Ratiometric detection of biothiols by using the DNA-templated silver nanoclusters–Hg2+ system

A novel fluorescent sensor for the ratiometric detection of biothiols, such as cysteine (Cys) and glutathione (GSH), was developed. This sensor was based on the system composed of fluorescent silver nanoclusters stabilized by single-stranded DNA (DNA–Ag NCs) and Hg2+. The Ag NCs we synthesized had two fluorescence emission peaks, red and green. The red peak was strongly quenched by Hg2+ while the green peak showed a concomitant increase in fluorescence intensity in the presence of Hg2+. In contrast, when biothiols were added to the DNA–Ag NCs–Hg2+ system, there was an increase in the intensity of the red emission peak and a decrease in the intensity of the green emission peak because of the robust Hg–S interaction. By employing the ratio of the DNA–Ag NCs–Hg2+ system's red to green fluorescence emission intensity as a function of biothiol concentration, we obtained satisfactory detection limits and linear relationships of Cys and GSH. Cys and GSH were detected at concentrations as low as 1.59 nM and 2.88 nM, respectively. The capability and potential for practical applications of this method were also demonstrated by detecting biothiols in human serum samples.