A specific discriminating GSH from Cys/Hcy fluorescence nanosensor: The carbon dots-MnO2 nanocomposites

Herein, a novel nanosensor was designed to discriminate glutathione (GSH) from cysteine (Cys) and homocysteine (Hcy) with a two-stage fluorescent switch. The nanosensor (CDs-MnO2 NFs) was fabricated via an amidation coupling reaction between Carbon dots (CDs) and manganese dioxide nanoflowers (MnO2 NFs) that gave rise to the opposite fluorescent responses to GSH and Cys/Hcy. A "turn-off" state generated because the fluorescence of CDs was quenched by fluorescence resonance energy transfer (FRET) between CDs and MnO2. The nanosensor further triggered different fluorescence behaviors in the presence of three thiols. On the one hand, GSH reduced MnO2 into Mn2+ and subsequently restored the fluorescence of CDs, concomitant "turn-off-on" fluorescence shift. On the other hand, Cys/Hcy similarly led to the decomposition of MnO2 but provoked a further fluorescence quench into the "turn-off-off" state. It turned out that the reduction product of Cys/Hcy was SO32- instead of disulfide bond from GSH, which further quenched the fluorescence of CDs. Thus, the discriminating GSH from Cys/Hcy was achieved based on the different oxidation degrees through the nanosensor. As a result, GSH could be sensitively detected in a proportional range of 2.0–200 μM with a LOD of 0.558 μM. Meanwhile, the sensor was applied to recognize cancer cells by monitoring GSH levels. Therefore, the nanosensor with brand new sensing principle for specific recognition of GSH, which is a good candidate for GSH sensing in biological and clinical applications.