Antibacterial activity of Ag–Au alloy NPs and chemical sensor property of Au NPs synthesized by dextran

Gold and silver–gold alloy nanoparticles with mean diameter of 10 nm and narrow size distribution were prepared by reduction of the correspondent metal precursors using aqueous dextran solution which acts as both a reducing and capping agent. The formation of nanoparticles was characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS). The silver and gold nanoparticles exhibited absorption maxima at 425 and 551 nm respectively; while for the bimetallic Ag–Au alloy appeared 520 nm in between them. TEM images showed monodispersed particles in the range of 8–10 nm. The crystallinity of the nanoparticles was assured by XRD analysis. DLS data gave particle size distribution. The dextran stabilized Au nanoparticles used as a colorimetric sensor for detection and estimation of pesticide present in water. The dextran stabilized Ag–Au alloy nanoparticles exhibited interesting antimicrobial activity against bacteria at micromolar concentrations.