Microwave-assisted biosynthesis of gold–silver alloy nanoparticles and determination of their Au/Ag ratio by atomic absorption spectroscopy

In this investigation, our research interest focused on the microwave-assisted biosynthesis of Au–Ag alloy nanoparticles and their purification and characterisation. Dextrose and the ethanol extract of black tea (Camellia sinensis) were used as natural reducing agents for preparing Au–Ag alloy nanoparticles under microwave irradiation. The synthesised alloy nanoparticles were further purified with the agarose gel electrophoresis technique. The characterisation of the separated nanoparticles as particle shapes, size and their chemical composition was studied with UV–Vis spectroscopy, transmission electron microscopy and atomic absorption spectroscopy. Purified Ag–Au alloy nanoparticles were spherical in the size range of ≤200 nm, and possessed an average size of 92 nm. The results of atomic absorption spectroscopy show the presence of both metals (gold and silver) in the purified bimetal nanoparticles at a molar ratio of 3 : 1. Although we selected the Au3+/Ag+ mixture solution with a molar ratio of 1/1, we did not obtain Au–Ag alloy nanoparticles with the same portion. In the further investigation using resolution IV 2(4−1) fractional factorial design, we established that the final concentrations of glucose and plant extract should be considered the main significant parameters affecting the Ag/Au ratio in the Ag–Au alloy nanoparticles.