Correlation Between Spectroscopic and Structural Features of Dimeric DNA-Templated Silver Nanoclusters Using Mass Spectrometry

DNA-templated silver nanoclusters (DNA/AgNCs) are a special class of nanomaterial fluorophores that are versatile for the development of biosensing strategies in the detection of DNA, small molecules, and metal ions. Despite their unique photophysical properties, the mechanisms that mediate both the formation of DNA/AgNCs and the resulting optical properties are still not fully understood. Here, we utilize an advanced mass spectrometry, such as ESI-MS and activated-electron photodetachment (a-EPD), to provide new insight into the fluorescence mechanisms of DNA/AgNCs and allows the correlation of spectroscopic properties with structural features, stoichiometries, and compositions of the DNA/AgNCs with the analysis of seven 10-mer DNA templates. The mass spectra reveal the presence of complexes containing one (monomeric) or two (dimeric) DNA hosts and a variable number of silver atoms. Interestingly, while monomeric species incorporate a low number of silver atoms (Ag1 - Ag4), the dimeric complexes contain a higher number of silver atoms (Ag4 - Ag18). The formation of nanocluster cores and the resulting spectroscopic properties vary by the base composition of the DNA template. Given the enhanced abundance of specific dimeric DNA/AgNCs, we hypothesize that certain magic-number of Ag atoms (e.g., Ag6, Ag10, and Ag11) with dimerization of short DNA may be a clue for having fluorescence with the different emission wavelengths (490 - 680 nm) observed. Dimeric complexes that contain the largest AgNCs (Ag14 - Ag18 Ag atoms) present the shortest excitation and emission wavelengths. This study suggests that fluorescence can be controlled by the strategic design (e.g., consecutive cytosines and GC contents ratio) of the DNA host to guide the formation of monomeric or dimeric species with magic-number of silver atoms.