Label-free room-temperature phosphorescence turn-on detection of tiopronin based on Cu2+-modulated homocysteine-capped manganese doped zinc sulfide quantum dots

A label-free turn-on room-temperature phosphorescence (RTP) sensor for tiopronin based on Cu2+-modulated homocysteine (Hcy)-capped Mn-doped ZnS quantum dots (QDs) was described in this paper. The RTP of Hcy-capped Mn-doped ZnS QDs can be effectively quenched by Cu2+ due to the binding of Cu2+ to the Hcy on the surface of the QDs and the electron transfer generated from the photoexcited QDs to Cu2+. The high affinity of tiopronin to Cu2+ enables the dissociation of the ion from the surface of the QDs, thereby forming a stable complex with tiopronin in the solution, and recovering the RTP of the QDs. The Cu2+-induced RTP quenching and subsequent tiopronin-induced RTP recovery for MPA-capped ZnS QDs provide a solid basis for the present RTP sensor based on QDs for the detection of tiopronin. The detection limit for tiopronin is 0.18 ng mL−1, the relative standard deviations is 1.9%, and the recovery of urine and serum samples with tiopronin addition range from 96% to 106% under optimal conditions. The proposed method was successfully applied to biological fluids and obtained satisfactory results.