4.5 mL of 50 mg L−1 Mn/ZnS QDs solution, 5.0 mL of PBS (pH 8.0) and various concentrations of AA standard or urine sample were introduced into a 10 mL calibrated test tube. Then the mixture was diluted to the volume with high-purity water and mixed thoroughly. The tube was stood for 10 min and a portion of the solution was transferred into a 10-mm silica cuvette for phosphorescence measurement.