Bio-photocapacitive Tactile Sensors as a Touch-to-Audio Braille Reader and Solar Capacitor

Human-machine interfaces in emerging smart-skin technologies tend to be focussed towards high-sensitivity tactile sensing primarily with visual/numerical feedback, and research on e-skin technologies for the visually impaired is sparse. Here we demonstrate a proof-of-concept six-pixel tactile sensor that converts touch stimuli based on Braille codes into an auditory output, and which could potentially be miniaturized as an ‘energy-autonomous on-skin e-Braille reader’ for the visually impaired. By applying the concepts of electric double layer capacitance and bio-photo capacitance, a self-powered sensor is constructed that generates electrical signals as large as 2 V by modulating a bio-electrochemical liquid bridge between electrodes of opposite wetting characteristics. The liquid bridge, composed of photosynthetic pigment-proteins with a redox electrolyte, both augments the sensory response and serves as a standalone solar-capacitor that can generate a photocurrent as high as 140 µA cm-2, and which displays a long discharge time of ~20 mins with just ~3 mins of photo charging.