Title: A miniaturized electrochemical biosensor for real-time in vivo potassium monitoring in the inner ear
Abstract:
This work presents a miniaturized potassium-selective biosensor with a solid-state reference electrode, designed for real-time, in vivo monitoring of potassium ion (K?) dynamics in the cochlea. Potassium plays a central role in auditory transduction and mechano-electrical signal conversion, and disruption of K? homeostasis is associated with inner-ear disorders. However, the lack of tools capable of continuous in vivo ionic monitoring has limited investigation of these processes.
The sensor consists of two miniaturized electrodes fabricated on 50 µm copper wire substrates. The working electrode was modified with a palladium layer to enhance surface roughness, followed by electrochemical polymerization of PEDOT/PSS as an ion-to-electron transducer and deposition of a potassium-selective membrane. The reference electrode was fabricated by silver coating, chlorination to form Ag/AgCl, and application of a reference membrane to ensure potential stability in varying ionic environments. The compact assembly enables implantation within the confined cochlear space.
Benchtop characterization demonstrated excellent electrochemical performance, including high repeatability, a near-Nernstian sensitivity of 52.8 mV/decade, a linear detection range from 10?? to 10?¹ mol/L, and stable operation over two months. Selectivity tests in artificial perilymph confirmed minimal interference from competing ions under physiologically relevant conditions.
In vivo validation was performed by implanting the sensor into the guinea pig cochlea. Local potassium elevation induced a rapid sensor response, confirming real-time monitoring capability. Furthermore, acoustic stimulation elicited measurable increases in perilymphatic potassium concentration, providing direct evidence of sound-induced ionic fluxes. This platform represents a significant advance toward real-time electrochemical monitoring of ionic dynamics in the inner ear.
