Regulating the Direct Electron Transfer of Bilirubin Oxidase in a Glucose/Oxygen Biofuel Cell for Self-Powered Detection of Aflatoxin B1

Enzymatic biofuel cell (EBFC)-based self-powered sensors (SPSs) have emerged as a promising class of portable sensing devices; therefore, it is crucial to develop a novel and efficient strategy for the fabrication of EBFC-SPSs. Herein, we present a novel strategy for self-powered sensing by regulating the direct electron transfer (DET) of bilirubin oxidase (BOD) in a glucose-oxygen biofuel cell. The cathode is fabricated by immobilizing BOD on a gold nanoparticle (AuNP)-multiwalled carbon nanotube (MWCNT) nanocomposite by using an aptamer-complementary DNA (cDNA) duplex as a bridge. In the absence of aflatoxin B1 (AFB1), BOD remains distant from the AuNP-MWCNT nanocomposite, so the DET of BOD is hindered, preventing the catalytic reduction of oxygen at the cathode. In the presence of AFB1, the specific binding of the aptamer to AFB1 triggers its dissociation from the cathode, while the cDNA forms a hairpin structure due to the self-complementary sequences at both ends. The DNA structure switching brings BOD into close proximity with the AuNP-MWCNT nanocomposite, so BOD can effectively catalyze the reduction of oxygen at the cathode through DET. As a result, the biofuel cell transitions from the initial "open-circuit" to the "closed-circuit" state, enabling self-powered sensing of AFB1. The linear range for AFB1 detection is from 10-2 to 105 pg mL-1, with an ultralow detection limit of 3 × 10-3 pg mL-1. This work not only offers a novel strategy for self-powered sensing but also develops a portable device for fungal toxin detection.