Chemical Reaction Driven Photoelectrochemical and Colorimetric Dual‐Mode Biosensing: A Label‐Free Strategy for Adenosine Deaminase Detection Based on IDIC‐4Cl

Photoelectrochemical (PEC) sensing offers high sensitivity and rapid response, but its broader bioanalytical utility is constrained by the lack of intrinsic molecular recognition in most photoactive materials. Here, we present the non‐fullerene acceptor (NFA) IDIC‐4Cl as a chemically addressable photoactive material that integrates chemical responsiveness and signal transduction within a single material platform. By exploiting the nucleophilic addition reaction between the electron‐deficient C═C bonds of IDIC‐4Cl and OH − , highly selective detection of adenosine deaminase (ADA) is achieved without the use of aptamers or antibodies. An energy level matching polymer donor (D18) was introduced to form a heterojunction architecture, significantly enhancing photogenerated charge‐carrier separation and enabling high analytical sensitivity. Notably, the OH − ‐induced chemical transformation could be partially reversed upon subsequent H + treatment, accompanied by both color recovery and photocurrent restoration. The resulting dual‐mode PEC‐colorimetric platform achieves low limits of detection for ADA of 0.54 U L − 1 (PEC) and 2.98 U L − 1 (colorimetric). The platform exhibits strong resistance to interference and delivers reliable performance in human serum, with recovery values greater than 89%. This work demonstrates a chemically responsive sensing approach that couples organic semiconductor reactivity with PEC signal transduction.