A simple and sensitive method for L-cysteine detection based on the fluorescence intensity increment of quantum dots.

In this contribution, a simple and sensitive method for L-cysteine detection was established based on the increment of the fluorescence intensity of mercaptoacetic acid-capped CdSe/ZnS quantum dots (QDs) in aqueous solution. Meanwhile, the fluorescence characteristics and the optimal conditions were investigated in detail. Under the optimized conditions, the linear range of QDs fluorescence intensity versus the concentration of L-cysteine was 10-800 nmol L(-1), with a correlation coefficient (R) of 0.9969 and a limit of detection (3sigma black) of 3.8 nmol L(-1). The relative standard deviation (R.S.D.) for 0.5 micromol L(-1) L-cysteine was 1.1% (n = 5). There was no interference to coexisting foreign substances including common ions, carbohydrates, nucleotide acids and other 19 amino acids. The proposed method possessed the advantages of simplicity, rapidity and sensitivity. Synthetic amino acid samples, medicine sample together with human urine samples were analyzed by the methodology and the results were satisfying.