Fully invisible and unperceivable skin electrodes for facial physiological monitoring free from appearance artifacts

Facial electrophysiological signals are crucial to assess human emotions, cognitive states, and diagnosis of neurological disorders. Soft and skin-conformable electrodes enabled long-term and comfortable signal monitoring. However, the appearance of the electrodes affects the wearer’s social interactions and self-identity, making daily usage difficult and leaving appearance artifacts in their psychological conditions. Here, we developed fully invisible and unperceivable on-skin electrodes free from appearance artifacts. Neither the wearer nor observers can detect the visual and tactile presence of the electrodes on the skin. The unperceivable property was confirmed with sensory experiments, and physical characterizations of the film on skin. Furthermore, our invisible electrodes did not affect the psychological conditions of the wearers, which confirms the feasibility of aesthetic artifact-free monitoring in daily lives. Finally, we demonstrated the functionality of our electrode with successful monitoring of various facial electrophysiological signals, including electrooculogram (EOG), electromyogram (EMG), and electroencephalogram (EEG). Our fully invisible electrodes provide a new direction in developing on-skin bioelectronics, seamlessly integrating health monitoring and human-computer interaction technologies into people's daily lives.