The medium effect on electrodissolution of adsorbed or suspended Ag nanoparticles

Correlation notice on the electrochemical dealloying and antibacterial properties of gold-silver alloy nanoparticles

Galvanic replacement reaction was used in the synthesis of bimetallic gold-silver alloy nanoparticles (Au-Ag NPs), where pre-synthesized Ag nanoparticles-polyvinylpyrrolidone (AgNPs-PVP) were used to reduce the aryldiazonium tetrachloroaurate(III) salt in water. TEM images and EDS elemental analysis showed the formation of spherical Au-Ag NPs with sizes of 12.8 ± 4.9 nm and 25.6 ± 14.4 nm for corresponding Au-Ag ratios and termed as Au_0.91Ag_0.09 and Au_0.79Ag_0.21, respectively, with different concentrations of the gold precursor. The hydrodynamic sizes measured using dynamic light scattering are 46.4 nm and 74.8 nm with corresponding zeta potentials of - 44.56 and - 25.09 mV in water, for Au_0.91Ag_0.09 and Au_0.79Ag_0.21 respectively. Oxidative leachability of Ag ion studies from the starting AgNPs-PVP in 1 M NaCl showed a significant decrease in the plasmon peak after 8 h, indicating the complete dissolution of Ag ions, however, there is enhanced oxidation resistivity of Ag from Au-Ag NPs even after 24 h. Electrochemical studies on glassy carbon electrodes displayed a low oxidation peak in aqueous solutions of 20 mM KCl at 0.16 V and KNO₃ at 0.33 V vs. saturated calomel electrode (SCE). We studied the antibacterial activity of Au-Ag alloy nanoparticles against gram-positive Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, and gram-negative Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa. Our findings demonstrated superior antibacterial activity of Au-Ag NPs compared with AgNPs-PVP. Moreover, the nanoparticles inhibited the S. epidermidis biofilm formation.

A magneto-controlled microfluidic device for voltammetric immunoassay of carbohydrate antigen-125 with silver-polypyrrole nanotags

An innovative magnetic immunoassay was developed for the voltammetric detection of carbohydrate antigen-125 (CA-125) on a home-made microfluidic device including a multisyringe pump, selection valve and magneto-controlled detection cell. Two kinds of biofunctionalized nanostructures including anti-CA-125 capture antibody-conjugated magnetic beads and anti-CA-125 detection antibody-labeled silver-polypyrrole (Ag-PPy) nanohybrids were utilized for a sandwiched immunoreaction in the presence of CA-125. With the help of an external magnet, the formed magnetic immunocomplexes were attached to the sensing interface to activate the electrical contact between Ag-PPy nanohybrids and the base electrode, thus resulting in the switching on of the sensor circuit for the generation of voltammetric signals thanks to electroactive Ag-PPy nanohybrids. Compared to silver nanoparticles (AgNPs) alone, improved analytical properties were acquired with Ag-PPy nanohybrids. Under the optimal conditions, the currents depended on the concentrations of target CA-125, and exhibited a linear relationship within the ranges of 0.001-300 U mL-1 at a detection limit of 7.6 mU mL-1. For the determination of CA-125, the magnetic immunoassay had acceptable reproducibility, high specificity against other biomarkers and long-term storage stability. Moreover, good accuracy was obtained for the CA-125 detection in human serum samples with the developed voltammetric immunoassay relative to commercial enzyme-linked immunosorbent assay (ELISA). Importantly, the magneto-controlled immunosensing interface could be repeatedly used via detaching/attaching the external magnet.