Chiral recognition and quantitative analysis of tyrosine enantiomers using L-cysteine capped CdTe quantum dots: Circular dichroism, fluorescence, and theoretical calculation studies

In this work, L-cysteine-capped CdTe quantum dots (L-Cys/CdTe QDs) were used as novel chiral probes for in enantioselective recognition and quantitative determination of tyrosine (Tyr) enantiomers using both fluorescence and circular dichroism (CD) spectroscopies. Different quenching percentages in fluorescence of L-Cys/CdTe QDs in the presence of similar concentrations of Tyr enantiomers were clearly observed. Quantum mechanical (QM) calculations were also used to confirm such different interactions of L- and D-Tyr enantiomers with L-Cys/CdTe QDs. However, the CD spectroscopy exhibited higher capability and sensitivity, compared to fluorescence spectroscopy, to distinguish between these enantiomers. While, Tyr enantiomers provided no sensible CD signals at micromolar concentration levels, they exhibited remarkable and opposite CD spectra at these concentration levels in the presence of L-Cys/CdTe QDs. Under the optimized conditions, the CD signals of L- and D-Tyr enantiomers showed good linear relationships with the concentrations of both enantiomers over the range of 10-80 mu M with limit of detections (LODs) of 1.5 and 1.6 mu M, respectively. This method was also successfully applied to enantiomeric excess determination of Tyr at the total concentration of 50 mu M with a LOD of 1.2%.