Time dependent gold nanoclusters and nanocrystals formation on BSA at solid-water and air-solid interfaces

Abstract

A straight forward process of growing nanoclusters and in later stage from nanoclusters to nanocrystals growth is explored on BSA protein thin films using UV–Vis and photoluminescence spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and dynamic light scattering (DLS) techniques. It is observed that if different interaction times are provided between BSA thin films and HAuCl4 aqueous solutions of mM concentration, then initially formed tiny gold nanoclusters transform into nanocrystals of different shapes and sizes. From UV–Vis experiments growth of gold nanoclusters from AuCl4− ions at solid-air interface and in later stage from nanoclusters to nanocrystals growth at solid-air interface is confirmed by the presence of peaks at 320nm and 525nm respectively. If the nanoclusters embedded films are kept undisturbed in air and also in dark condition nearly for 30days then nanoclusters convert into nanocrystals. XRD analysis shows the formation of both gold nanoclusters and nanocrystals of faced-centered cubic lattice along (111) crystalline direction and AFM studies confirm the presence of triangular and spherical nanostructures. DLS technique is used to have the average sizes of the nanocrystals. Langmuir-like growth behavior is identified for BSA films induced gold nanoclusters and nanocrystals formation and it is found that both have nearly the same growth dynamics.