Electron Transfer-Induced Blinking in Ag Nanodot Fluorescence

Various single-stranded DNA-encapsulated Ag nanoclusters (nanodots) exhibit strong, discrete fluorescence with solvent polarity-dependent absorption and emission throughout the visible and near-IR. All species examined, regardless of their excitation and emission energies, show similar microsecond single-molecule blinking dynamics and near IR transient absorptions. The polarity dependence, microsecond blinking, and indistinguishable microsecond-decaying transient absorption spectra among multiple nanodots suggest a common charge transfer-based mechanism that gives rise to nanodot fluorescence intermittency. Photoinduced charge transfer that is common to all nanodot emitters is proposed to occur from the Ag cluster into the nearby DNA bases to yield a long-lived charge-separated trap state that results in blinking on the single molecule level.