Fluorescence-Enhanced Sensing Mechanism of BSA-Protected Small Gold-Nanoclusters to Silver(I) Ions in Aqueous Solutions

We report the clarification of responsive mechanism of the BSA-protected small gold nanoclusters (Au16NCs@ BSA) to silver(I) ions (Ag+). The titration of Au16NCs@BSA solutions with Ag+ produces a blue-shift and enhancement of the fluorescence spectra, but no similar effects can be observed for other metal ions. Meanwhile, an isosbestic point in UV-vis absorbance spectra of Au16NCs@BSA induced by Ag+ is observed, which indicates a stoichiometric conversion of one substance to another. Through X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and MALDI-TOF mass spectrum measurements, the reduction of Ag+ to Ag-0 by Au16NCs@BSA have been ascertained, where the Au16NCs act as reductant toward Ag+ in forming hybrid Au@AgNCs adducts. The mechanism revealed provided a facile and mild method to build high luminescent alloy nanoclusters.