Highly Accurate, Stable Solid-State Microelectrode for an Electrochemical Glucose Sensor

Abstract

Wearable glucose sensors offer the promise of determining necessary insulin doses by analyzing bodily fluids in a noninvasive and continuous manner. Beyond ionotropic and optical methods that are already commercially available, electrochemical sensors can offer a small form factor, low cost, and easy fabrication process, enabled by its two-electrode configuration. Recent works have demonstrated an enhancement of sensing capabilities in the working electrode regarding both enzymatic and non-enzymatic materials. However, a reference electrode that uses the well-known silver/silver chloride (Ag/AgCl), still requires a performance improvement, especially as a form of a low-profile, solid-state configuration. The design of a solid-state electrode has reliability issues, driven in part by the non-use of a liquid chloride-based solution where the existing sensors are stored. Therefore, it is urgently needed to develop a new sensor with higher sensitivity and durability, while covering a broader range of concentrations. Here, this study reports a newly developed solid-state Ag/AgCl electrode that offers enhanced accuracy and long-term stability in a very small form factor. Ag-deposited Si wafer was annealed to address a delamination issue before anodic chlorination. Fast scan cyclic voltammetry was performed to make conformal AgCl film on the Ag, providing an intimate contact. The correlation between electrochemical variables and stability was analyzed by changing the voltage range and the number of cycles. The initial stage of nucleation, surface morphology and structure of the multilayer were also studied to validate the improved flexibility. The resultant electrode shows high stability in DI water, pH buffer, and saline solution after adopting Nafion as an uppermost membrane. Collectively, this work provides a long-term stable (> 1 week) solid-state reference electrode which can be used for developing a wearable electrochemical glucose sensor. Figure 1