Glutathione (GSH) was commonly used as a diagnostic biomarker for many diseases. In this study, based on carbon quantum dots prepared from dragon fruit peel (D-CQDs) and T-Hg(Ⅱ)-T mismatch, a dual-mode biosensor was developed for the detection of GSH. This system consists of two single-stranded DNA (ssDNA). DNA1 was the T-rich sequence; DNA2 was attached to streptavidin-coated magnetic beads, and consisted of T-rich and G-rich fragment. Due to the presence of Hg(Ⅱ), the T-Hg(Ⅱ)-T mismatch was formed between T-rich fragment of two ssDNA. In the presence of GSH, Hg(Ⅱ) detached from dsDNA and bound with GSH to form a new complex. The G-rich fragment assembled with the hemin shed from D-CQDs to form the G-quadruplex/hemin complex. At this time, in fluorescence mode, the fluorescence of D-CQDs quenched by hemin could be restored. In colorimetric mode, after the magnetic beads separate, a visual signal could be produced by catalyzing the oxidation of ABTS using the peroxide-like activity of G-quadruplex/hemin complex. This biosensor in fluorescence mode and colorimetric mode both had excellent selectivity and sensitivity, and the limit of detection was 0.089 μM and 0.26 μM for GSH, respectively. Moreover, this proposed dual-mode biosensor had good application prospects for detection of GSH.

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