Concentration Gradient-Controlled Electrochemical Etching: A Universal Strategy for Nanoelectrodes with Tunable Geometries.

High-fidelity intracellular sensing necessitates minimally invasive nanoelectrodes with precisely controlled tip geometries to mitigate cellular trauma and enhance signal stability. However, conventional etching techniques often struggle with the reproducible modulation of tip morphology, particularly the cone angle. In this work, we report a concentration gradient-controlled electrochemical etching (CG-CEE) strategy that facilitates the deterministic fabrication of carbon fiber nanoelectrodes with tailored geometries. By leveraging spatial confinement within a micro-capillary sleeve to restrict etchant diffusion, CG-CEE establishes a stable axial concentration gradient, enabling spatially regulated etching kinetics. Modulating the sleeve diameter allows for the precise adjustment of the concentration profile, thereby enabling the controlled fabrication of tip angles ranging from 6° to 40°. This robust and highly reproducible method not only provides specialized nanoelectrodes for real-time intracellular sensing but also exhibits exceptional versatility, as demonstrated by the fabrication of high-precision tungsten needles. The CG-CEE approach offers a powerful platform for the customized preparation of various nanotip electrodes in bioanalytical chemistry and micro-fabrication.