Biocompatible PEDOT:Nafion Composite Electrode Coatings for Selective Detection of Neurotransmitters in Vivo

A Nafion and poly(3,4-ethylenedioxythiophene) (PEDOT) containing composite polymer has been electropolymerized on carbon-fiber microelectrodes with the goal of creating a mechanically stable, robust, and controllable electrode coating that increases the selectivity and sensitivity of in vivo electrochemical measurements. The coating is deposited on carbon-fiber microelectrodes by applying a triangle waveform from +1.5 V to -0.8 V and back in a dilute solution of ethylenedioxythiophene (EDOT) and Nafion in acetonitrile. Scanning electron microscopy demonstrated that the coating is uniform and similar to 100 nm thick. Energy-dispersive X-ray spectroscopy demonstrated that both sulfur and fluorine are present in the coating, indicating the incorporation of PEDOT (poly(3,4-ethylenedioxythiophene) and Nafion. Two types of PEDOT:Nafion coated electrodes were then analyzed electrochemically. PEDOT:Nafion-coated electrodes made using 200 mu M EDOT exhibit a 10-90 response time of 0.46 +/- 0.09 s versus 0.45 +/- 0.11 s for an uncoated fiber in response to a 1.0 mu M bolus of dopamine. The electrodes coated using a higher EDOT concentration (400 mu M) are slower with a 10-90 response time of 0.84 +/- 0.19 s, but display increased sensitivity to dopamine, at 46 +/- 13 nA/mu M, compared to 26 +/- 6 nA/mu M for the electrodes coated in 200 mu M EDOT and 13 +/- 2 nA/mu M for an uncoated fiber. PEDOT:Nafion-coated electrodes were lowered into the nucleus accumbens of a rat, and both spontaneous and electrically evoked dopamine release were measured. In addition to improvements in sensitivity and selectivity, the coating dramatically reduces acute in vivo biofouling.