To reduce carbon emissions by converting CO₂ into valuable products researchers have focused on the development of solar-light-driven hybrid artificial photosynthetic systems based on photo-enzyme-catalytic reactions and cost-competitive cofactor regeneration processes. Herein, the use of conjugated-polymer-based water-processable nanoparticles as photosensitizer in artificial photosynthetic systems for the efficient photoregeneration of methylviologen and the conversion of CO₂ to formate is proposed.

Solar-energy-based bio- and photocatalytic hybrid systems offer a sustainable approach to reducing carbon emissions by converting carbon dioxide (CO₂) into valuable chemicals and fuels, such as carbon monoxide (CO), formate, or methanol. A key strategy involves coenzyme-dependent oxidoreductases, necessitating efficient and cost-effective coenzyme regeneration methods using economical energy sources. Herein, the oxidized form of methylviologen dichloride (MV²⁺) is reduced to MV^•+ under visible light using triethanolamine (TEOA) as an electron donor and conjugated-polymer-based water-processable nanoparticles (WPNPs) as both photosensitizer and mediator, achieving a regeneration efficiency of ≈95%. The regenerated cofactor enables the enzymatic conversion of sodium bicarbonate (NaHCO₃) to formate via Candida boidinii formate dehydrogenase (CbFDH) biocatalyzed reaction, with a yield of ≈20%. Formate production is validated by adding nicotinamide adenine dinucleotide (NAD⁺), which is reduced to NADH thanks to the synthesized formate and CbFDH, thus leading to a simple NADH regeneration method. To the best of authors’ knowledge, this is the first successful use of conjugated polymers in the form of WPNPs as both photosensitizer and mediator in a photocatalytic system for selective coenzyme regeneration, facilitating an efficient bicarbonate-to-formate conversion.