Detection of Sulfide Using Mercapto Tetrazine-Protected Fluorescent Gold Nanodots: Preparation of Paper-Based Testing Kit for On-Site Monitoring

This work demonstrates the development of a highly sensitive method to detect and quantify sulfide ions (S2-) in water samples. First, we synthesized 6-mercapto-s-triazolo(4,3-b)-s-tetrazine (MTT) by the reaction between formaldehyde and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole at room temperature. The synthetic MTT was used as a capping ligand for the synthesis of gold nanodots (AuNDs) via a one-pot green method at room temperature with only a 10 min reaction time. Transmission electron microscopy images exhibited that the MTT-AuNDs have an average particle size of 1.9 nm and an emission maximum at 672 nm upon excitation at 360 nm. The synthesized highly red emissive MTT-AuNDs are used as specific fluorescent probes for the detection of S2-. The fluorescence of MTT-AuNDs was significantly and dose-dependently quenched by the addition of S2-. The observed fluorescence quenching was ascribed to the formation of an Au2S complex, which was determined by Raman and mass spectroscopy. A good linearity was achieved for the increasing concentration of S2- from 870 nM to 16 mu M, and the detection limit was found to be 2 nM (S/N = 3). The S2- detection system that is described in this study was validated and agreed well with the standard methylene blue method. Furthermore, the present sensor was examined for its use in quantifying S2- in real water samples obtained from lakes and rivers. In addition, the specificity was checked against the most likely ion interferences in real water. Moreover, a cost-effective and viable paper-based S2- sensor was fabricated for environmental monitoring based on the use of MTT-AuNDs. The developed system would be an environmentally friendly and easy-to-use detection device for S2- in water.