# CMOS-Based Implantable Multi-Ion Image Sensor for Mg2+ Measurement in the Brain

## TL;DR

A new implantable sensor was developed to selectively measure magnesium and calcium ions in the brain, enabling real-time imaging of their concentrations.

## Contribution

The sensor combines Mg2+ and Ca2+ sensitive membranes on a CMOS array to achieve selective multi-ion imaging in the brain.

## Key findings

- The sensor achieved Ca2+ sensitivity of 26.5 mV/dec and Mg2+ sensitivity of 19 mV/dec.
- Selective Mg2+ and Ca2+ measurements were validated with varying concentrations.
- Real-time imaging and quantification of Mg2+ and Ca2+ concentration changes were successfully performed.

## Abstract

An implantable multi-ion image sensor equipped with magnesium-(Mg2+) and calcium-(Ca2+)-sensitive membranes was successfully fabricated.

Selective Mg2+ measurement and multi-imaging of Mg2+ and Ca2+ were demonstrated.

An implantable multi-ion image sensor equipped with magnesium ion (Mg2+)-and calcium ion (Ca2+)-sensitive membranes was fabricated for the selective measurement of extracellular Mg2+ in the brain, and the sensor performance was evaluated. This sensor complements the low selectivity of the Mg2+-sensitive membrane for Ca2+ by depositing a Ca2+-sensitive membrane in addition to the Mg2+-sensitive membrane on a CMOS (Complementary Metal Oxide Semiconductor)-based potentiometric sensor array with 5.65 × 4.39 µm2 pitch, enabling selective measurement of Mg2+ and Ca2+. Characterization of the sensor confirmed a Ca2+ sensitivity of 26.5 mV/dec and Mg2+ sensitivity of 19 mV/dec. Based on validation experiments with varying concentrations of Mg2+ and Ca2+, selective Ca2+ and Mg2+ measurements were successfully achieved. Furthermore, real-time imaging of Mg2+ and Ca2+ and quantification of their concentration changes were performed. The developed sensor may be successfully applied for extracellular multi-ion imaging of Mg2+ and Ca2+ in the living brain.