Synthesis and Fabrication of Single Walled Carbon Nanotube Microelectrode Arrays on Flexible Probes for Neurotransmitter Detection

Implantable microelectrode arrays are an effective method for understanding neurotransmitter dynamics with high spatial resolution. In particular, carbon-based electrodes are efficient for electrochemical detection of dopamine, a neurotransmitter studied for its role in motor movement and reward-seeking behavior. However, very few options exist for arrayed carbon microelectrodes, specifically on flexible polymeric probes. We demonstrate fabrication of polyimide probes featuring single walled carbon nanotube (SWCNT) microelectrode arrays and characterize their dopamine detection performance. First, SWCNT synthesis parameters were optimized to grow high density SWCNT “forests” that have uniform height with electrode diameters ranging from 15 μm to 100 μm, as these dimensions are spatially relevant to chemical sensing in an animal model. These SWCNT microelectrodes were then incorporated into a microfabrication process involving deposition and patterning of polyimide substrate and metal traces. The process flow was designed such that the polyimide was not exposed to the high temperatures required to grow SWCNTs. Instead, a bottom-up approach was utilized, in which the SWCNT catalyst was first patterned, the SWCNTs were synthesized on a silicon substrate, then polyimide and trace metal layers were deposited and patterned. Prototype probes were fabricated containing the same range of electrode diameters as those used for SWCNT synthesis development to determine the effect of electrode diameter on ease of microfabrication. Microelectrodes ranging from 15 μm to 50 μm in diameter were found to release from the carrier wafer more easily, while larger electrodes demonstrated poor release. These probes demonstrate a concentration-dependent response to dopamine, with high sensitivity compared to microelectrode arrays consisting of bare metal. Further development of this electrode material will enable neuroscientists to study dopamine at higher spatial resolution, with the benefit of utilizing flexible probes.