Simulation-Guided Optimization Of Electrode Arrays For Electrochemical Imaging Of Quantal Exocytosis

Fluorescence imaging can provide important information about the mechanisms of exocytosis at the single-vesicle level, e.g., conformational changes in SNARE proteins reported via FRET. FRET signals are very small and therefore the time and location of the fusion events are not readily apparent to allow signal analyses. The Lindau lab has pioneered the use of “electrochemical imaging” to identify the time and location of quantal exocytosis by comparing the amperometric signal between 4 electrodes arranged around a cell. Since it is necessary to obtain a measurable signal in at least three electrodes in order to “triangulate” the position, a limitation of this method is that it can only localize exocytosis events that originate near the center of the electrode arrays. We therefore carried out finite-element-array (COMSOL) reaction-diffusion simulations to guide the design of electrode arrays that can maximize the area on the cell surface where a release event can be localized with high precision. The number and placement of electrodes around the cell were varied and the SD of localization precision was simulated. Our results indicate that as the number of electrodes arranged circumferentially around the cell increases, the detectable area further from the center of the array increases, however, the precision of localization in the center decreases because the amperometric charge is divided between more electrodes. Thus the optimal number of electrodes depends on the signal-to-noise ratio of the amperometric recordings and the acceptable location precision. Under our simulation conditions, if a localization precision (SD) less than 0.23 μm is needed, an array of 4 electrodes will give the largest detectable area. However, if slightly less precision is acceptable, 5 or 6 electrodes allows a larger detectable area than 4 or 3 electrodes. Supported by NIH R44MH096650.