Engineered biochar in electrochemical sensing and biosensing.

The rising demand for sustainable, high-performance materials in electrochemical (bio)sensing (EB) has driven the exploration of carbon materials derived from renewable resources. While graphene, carbon nanotubes, and similar nanocarbons are currently leading the field, their widespread use is limited by energy-intensive synthesis processes, high costs, and dependence on non-renewable or geopolitically sensitive materials. In this setting, biochar, a carbon-rich, porous material produced by controlled pyrolysis of biomass, has gained attention as a versatile form of disordered carbon with inherent electrochemical properties. Beyond sustainability, biochar (BC) provides tunable surface chemistry, hierarchical porosity, and electronic properties, all influenced by feedstock type and pyrolysis conditions. These features enable effective biomolecule immobilization, defect-mediated charge transport, and competitive performance in enzymatic, immunological, and nucleic acid biosensors across various applications. This review critically explores how structure-function relationships influence biochar behavior, linking feedstock selection, thermal processing, and post-synthesis modifications, such as activation and heteroatom doping, to device performance. We examine various integration methods, from traditional electrode modifications to printed and additively manufactured devices, and discuss challenges related to reproducibility, standardization, and scalability. While the main emphasis is on BC-based biosensors, we also include selected studies on technological advancements in incorporating BC into innovative electroanalytical platforms, as these provide a valuable foundation for the future development of biosensors and bioanalytical devices. This article presents a rational framework for proposing biochar as a scalable and sustainable source for next-generation electrochemical and biosensing technologies, spanning from material design to electroanalytical needs.