Enhancing the stability of Ion-Selective Electrodes for simulated inner ear ion monitoring

<p dir="ltr">The inner ear, containing the hearing (cochlea) and balance (vestibular) system is a highly sensitive signal detection system, which has evolved over dysregulation of potassium (K⁺) and calcium (Ca²⁺) ion levels in the inner ear has been implicated in a variety of auditory and balance disorders. Accurate, long-term monitoring of these ions is critical for advancing both diagnosis and treatment. This study introduces a novel solid-contact layer based on a PEDOT:PSS/Polydopamine(PDA)/PEDOT:PSS for efficient ion-to-electron transduction of K⁺ and Ca2+-ion-selective electrodes. Low potential drift is one of the key performance criteria in the design of all-solid-state ion selective electrodes (SC-ISEs). The polymer films were fabricated using electro-polymerization and self-polymerization on a platinum disk electrode, followed by drop-casting of the ion-selective membranes. The K⁺ and Ca²⁺-ISEs exhibited Nernstian slopes of 51.27 ± 1.42 mV/decade and 24.84 ± 1.34 mV/decade, respectively. The synergistic properties of PEDOT:PSS and PDA enhanced redox capacitance compared to bare PEDOT:PSS, yielding superior potential stability, with drift rates of 0.360 ± 0.01 mV/h (K⁺-ISE) and 0.610 ± 0.05 mV/h (Ca²⁺-ISE) over 20 hours. Performance was validated in artificial perilymph and endolymph, mimicking inner ear fluids. The sensors effectively detected ion fluctuations under simulated pathological conditions, highlighting their potential for real-time inner ear monitoring and future biomedical use.</p>