Agenda

MSc ME Thesis Presentation

• Wednesday, 26 May 2021
• 15:00-16:00

Improving electrical characteristics of graphene neural electrode

Abstract

Neuroscientists use neural electrodes to explore the working mechanisms of the nervous system. Therefore, ideal electrodes should have a small size and the ability to record and stimulate at a single cell resolution with low noise. Materials used for fabrication should be flexible and stable for a long period in the biological media. However, conventional recording and stimulation techniques do not have sufficient spatiotemporal resolution for neuroscience research. Combining electrical and optical modalities into one device helps overcome the resolution limits and record more detailed information. For this application, transparent conductive materials are needed.

Graphene is a potential solution due to its advantageous combination of properties, such as high conductivity, transparency, and flexibility. However, important characteristics of recording and stimulation electrodes, such as the impedance and charge injection capacity of graphene electrodes, do not reach the levels of conventional materials. The electrical characteristics of graphene could be improved further with surface modification, chemical doping, or stacking. Each method has been shown to improve the conductivity of graphene, although some affect the transparency of the layer.

In this work, three methods were used to improve the electrical characteristics of multilayer graphene neural electrode without losing transparency or flexibility. These methods include growing a thicker layer of graphene, adding metal nanoparticles to the surface of the electrode, and nitric acid doping of graphene. For that purpose, graphene electrodes were fabricated on a silicon wafer. The electrical characteristics of these electrodes were assessed with electrochemical impedance spectroscopy, cyclic voltammetry and four point probe measurements. Furthermore, the optical transmittance was measured. The improvement methods were then tested on these electrodes, and the performance was evaluated.

Adding metal nanoparticles to the surface of the electrode showed the most promising results. With gold nanoparticles, the impedance at 1 kHz was lowered 82%, and charge storage capacity increased 529%. However, at the same time, 30% of the optical transmittance was lost. With lower nanoparticle density, 6% of transmittance was lost, and 7% of impedance gained. Nitric acid doping did not improve the impedance, but the charge storage capacity was increased up to 66%. Thicker layers of graphene displayed a lower sheet resistance. However, impedance or charge storage capacity were not improved.

Overview of MSc ME Thesis Presentation