L- and D-cysteine functionalized CdS quantum dots as nanosensors for detection of L-morphine and D-methamphetamine

A new method in differentiation of chiral molecules is reported based on the fluorescence quenching of functionalized CdS quantum dots (CdS-QDs) as nanosensor by differing in the chirality of functionalization species. The chemically functionalized CdS-QDs with strong yellow emission were prepared using chiral L-cysteine (L-Cyst) and D-cysteine (D-Cyst) molecules. Then, the functionalized CdS-QDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, photoluminescence (PL), ultraviolet-visible (UV-Vis), and Fourier transform infrared (FT-IR) spectroscopies. The prepared L- and D-cysteine functionalized CdS-QDs were exploited as fluorescence probes for detection and determination of L-morphine and D-methamphetamine. It was found that the fluorescence of D- and L-cysteine functionalized CdS-QDs were efficiently quenched by adding D-methamphetamine and L-morphine to them, respectively. The magnitude of fluorescence quenching depended on the concentration of L-morphine and D-methamphetamine solutions according to the Stern-Volmer equation. So, the functionalized CdS-QDs can be used as simple, quick, cheap, and sensitive nanosensor for practical detection of morphine and methamphetamine.