Fabrication of highly luminescent SiO2–Au nanostructures and their application in detection of trace Hg2+

Abstract

Photoluminescence of gold nanoclusters (AuNCs) make them attractive in many fields including biological labeling and chemical detection. However, compared with organic dyes or quantum dots, the generally lower fluorescence efficiency of AuNCs limits their application. Here, an efficient and facile strategy is developed to fabricate highly luminescent SiO2–Au NCs nanostructures with a high quantum yield (33.3%) via a three-step procedure involving peptide self-assembly, biomimetic mineralization of silica, and conjugation of AuNCs. Photoluminescence lifetime, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy were used to in-depth explore the mechanism for fluorescence enhancement. The results indicated that the fluorescence enhancement of SiO2–Au NCs is mainly attributed to the suppression of strong Au(I) → ligand charge transfer and non-radiative decay triggered by confinement effect. The SiO2–Au NCs solution presents relatively high fluorescence intensity over a wide range of pH and salt concentration. These superior properties make them an ideal candidate of fluorescent probes with excellent sensitivity and selectivity in the detection of Hg2+ ions. Moreover, the quenched fluorescence of SiO2–Au NCs can be recovered by the introduction of glutathione. Therefore, SiO2–Au NCs can serve as a recyclable fluorescent probe for the detection of Hg2+ and glutathione through the “fluorescence off” or “fluorescence on” process. The results provide a promising step toward the fabrication of highly fluorescent probes of AuNCs and further expand their application in chemical detection.