Detection of glutathione with an “off–on” fluorescent biosensor based on N-acetyl-l-cysteine capped CdTe quantum dots

Abstract

This paper reports a quantum dot (QD)-based “off–on” fluorescent biosensor specifically for the determination of glutathione (GSH) with high sensitivity. The biosensor was based on the following two properties. Firstly, the high fluorescence of N-acetyl-L-cysteine (NALC) capped CdTe QDs could be effectively quenched by Hg²⁺ due to the binding of Hg²⁺ to the NALC on the surface of the QDs and the electron transfer from the photoexcited NALC-capped CdTe QDs to Hg²⁺. Secondly, in the presence of GSH, the fluorescence intensity of NALC-capped CdTe QDs was found to be efficiently recovered. Under some optimized conditions, the relatively restored fluorescence intensity was proportional to the concentration of GSH in the range of 4–64 μg mL⁻¹, with a correlation coefficient of 0.9980 and a limit of detection of 2.49 ng mL⁻¹. In addition, the established method shows a high selectivity for some amino acids except cysteine. Moreover, to further investigate its performance, the biosensor was applied to the determination of GSH in human serum samples through a standard addition method and determination of normal GSH concentration in original human serum samples with satisfactory results.