A novel competitive-displacement fluorescence assay for L-penicillamine based on the reaction between the target and N-acetyl-L-cysteine-capped CdTe quantum dots for copper ions

D-Penicillamine (d-PA), as the dominant enantiomer, is usually used in many clinical drugs, but the other enantiomer, l-penicillamine (l-PA) is a toxic enantiomer. Therefore, it is of great significance to analyze and detect l-PA in biomedical or environmental samples. CdTe quantum dots (CdTe QDs) were modified by N-acetyl-l-cysteine (NALC) as novel fluorescent probes and were successfully utilized for the determination of l-penicillamine. The fluorescence of the CdTe QDs decreased significantly in the presence of cupric ions (Cu2+) due to the binding of Cu2+ to NALC on the surface of the CdTe QDs, but the addition of l-PA immediately resulted in efficient fluorescence recovery of the modulated CdTe QDs. The experimental results showed that the pH of the buffer solution and the concentration of Cu2+ affected the fluorescence intensity upon adding l-PA. Under the optimum conditions, the recovered fluorescence intensity was linearly proportional to the increasing l-PA concentration in the range of 2 x 10(-7) to 4 x 10(-6) mol L-1, with correlation coefficient R-2 = 0.9980. So, a new, simple and rapid method for the determination of l-PA has been developed and its potential has been demonstrated in human serum samples and environmental samples with satisfactory results.