Temporary Tattoo pH Sensor with pH‐Responsive Hydrogel via Initiated Chemical Vapor Deposition

In the expanding field of physiological pH skin sensors, thin temporary tattoo-based devices have gained attention because ultra-conformal adhesion while providing excellent water vapor transmission. Here, a sensor tattoo made paper, screen-printed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate electrodes, and pH-responsive hydrogel deposited via initiated chemical deposition, is proposed. The easily transferred on skin, maintaining full functionality, shows conformability to topographical features epidermis. investigation morphology all layers within verifies control desired width thickness hydrogel, deposition shielded areas. layer exhibits reversible swelling 24.7 ± 0.3% 38 1%, with respect dry state, at 4 6, respectively. Impedance spectroscopy identifies phase shift 10 1000 Hz as an pH-related property sensor, which can be only ascribed presence hydrogel. sensors ability operated non-sophisticated read-out hardware software also demonstrated.