Nitrogen-doped carbon quantum dot-cerium oxide (NCQD-CeO2) nanocomposites were developed as an enzyme-free, multi-analyte sensing platform based on fluorescence resonance energy transfer (FRET). The sensing mechanism arises from the redox-active Ce3+/Ce4+ couple of cerium oxide, which catalyzes analyte-specific reactions and generates in situ FRET acceptors that modulate NCQD fluorescence. CeO2 nanoparticles catalyze the oxidation of dopamine to aminochrome (quinone), whose absorption overlaps with NCQD emission, resulting in fluorescence quenching in both acidic and basic conditions. Dopamine self-polymerization under basic conditions is suppressed by glutathione through its antioxidant activity, while nanoceria enhances electron-transfer kinetics. Glutathione further regulates the Ce3+/Ce4+ redox equilibrium, enabling indirect detection via modulation of FRET efficiency. In the case of methyl paraoxon, CeO2 exhibits phosphatase-like activity and catalyzes its conversion to p-nitrophenol, which acts as a FRET acceptor and quenches NCQD fluorescence. The analyte-dependent formation of distinct FRET acceptors allows selective signal transduction, establishing the NCQD-CeO2 nanocomposite as a versatile platform for multi-analyte sensing.
Chawre et al. (Thu,) studied this question.