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%.