How to prepare an ultramicroelectrode with a precise geometry

A versatile protocol for fabricating ultramicroelectrodes (UMEs) with precise geometry is presented. This new method produces highly concentric UMEs with micron-sized electroactive wires sealed in a thin borosilicate sheath. The method also permits easy repolishing without significantly changing the electrode dimensions. Furthermore, the simple, single-step pulling process—providing simultaneous micro-wire sealing and capillary-thinning—avoids additional sealing and tip-sharpening steps of traditional fabrication methods, which require fastidious hands-on fabrication and have low reproducibility/success-rates. Diverse types of electrodes (i.e., gold, carbon-fiber, and platinum) can be fabricated by this new method in a short time (≤30 min) while requiring little training or prior knowledge in UME fabrication. In addition, we describe the assembly and operation of 3D-printed custom polishing and beveling apparatuses; that can rapidly (≈2 min) and impeccably polish and bevel the newly designed UMEs into various final UME geometries (i.e., disk, beveled, and double-beveled); a critical issue often overlooked in UME preparation literature. The characteristically small ratio of the insulating sheath to the electroactive core (RG ≤ 3) of prepared disk UMEs is highly desirable for applications in scanning electrochemical microscopy (SECM). Similarly, these features are maintained when beveled or dual-bevel chisel-tip UMEs are prepared, which are highly desirable features for UMEs employed in intracellular recordings. The straightforward fabrication method described here is readily extended to other electroactive cores and micropipettes, allowing even novices to produce high quality probes for various applications. Keywords: Ultramicroelectrode, disk, beveled electrode, chisel-tip electrode, scanning electrochemical microscopy, electrochemistry, 3D printing.