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Herein we report the fabrication of a simple electrochemical sensor based on an electrode containing reduced graphene oxide and molybdenum disulphide (RGO/MoS2) as a conducting film onto the glassy carbon electrode (GCE) via a drop dry method to form GCE‐RGO/MoS2. The surface (GCE‐RGO/MoS2) was further modified with nickel hydroxide thin film using electrodeposition method to form GCE‐RGO/MoS2/Ni(OH)2. The materials and modification steps were thoroughly characterized using microscopy and spectroscopy methods. The composite electrode, GCE‐RGO/MoS2/Ni(OH)2, showed excellent electrocatalytic potential separation for the detection of dopamine, uric acid, and ascorbic acid. The electrocatalytic oxidation peak potentials were at 3 mV, 157 mV and 303 mV for AA, DA and UA, respectively. The composite electrode was also selective towards the determination of ascorbic acid (AA), dopamine (DA), uric acid (UA), and simultaneously in mixture of analytes. The low detection limits for AA, DA and UA were 1.17 μM, 0.15 μM and 1.15 μM, respectively. The composite electrode was applied for the detection of AA, DA and UA in spiked newborn calf serum samples with high percentage recoveries ranging from 96.6–100.8 % for AA, 92.8–104.2 % for DA and 99.4–102.3 % for UA. [ABSTRACT FROM AUTHOR]

Nanozymes are nanomaterials that exhibit enzyme-like activity upon exposure to a substrate solution. The use of noble and platinum group metals enhances enzyme-like catalytic activity. However, noble metals are obtained at a high cost; therefore, their recovery after use is of high importance. Herein, we report the fabrication of indium tin oxide–silica nanoparticles decorated with palladium nanoparticles (ITO-SiO2-prS-PdNPs). The ITO-SiO2-prS-PdNPs were evaluated for peroxidase-like activity toward the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. A colour change from clear or colourless TMB to blue colour (oxidized TMB products) was observed confirming the peroxidase-like activity. A typical Michaelis–Menten enzyme-like behaviour is observed with Km values of 0.68 mM for H2O2 and 0.47 mM for TMB, which are better than the reported values for horse-radish peroxidase (HRP) for the same substrate. The peroxidase-like activity of ITO-SiO2-prS-PdNPs was found to proceed via the electron-transfer mechanism. The ITO-SiO2-prS-PdNPs were cleaned successfully after each use by rinsing with water and ethanol solution thus making the surface simple and easy to recover and reuse. A reusable and highly selective colorimetric assay for glucose detection based on the peroxidase-like activity of ITO-SiO2-prS-PdNPs gave excellent results. ITO-SiO2-prS-PdNPs exhibited a good linear range of 5.0–30 μM, a low limit of detection (LOD) of 1.84 μM and a limit of quantification (LOQ) of 6.14 μM. Finally, the nanozyme (ITO-SiO2-prS-PdNPs) was successfully used to detect glucose in a complex newborn calf serum (NCS), representing a real sample. [ABSTRACT FROM AUTHOR]

Nanomaterials of gold and palladium have received research attention due to their excellent catalytic properties. Their recovery after the catalytic reaction still remains a challenge rendering the catalytic application of these nanomaterials for single use. Herein, we report a method of fabricating nanomaterials as thin nanoparticle (NP) films on catalytically inert surfaces, while allowing for their recovery and reuse is investigated. Indium tin oxide (ITO) glass slides were first hydroxylated (ITO-OH) and used to attach the silica NPs (SiO2NPs) to form ITO-SiO2NPs. The ITO-SiO2NPs surface was used as an adsorbent for gold and palladium mono- and bimetallic NPs (Au/PdNPs) to form ITO-SiO2-prS-Au/PdNPs, which was evaluated for the enzyme-like catalytic activity. The fabricated film with bimetallic NPs, ITO-SiO2-prS-Au/PdNPs, exhibited excellent peroxidase-like activity for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with H2O2 when compared with monometallic thin NP films, ITO-SiO2-prS-AuNPs, and ITO-SiO2-prS-PdNPs. A typical Michaelis–Menten enzyme-like behavior of the bimetallic NP film, ITO-SiO2-prS-Au/PdNPs, was observed for H2O2 and TMB with Michaelis–Menten constants (Km) of 0.33 and 3.46 mM, respectively. A simple, sensitive, and selective colorimetric assay for ascorbic acid (AA) detection was fabricated based on the reduction effect of AA on the oxidized TMB. The fabricated AA colorimetric sensor exhibited a good linear range from 0.50 to 30.0 μM, with the limit of detection of 0.50 μM and the limit of quantification of 1.65 μM. Finally, our proposed colorimetric sensor, ITO-SiO2-prS-Au/PdNPs, successfully detected AA in new-born calf serum samples, as a real sample representative. [ABSTRACT FROM AUTHOR]

Selective purification of biological materials for their detection in complex sample matrix is a general challenge for many researchers working in the field of diagnostics. Magnetic nanoparticles functionalized with biological molecules that impart biomolecular selectivity are therefore of major interest as capture probes thus allowing for magnetic separations. Nanoparticles can also be used for the enhanced detection of biomarkers. In this work, an ultrasensitive sandwich‐based impedimetric immunosensor was fabricated for the detection of C‐reactive protein antigen (CRPAg). Stable and oriented immobilization of anti‐CRP monoclonal antibody was achieved onto electrografted phenylethylamine derivatized with succinic anhydride and phenylboronic acid via carbodiimide chemistry. The detection of CRPAg was achieved using Electrochemical Impedance Spectroscopy (EIS). The enhancement of the impedance charge‐transfer resistance (RCT) signal was achieved using the sandwich approach. The anti‐CRP polyclonal antibody was immobilized in an oriented manner onto magnetic nanoparticles functionalized with phenylboronic acid. The increase in the change in charge‐transfer resistance (ΔRCT) values was linearly proportional to the concentration of CRPAg in the range 10 to 200 ng mL−1 covering the clinical range for CRPAg detection and with a detection limit of 0.34 ng mL−1. [ABSTRACT FROM AUTHOR]