An ultrasensitive colorimetric and fluorescence dual-readout assay for glutathione with a carbon dot–MnO(2) nanosheet platform based on the inner filter effect

An ultrasensitive colorimetric and fluorescence dual-readout assay based on the inner filter effect (IFE) was developed for glutathione (GSH) determination, in which carbon dots (C-dots) were used as a fluorophore and MnO(2) nanosheets as an absorber. Due to the excellent optical absorption properties of MnO(2) nanosheets and the good spectral overlap between the fluorophore and absorber, MnO(2) nanosheets could effectively quench the fluorescence of C-dots via the IFE. As the target, GSH could reduce MnO(2) nanosheets to Mn(2+) ions, which inhibited the IFE and resulted in the fading of solution color and the recovery of the fluorescence signal. And these two kinds of signals were respectively used for qualitative and quantitative detection of GSH. The results showed that this proposed assay could distinguish 10 μM GSH with the naked eye and quantitatively detect GSH within the concentration range of 0.1–400 μM. The limit of detection was 6.6 nM. Moreover, this assay showed sensitive responses in human serum and urine samples, which indicated that this IFE-based assay has great potential in GSH-related clinical and bioanalytical applications.