Using zinc ion-enhanced fluorescence of sulfur quantum dots to improve the detection of the zinc(II)-binding antifungal drug clioquinol

A turn on-off fluorometric assay for clioquinol (CQ) is described here. It is based on modulation of the fluorescence of sulfur quantum dots (SQDs; best measured at excitation/emission wavelengths of 360/426 nm) by using the Zn2+-CQ affinity pair. Although the fluorescence enhancement effect of Zn2+ on SQDs was not obvious, a good quenching modulation effect was observed in the presence of CQ. This resulted in a linear analytical range that is increased by two orders of magnitude (from 0.024 mu M to 0.24 mu M, and 0.62 mu M to 30 mu M), with a detection limit (3 s) of 0.015 mu M. The selectivity of the method is also improved.