Graphene-based microfabricated platform technologies for multimodal neural interfaces

Abstract

Technologies that are employed to record and modulate neural activities are rapidly advancing. This advancement could bring breakthroughs in our understanding of brain function and enable scientists to diagnose and treat neural diseases and disorders. Combining multiple modalities to study brain function, from single cells to large networks, offers insights beyond those offered by a single-modal platform using only electrical recording or modulation. However, the tools to enable such studies are yet to be developed and still face significant challenges that remain to be resolved to allow multimodal measurement without any of the modalities interfering with one another.
Recently, graphene-based neural electrodes have shown great promise for combining optical and electrical modalities in a single device. However, their complicated fabrication process, high impedance, and low charge storage capacity currently limit their application. In addition, their compatibility with the magnetic domain remains to be proven.
In this thesis, graphene-based microfabricated platform technology is introduced for the manufacturing of multimodal neural interfaces. First, a transfer-free fabrication process is demonstrated to fabricate multilayer graphene electrodes on parylene-C substrates. Full electrochemical characterization is performed on these graphene electrodes and a comparison is made with conventional metal-based electrodes. Second, a nanoparticle printing technique, spark ablation, is leveraged to print platinumnanoparticles on the graphene electrode surface to enhance its electrochemical characteristics even further without compromising its optical transparency. Third, a hybrid encapsulation stack is fabricated and validated that includes parylene C and PDMS with thin ceramic interlayers to be employed as the encapsulation layer on the final neural-interface device.
The multimodal platform technology introduced in this thesis can be used as a tool inmultimodal measurements combining electrical, optical, and magnetic domains. The fabricated multilayer graphene electrodes showthe highest charge storage capacity among all CVD graphene electrodes to date. They show no optical and MRI artifacts. Moreover, the fabricated electrodes and encapsulation stack both reveal the high optical transparency required for optical measurements. Local platinum nanoparticle printing can improve the impedance, charge storage, and charge injection capacity by 4.5, 15, and 3.6 times, respectively.