Substrate-Switched\nDual-Signal Self-Powered Sensing\nSystem Based on Dual-Nanozyme Activity of Bimetal-Doped CeO<sub>2</sub> Nanospheres for Electrochemical Assay of Aflatoxin B1

The long-term operation feature of enzymatic biofuel\ncell-based\nself-powered biosensor (EBFC-SPB) endows them with the potential to\nexecute dual-signal biosensing without having to integrate an extra\nsignal acquisition device. Herein, cobalt and manganese codoped CeO<sub>2</sub> nanospheres (CoMn-CeO<sub>2</sub> NSs) with glucose-oxidase-like\nand peroxidase-like activities have been developed as substrate-switched\ndual-channel signal transduction components in EBFC-SPB for a dual-signal\nassay of aflatoxin B1 (AFB1). The CoMn-CeO<sub>2</sub> NSs modified\nwith aptamer are anchored to a complementary DNA-attached bioanode\nof EBFC-SPB by base complementary pairing, which catalyze the glucose\noxidation together with the glucose oxidase (GOx) on the bioanode.\nOnce the AFB1 appears, CoMn-CeO<sub>2</sub> NSs will be released from\nthe bioanode due to the binding specificity of the aptamer, resulting\nin a decreased catalytic efficiency and the first declining stage\nof EBFC-SPB. Accompanied by the introduction of H<sub>2</sub>O<sub>2</sub>, the residual CoMn-CeO<sub>2</sub> NSs on the bioanode switch\nto peroxidase-like activity and mediate the production of benzo-4-chlorohexadienone\n(4-CD) precipitate, which increases the steric hindrance and yields\nanother declining stage of EBFC-SPB. By assessing the variation amplitudes\nduring these two declining stages, the dual-signal assay of AFB1 has\nbeen realized with satisfying results. This work not only breaks ground\nin dual-signal bioassays but also deepens the application of nanozymes\nin EBFC-SPB.