Fluorescent sensing of sulfide ions based on papain-directed gold nanoclusters

A sensitive and selective method has been developed for the determination of sulfide ions (S2-) based on S2- triggered fluorescence quenching of papain-directed Au nanoclusters. Under the optimized experimental conditions, the proposed method facilitated the determination of S2- in the linear range 0.5-80.0 mu M; the limit of detection was 0.38 mu M at a signal-to-noise ratio of 3. In addition, the fluorescence intensity decreased selectively in response to S2- relative to other ions. Based on multiple analyses, it is proposed that the fluorescence was quenched through the unique reactions between S2- and the Au atoms/ions, and that the formation of Au2S induced aggregation of the Au nanoclusters. The practicality of the proposed method for the determination of S2- in natural water samples was verified. The results were in good agreement with those determined by the methylene blue colorimetric method. This new method may broaden the scope of techniques available for the determination of S2-.