Advances in Reference Membranes for Potentiometric Sensing Applications

Accurate potentiometric sensing critically depends on the stability and reproducibility of the reference electrode potential. Conventional liquid-filled Ag/AgCl or calomel electrodes, though well-established, are poorly compatible with miniaturized, portable, or long-term in situ sensing devices due to electrolyte leakage, junction potential instability, and maintenance requirements. Recent advances in solid-state and membrane-based reference electrodes offer a promising alternative by eliminating the liquid junction while maintaining stable and well-defined potential. This review summarizes the advancements in polymer-based and composite reference membranes, focusing on material strategies, stabilization mechanisms, and integration approaches. Emphasis is placed on ionic-liquid-doped membranes, conducting polymers, lipophilic salts, and carbon nanomaterials as functional components enhancing interfacial stability and charge transfer. The performances of various architectures, solid-contact, liquid-junction-free, and quasi-reference systems, are compared in terms of potential drift, matrix resistance, biocompatibility, and manufacturability. Furthermore, recent developments in printed, microfluidic, and wearable potentiometric platforms demonstrate how reference membrane innovations enable reliable operation in compact, low-cost, and flexible analytical systems. The review outlines current trends, challenges, and future directions toward universal, miniaturized, and leak-free reference electrodes suitable for innovative sensing technologies.