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Fabrication of new transparent MEAs made from pure PEDOT:PSS and their optical/electrical properties for neurons' activity assessment in the frame of Alzheimer disease case study

Anna Susloparova1, 2*, Yannick Coffinier1, 2, Fabien Alibart1, 2, 3, Vincent Thomy1, 2, Steve Arscott1, 2, Emiliano Pallecchi1, 2, Séverine Begard2, Sophie Halliez2, Morvane Colin2 and Luc Buée2
  • 1 Université de Lille, Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520 - IEMN, France
  • 2 Université de Lille, Univ. Lille, Inserm, CHU-Lille, Jean-Pierre Aubert research centre (JPARC, UMR- S 1172), France
  • 3 Université de Sherbrooke, Unité mixte internationale - Laboratoire Nanotechnologies & Nanosystèmes (UMI-LN2), Canada

Abstract In this study, the fabrication of the microelectrode array (MEA) devices with electrodes made of pure PEDOT:PSS is presented. Their electrical characteristics were assessed prior further biological application. The influence of the electrode size as well as the thickness of the PEDOT:PSS electrodes on the impedance was demonstrated. Long-time experiments confirmed stability of the MEA devices. This work shows that microelectrodes from pure PEDOT:PSS are very promising as an alternative to metal based MEAs. Introduction Microelectrode arrays (MEAs) are the most common tool used to record and/or stimulate the neural electrical activity from cell cultures and brain slices. Typically metals (such as gold and platinum) are used for the fabrication of the electrodes. However, manufacturing electrodes with size comparable to single neurons, results in an increase in their electrical impedance, thus limiting the use of metals. Although that earlier reports showed that the deposition of carbon nanotubes and conducting polymers as an additional coating on metallic microelectrodes improved their impedance compared to bare metal electrodes (Koutsouras et al., 2017) (Ganji et al., 2017) (Sessolo et al., 2013) (Gerwig et al., 2012), it is still a great challenge to surmount. In addition, metal-based electrodes are not transparent at all and do not allow dual characterization of neuron network via simultaneous optical (high resolution fluorescence imaging)/electrical read-out. Thus, the goal of our study is to fabricate transparent small-size electrodes with low impedance. Here, we present, for the first time, the fabrication of electrodes made of pure poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS), their optical/electrical characterizations for measuring neural activity. Material and methods The MEA devices were fabricated on glass substrates. The dimension of the device (49 mm × 49 mm × 1 mm), the configuration of the contact pads and the placement of the internal reference electrode on the left side are compatible with the layout of the MEA-System (MEA2100-System, Multi Channel Systems). The contact pads and tracks were patterned from gold, while 59 round electrodes and one big internal reference electrode from pure PEDOT:PSS. As insulating material, we used parylene C (2µm thick). To investigate the influence of the electrode size on the impedance, the electrodes with two different sizes, 10 µm and 30 µm in diameter, were fabricated on the same device. Moreover, to show the influence of the thickness of the PEDOT:PSS layer on the electrical impedance, different thicknesses were also considered. Results and discussion The fabricated MEA devices were electrical characterized using impedance spectroscopy. The measurements were performed in presence of phosphate buffer saline (PBS) solution by applying a 100 mV sine wave with frequency varied from 20 Hz to 1 MHz. It was demonstrated that electrodes with bigger diameter have lower impedance value, due to expected lower interfacial capacitance. For example, the impedance value of an electrode with thickness of PEDOT:PSS of 150 nm and a diameter of 10 µm is around 360 kΩ, while the impedance value of an electrode with a diameter of 30 µm is around 130 kΩ, respectively (Figure 1a). A significant impedance decrease for the thickest PEDOT:PSS electrodes was observed. For example, the impedance value at 1 kHz, the typical frequency used for neuronal signals recording, for an electrode with a diameter of 30 µm for the PEDOT:PSS layer of 150 nm is around 130 kΩ, while the impedance value for the PEDOT:PSS layer of 300 nm is around 40 kΩ, respectively (Figure 1b). Moreover, long-time experiments confirmed the stability and robustness of our MEA devices. It is important that electrodes are stable and maintain the same impedance values over time to obtain consistent data. Indeed, impedances of our MEA devices were measured during several weeks (3 ̶ 4 measurements per week) in PBS solution. Between two measurements, the MEA devices were kept in deionized water, in order to avoid any increase of impedance. The insignificant change in impedance (the impedance values (mean ± standard deviation) at 1 kHz were 410.11 kΩ ± 32.01 kΩ for an electrode with a diameter of 10 µm and 51.09 kΩ ± 3.02 kΩ for an electrode with a diameter of 30 µm, respectively) after measurements during 3 weeks indicated the stability of our devices and their ability for long-time experiments without influence on the results (Figure 2). Small variation in impedance from electrode to electrode on the same device were demonstrated as well (the impedance values (mean ± standard deviation) at 1 kHz were 433.15 kΩ ± 58.49 kΩ for 20 electrodes with a diameter of 10 µm and 46.55 kΩ ± 3.69 kΩ for 20 electrodes with a diameter of 30 µm). The measured transmittance of the PEDOT:PSS films demonstrated their transparency. Then, we also attempted neural activity measurement via electrical and optical read-out. Conclusion In conclusion, we presented the MEA devices with electrodes from pure PEDOT:PSS. The devices were electrically characterized and it was shown that the obtained impedance values are comparable to the impedance values of the most use commercial MEA devices with TiN electrodes (the impedance of TiN electrodes ranges between 30 ̶ 50 kΩ for the electrodes of 30 µm in diameter and 250 ̶ 400 kΩ for the electrodes of 10 µm in diameter). The novelty of the presented MEA devices is that our electrodes are transparent. Then, electrical and optical measurements performed on neurons were attempted.

