DNA-Stabilized Silver Nanoclusters with High Yield of Dark State Probed by Fluorescence Saturation Spectroscopy

Abstract

Polymer-stabilized silver nanoclusters have gained much attention as a promising higly fluorescent biolabels [1]. While a wide palette of DNA-stabilized nanoclusters has been created, a little attention has been paid to their excited state properties. Meantime, dark long-lived non-emitting states have gained increasing interest in ultrahigh resolution microscopy, transient state imaging, and optically modulated microscopy [2] in the last years. The photoinduced dark states are used to be probed by pump-probe spectroscopy. However, it requires relatively high concentrations and it is not easily applied for heterogeneous samples.We applied fluorescence saturation spectroscopy for determining the photophysical constants of DNA-stabilized silver nanoclusters. This method allows one to determine the photophysical parameters of the ground and excited states such as absorption cross section, rate of intersystem crossing and others. Herein we report on extremely high yield of 25% of the dark state observed for the yellow-emitting Ag nanoclusters formed on calf thymus DNA [3]. This result seems to be promising in further creating polymer-stabilizing Ag nanoclusters with specially designed structure providing high efficiency of the dark state formation.[1] Obliosca, J. M.; Liu, C.; Batson, R. A.; Babin, M. C.; Werner. J. H.; Yeh, H.-C. DNA/RNA Detection Using DNA-Templated Few-Atom Silver Nanoclusters. Biosensors 2013, 3, 185-200.[2] Richards, C. I.; Hsiang, J.-C.; Senapati, D.; Patel, S.; Yu, J.; Vosch, T.; Dickson, R. M. Optically Modulated Fluorophores for Selective Fluorescence Signal Recovery. Journal of the American Chemical Society 2009, 131 (13), 4619-4621.[3] Volkov, I. L.; Ramazanov, R. R.; Ubyvovk, E. V.; Rolich, V. I.; Kononov, A. I.; Kasyanenko, N. A. Fluorescent Silver Nanoclusters in Condensed DNA. ChemPhysChem 2013, DOI: 10.1002/cphc.201300673.