Few-atom silver cluster fluorophores stabilized and arranged at the nanoscale with DNA

DNA oligomers can stabilize few-atom silver clusters in aqueous solutions. Some of these “AgDNAs” are fluorescent, and the DNA sequence largely determines their excitation and emission wavelengths, fluorescence quantum yields, and chemical lifetimes. This dissertation focuses primarily on fundamental characterization of these intriguing fluorophores. Using a series of DNA hairpins with single-stranded loops consisting of 3 to 12 cytosines, we identify four different groups of emitters characterized by their fluorescence wavelengths and chemical stabilities. We identify red Ag13 and green Ag 11 emitters stabilized by a DNA sequence predicted to form a hairpin with 9 cytosines in its loop, and demonstrate purification of the Ag 11:DNA. We compare the size, charge, and conformation of these two emitters and find that, while they differ in composition by only two atoms, they differ in size by ∼ 30%. We further observe that perturbations to the hairpin stem sequence inhibit only the formation of the smaller green emitter. These results suggest that Ag11-binding disrupts the DNA’s secondary structure while Ag13 binds in the hairpin structure.;We observe that 8 different AgDNAs, with emission ranging from blue to the near-infrared, all exhibit two resonant excitation peaks: a visible peak that varies widely among different emitters, and a UV peak in the narrow wavelength range of 260-270 nm. Excitation on either peak yields the same emission spectrum. We conclude that UV excitation is universal to AgDNAs and that it proceeds via energy transfer from the DNA bases.;Related to our long-term goal of exploiting DNA self-assembly for the nanoscale positioning of optical emitters, we demonstrate AgDNA assembly at hairpin sites programmed into DNA nanotubes and estimate the chemical yield. If parallel studies regarding the low temperature optical spectra of AgDNAs reveal sufficiently stable and narrow resonances, such emitter arrays could enable exciting studies of quantum optical phenomena, for example, in which entangled states are generated by coherent coupling of transition dipoles.