Accurate neuronal tracing of microelectrodes based on PEDOT-dye coatings

Penetrating microelectrode probes offer the opportunity to precisely monitor neuronal signals over several months. After the experimental end point, histological methods are used to analyze the tissue and to correlate recorded signals to histological findings. However, accurate retroactive tracing of the position of individual microelectrodes is currently hampered by the lack of suitable techniques to mark their positions. Here we describe a poly (3, 4-ethylene dioxythiophene) (PEDOT) based microelectrode coating, which is optimized for an active, electrochemically controllable release of the neuronal tracer DiI. The tracer is incorporated into the polymer coating by an ion exchange mechanism. Active cycling showed a 3.6 times higher dye incorporation rate compared to reference samples which were solely immersed in the dye. A bi-layer system was used to optimize drug storage ability and could suppress passive leakage of DiI from the film by more than a factor 6. The PEDOT/dye system was characterized in vitro in terms of its ability to store the dye over the time course of the experiment, deliver a precise quantity upon electroactivation and continuously support stable recordings throughout an implantation.