Fibrous Ag/AgCl Reference Electrode Guided by Failure Analysis for Real-Time Wearable Sweat Analysis

The reference electrode (RE) in an electrochemical sensor provides the potential standard for the measurement and is closely related to the stability and reliability of the detection results. Although commercial REs have reached a high level of technical maturity, the acquisition of miniaturized RE for skin-attachable sensors is still challenging. Herein, we apply a failure analysis process to summarize the risks affecting the stability of Ag/AgCl REs in wearable sensors. Accordingly, the fibrous Ag/AgCl REs with excellent potential stability against the changes in curvature, ionic environment, temperature, and so on are developed, which allows a skin-attached four-ion-channel organic field-effect transistor to monitor the concentrations of $\text{K}^{+}$ , Na $^{+}$ , NH $_{{4}}^{+}$ , and $\text{H}^{+}$ (pH) in human sweat instantly and simultaneously. To assess the interfacialintegrity of the fibrous Ag/AgCl RE, a theoretical model is further established. The results herein demonstrate that failure analysis does not just help us to construct miniaturized REs with high stability, but also offers a feasible strategy for the design of electrochemical microsensors operable in harsh and dynamic environments.