Hairpins with Poly-C Loops Stabilize Four Types of Fluorescent Agn:DNA

Few-atom Ag clusters self-assemble on single-stranded DNA and exhibit sequence-dependent fluorescence ranging from the blue to the NIR. DNA sequence presents a very large parameter space for creating new Ag-n:DNA emitters, with potential for improved fluorescence and chemical stability. Exploration of this parameter space may be greatly facilitated by the identification of classes of emitters that share similar features, helping provide insight into their fluorescence-determining physical features. We synthesize Ag clusters on DNA hairpins with 3 to 12 cytosines (C's) in the loop, and observe loop-dependent fluorescence. All of these hairpins support fluorescence, and all but the smallest yield more than one spectral peak. The 19 fluorescence peaks fall into four groups based on their wavelengths and chemical stability. Correlations between fluorescence and mass spectroscopy of the 9C hairpin emitters link Ag-n:DNA with green fluorescence and Ag[3:DNA with red fluorescence.