Switchable fluorescence of MoS2 quantum dots: a multifunctional probe for sensing of chromium(VI), ascorbic acid, and alkaline phosphatase activity

A simple strategy for modulating the fluorescence of MoS2 quantum dots (QDs) is described. The fluorescence of MoS2 QDs was firstly switched off by the addition of Cr(VI), and the quenched fluorescence was further switched on by introducing ascorbic acid (AA) into the mixture. The fluorescence quenching of MoS2 QDs by Cr(VI) was attributed to the fluorescence inner filter effect. After the addition of AA, Cr(VI) was reduced to Cr(III), and the fluorescence was restored. This finding has been applied for the fluorescent sensing of Cr(VI) in drinking water and AA in serum samples. In addition, the present method has been extended for turn-on sensing of an important biomarker alkaline phosphatase (ALP). There is a linear relationship between the fluorescence intensity and the concentrations of ALP in the range from 2.5 to 50U/L, and the limit of detection is 0.34U/L. The results showed MoS2 QDs hold great potential as a multifunctional fluorescent probe for the detection of metal ions, biological small molecules, and proteins.