On the Influence of Diffusion, Double Layer, and Glass Conduction on the Electrical Resistance of Open Tip Glass Microelectrodes

A theoretical study of the electrical resistance of open tip glass microelectrodes based on the main physicochemical phenomena occurring at the microtip is described. An analytical expression for the total resistance of a microelectrode is derived from a model which assumes an electrically insulated glass wail. The model takes into account the diffusion process through the open tip, the ionic conduction in the bulk solutions, and the ionic conduction in the electrochemical double layers. These latter elements embody to some extent the conduction in a hydrated glass layer at the glass surface. A detailed study of the ionic flow through the microtip is also presented. The validity of this model is supported by experimental results presented at the end of this paper. Comparisons between these experimental results and their theoretical predictions are shown to be of electrophysiological interest. Practical comments involving an improved utilization of glass microelectrodes are also discussed throughout this paper.