Evaluating and benchmarking the EEG signal quality of high-density, dry MXene-based electrode arrays against gelled Ag/AgCl electrodes.

&#xD;To evaluate the signal quality of dry MXene-based electrode arrays (also termed "MXtrodes") for electroencephalographic (EEG) recordings where gelled Ag/AgCl electrodes are a standard.&#xD;&#xD;Approach: &#xD;We placed 4x4 MXtrode arrays and gelled Ag/AgCl electrodes bilaterally on the forehead. The scalp was cleaned with alcohol and rewetted with saline before application. We recorded from both electrode types simultaneously while participants performed a vigilance task. &#xD;&#xD;Main results: &#xD;The RMS amplitude of MXtrodes was slightly higher than that of Ag/AgCl electrodes (.24 to 1.94 uV). Most MXtrode pairs had slightly lower broadband spectral coherence (.05 to .1 dB) and Delta- and Theta-band timeseries correlation (.05 to .1 units) compared to the Ag/AgCl pair (p < .001), though the magnitude of correlation and coherence was high across both electrode types. The observed differences were likely due to less spatial averaging on the smaller MXtrodes compared to the broad gel base and larger contact surface of the Ag/AgCl electrodes. Beta-band timeseries correlation and spectral coherence was higher between neighboring MXtrodes in the array (.81 to .84 units) than between any other pair (.70 to .75 units). This result suggests that the close spacing of the nearest MXtrodes (3mm) more densely sampled high spatial-frequency topographies. ERPs were more similar between MXtrodes (ρ >= .95) than equally spaced Ag/AgCl electrodes (ρ <= .77, p < .001). Dry MXtrode impedance (x̄ = 5.15 KΩ cm2) was higher and more variable than gelled Ag/AgCl electrodes (x̄ = 1.21 KΩ cm2, p < .001).&#xD;&#xD;Significance: &#xD;Dry MXene-based electrodes record EEG at quality comparable to conventional gelled Ag/AgCl, while requiring minimal scalp preparation and no gel. MXtrodes can record independent signals at a spatial density four times higher than conventional electrodes, thus opening novel opportunities for research and clinical applications that could benefit from dry and higher density configurations.