CMOS-Based Implantable Multi-Ion Image Sensor for Mg Measurement in the Brain.

An implantable multi-ion image sensor equipped with magnesium ion (Mg)-and calcium ion (Ca)-sensitive membranes was fabricated for the selective measurement of extracellular Mg in the brain, and the sensor performance was evaluated. This sensor complements the low selectivity of the Mg-sensitive membrane for Ca by depositing a Ca-sensitive membrane in addition to the Mg-sensitive membrane on a CMOS (Complementary Metal Oxide Semiconductor)-based potentiometric sensor array with 5.65 × 4.39 µm pitch, enabling selective measurement of Mg and Ca. Characterization of the sensor confirmed a Ca sensitivity of 26.5 mV/dec and Mg sensitivity of 19 mV/dec. Based on validation experiments with varying concentrations of Mg and Ca, selective Ca and Mg measurements were successfully achieved. Furthermore, real-time imaging of Mg and Ca and quantification of their concentration changes were performed. The developed sensor may be successfully applied for extracellular multi-ion imaging of Mg and Ca in the living brain.