A label-free fluorimetric detection of biothiols based on the oxidase-like activity of Ag+ ions

In this work, a label-free and sensitive fluorimetric method has been developed for the detections of biothiols including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), based on the specific biothiol-induced inhibition of the oxidase-like activity of silver ions (Ag + ). It is well established that o -phenylenediamine (OPD) can be oxidized by Ag + ions to generate fluorescent 2,3-diaminophenazine (OPDox). The introduction of biothiols would inhibit the oxidation of OPD by Ag + due to the strong coordination between biothiols and Ag + . The changes of fluorescence intensities obtained in the Ag + -OPD system exhibited good linear correlations in the ranges of 0.50–30.0   μM for Cys, 1.0–45.0   μM for Hcy and 0.50–40.0   μM for GSH. The detection limits (S/N   =   3) of Cys, Hcy and GSH were 110   nM, 200   nM and 150   nM, respectively. Subsequently, the developed fluorimetric method was successfully applied for the detection of biothiols in human serum.