Surface Transmon Resonance (STR): a handheld nanogap biosensor for real-time, label-free molecular binding kinetics

Despite the exponential growth of microelectronics driven by Moore’s law over half a century, biosensing has remained largely dominated by optical methods such as fluorescence assays and surface plasmon resonance (SPR). Electronic biosensors, particularly field-effect transistor (FET)-based platforms, have historically faced challenges related to Debye screening and the lack of compact, high-frequency instrumentation necessary for label-free, high-sensitivity measurements in conductive solutions. Here, we present a Surface Transmon Resonance (STR) biosensor, a nanogap-enabled electronic platform that exploits a handheld vector network analyzer (nanoVNA) for real-time, phase-resolved detection of protein-protein interactions. Operating at radio frequencies in the hundreds of MHz range, STR decreases Debye screening limitations and provides an SPR-like readout with significantly reduced cost and footprint compared to benchtop optical systems. By characterizing specific bovine serum albumin (BSA) and anti-BSA binding kinetics, we demonstrate that STR biosensors can quantitatively assess molecular affinity and interaction dynamics, capabilities traditionally reserved for optical gold-standard techniques like SPR. This work positions STR as a compact, scalable, and cost-effective electronic alternative to conventional optical biosensors.