Chronic in vivo nerve electrical recordings of Aplysia californica using a boron-doped polycrystalline diamond electrode

Custom diamond electrodes for in vivo, passive electrical nerve recording were developed and implanted in an intact, freely behaving Aplysia californica. A diamond electrode may have advantages for electrical recording because of its chemical stability, higher signal-to-noise ratio, and reduced biological fouling relative to traditional nerve-recording electrode materials. For example, thin stainless steel electrodes used for chronic extracellular recording in Aplysia typically last on the order of seven days in vivo. We have developed a first-generation diamond electrode with a flexible lead to withstand the complicated movements of Aplysia and to enable direct comparison with implanted stainless steel electrodes.Boron-doped polycrystalline diamond was grown onto tungsten wire substrates by hot filament chemical vapor deposition. The wires were pre-shaped into a hook (for nerve recording) or a loop (for a ground wire) and masked for selective growth on only 2–3 mm of the wire. After diamond growth, the uncoated portion of the wire substrates was removed and the intact diamond-coated hook or loop attached to a stainless steel electrical lead with conductive epoxy. After epoxy curing, these electrodes were insulated and implanted in the animal.The diamond and stainless steel electrodes were attached extracellularly to buccal nerve 2, a primary nerve for the feeding behavior of A.californica. The two electrodes were implanted adjacent to each other so that the recordings would be nearly synchronous. In vivo recordings were successfully obtained on a diamond hook electrode during a feeding behavior for up to 9 days after the implantation. The electrode remained intact for a total of 28 days in the animal and upon retrieval.