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Carbon 3D microelectrode arrays for neuron and brain slice measurements

Joonas J. Heikkinen1*, Ville Rontu1, Emilia Peltola2, Tiina Kaarela3, 4, Niklas Wester5, Jari Koskinen5, Tomi Taira3, 4, Sari E. Lauri3, 6, Tomi T. Laurila2, Ville Jokinen1 and Sami Franssila1
  • 1 Aalto University, Department of Chemistry and Materials Science, Finland
  • 2 Aalto University, Department of Electrical Engineering and Automation, Finland
  • 3 Neuroscience Center, University of Helsinki, Finland
  • 4 University of Helsinki, Department of Veterinary Biosciences, Finland
  • 5 Aalto University, Department of Chemistry and Materials Science, Finland
  • 6 University of Helsinki, Department of Biosciences, Finland

The aim of the research is to study carbon material feasibility for neuron electrophysiological measurements. Carbon materials possess many advantageous and unique properties compared to conventional biocompatible materials used widely in neuronal arrays. Here we study fabrication techniques for applying patterned carbon thin films on top of complex microstructures with the goal of utilizing them in 3D microelectrode arrays. Nerve cells act as data highways in multicellular animals, and they have strict demands for their surrounding environment in order to grow successfully and to create neuronal networks. Studying neurons and neuronal networks in vitro has been challenging because of limitations of neurocompatible materials. Carbon has showed promising results not only with its neurocompatibility, but also with other properties like electrical conductivity, low toxicity, chemical inertness, and thin film transparency. Many of these properties can be tailored by adjusting the chemical bonds between carbon atoms. With these properties, carbon films allow neuronal cultivation, networking, and measurements (optical and electrical) in single dish without the need of transferring the culture, which is a high-risk process for cell population’s health and morphology. In our previous research, we have successfully fabricated microelectrode arrays (MEA) with carbon as the active material that is in contact with the cells (publication under peer-review). Many of the available MEAs have indium tin oxide (ITO) as the conductive material for electrodes, because it is transparent and allows optical inspection. However, usually the electrode tip, which is in contact with studied sample, is opaque material (like platinum black) to have a higher neurocompatibility or surface area compared to ITO. The carbon films we use in our research are highly sp2 bonded diamond like carbons (DLC), which possess good electrical conductivity and optical transparency. In our current research, we aim to increase the MEA electrode surface area by creating 3D microstructures (e.g. micropillars). 3D structures not only increase the surface area, but also changes the topography of the substrate where neurons attach. The effect of both properties are under study. We create the pillars from either silicon or copper, and passivate the surface with atomic layer deposition (ALD) film. The chosen materials are used for different application: the copper pillars are further roughened with wet etching creating nanopores to increase the surface area drastically while the silicon pillars are sharpened to act as needles. In the case of copper, the high surface area will have a high impact on electrode impedance and signal-to-noise ratio, which are crucial to develop MEAs with better sensitivity, whereas the sharp silicon needles are used to measure acute brain slices. Both pillar types are protected with two thin films: first with an ALD thin film, and then with sputtered tetrahedral amorphous carbon (ta-C) film which has the most important role of being in contact with the sample. The roles of different materials in our fabrication process is as follows: copper has high electrical conductivity, and it is possible to roughen it with easy methods, allowing us to increase the surface area. Silicon has good mechanical properties and it enables the fabrication of long, strong, and sharp needles that can be punctured through tissue. ALD is a conformal process that allows a pinhole free durable coating of even the most complex 3D structures, and with correct material selection, we can negate all possible toxicity the core materials may possess. Finally, the critical carbon layer is applied on top of all layers to provide a neurocompatible cell interface.

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Keywords: Carbon, high-surface area MEA, ALD, 3D MEA, Microfabrication techniques

Conference: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays, Reutlingen, Germany, 4 Jul - 6 Jul, 2018.

Presentation Type: Poster Presentation

Topic: Microelectrode Array Technology

Citation: Heikkinen JJ, Rontu V, Peltola E, Kaarela T, Wester N, Koskinen J, Taira T, Lauri SE, Laurila TT, Jokinen V and Franssila S (2019). Carbon 3D microelectrode arrays for neuron and brain slice measurements. Conference Abstract: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays. doi: 10.3389/conf.fncel.2018.38.00038

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Received: 18 Mar 2018; Published Online: 17 Jan 2019.

* Correspondence: Mr. Joonas J Heikkinen, Aalto University, Department of Chemistry and Materials Science, Otakaari, Uusimaa, 02150, Finland, joonas.heikkinen@aalto.fi