Optical properties of DNA-templated silver-gold hybrid nanoclusters.

DNA templated silver nanoclusters (AgNCs@DNA) comprise only a few silver atoms. Due to quantum confinement effect which becomes strong at such a small size of AgNCs, these small clusters possess unique optical properties, including strong fluorescence. Size, shape, and composition are important factors defining emissive states of a cluster. In this study we explore the effect of atomic composition on optical properties of nanoclusters by replacing silver with gold. The effect is measured using 2D Excitation Emission Maps (EEMs). We use a unique hairpin loop structure of DNA with a certain number of cytosines and adenines in the loop, and 7 base pair double stem to probe the optical properties of AgNCs@DNA. A C12-DNA containing a loop with 12 cytosines hosts a Ag₁₀ cluster with maximum excitation, , and emission, . By careful titrations of silver and gold mixtures we demonstrate that gold replacements affect the intensity of emission. Additionally, introducing adenine bases in key positions which favor binding of gold over silver we show that gold bound to adenine produces different emission patterns. We also report theoretical calculations using Density Functional Theory we used to verify optical behavior of Ag/Au hybrid nanoclusters. Our studies provide a better understanding of nanoclusters’ optical properties. This in turn could lead to our ability to tune emissive patterns in a controllable manner benefiting the field of bioimaging.