Generation of luminescent silver nanodots in the presence of amino silane and sodium polyacrylate

Abstract

Amino silane has been introduced to suppress the further growth of luminescent silver clusters (silver nanodots) to non-luminescent silver nanoparticles in the stabilization of the just-reduced silver clusters with sodium polyacrylate (PAA). The roles of the silver, silane, and sodium polyacrylate in the generation of such chromophores are still vague. We found that silver ions and the PAA chain formed chromophoric complexes in the aqueous solution. However, silver nanodots were generated only after chemical reduction. The silane with two or three amino groups promoted the generation of silver nanodots, but an increase in hydrophobicity of the silane, i.e., flanked by a single amino group, stimulated the formation of near-IR silver nanodot emitters. Nevertheless, the absorption spectrum of the reaction mixture did not superimpose in shape with the excitation spectrum of the silver nanodot, suggesting that there were multiple-species that caused strong absorptions in the visible and near-IR region. The pH of the solution strongly influenced the generation and stability of silver nanodots. Silver nanodots were generated efficiently when the reaction pH was between 6 and 8, whereas the already-formed silver nanodots were stable at the pH values between 6 and 10, suggesting that disruption of the silver nanodot protection by competitive species in the solution was slowed down due to the chelate effect of multiple bonding from the polymer chain. Our results suggest that the microenvironment of silver nanodots influences strongly the properties of silver nanodots.