Plasmonic Quenching of DNA-templated Silver Clusters by Gold Nanospheres.*

DNA-templated silver nanoclusters (AgNCs@DNA) possess unique optical properties due to their small size. AgNCs@DNA develop discrete electronic level structure leading to molecule-like properties such as strong fluorescence. This fluorescence can be tuned by internal factors such as composition, size, and shape of AgNCs but also by external factors, for example by the presence of plasmonic gold nanoparticles (AuNPs). We study the effect of AuNPs on fluorescence by AgNC@DNA. For that purpose, we designed AgNCs@DNA using the C13 loop consisting of 13 cytosine bases. The loop binds and protects AgNCs leading to a specific pattern of excitation/emission as assessed by 2D Excitation Emission Maps (EEMs). The AgNCs@C₁₃-DNA get excited by light with maximum at 545 nm. Coincidently, AuNPs also absorb light in the range of 500-550 nanometers due to plasmonic effect which is highly dependent on their size. We tested various sizes of gold nanoparticles, in a range of 10 nm to 80 nm in diameter on fluorescence of AgNCs@C₁₃-DNA. By doing so, we delineated the effects of competitive absorption versus plasmonic quenching by AuNPs to surface plasmon resonance (SPR) of AuNPs. Our experiments establish that the fluorescence of AgNCs@DNA experiences effective quenching based on the size and concentration of AuNPs. This discovered capability allows us to control and fine-tune the fluorescence of AgNCs@DNA opening up new possibilities for practical applications, including molecular computing and bioimaging.