Water-soluble Eu(III)-doped ZnS quantum dots for the room-temperature phosphorescence detection of melamine in milk products

A new type of water-soluble Eu(III)-doped ZnS quantum dots (QDs) was synthesized and characterized. A novel, simple, sensitive and precise room-temperature phosphorescence (RTP) method was developed based upon measurement of the quenching of the phosphorescence intensity of the Eu(III)-doped ZnS QDs. Remarkable quenching of the phosphorescence intensity of Eu(III)-doped ZnS QDs by various concentrations of melamine was achieved at lambda(ex) = 290 nm and pH 7.4 with a linear range of 5-500 ng mL(-1) and a detection limit (3 sigma) of 1.22 ng mL(-1). The relative standard deviation for five replicate measurements was 1.2%. The proposed method was satisfactorily applied in the detection of melamine in several milk products with recoveries of 96-103%.