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

Silver nanoclusters templated on DNA (AgNCs@DNA) comprise only a few silver atoms and possess unique optical properties such as strong luminescence. The luminescence of AgNC exhibits a complex nature with plenty of possibilities for tuning specifically in the near infrared region. We utilized a unique hairpin loop DNA structure to create NIR active AgNCs. The design contains a certain number (N) of cytosines in the loop, 7 base pair double-stranded stem, and a random STR-tail (STR-hpCN) and produces NIR peak with λMAX=830 nm. In this study, we explore the effect of loop size (N) on the yield of the NIR emission showing that STR-hpC13 has the largest yield. We also demonstrate that fine-tuning of NIR emission is possible by replacing cytosines at certain positions in the loop suggesting strong impact of cytosine-Ag interactions on the emissive NIR states of AgNC@R-hpC13. Not all cytosines are equivalent in generating of high-yield NIR peak. Single cytosine-to-thymine replacements in the hpC12T1 helped us identify critical involvement of cytosines for the NIR emission. Noteworthy, weakening C8-AgNC connection with C8->T8 replacement significantly increases the quantum yield of the NIR peak. We also examine the relationship between environmental factors on florescence intensity, such as pH and temperature. Our studies provide a better foundation for refining fluorescent properties of AgNCs, with a particular focus on the NIR region, which holds significant practical significance especially in bioimaging