-1 of Ag) and two-fold dilution (corresponding to 2.5 g L^-1 of BBR and 10 mg L^-1 of ZnO), respectively, while that of the Ag/BBR complex against S. enteritidis showed at a concentration of two-fold dilution corresponding to 2.5 g L^-1 of BBR and 92.5 mg L^-1 of Ag. The results obtained in this study support that Ag/BBR and ZnO/BBR complexes can be potential therapeutic agents against gastrointestinal infections.

Construction of 3D Bi/ZnSnO3 hollow microspheres for label-free highly selective photoelectrochemical recognition of norepinephrine

Herein, we reported a label-free and reliable photoelectrochemical (PEC) platform for highly selective monitoring of norepinephrine (NE) based on metallic Bi nanoparticles anchored on hollow porous ZnSnO3 microspheres (3D Bi/ZnSnO3) via a simple solvothermal strategy. The designed 3D Bi/ZnSnO3 Schottky junction exhibited a unique photoanodic response toward NE among other catechol derivatives, such as epinephrine (EP) and dopamine (DA), and effectively shielded the interference from thirteen coexisting biomolecules like uric acid (UA) and ascorbic acid (AA). High selectivity and excellent sensitivity could be correlated to the unique chelating coordination interaction between NE and Zn2+ at surface sites as well as the efficient carrier separation of Bi/ZnSnO3, thereby developing a novel "signal-on" label-free and selective strategy for NE detection. The proposed Bi/ZnSnO3-based PEC sensor achieved remarkable NE biosensing with a low detection limit of 0.68 nmol L-1 and a wide response ranging from 0.002 to 350.0 μmol L-1. The applicability of this biosensor was realized for the selective analysis of NE in human serum, human urine and injection samples, laying the foundation for the label-free PEC monitoring of NE in biological fluids.

Voltammetric Sensor Based on Molecularly Imprinted Chitosan-Carbon Nanotubes Decorated with Gold Nanoparticles Nanocomposite Deposited on Boron-Doped Diamond Electrodes for Catechol Detection

Phenolic compounds such as catechol are present in a wide variety of foods and beverages; they are of great importance due to their antioxidant properties. This research presents the development of a sensitive and biocompatible molecular imprinted sensor for the electrochemical detection of catechol, based on natural biopolymer-electroactive nanocomposites. Gold nanoparticle (AuNP)-decorated multiwalled carbon nanotubes (MWCNT) have been encapsulated in a polymeric chitosan (CS) matrix. This chitosan nanocomposite has been used to develop a molecular imprinted polymers (MIP) in the presence of catechol on a boron-doped diamond (BDD) electrode. The structure of the decorated MWCNT has been studied by TEM, whereas the characterization of the sensor surface has been imaged by AFM, demonstrating the satisfactory adsorption of the film and the adequate coverage of the decorated carbon nanotubes on the electrode surface. The electrochemical response of the sensor has been analyzed by cyclic voltammetry (CV) where excellent reproducibility and repeatability to catechol detection in the range of 0 to 1 mM has been found, with a detection limit of 3.7 × 10-5 M. Finally, the developed sensor was used to detect catechol in a real wine sample.

A novel non-enzymatic zinc oxide thin film based electrochemical recyclable strip with device interface for quantitative detection of catechol in water

Catechol, one of the major effluents released by various chemical and metal processing industries, causes severe pollution of groundwater. Monitoring of catechol in water using cost-effective, handheld sensor is demanding for the safety of the environment. In this work, non-enzymatic zinc oxide thin film based electrochemical strip sensor is developed on conducting glass substrate for detection of catechol. The preparation of strip without employing standard Pt or Ag/AgCl electrodes and simply depositing ZnO through wet chemical process represents a cost-effective innovative technique. The ZnO thin film is characterized using field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM) and grazing incidence X-ray diffractometer (GIXRD). Catechol is electrochemically detected by means of cyclic voltammetry and amperometry. A prominent redox peak of the developed strip attributed to the detection of catechol is observed at -0.26 V in cyclic voltammetry. The strip is integrated with readout meter and an algorithm is built based on the experimentally observed linear variation of amperometric current with catechol concentration. The quantitative detection performance is demonstrated by testing 0.1-12 ppm catechol solutions.

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.

An electronic device based on gold nanoparticles and tetraruthenated porphyrin as an electrochemical sensor for catechol

The aim of this study was to obtain an electrochemical device between the electrostatic interaction of the electropolymerized porphyrin {CoTPyP[RuCl₃(dppb)]₄}, where TPyP = 5,10,15, 20-tetrapyridilphorphyrin and dppb = 1,4-bis(diphenylphosphino)butane, and gold nanoparticles (AuNPs^n-), to be used as a voltammetric sensor to determine catechol (CC). The modified electrode, labelled as [(CoTPRu₄)_n⁸⁺-BE]/AuNPs^n- {where BE = bare electrode = glassy carbon electrode (GCE) or indium tin oxide (ITO)}, was made layer-by-layer. Initially, a cationic polymeric film was generated by electropolymerization of the {CoTPyP[RuCl₃(dppb)]₄} onto the surface of the bare electrode to produce an intermediary electrode [(CoTPRu₄)_n⁸⁺-BE]. Making the final electronic device also involves coating the electrode [(CoTPRu₄)_n⁸⁺-BE] using a colloidal suspension of AuNPs^n- by electrostatic interaction between the species. Therefore, a bilayer labelled as [(CoTPRu₄)_n⁸⁺-BE]/AuNPs^n- was produced and used as an electrochemical sensor for CC determination. The electrochemical behaviour of CC was investigated using cyclic voltammetry at [(CoTPRu₄)_n⁸⁺-GCE]/AuNPs^n- electrode. Compared to the GCE, the [(CoTPRu₄)_n⁸⁺-GCE]/AuNPs^n- showed higher electrocatalytic activity towards the oxidation of CC. Under the optimized conditions, the calibration curves for CC were 21-1357 µmol l^-1 with a high sensitivity of 108 µA µmol l^-1 cm^-2. The detection limit was 1.4 µmol l^-1.