DNA Encapsulation of 10 Silver Atoms Producing a Bright, Modulatable, Near-Infrared-Emitting Cluster

Photostability, inherent fluorescence brightness, and optical modulation of fluorescence are key attributes distinguishing silver nanoclusters as fluorophores. DNA plays a central role both by protecting the clusters in aqueous environments and by directing their formation. Herein, we characterize a new near-infrared-emitting cluster with excitation and emission maxima at 750 and 810 nm, respectively, that is stabilized within C(3)AC(3)AC(3)TC(3)A. Following chromatographic resolution of the near-infrared species, a stoichiometry of 10 Ag/oligonucleotide was determined. Combined with excellent photostability, the cluster's 30% fluorescence quantum yield and 180 000 M-1 cm(-1) extinction coefficient give it a fluorescence brightness that significantly improves on that of the Organic dye Cy7. Fluorescence correlation analysis shows an optically accessible dark state that can be directly depopulated with longer wavelength coillumination. The coupled increase in total fluorescence demonstrates that enhanced sensitivity can be realized through Synchronously Amplified Fluorescence Image Recovery (SAFIRe), which further differentiates this new fluorophore.