Methyl viologen induced fluorescence quenching of CdTe quantum dots for highly sensitive and selective "off-on" sensing of ascorbic acid through redox reaction.

A turn-on fluorescent sensor based on CdTe quantum dots (QDs) is designed for highly sensitive and selective ascorbic acid (AA) detection. CdTe shows a strong emission centered at 578 nm. When assembled with poly(sodium 4-styrenesulfonate) (PSS) and methyl viologen (Mv2+) through electrostatic interaction, the emission is found to be effectively quenched. In the presence of AA, Mv2+ is reduced to Mv+, making the fluorescence of CdTe QDs restored. Under the optimal conditions, the proposed AA sensing method shows a linear proportional response from 0.8 µM to 20 µM, with the detecting limit as low as 50 nM. The developed method was successfully applied in the analysis of AA in human serum samples and cell lysates with satisfactory results.