Tuning near-infrared fluorescence in DNA-templated silver nanoclusters.

Silver nanoclusters templated on DNA (AgNCs@DNA) comprise only a few silver atoms. AgNCs@DNA develop a structure of discrete electronic levels leading to molecule-like properties such as strong luminescence with high quantum yield. Unlike molecular fluorescence, the luminescence of AgNC features a more complex nature with plenty of possibilities for tuning. We demonstrate that a rational optical tuning can allow for specific generation of emission in the near infrared region. A unique hairpin loop structure with N cytosines in the loop, 7 base pair double-stranded stem, and a random R-tail (R-hpC_N) produces NIR peak with high yield at λ_MAX=830 nm. In this study, we explore the effect of loop size (N) on the yield of the NIR emission showing that R-hpC₁₃ has the largest yield. AgNC@R-hpC₁₃. Single cytosine-to-thymine replacements in the hpC₁₂T₁ allowed us to identify critical involvement of cytosines for the NIR emission demonstrating the possibility for fine-tuning of NIR emission. Noteworthy, weakening C8-AgNC connection significantly increases the quantum yield of the λ_MAX=830 nm peak. Our studies point to the complexity of the electronic structure of the AgNCs, suggesting plenty of possibilities for fine-tuning of AgNC’s NIR emission with practical applications for bioimaging.