Optoionic Sensing

The eye converts an optical signal to an ionic signal. This transduction is mimicked here using a photodiode in contact with ionic conductors, such as hydrogels. Photons generate electron‐hole pairs in the photodiode. The photodiode/hydrogel interface forms capacitive coupling so that movements of electrons and holes in the photodiode induce movements of ions in the hydrogels. The hydrogels can be readily made stretchable and biocompatible to mimic the function of nerves. When light is turned on and off, the voltage between the hydrogels responds within 10 ms, comparable to the response in the human eye. A photosensitive skin is demonstrated to generate a voltage in response to light but not to stretch. Furthermore, a photosensitive actuation is demonstrated to mimic the light‐triggered reflex, such as blinking of the eye and camouflage of the skin. Optoionic transduction has potential applications for wearable devices, implantable devices, and robotics. The physics of optoionic transduction in photodiode‐hydrogel hybrids is explored. Optoionic sensors are used for mimicking biological functions such as optoionic transduction, photosensitive skin, and light‐triggered actuation. Potential applications of optoionic sensing include wearable and implantable devices, as well as soft robots.