High Fidelity Bidirectional Neural Interfacing with Carbon Fiber Microelectrodes Coated with Boron-Doped Carbon Nanowalls: An Acute Study

Implantable electrodes that can communicate with a small, selective group of neurons via both neural stimulation and recording are critical for the development of advanced neuroprosthetic devices. Microfiber electrodes with neuron-scale cross-sections have the potential to improve the spatial resolution for both stimulation and recording, while minimizing the chronic inflammation response after implantation. In this work, glass insulated microfiber electrodes are fabricated by coating carbon fibers with boron-doped carbon nanowalls. The coating significantly improves the electrochemical properties of carbon fibers, leading to a charge injection capacity of 7.82 ± 0.35 mC cm⁻², while retaining good flexibility, stability and biocompatibility. When used for neural interfacing, the coated microelectrodes successfully elicit localized stimulation responses in explanted retina, and are also able to detect signals from single neurons, in vivo with a signal-to-noise ratio as high as 6.7 in an acute study. This is the first report of using carbon nanowall coated carbon fibers for neural interfacing.