Ultra-conductive and transparent epidermal electrodes for simultaneous dual-mode assessment of brain function

In brain science, neural activity inevitably leads to the fluctuation of cerebral blood flow. Toward comprehensively understanding brain, it is necessary to develop an epidermal electrode that can concurrently monitor the brain's electrical activity and hemodynamic activity. Here, we report an ultra-conductive and transparent epidermal electrode for simultaneous dual-mode assessment of brain function. The electrode can accurately and imperceivably detect electrophysiological signals and functional near-infrared spectroscopy (fNIRS) optical signals. It is fabricated by two monolayer graphene with confined poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) in between, namely GPG. Its extremely low sheet resistance (20.8 Omega/sq, 3727 S/cm, 129 nm) and high transmittance (similar to 80%) can be attributed to the more ordered alignment and dense packing of PEDOT due to the nano-confinement effect of bi-layer graphene. The strong pi-pi interaction between graphene and PEDOT:PSS results in the decreased stacking distance between PEDOT. Leveraging the excellent electrical property and ultrathin nature, this epidermal electrode is able to achieve low skin-electrode impedance and monitor various electrophysiological signals accurately and stably, even if the participant is in motion. Beneficial from the appropriate transparency, it can simultaneously record very weak EEG electrical signals and fNIRS optical signals, enabling dual-model brain activity analysis with high temporal and spatial resolution.

Automated summary

In this study, an ultra-conductive and transparent epidermal electrode was developed for simultaneous monitoring of brain electrical activity and hemodynamic activity. The electrode exhibited extremely low sheet resistance and high transmittance, allowing accurate and stable detection of electrophysiological signals and functional near-infrared spectroscopy (fNIRS) optical signals. The electrode also enabled the recording of weak EEG electrical signals and fNIRS optical signals, providing high temporal and spatial resolution for dual-model brain activity analysis.