Red‐Light‐Absorbing Donor–Acceptor Conjugated Polymer Nanoparticles Enable Efficient and Biocompatible Photobiocatalysis

Redox enzymes offer high selectivity in chemical transformations, but their practical applications require continuous regeneration of expensive and unstable redox cofactors. Photocatalytic cofactor regeneration has shown promise as an efficient and sustainable strategy. However, most reported systems rely on ultraviolet or blue‐light excitation, frequently leading to photodamage and enzyme deactivation. Here, we report a red‐light‐driven photobiocatalytic platform based on well‐dispersible nanoparticles of indacenodithiophene– co –benzothiadiazole (IDTBT), a conjugated polymer known for its strong red‐light absorption and favorable optoelectronic properties. By employing nonionic surfactants, IDTBT nanoparticles remain colloidally stable in enzyme‐compatible aqueous buffers, enabling their application in photobiocatalysis. Under red‐light irradiation, these nanoparticles efficiently catalyze the oxidation of NADH and FADH ₂ while significantly improving enzyme activity compared to conventional blue‐light systems. To further suppress enzyme deactivation caused by reactive oxygen species (ROS), we implement a dual protection strategy combining silica encapsulation and catalase, effectively protecting enzymes against short‐ and long‐lived ROS over multiple catalytic cycles. These results highlight IDTBT‐based red‐light‐driven photocatalysis as an efficient and enzyme‐compatible strategy for sustained cofactor regeneration under mild aqueous conditions.