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

Abstract

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 × 10⁻⁷ to 4 × 10⁻⁶ mol L⁻¹, with correlation coefficient R² = 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.