Initial growth kinetics of luminescent quantum clusters of silver within albumin family protein templates

We probed the initial growth kinetics of luminescent quantum clusters of silver (AgQCs) within two albumin family proteins, bovine serum albumin (BSA) and ovalbumin (Ova). Shorter time scale (seconds to minutes) growth of AgQCs monitored using real time photoluminescence spectroscopy has shown that, at lower concentrations of Ag⁺, only unstable QCs were formed. The major role of basic pH in the synthesis was not only to facilitate Ag⁺-BSA conjugation but also to provide well dispersed medium for controlled nucleation of QCs. Increase in the concentration of NaBH<inf>4</inf> affects growth kinetics greatly and leads to increase in the growth rate of AgQCs; but for NaBH<inf>4</inf> concentrations higher than the optimum value, growth rate becomes constant. Precise measurements have shown that excitation and emission of AgQCs exhibit linear red-shift with the increasing concentration of NaBH<inf>4</inf> whereas protein excitation remains constant. Similar results were observed for both the proteins, Ova and BSA. We believe that various insights provided by this study will be helpful for further improvements in the synthetic methodology and applications of protein protected AgQCs.