Subcellular-Scale Stimulation Electrode Arrays (3SEA) Enabled by Diffusion-Tuned PEDOT:PSS Galvanostatic Deposition

Achieving neuromodulation at subcellular scales requires stimulation electrodes that integrate micrometer-scale footprints, high spatial density, and an efficient, reliable charge-delivery capability. Here, we introduce a diffusion-tuned galvanostatic deposition strategy, guided by mass transport mediation, to uniformly and array-widely coat PEDOT:PSS onto densely packed electrodes with diameters ranging from 3 to 10 μm. The resulting Subcellular-Scale Stimulation Electrode Arrays (3SEA) exhibit robust electrochemical performance, with a tens to hundreds kilohms impedance at 1 kHz and charge-storage capacities of 22.1-54.1 mC/cm². They also achieve charge-injection capacities of 2.31-10.1 mC/cm², surpassing previously reported values of microelectrodes. Functional validation of 3SEA upon neurostimulation using calcium imaging of HT-22 neurons exhibits reliable stimulus-evoked Ca²⁺ transients, confirming subcellular-scale and efficient stimulation capability with biphasic pulses as low as 1 nC/phase. Our results establish a scalable framework for fabricating high-performance subcellular-scale stimulating bioelectronics and high-precision neural interfaces.