A label-free method for detecting biological thiols based on blocking of Hg2+-quenching of fluorescent gold nanoclusters

A novel, label-free, fluorescent, turn-on sensor for biological thiol detection that uses highly fluorescent gold nanoclusters (AuNCs), prepared by a bovine serum albumin (BSA)-templated green synthetic route, has been developed. The assay relies on blocking Hg2+-induced quenching of the fluorescence of AuNCs, caused by metallophilic Hg2+–Au+ interactions, through selective coordination of biological thiols with Hg2+ ions. Biological thiols entrap added Hg2+ ions via a robust Hg–S interaction. This phenomenon prevents Hg2+-induced quenching and results in fluorescence from AuNCs. By employing this turn-on sensor, biological thiols, such as cysteine (Cys), glutathione (GSH) and homocysteine (Hcy), are successfully detected at concentrations as low as 8.3nM for Cys, 9.4nM for GSH, and 14.9nM for Hcy. The diagnostic capability and potential in practical applications of this method have been demonstrated by detecting biological thiols in human blood serum. ► This is the first report in which AuNCs are employed for detection of biological thiols. ► Biological thiols are analyzed with high selectivity and satisfactory detection limits. ► The diagnostic capability is verified by detecting biological thiols in human blood. ► This method does not require any complicated modifications and expensive instrumentation. ► This work could serve as a good model for the design of new fluorescence-based turn-on biosensors.