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

脑电图（EEG）测量沿头皮的细微电压波动，这是由大脑神经元内的离子电流引起的。脑电图作为一种低成本、便携、无创的手段被广泛使用，不仅可以捕捉认知和记忆表现，还可以捕捉癫痫和中风等脑部疾病。传统的脑电图记录是通过在皮肤磨损后用导电凝胶在头皮上放置单独的厚而硬的电极来获得的，这样可以增强电极与皮肤的接触。几十年来，脑电图技术一直存在空间分辨率低、信号放大效果差、电极连接耗时和阻塞、凝胶干燥导致测量时间短等局限性。这种限制部分是由于柔软的、曲线的、可变形的人体皮肤与坚硬的、平面的、刚性的电极和电子设备之间的不兼容性。原子厚度二维材料的超薄、高电子性能和透明度，在神经电子学方面比硅具有明显的机械、电子和光学优势。本研究提出了用纹身样的超薄、超软、干电极和由二维材料制成的信号放大器取代传统刚性脑电图电极的想法。初步结果表明，这一想法是可行的，进一步的研究将证明这种类似纹身的、持久的、高性能的神经电子设备的可行性和未来前景，以造福社会。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在工业、学术界或政府研究生职业生涯中成为技术领导者所需的先进科学和工程技能。此外，将招募来自不同背景的本科生参与研究工作，以促进先进的科学和工程事业。本课题旨在开展石墨烯和原子级薄二硫化钼等二维材料作为无创、长期、高保真脑电图传感电极和放大材料的可行性研究。基于二维材料的表皮主动脑电传感器的主要技术障碍在于器件设计、异质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结构，其中石墨烯作为传感电极和栅极，二硫化钼与超薄聚合物电介质和石墨烯源/漏相结合作为现场信号放大器。为了完成可行性研究，提出了两个研究重点：1)制造和验证基于石墨烯的被动表皮脑电图电极；2)在石墨烯电极上垂直集成二硫化钼与超薄聚合物电介质和石墨烯源/漏极作为有源脑电图记录的晶体管放大器。预期的结果是对集成神经电子学可行性的肯定决定，这种集成神经电子学可以在没有导电凝胶的情况下在人体皮肤上共形层压，但仍然能够记录具有数量级信号放大的长期高保真脑电图。对于几百的目标增益，有源电极使外部噪声最小化，并允许大幅度减少电极阵列。

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.