Zr‐MOF Mediated Gate Polarity Switching in Organic Photoelectrochemical Transistor‐Photoelectrochemical‐Colorimetric Three‐Mode Biosensor for m ⁶ A RNA Detection

Abstract A Bi ₄ O ₅ I ₂ /BiOBr Z‐Scheme heterojunction‐gated organic photoelectrochemical transistor (OPECT) biosensor is developed for ultrasensitive detection of N ⁶ ‐methyladenosine (m ⁶ A). Catalyzed by the FTO protein, m ⁶ A in RNA is oxidized to be N ⁶ ‐hydroxymethyladenosine (hm ⁶ A), and this RNA sequence is then hydrolyzed by RNase A to generate N ⁶ ‐hydroxymethyladenosine monophosphate (hm ⁶ AMP), which is further captured on the gate by hexakis‐(6‐mercapto‐6‐deoxy)‐α‐cyclodextrin based on the covalent reaction between ─CH ₂ OH and ─SH. Subsequently, Zr‐MOF is immobilized through coordination between the phosphate group of hm ⁶ AMP and Zr ⁴⁺ . Leveraging its phosphatase‐like activity, Zr‐MOF catalyzes the hydrolysis of Na ₃ SPO ₃ to generate H ₂ S, which in situ reacts with Bi ₄ O ₅ I ₂ /BiOBr gate to form double‐II heterojunction of Bi ₂ S ₃ /Bi ₄ O ₅ I ₂ /BiOBr gate, enabling photocurrent polarity inversion and better adapting to depletion transistors employing PEDOT:PSS as the organic semiconductor layer. Concurrently, Zr‐MOF catalyzes the conversion of colorless p ‐nitrophenyl phosphate to yellow p ‐nitrophenol, achieving the colorimetric (CL) detection of m ⁶ A‐RNA. Most importantly, the prepared novel OPECT‐PEC‐CL three‐mode biosensor has excellent selectivity and high sensitivity for m ⁶ A detection with detection limits as low as 3 f m , 0.15 p m, and 0.24 n m , respectively. Additionally, this study explores the effects of plasticizers and microplastic contaminants on root and leaf growth and m ⁶ A levels in rice seedlings.