Leak‐Free and Chemically Resistant Epoxy‐Sealed Ultramicroelectrodes from Diverse Conductor Materials

ABSTRACT Ultramicroelectrodes (UMEs) are powerful electrochemical tools due to their high sensitivity, fast steady‐state response, minimal ohmic losses, and compatibility with in situ/operando measurements. To enable broader utilization of UMEs in electroanalysis, a reliable and broadly applicable fabrication method is needed, one that ensures chemical stability across various environments and supports diverse conductor materials. Here, we report a simple epoxy‐sealing method for fabricating leak‐free and chemically robust UMEs under mild curing conditions (60°C). A systematic investigation of resin‐to‐hardener ratios reveals that a 2:1 ratio optimizes seal integrity and electrochemical performance by eliminating interference from residual unreacted hardener species. The resulting UMEs maintain stable electrochemical responses in both highly acidic (1 M H 2 SO 4 ) and alkaline (1 M KOH) environments. Importantly, this low‐temperature process enables the successful fabrication of UMEs from heat‐sensitive materials (e.g., C, Cu, Mo, W) that are unsuitable for conventional high‐temperature glass sealing. The practical applicability of the epoxy‐sealed UMEs is demonstrated through chloride ion sensing using Ag UMEs (limit of detection: 0.02 m m , achieved without supporting electrolyte) and high‐resolution scanning electrochemical microscopy (SECM) using beveled epoxy‐sealed UMEs. These results underscore the broad utility of the epoxy‐sealing approach for diverse electroanalytical applications.