Vertically Aligned Carbon Nanofibers Arrays Record Electrophysiological Signals

Zhe Yu and Barclay Morrison III, (Department of Biomedical Engineering, Columbia University), T. E. McKnight,
M. N. Ericson, (ESTD, ORNL) A. V. Melechko, and M. L. Simpson (CNMS, ORNL)

Achievement
The controlled synthesis and directed assembly of nanoscale materials is a key requirement to create functional interfaces between synthetic and biological systems. Along these lines, recent advances in the controlled synthesis of vertically aligned carbon nanofibers enabled a 3D array of elements which has the potential to perform dual-mode recordings of both neuroelectrical activity and neurotransmitter release in neuronal biological networks. The ultramicroelectrode VACNF array was used for stimulation and extracellular recording of spontaneous and evoked neuroelectrical activity in organotypic hippocampal slice cultures. This successful demonstration is based on the ability to control nanofiber synthesis in catalytic plasma enhanced chemical vapor deposition process. In this particular case, it involved gaining the understanding of catalyst nanoparticle-substrate, catalyst-plasma, plasma-substrate interactions. Compared to the synthesis of carbon nanomaterials on single solid uniform substrates, such Si or SiO₂, usually used to study fundamental aspects, the controlled growth of carbon nanofibers on thin metal films presents significant challenges. Overcoming these challenges required gaining understanding of the behavior of the involved materials in these extreme conditions essential for growth of desired quality and architectures of carbon nanomaterals.

Significance
One of the challenges in material science is controlling the structure and dimensions of materials. This challenge is exacerbated when the synthesis process involves integration of many materials that are required to create new functionality. The synthesis of VACNFs on metal electrodes allowed this successful demonstration of the functional interface to neuronal tissue culture. This demonstration highlights how control of nanoscale synthesis: (1) improved biocompatibility due to their covalent carbon structure; (2) provides excellent electrochemical properties and inertness; (3) reduces tissue injury response due to electrode size and geometry; (4) allows functionalization with specific proteins to improve neuronal interfacing; and (5) enables direct neurochemical sensing through amperiometry or cyclic voltametry. It also suggests that vertically aligned carbon nanofibers are poised to make a significant impact in the fields of electrophysiology and neuroscience by enabling multimode recordings (electrical and neurotransmitter) at high spatial resolution.

Publications
Z. Yu, T. E. McKnight, M. N. Ericson, An. V. Melechko, M. L .Simpson, and B. Morrison III, "Vertically Aligned Carbon Nanofiber Arrays Record Electrophysicological Signals from Hippocampal Slices," Nano Lett. 7, 2188-2195 (2007).

A portion of this research was conducted as a user project at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities (DOE).This study was supported in part by Grant 1R21NS052794 (NINDS) to B.M.III and in part by R01EB006316 (NIBIB), by the Material Sciences and Engineering Division Program of the DOE Office of Science (DE-AC05-00OR22725) with UT-Battelle, LLC, and through the Laboratory Directed Research and Development funding program of the Oak Ridge National Laboratory, which is managed for the U.S. Department of Energy by UT-Battelle, LLC. A.V.M. and M.L.S. acknowledge support from the Material Sciences and Engineering Division Program of the DOE Office of Science.

Images of VACNF arrays: (A) Light micrograph of a VACNF array before use. (B) SEM image of the entire VACNF array from (A) acquired after several electrophysiological recordings. (C) An SEM image of a VACNF electrode from the same array in (B). (D) Light micrograph of a hippocampal slice (22 DIV) on the VACNF array chip. Hippocampal slices were cultured separately and then transferred to precoated arrays. Inset: One-dimension current source density (CSD) was calculated and plotted for 20 channels (odd electrodes from 1 to 39), in response to a constant current, bipolar, biphasic stimulus of 100 µA applied to electrodes 11 and 29; the location of electrode 1 was set to the origin. The R and â denoted different current sinks in the CSD plot.