A Real-Time Self-Powered Equivalent Circuit Extraction Technique to Monitor the Degradation of a Field-Deployable ISE.

Drift and degradation reduce the lifetime and precision of wearable, implantable, and environmental (WIE) electrochemical sensors. Real-time degradation monitoring and isolation of the degradation modes can help improve the design and manufacture of these sensors. Various laboratory-based analytical techniques are available to characterize WIE sensors, but the complex instrumentation, high power requirements, need for frequent calibration, and sample preparation make these techniques unsuitable for real-time degradation monitoring. In this paper, we develop a voltage-pulse-based technique and a corresponding scaling algorithm to measure the transient response and interpret the equivalent circuit of potentiometric ion-selective sensors (ISE) in real time. Our in-field characterization enables monitoring of ISE's bulk and interfacial properties change over time. We validated the approach through simulation and experiments by analyzing the long-term degradation of nitrate ISEs under various stress conditions.