CuInS2 quantum dots-based fluorescence turn off/on probe for detection of melamine

In this paper, a sensitive and simple method for the determination of melamine (MA) was developed based on the fluorescence changes of the water-soluble CuInS2 quantum dots (QDs). The water-soluble CuInS2 QDs capped by mercaptopropionic acid (MPA) was directly synthesized by hydrothermal method based on our previous report. The fluorescence emission of CuInS2 QDs was quenched by the oxidation of the surface of the QDs with H2O2, and the quenched fluorescence of CuInS2 QDs could be recovered upon the addition of small amounts of MA, which might be due to the surface passivation of the CuInS2 QDs by MA. The other amino acids such as glycine and lysine had no effect on the quenched fluorescence of CuInS2 QDs. Under optimum conditions, there was a good linear relationship between the fluorescence intensity of CuInS2 QDs and the concentration range of MA from 1.0×10−8 to 1.0×10−5 mol/L with a detection limit as low as 5 nM. The proposed method was successfully applied to detect trace MA in raw milk with satisfactory results. Compared with previous reports, the proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.