AuNCs-Catalyzed Hydrogen Selenide Oxidation: Mechanism and Application for Headspace Fluorescent Detection of Se(IV)

The excellent fluorescence property of Au nano-clusters (AuNCs) has received great attention for various chemosensing and biorelated applications, but the sample matrix is still an important problem that causes undesirable fluorescence variation. On the one hand, hydride generation (HG) is an effective strategy to separate the target analyte from the complex sample matrices, but the implementation of HG with AuNC-based fluorescent assays was not realized. On the other hand, due to the ultrasmall size of AuNCs and good catalytic performance of Au, AuNCs are also featuring intriguing catalytic applications. Herein, we proposed a new type of AuNC-based fluorescence assay for Se(IV) detection, in which hydride generation of Se(IV) was coupled with the fluorescence/catalytic dual functions of AuNCs. In a batch hydride generation mode, Se(IV) was first converted to volatile H2Se. When it spread in the headspace to contact with AuNCs supported paper, AuNC-catalyzed oxidation of H2Se by O-2 to yield elemental selenium occurred, which further deposited on the surface of AuNCs to induce fluorescence quenching. The catalytic effect of AuNCs was studied in depth via both experimental and theoretical (density functional theory) investigations. Three main steps for H2Se oxidation were identified, with energy barriers in the presence of AuNCs significantly lower than those without. Benefiting from the reduced matrix interference by hydride generation and the unique catalysis/fluorescence of AuNCs, the proposed assay featured high selectivity, good sensitivity, and simplicity, with successful applications for selenium detection in real samples.