A miniaturized electrochemical biosensor for real-time in vivo potassium monitoring in the inner ear

: The ability to continuously monitor key biomarkers is crucial for advancing personalized medicine and enabling early disease intervention. Potassium ions (K + ) play a vital role in neural signaling, cardiac function, and sensory processing, particularly in the cochlea, where potassium imbalances are linked to disorders such as Ménière's disease. However, existing diagnostic methods cannot monitor K + in the inner ear in real time, limiting insight into the ionic mechanisms that underlie auditory function and related disorders. This study presents a miniaturized potassium-selective biosensor, incorporating a stable reference electrode, for continuous and real-time monitoring of K + dynamics in the inner ear. The sensor underwent extensive benchtop validation, demonstrating high sensitivity (⁓52.8 mV/dec), a broad linear range (10 -5 –10 -1 mol/L), a limit of detection of 10 -5 · 16 mol/L, strong selectivity coefficients (−2.62 for Na + , −4.10 for Mg 2+ , and −3.85 for Ca 2+ ), and excellent stability over two months. In-vivo experiments in a guinea pig model confirmed the biosensor’s capability to track dynamic potassium fluctuations under physiological conditions, such as responses to controlled potassium administration. These findings establish the feasibility of real-time K + monitoring in the cochlea, providing a valuable tool for studying auditory physiology, understanding potassium regulation in the inner ear, and advancing targeted diagnostics and treatments for inner ear disorders.