EAGER: Two-Dimensional Material-Based Epidermal Active Sensors for Brain Monitoring.

脑电图（EEG）测量由大脑神经元内的离子电流流动引起的沿头皮沿着的微妙电压波动。EEG作为一种低成本、便携式和非侵入性的手段被广泛使用，不仅可以捕获认知和记忆表现，还可以捕获癫痫和中风等大脑疾病。传统的EEG记录是通过在皮肤磨损后将单独的厚而硬的电极放置在具有导电凝胶的头皮上来获得的，这增强了电极-皮肤接触。几十年来，EEG技术一直受到诸如低空间分辨率、没有适当信号放大的低信噪比、耗时且阻碍性的电极连接以及随着凝胶变干的短测量时间的限制。这种限制部分是由于柔软、曲线和可变形的人类皮肤与坚硬、平面和刚性的电极和电子器件之间的不兼容性造成的。原子级厚度的二维材料的可折叠性、高电子性能和透明性在神经电子学中提供了明显的机械、电子和光学优势。本研究旨在探索用二维材料制成的纹身状超软干电极和信号放大器代替传统的刚性EEG电极的想法。初步结果表明，这一想法是可行的，进一步的研究将证明纹身般的，持久的，高性能的神经电子学造福社会的可行性和未来前景。此外，从事这项研究工作的研究生和博士后研究人员将获得成为工业、学术界或政府研究生职业技术领导者所需的先进科学和工程技能。此外，本项目还将招募不同背景的本科生参与研究，以促进先进的科学和工程事业。本项目的目标是开展一项可行性研究，即石墨烯和原子级薄二硫化钼等二维材料可用作无创、长期、高保真的脑电传感电极和放大器材料。基于二维材料的表皮有源脑电传感器的主要技术障碍在于器件设计、异质性制造和可靠的生物集成，最终目标是增强脑电传感。提出了一种创新的有源电极架构，其中石墨烯被用作传感电极和栅电极，二硫化钼与石墨烯聚合物半导体和石墨烯源极/漏极集成作为现场信号放大器。提出了两个研究重点来完成可行性研究：i）制造和验证基于石墨烯的被动表皮EEG电极，以及ii）将二硫化钼垂直地集成在石墨烯电极的顶部上，其中石墨烯聚合物电极和石墨烯源极/漏极作为用于主动EEG记录的晶体管放大器。预期结果是对集成神经电子器件的可行性的肯定决定，该集成神经电子器件可以在没有导电凝胶的情况下共形地层压在人类皮肤上，但仍然能够记录具有数量级信号放大的长期高保真EEG。对于几百的目标增益，有源电极最小化了外部噪声，并允许大幅减少电极阵列。

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.