Nitrogen‐Doped Multilayer Graphene Microtubes for High‐Density Recording of Occipital EEG Signals

Abstract

The epidermal electroencephalography (EEG) electrodes connect the human brain with the external world and generate braincomputer interfaces (BCIs). [2] BCIs have advanced considerably in the fields of medical treatment, communication, and control. [3] Currently, steady-state visually evoked potential (SSVEP)-based BCI is attracting increasing attention owing to its fast and efficient information transfer rate (ITR). [4] The frequency of an EEG signal evoked by certain stimuli can be analyzed to determine the stimuli that the subject is observing and to obtain the information the user wishes to convey. [5] Human beings exhibit remarkable response only in the limited frequency range of 5-30 Hz. According to literature, the ITR is increased by over 27% when the frequency resolution is optimized from 0.2 to 0.1 Hz. [5a] If the frequency recognition is improved from the epidermal EEG electrodes, more available SSVEP stimulation frequencies can be provided for the target coding design in the online system, and the ITR can be improved substantially.The occipital EEG sensor can be developed as a key component of BCIs with highly effective functions because the occipital region is a brain region with strong, spontaneous, and visually evoked EEG signals. The high-density distribution of small-size electrodes with low scalp-contact impedance (R scalp ) and high signal-to-noise ratio (SNR) can improve the frequency resolution of feedback signals and accurately record EEG with more information compared with conventional electrodes. [6] Graphene derivatives, such as graphene oxide (GO), doped graphene, and multilayer graphene are 2D carbon nanomaterials. [7] Various graphene-based materials have been used in the field of bioelectrical signal collection as a substitute for precious metals owing to their advantageous properties of good conductivity, large specific surface area, high electron mobility, and high biocompatibility. [8] Nevertheless, the exceptionally regular arrangement of the inert carbon plane and its zero bandgap structure limit the further development of graphene. Among the numerous modification approaches, heteroatom doping is a significant technique for regulating the electronic structure and appending additional active sites onto the inert reticular graphene plane. Nitrogen (N)-doping is an effective method to improve biological affinity and enrich active sites. [9] Graphene microelectrodes exhibit potential in recording high-density electroencephalography (EEG) signals from various brain regions. In this study, microtubes composed of nitrogen-doped graphene (NG) nanosheets are synthesized by chemical vapor deposition to record high-density EEG signals. The N-content of the NG samples ranges from 1.35 to 2.22 at.%. One of the fabricated microtubes with an N-content of 2.22% exhibits low scalp-contact resistance and high signal-to-noise ratio (SNR) of EEG signals. The NGmicrotube has the advantages of high water-retention, scalp affinity, water absorption, salt interception, and low resistance; these adva...