A quantum dot-based "off-on" fluorescent probe for biological detection of zinc ions

Since zinc ions play an important role in various physiological activities, developing a facile detection method for Zn(2+) is highly desirable. Owing to their superior optical properties, semiconductor quantum dots (QDs) have been developed as a promising alternative for organic fluorophores in fluorescence analysis. In this study, water soluble di-2-picolylamine-dithiolcarbamate (DPA-DTC)/proline-dithiolcarbamate (P-DTC) co-capped CdSe/ZnS QDs as a sensitive and selective "turn-on" fluorescence probe for Zn(2+) was reported. The probe was easily obtained via ligand exchange. The initial bright fluorescence of QDs was effectively quenched by DPA-DTC that acted as an effective hole trapper. Upon complexation with Zn(2+), the formation of Zn(2+)-DPA-DTC complex altered the energetic position of the HOMO for DPA-DTC, which rendered it unfavorable for the hole transfer. Thus the QDs PL was switched on. Under optimal conditions, a good linear relationship between the fluorescence response and Zn(2+) concentration could be obtained in the range from 0.9 to 16 μM. The limit of detection for Zn(2+) was found to be 0.7 μM. Furthermore, the present probe exhibited a high selectivity for Zn(2+) over other common metal ions and was successfully used in the detection of Zn(2+) in simulated biological fluids.