Field-effect transistor biosensors for biomedical applications: material platforms, interfacial engineering, and translational challenges

Field-effect transistor (FET) biosensors provide label-free, miniaturized, and electrically readable platforms for biomedical analysis by converting molecular-recognition events at bioelectrical interfaces into changes in channel current, conductance, threshold voltage, or related electrical outputs. Their potential for rapid diagnostics, pathogen screening, wearable biofluid monitoring, and biohybrid sensing has driven extensive development of new device architectures, channel materials, and recognition interfaces. This review discusses FET biosensors from an integrated perspective that connects molecular recognition, signal transduction, device architecture, material platforms, interfacial engineering, biomedical applications, and translational challenges. Particular emphasis is placed on the distinct operating mechanisms of conventional and electrolyte-gated FETs, extended-gate configurations, and organic electrochemical transistors, as well as on how channel transport, receptor organization, interfacial chemistry, electrolyte composition, ionic screening, sample-matrix effects, and readout conditions jointly determine practical sensing performance. Representative silicon, carbon-nanotube, graphene, semiconducting two-dimensional-material, and organic-transistor-based platforms are compared in terms of their operational strengths, fabrication constraints, interfacial compatibility, and biomedical applicability. Interface-design and measurement strategies, including low-profile probe anchoring, receptor organization, localized signal generation, noise-aware analysis, and fluidic integration, are further examined in relation to practical sensing performance. Finally, key barriers to translation are discussed, including scalable fabrication, device-to-device variability, reference-electrode instability, interface degradation, incomplete analytical reporting, and limited validation in authentic samples. Future progress will require reproducible manufacturing, standardized performance evaluation, matrix-compatible workflows, controlled fluid handling, and system-level integration to enable reliable and clinically relevant transistor-based biosensing.