UCLA

Continuous monitoring of deep-tissue biochemical processes is constrained by a persistent tradeoff in implantable biotelemetry: achieving multiplexed, electrochemically faithful sensing has generally required active, integrated-circuit-based architectures whose power demands limit subjects to tethered, benchtop-instrumented, or heavily energized settings, precluding genuinely ambulatory, longitudinal measurement. Here we present a wearable-paired, battery-free implant that resolves this tradeoff through a zero-integrated-circuit architecture centered on a single junction field-effect transistor (JFET). Exploiting the intrinsic device physics of the depletion-mode JFET gate junction, this transistor simultaneously performs biochemical-to-electrical signal transduction, self-generated electrochemical biasing, and passive noise suppression and RF-carrier isolation, eliminating the implant-side circuitry conventionally required for each function separately. The implant-reader link is engineered to operate in the overcoupled resonant regime, with the fixed interrogation carrier placed at the impedance trough between the resulting split resonant modes, converting a phenomenon typically treated as a liability in wireless power transfer into a passive sensitivity-amplification mechanism for fixed-carrier amplitude readout. A secondary, low-power calibration channel independently tracks coupling-induced variation from implant-reader distance and alignment, allowing this drift to be separated from genuine biochemical signal during continuous, freely moving measurement. The platform supports amperometric, pseudo-voltammetric, and potentiometric sensing modalities within the same transduction and readout framework, with wearable readouts closely matching benchtop electrochemical reference measurements across analytes. In vivo, a flexible, PDMS-encapsulated implant preserved locomotor activity comparable to non-implanted controls over a four-week period, in contrast to a significant, progressive activity reduction observed with a rigid implant of matched encapsulation, while wireless readout remained stable across the same period. Finally, the platform resolved dynamic, internal potassium fluctuations during an induced tissue-injury model, demonstrating its capacity to capture local biochemical dynamics that intermittent, systemically buffered blood sampling would not readily reveal. Together, these results establish a battery-free, multimodal telemetry architecture for continuous internal biochemical monitoring in freely moving subjects.