Highly selective and sensitive detection of glutathione over cysteine and homocysteine with a turn-on fluorescent biosensor based on cysteamine-stabilized CdTe quantum dots.

In this work, cysteamine (CA) stabilized CdTe quantum dots (QDs) (CA-CdTe QDs) and sodium citrate stabilized gold nanoparticles (AuNPs) were prepared. Because of the strong electrostatic interaction and spectral overlap of emission spectrum of CA-CdTe QDs and absorption spectrum of AuNPs, a highly effective fluorescence resonance energy transfer (FRET) system was formed and the fluorescence of CA-CdTe QDs was strongly quenched. The synthesized CA-CdTe and AuNPs were self-assembled to large clusters due to the electrostatic attraction and the fluorescence of CA-CdTe was sharply quenched as a result of FRET. Under the optimum pH of 5.5, the positive GSH could assemble with negative AuNPs through electrostatic interaction and destroy the FRET system of CA-CdTe and AuNPs, due to the red shift of absorption wavelength of AuNPs caused by aggregation. The fluorescence of CA-CdTe recovered, and the recovered fluorescence efficiency shows a linear function against the GSH concentrations from 6.7 nM to 0.40 μM, with a detecting limit of 3.3 nM. The quenched emission of CA-CdTe could be recovered attributed to the aggregation of AuNPs by GSH. Under optimal conditions, the sensing system was successfully applied in the detection of GSH in real human blood plasma samples with a recovery of 99.5-102.3%, showing a promising future for the highly sensitive and selective GSH detection in the human blood plasma samples.