Dual-mode fluorescence and colorimetric sensing of sulfide anion in natural water based on near-infrared AgS quantum dots and MnO nanosheets complex.

Near infrared (NIR) emission AgS quantum dots (QDs) are of great value for biochemical sensing with strong anti-interference and low toxicity. Herein, NIR fluorescence AgS QDs were synthesized successfully. Combined with the excellent oxidase-like characteristics of manganese dioxide (MnO) nanosheets, a fluorescence and colorimetric dual-mode sensor for sulfide anion was developed. MnO nanosheets could effectively catalyze the oxidation of TMB to produce blue TMB oxide (ox TMB), at the same time, the fluorescence of AgS QDs could be effectively quenched by fluorescence internal filtration effect (IFE) and dynamic quenching effect. The enzyme-like activity was weakened and the NIR fluorescence of AgS QDs was restored when sulfide anion (S) was added, due to the reduction of MnO to Mn.The linear ranges for fluorescence and colorimetric analysis of S were 2-250 μM and 0.3-50 μM, with detection limits of 0.6 and 0.215 μM, correspondingly. The dual-mode sensor had a wider detection range, higher sensitivity and shorter reaction time, which could be used for highly selective detection of S in different concentration ranges. In addition, it had been successfully applied to the determination of sulfide in water samples with satisfactory accuracy and sensitivity.