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[Display omitted] • Hydroquinone-mediated OPECT biosensing strategy was developed. • ZnSe/Bi 2 MoO 6 heterojunction was employed as photoactive material. • Sensitive and selective detection of FTO protein was achieved. • Hemin catalyzed the oxidation of ZnSe and hydroquinone by H 2 O 2 was employed to achieve signal suppression. • Rhein and perfluorohexane sulfonate inhibited FTO protein activity. Organic photoelectrochemical transistor (OPECT) biosensing is a new concept that combines photoelectrochemical and organic electrochemical transistor biosensing. It reduces background noise and combines both signal amplification for low abundance biomolecule detection. In this work, an OPECT biosensor for the detection of fat mass and obesity-associated protein (FTO) was constructed, in which ZnSe/Bi 2 MoO 6 was chosen as the gate material, hm6ARNA (containing N6-methyladenine RNA sequence) as the target molecule, and hydroquinone as the electron donor. Under FTO oxidation induced RNA demethylation, the formation of hemin loaded with G-quadruplex on the electrode surface was triggered. With the catalysis of hemin-based DNAzyme towards the oxidation reaction caused by H 2 O 2 towards hydroquinone and ZnSe, the electron donor was consumed and ZnSe was oxidized in situ to form SeO 2 which reduced the photo-anodic response. The variation of the gate effectively gated the state of the channel polymer thus producing different channel current responses, a process that was closely related to the content of FTO. In addition, the effects of rhein and potassium perfluorohexanesulfonate on FTO activity were also investigated in this experiment, with IC 50 values of 10.62 μM, 31.28 mg/L respectively. [ABSTRACT FROM AUTHOR]