Active Control of Dye Release for Neuronal Tracing Using PEDOT-PSS Coated Electrodes

Penetrating neural probes comprising arrays of microelectrodes are commonly used to monitor local field potentials and multi-unit activity in animal brain over time frames of weeks. To correlate these recorded signals to specific tissue areas, histological analysis is performed after the experimental endpoint. Even if the lesion of the penetrating probe shaft can be observed, a precise reconstruction of the exact electrode positions is still challenging. To overcome these experimental difficulties, we developed a new concept, whereupon recording electrodes are coated with a poly (3, 4-ethylenedioxythiophene/ polystyrenesulfonate) (PEDOT/PSS)-based film. The conducting polymer acts as dye reservoir over several weeks and afterwards provides controlled delivery of neurotracers. This paper presents a recording electrode based on a PEDOT/PSS bilayer optimized for dye delivery and with reduced impedance. Controlled exchange of neurotracer dye is successfully demonstrated in vitro using spectrofluorometry and in neuroblastoma cell cultures. A second PEDOT/PSS capping layer on top of the dye reservoir lowers the passive leakage of dye by a factor of 6.4 and prevents a direct contact of the dye filled layer with the cells. Stability tests over four weeks demonstrate the electrochemical stability of the PEDOT coating, as well as retained functionality of the dye delivery system.