Doped zinc sulfide quantum dots based phosphorescence turn-off/on probe for detecting histidine in biological fluid

We report a turn-on phosphorescence probe for detection of histidine based on Co(2+)-adsorbed N-acetyl-L-cysteine (NAC) capped Mn: ZnS quantum dots (QDs) which is directly synthesized by the hydrothermal method. The phosphorescence of NAC-Mn: ZnS QDs is effectively quenched by Co(2+) attributing to the adsorption of Co(2+) onto the surface of QDs with a concomitant in suppressing the recombination process of hole and electron of QDs. The phosphorescence of Co(2+)-adsorbed NAC-Mn: ZnS QDs can be recovered by binding of Co(2+) with histidine. The quenching and regeneration of the phosphorescence of NAC-Mn: ZnS QDs have been studied in detail. The as-prepared QDs-based probe is applied to determine histidine with a linear range of 1.25-30 μM and a detection limit of 0.74 μM. The relative standard deviation for eleven repeat detections of 20 μM histidine is 0.65%. Co(2+)-adsorbed NAC-Mn: ZnS QDs show high sensitivity and good selectivity to histidine over other amino acids, metal ions and co-existing substances. The proposed QDs probe has been successfully applied to determination of histidine in human urine samples with good recoveries of 98.5-103%.