High density carbon fiber arrays for chronic electrophysiology, fast scan cyclic voltammetry, and correlative anatomy

Abstract

Objective. Multimodal measurements at the neuronal level allow for detailed insight into local circuit function. However, most behavioral studies focus on one or two modalities and are generally limited by the available technology. Approach. Here, we show a combined approach of electrophysiology recordings, chemical sensing, and histological localization of the electrode tips within tissue. The key enabling technology is the underlying use of carbon fiber electrodes, which are small, electrically conductive, and sensitive to dopamine. The carbon fibers were functionalized by coating with Parylene C, a thin insulator with a high dielectric constant, coupled with selective re-exposure of the carbon surface using laser ablation. Main results. We demonstrate the use of this technology by implanting 16 channel arrays in the rat nucleus accumbens. Chronic electrophysiology and dopamine signals were detected 1 month post implant. Additionally, electrodes were left in the tissue, sliced in place during histology, and showed minimal tissue damage. Significance. Our results validate our new technology and methods, which will enable a more comprehensive circuit level understanding of the brain.

Benchtop Carbon Fiber Microelectrode Array Fabrication Toolkit

“…While the arrays discussed in this paper are an excellent starting point for many labs, newer probes using carbon fibers have also been developed to chronically target deeper areas. The Chestek lab high density carbon fiber array provide users the ability to insert 16 carbon fibers to depths up to 9 mm with minimal scaring [50]. The Maharbiz lab has also developed a higher channel probe that was inserted to depths of 2.5-3 mm [51].…”

“…The carbon fibers arrays in this paper have also been successfully fabricated using the methods presented here and utilized to create dopamine sensing arrays. This is accomplished by ablating the parylene-c away from the tip of the probe using the Nd:YAG laser, at a lower power setting, and exposing 50 μm of fiber [50]. Using custom hardware and software, simultaneous high density channel recording has recently been achieved [50].…”

“…This is accomplished by ablating the parylene-c away from the tip of the probe using the Nd:YAG laser, at a lower power setting, and exposing 50 μm of fiber [50]. Using custom hardware and software, simultaneous high density channel recording has recently been achieved [50]. The probe’s ability to be customized for ePhys or dopaminergic recordings offers yet another layer of adaptability to our carbon fiber array.…”

“…For acute surgeries, blunt tips can be used if the site size of the electrode is important, however they will only insert into softer tissue (brain) and only at sub-500 µm target depths. Going into deeper brain structures is possible using a glass cannula [50], but this can cause scarring and associated unreliability in ePhys recordings. Fibers must be less than 300 µm when sharpened to be able to penetrate the nerve tissue as the shorter length provides a stiffer backbone for insertion.…”

“…Other coatings such as PEDOT/graphene oxide [58] and gold [59] have been utilized to lower carbon fiber electrode impedances, though these coatings are typically used for chemical sensing probes rather than for ePhys recordings. Due to the inherent properties of carbon fibers [60], the carbon fiber array presented here can be converted from a probe optimized for ePhys to a chemical sensing device with a simple change of tip preparation [50].…”