Redox Polymers in Electrochemical Biosensing: Molecular Design, Electron Transfer, and Hybrid Nanocomposites

Redox-active polymers have become an important component of second-generation electrochemical biosensors, solving the problem of efficient charge transfer between the biological recognition material and the electrode surface. In this review, we discuss the basic design principles, electron transfer mechanisms, and synthesis strategies from the perspective of biosensor applications. Three main classes of redox centers are considered—metal complexes, metallocenes, and organic radicals—as well as polymer matrices, and the factors affecting their stability and operability are discussed. Particular attention is paid to hybrid nanocomposites based on carbon nanotubes, graphene, and metal nanoparticles. The review concludes that despite significant advances in molecular design and the development of nanocomposites, the commercialization of biosensors based on redox polymers is hindered by unresolved issues related to biofouling, metal center instability, and low reproducibility. This emphasizes the need for standardized synthesis and integration of machine learning-based design to achieve a balance between electron transfer kinetics, biocompatibility, and operational properties.