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Acknowledgements

We acknowledge the Labex DistalZ project (Development of Innovative Strategies for a Transdisciplinary approach to ALZheimer’s disease), the University of Lille and CNRS for financial support. This work was also partly supported by the French RENATECH network (French national nanofabrication platform).

References

Ganji, M., Kaestner, E., Hermiz, J., Rogers, N., Tanaka, A., Cleary, D., Lee, S.H., Snider, J., Halgren, M., Cosgrove, G.R., Carter, B.S., Barba, D., Uguz, I., Malliaras, G.G., Cash, S.S., Gilja, V., Halgren, E., Dayeh, S.A., 2017. Development and Translation of PEDOT : PSS Microelectrodes for Intraoperative Monitoring 1700232, 1–11. doi:10.1002/adfm.201700232
Gerwig, R., Fuchsberger, K., Schroeppel, B., Link, G.S., Heusel, G., Kraushaar, U., Schuhmann, W., Stett, A., Stelzle, M., 2012. PEDOT – CNT composite microelectrodes for recording and electrostimulation applications : fabrication , morphology , and electrical properties 5, 1–11. doi:10.3389/fneng.2012.00008
Koutsouras, D.A., Hama, A., Pas, J., Gkoupidenis, P., Supérieure, E.N., 2017. PEDOT : PSS microelectrode arrays for hippocampal cell culture electrophysiological recordings 7, 259–265. doi:10.1557/mrc.2017.34
Sessolo, M., Khodagholy, D., Rivnay, J., Maddalena, F., Gleyzes, M., Steidl, E., Buisson, B., Malliaras, G.G., 2013. Easy-to-Fabricate Conducting Polymer Microelectrode Arrays 2135–2139. doi:10.1002/adma.201204322

Keywords: MEA, PEDOT:PSS, transparent electrode, impedance, Long-term

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: Susloparova A, Coffinier Y, Alibart F, Thomy V, Arscott S, Pallecchi E, Begard S, Halliez S, Colin M and Buée L (2019). Fabrication of new transparent MEAs made from pure PEDOT:PSS and their optical/electrical properties for neurons' activity assessment in the frame of Alzheimer disease case study. Conference Abstract: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays. doi: 10.3389/conf.fncel.2018.38.00035

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Received: 16 Mar 2018; Published Online: 17 Jan 2019.

* Correspondence: Dr. Anna Susloparova, Université de Lille, Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520 - IEMN, Lille, France, anna.susloparova@iemn.univ-lille1.fr