Phosphorescent sensing of Cr3+ with protein-functionalized Mn-doped ZnS quantum dots

It was found that the phosphorescence from denatured bovine serum albumin (dBSA)-capped Mn-doped ZnS QDs could be selectively quenched by Cr(3+), and a phosphorescent probe for Cr(3+) was thus developed. Based on phosphorescence decay as well as calculations of the relative energies of QDs and Cr(3+), the mechanism for phosphorescent quenching was preliminarily ascribed to electron transfer from photo-excited Mn-doped ZnS QDs to Cr(3+). Under the optimal conditions, good linear Stern-Volmer quenching was obtained for Cr(3+) in the range of 10 to 300 nM. The limit of detection of this phosphorescence probe (3 nM) was 1 to 2 orders of magnitude lower than those of previously reported nanosensors, owing to the effective elimination of background fluorescence and scattering from the sample matrix. The analytical potential of the proposed probe was evaluated through determination of Cr(3+) in water samples, with spike-recoveries ranging from 95 to 106%.