Porous Microneedle-Based Potentiometric Sensor for Intradermal Electrolyte Monitoring (Supporting Information)

A porous microneedle (PMN)-based potentiometric ion sensor for transdermal monitoring of electrolytes in the interstitial fluid was developed. The carbon coating with an ion-selective membrane was formed on half of the needle tip as the working electrode, while the Ag/AgCl reference electrode was mounted on the PMN chip. This design of a single needle-type configuration allows lower invasive transdermal sensing than the conventional system with multiple needle electrodes. The fabricated potentiometric sensor showed the near-Nernstian responses to Na⁺ concentration in the excised pig skin, demonstrating the applicability for monitoring intradermal electrolytes.