Portable bioactive capsule-integrated electrochemical-colorimetric dual-mode biosensor based on Mn/Ce MOF nanozyme for rapid detection of malathion in water.

To enable rapid and reliable on-site monitoring of organophosphorus pesticides a novel portable dual-mode biosensor has been developed which integrates electrochemical and colorimetric detection into a single freeze-dried bioactive capsule. This innovative design supports instrument-free operation and provides dual-signal cross-validation. The sensor is based on a newly synthesized Mn/Ce bimetallic metal-organic framework (MOF) nanozyme with high oxidase-like activity, co-immobilized with acid phosphatase (ACP) within a mannitol- and sucrose-stabilized lyophilized capsule to ensure long-term stability and field readiness. In the presence of malathion, the pesticide selectively inhibits ACP, thereby restoring the MOF's catalytic activity and enabling the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The resulting signal is detected both visually and through chronoamperometry after conversion to a yellow diimine product. This approach achieves a wide linear detection range of 1-2000 nM and an exceptionally low detection limit of 0.06 nM for malathion, along with high accuracy evidenced by recoveries of 93.31%-104.03% in real water samples. This work establishes a field-deployable and user-friendly sensing platform that combines innovative material design with integrated dual-mode detection, offering a robust and practical strategy for on-site environmental monitoring.