Electroencephalographic (EEG) measures subtle voltage fluctuations along the scalp resulting from ionic current flows within the neurons of the brain. EEG is widely used as a low cost, portable, and noninvasive means to capture not only cognitive and memory performance, but also brain disorders like epilepsy and stroke. Conventional EEG recording is obtained by placing individual thick and stiff electrodes on the scalp with conductive gel after skin abrasion which enhances electrode-skin contact. For many decades, EEG technology has suffered from limitations such as low spatial resolution, poor signal-to-noise ratio without proper signal amplification, time consuming and obstructive electrode connections, and short measurement time as gel dries out. Such limitations are partially due to the incompatibility between the soft, curvilinear, and deformable human skin and the hard, planar, and rigid electrodes and electronics. The ultrathin, high electronic performance, and transparency of atomically thick two-dimensional materials offer clear mechanical, electronic, and optical advantages over silicon in the neuroelectronics. This research proposes to explore the idea of replacing conventional rigid EEG electrodes by tattoo-like ultrathin, ultrasoft, dry electrodes and signal amplifiers fabricated from two-dimensional materials. Preliminary results indicate this idea is feasible and further research will prove the feasibility and future prospects for tattoo-like, long lasting, and high performance neuroelectronics to benefit society. In addition, the graduate student and post-doctoral researchers working on this research effort will gain advanced scientific and engineering skills needed to be technical leaders in industry, academia or government post-graduate careers. Moreover, undergraduate students from diverse backgrounds will be recruited to participate in the research effort to promote advanced science and engineering careers.
The objective of this proposal is to carry out a feasibility study that two-dimensional materials such as graphene and atomically thin molybdenum disulfide can be applied as the electrode and amplifier materials for noninvasive, long-term, high fidelity Electroencephalographic sensing. The major technical barrier towards two-dimensional materials based epidermal active EEG sensor lies in the device design, heterogeneous fabrication, and reliable bio-integration with the final goal of enhanced EEG sensing. An innovative active electrode architecture is proposed in which graphene is employed as both the sensing and gate electrodes, and molybdenum disulfide integrated with ultrathin polymer dielectrics and graphene source/drain as the on-site signal amplifier. Two research thrusts are proposed to accomplish the feasibility study: i) fabricating and validating graphene based passive epidermal EEG electrodes, and ii) integrating molybdenum disulfide vertically on top of the graphene electrode with ultrathin polymer dielectrics and graphene source/drain as a transistor amplifier for active EEG recording. The expected outcome is an affirmative decision on the feasibility of an integrated neuroelectronics that can be conformally laminated on human skin without conductive gel but still able to record long term, high fidelity EEG with orders of magnitude signal amplification. For the targeted gain of several hundreds the active electrode minimizes both the extrinsic noise and allows substantial reduction of the electrode arrays.
