Upconversion emission of fluorescent silver nanoclusters and in situ selective DNA biosensing

Due to their good photostability, high quantum yield and low toxicity, fluorescent silver nanoclusters (Ag NCs) have received much attention as novel fluorophores for sensing applications. In this work, we investigate the upconversion emission of Ag NCs templated by single- and double-stranded DNAs. DNA-templated Ag NCs exhibit upconversion emission at wavelengths identical to those observed for the corresponding Stokes emission. Consequently, the Ag NCs' upconversion behavior can be easily tuned by the used DNA sequences. In addition, the Ag NCs are more stable under such an NIR excitation with the upconversion mode relative to the Stokes mode. As a proof-of-concept application, DNA nucleobase recognition with the in situ formed Ag NCs is realized using the Ag NCs' upconversion emission. We expect that the Ag NCs' upconversion emission is more advantageous than the previously used rare-earth materials, at least with respect to easy modulation of the emission energies by DNA sequences, and could find wide application in sensor design.