Poly(3,4-ethylenedioxythiophene)-Single Walled Carbon Nanohorns Composite Coatings for Neural Sensing and Stimulation

Typical neural electrodes are fabricated with noble metals and alloys but recently other new materials, including glassy carbon based microelectrode arrays, have emerged. For neural stimulation, these electrodes should be... [ view full abstract ]

Typical neural electrodes are fabricated with noble metals and alloys but recently other new materials, including glassy carbon based microelectrode arrays, have emerged. For neural stimulation, these electrodes should be capable of injecting relatively large currents while minimizing electrode degradation due to faradaic effects, requirements generally satisfied by increasing the electrode size.

To improve electrochemical properties and stability of microelectrode arrays, conductive polymers (CPs), such as poly(3,4-ethylenedioxythiophene) (PEDOT), are often electrodeposited onto the metal underlayer in order to significantly reduce total impedance as well as to increase the total charge that can be accumulated, leading to higher S/N ratios, higher charge injection limits and less heat generated at the interface during stimulation.

Here, for the first time, (PEDOT) was electrodeposited in conjunction with oxidized single walled carbon nanohorns (ox-SWCNHs) onto gold microelectrode arrays in the framework of brain activity recordings and stimulation. The electrochemical, morphological and stability properties of coatings, as well as the ability of coated microelectrodes to record neural activity were investigated. Ox-SWCNHs based coatings have shown very promising properties in terms of charge injection limit, stability to pulsed electrical stimulus, neural sensing and biocompatibility. PEDOT/ox-SWCNHs composites were compared with films prepared with one of the most notorious carbonaceous material, multi-walled Carbon Nanotubes (MWCNTs). Our findings furnished comparable results for PEDOT/ox-SWCNHs and PEDOT/ox-SWCNHs coatings, in terms of surface characterization (SEM and XPS), electrochemical characterization (electrochemical impedance, cyclic voltammetry) and stability under fast pulsed charge stimulation. PEDOT/ox-SWCNHs and MWCNTs were found to be able to acquire the same neural signal information from the rat cortex with the best results in a relevant ECoG signal frequencies interval, from delta to high gamma bands, for brain-computer interfaces applications. More importantly, our preliminary results suggest that PEDOT/ox-SWCNHs material are very promising in terms of higher biocompatibility. Thanks to their extremely porous structure PEDOT/ox-SWCNHs films exhibited a higher charge storage capacity, with respect to PEDOT/MWCNTs, leading to an improved charge injection dynamic, with lower voltage excursion during electrochemical stimulation, which is very important in order to reduce, for instance, dramatic faradaic processes at the interface electrode/neural tissue.