Silver(I)-Induced Conformation Change of DNA: Gold Nanocluster as a Spectroscopic Probe

DNA-based materials are promising avenues for designing optical sensors, light-harvesting devices, energy conversion devices, and other potential applications. Therefore, the understanding of DNA conformation is important for designing such materials. Here, we investigate the conformation of DNA by a photoexcited energy transfer process where the Au cluster is covalently attached with AlexaFluor 488 (A488) dye tagged DNA. Fluorescence resonance energy transfer (FRET) is a well-known method to determine the donor-acceptor distance where A488 acts as donor and the gold nanoclusters (Au NCs) act as acceptor. Spectroscopic studies reveal that Ag+ ions are incorporated into dsDNA to produce a Ag+-C (cytosine) metal base pair bond as the used DNA contains 55.6% G-C base pairs. Steady-state and time-resolved spectroscopic studies reveal that the distances between donor and acceptor are found to be 98 and 83 angstrom in the absence and presence of Ag+ ion, respectively, indicating the rigid conformation of dsDNA becomes flexible in the presence of a Ag+ ion. The efficiency of energy transfer increases from 63% to 82% in the presence of the Ag+ ion because the conformation of DNA changes with the formation of DNA-metal base pairs. Analysis suggests that the Au cluster is a useful spectroscopic probe to understand the conformation of DNA and others. Furthermore, this energy transfer from dye to Au NCs using the DNA scaffold may open up new opportunities in designing an artificial light-harvesting system.