Rationally Designed Cerium-Assembled Carbon Dot Phosphatase-Like Nanozyme Hydrogel in Tandem with 5,7-Dimethoxycoumarin for Sensitive, Selective, Wide-Range, Complementary Dual-Mode Biosensing of Paraoxon

The development of a sensitive, selective, and wide-range biosensor for paraoxon detection is critically demanded due to its high toxicity and environmental prevalence. While complementary multimode biosensing platforms offer enhanced performance like high sensitivity and a wide detection range by synergizing multiple detection strategies, their implementation remains challenging because of compromised reaction compatibility. To address this, an integrated complementary colorimetric/fluorescence dual-mode biosensing platform based on a rationally designed cerium-assembled carbon dot phosphatase-like nanozyme hydrogel (Ce-CD_BM) in tandem with 5,7-dimethoxycoumarin (5,7-DMC) is presented for sensitive, selective, and wide-range detection of paraoxon. The Ce-CD_BM nanoarchitecture, synthesized via cerium coordination with a carbon dot derived from 2-methylimidazole and 1,2,3,4-butanetetracarboxylic acid, exhibits dual functionalities: high phosphatase-like activity and amplified fluorescence quenching capability. Ce-CD_BM enables specific hydrolysis of paraoxon to generate yellow 4-nitrophenol (4-NP), achieving colorimetric paraoxon detection with a limit of detection (LOD) of 1.2 μM. Simultaneously, the formation of a highly stable nonfluorescent ternary complex (5,7-DMC/4-NP/Ce-CD_BM) facilitates the highly efficient static photoinduced electron transfer, significantly amplifying fluorescence quenching for ultrasensitive paraoxon detection with a LOD of 15.4 nM. This colorimetric/fluorescence dual-mode biosensing platform overcomes the intrinsic limitations of single-signal approaches by operating under identical hydrolysis conditions while expanding the dynamic range by 3 orders of magnitude. Furthermore, a smartphone-assisted portable platform was developed for on-site visual quantification of paraoxon in cauliflower and Chinese cabbage matrices, demonstrating recoveries of 99-114% with relative standard deviations below 5%. This work establishes a paradigm for designing compatible multimode biosensors through rational nanozyme engineering and synergistic signal amplification strategies.