Luminescent Au-Ag nanoclusters entrapped in protein matrix: Conditions of sample maturing influencing Au-Ag synergistic effect

Abstract

Abstract Gold-silver synergism has been well documented in many scientific works already. Frequently, the ratio of Au : Ag in synthetic mixtures was varied to influence the extent of Au-Ag synergism. However, in our approach, a new step, maturing (under differing conditions) of the luminescent bimetallic samples entrapped in a protein, has been introduced and applied for the very first time. The maturing conditions involved either prolonged time (2.5h vs. 0 min) and/or elevated temperature (50 °C vs. room temperature). The prolonged time of samples maturing progressively influenced Au-Ag synergism (documented by fluorescent quantum yield increase); while elevated temperature during samples maturing led rather to changes of the protein secondary structure (determined by circular dichroism) and stagnation of Au-Ag synergism effect. Importantly, the selected maturing conditions led to significant increase of nanocluster sizes and broadening of particle size distribution as evidenced by scanning transmission electron microscopy (STEM) and dynamic light scattering (DLS). The results unravel that Au-Ag synergism can be tuned by setting appropriate maturing conditions of bimetallic nanoclusters embedded in the protein scaffold.