Immunoassay detection of tumor-associated autoantibodies using protein G bioconjugated to nanomagnet-silica decorated with Au@Pd nanoparticles.

A colorimetric immunosensor was developed for the detection of tumor-associated anti-p53 autoantibodies (anti-p53aAbs). The immunosensor platform was prepared by immobilizing human-protein (p53Ag) onto a high binding 96-well plate. The immunoassay was based on the immunometric sandwich protocol, and protein G functionalized nanomagnet-silica nanoparticles decorated with Au@Pd (Fe3O4@SiO2-NH2-Au@Pd0.30NPs-protG) was used as the detection nanobioprobe. The Fe3O4@SiO2-NH2-Au@Pd0.30NPs-protG exhibited a high binding affinity for the captured anti-p53aAbs and high catalytic performance towards the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The oxidation of TMB resulted in significant color change and a UV-vis absorption signal. The detection was achieved by measuring the changes in UV-Vis absorption as the concentrations of anti-p53aAbs changed. The apparent binding affinity (KD) between the p53aAbs and Fe3O4@SiO2-NH2-Au@Pd0.30NPs-protG was 35.2 ng mL-1. The plot of change in the absorption intensity against the logarithm of anti-p53aAbs was linear within 1.0-500.0 ng mL-1 with a correlation coefficient (R2) of 0.98. The detection limit (LoD) using 3σ was calculated to be 15 pg mL-1, which is lower than the conventional HRP-label based colorimetric immunoassay. The real sample detection was investigated using the serum recovery method. The recovery of the anti-p53aAbs ranges from 98.5% to 105.7%, demonstrating its potential for practical applications.

Bimetallic gold and palladium nanoparticles supported on copper oxide nanorods for enhanced H2O2 catalytic reduction and sensing.

The emergence of nanoscience and nanotechnology has revitalised research interest in using copper and its derived nanostructures to find exciting and novel applications. In this work, mono- and bimetallic gold and palladium nanoparticles supported on copper oxide nanorods (CuONRs) were prepared and their catalytic performance towards the reduction of H2O2 to form reactive oxygen radical species (ROS) was evaluated. The characterisation using microscopy and spectroscopic techniques confirms the successful synthesis of CuONRs, CuONRs@Au6NPs, CuONRs@Pd6NPs and CuONRs@Au3Pd3NPs. The efficient generation of ROS was confirmed using UV-vis spectroscopy and 1,3-diphenylisobenzofuran (DPBF) as a radical scavenger. The CuONRs possess excellent catalytic reduction activity for H2O2 by generating ROS. However, CuONRs also have lattice oxygens which do not participate in the catalytic reduction step. The lattice oxygens however allowed for the adsorption of gold and palladium nanoparticles (Au6NPs, Pd6NPs and Au3Pd3NPs) and thus enhanced catalytic reduction of H2O2 to produce ROS. The produced ROS was subsequently involved in the catalytic oxidation of a chromogenic substrate (TMB), resulting in blue coloured diimine (TMBDI) complex which was monitored using UV-vis and could also be observed using the naked eye. The catalyst dependence on pH, temperature, and H2O2 concentration towards efficient ROS generation was investigated. The gold and palladium-supported CuONRs nanocatalysts were evaluated for their potential applications in the fabrication of colorimetric biosensors to detect glucose oxidation by glucose oxidase (GOx). Glucose was used as a model analyte. The enzymatic reaction between GOx and ß-d-glucose produces H2O2 as a by-product, which is then catalytically converted to ROS by the nanoparticles.

Nanomagnet-Silica Nanoparticles Decorated with Au@Pd for Enhanced Peroxidase-Like Activity and Colorimetric Glucose Sensing.

Nanomagnet-silica shell (Fe3O4@SiO2) decorated with Au@Pd nanoparticles (NPs) were synthesized successfully. The characterization of Fe3O4@SiO2-NH2-Au@PdNPs was achieved using several spectroscopic and microscopic techniques. The quantitative surface analysis was confirmed using X-ray photoelectron spectroscopy. The Fe3O4@SiO2-NH2-Au@Pd0.30NPs exhibited excellent peroxidase-like activity by effectively catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. The absorption peaks at 370 and 652 nm confirmed the peroxidase-like activity of the Fe3O4@SiO2-NH2-Au@Pd0.30NPs. The Michaelis-Menten constant (Km) of 0.350 and 0.090 mM showed strong affinity toward H2O2 and TMB at Fe3O4@SiO2-NH2-Au@Pd0.30NPs. The mechanism of the peroxidase-like activity was found to proceed via an electron transfer process. A simple colorimetric sensor based on glucose oxidase and Fe3O4@SiO2-NH2-Au@Pd0.30NPs showed excellent selectivity and sensitivity towards the detection of glucose. The fabricated glucose biosensor exhibited a wide linear response toward glucose from 0.010 to 60.0 µM with an limit of detection of 60.0 nM and limit of quantification of 200 nM. The colorimetric biosensor based on Fe3O4@SiO2-NH2-Au@Pd0.30NPs as a peroxidase mimic was also successfully applied for the determination of glucose concentrations in serum samples. The synthesized Fe3O4@SiO2-NH2-Au@Pd0.30NPs nanozymes exhibited excellent potential as an alternative to horseradish peroxidase for low-cost glucose monitoring.