RESUMO
A room temperature ultrasound-assisted method was applied to synthesize L- and D-cysteine-capped CdSe quantum dots (QDs). The QDs were characterized by XRD, FT-IR, and TEM. They have diameters of 5-7 nm and are shown to be viable probes for highly selective chiral recognition of tryptophan (Trp) enantiomers by fluorometry. The green fluorescence of the capped QDs (with excitation/emission maxima at 380/527 nm and 380/520 nm for L-Cys and D-Cys QDs, respectively) is differently quenched by D- and L-Trp in a high selective manner, with negligible interference by other species. The calibration plots and corresponding Stern-Volmer plots for both Trp enantiomers were investigated by two different approaches: In the first, each individual enantiomer was tested. In the second, each enantiomer was tested in the presence of a 100-folds excess of the other enantiomer. The detection limits for the recognition of L- and D-Trp are 4.2 and 4.7 nM, respectively, for the first approach. In the presence of the other enantiomer, the LODs are 4.4 and 4.8 nM. The linear range extends from 0.1 to 15 µM for both enantiomers. Graphical abstractSchematic representation of tryptophan (Trp) chiral recognition process. The fluorescence (green, ON) of D- and L-Cys (cysteine)-capped CdSe QDs is quenched (black, OFF) through a preferential and selective interaction with L- and D-Trp, respectively.
RESUMO
A rapid, simple and inexpensive spectrofluorimetric sensor for determination of doxycycline based on its interaction with thioglycolic acid-capped cadmium telluride quantum dots (TGA/CdTe QDs) has been developed. Under the optimum experimental conditions, the sensor exhibited a fast response time of <10s. The results revealed that doxycycline could quench the fluorescence of TGA/CdTe QDs via electron transfer from the QDs to doxycycline through a dynamic quenching mechanism. The sensor permitted determination of doxycycline in a concentration range of 1.9×10(-6)-6.1×10(-5)molL(-1) with a detection limit of 1.1×10(-7)molL(-1). The sensor was applied for determination of doxycycline in honey and human serum samples.
