Needle-Type $5\ \mu\mathrm{m}$ Pixel Pitch pH-Image Sensor and Imaging of Proton Emissions in the Cerebral Cortex

We developed a
$256\times 32$
-pixel needle-type pH image sensor to visualize ion behavior at the cellular level under in vivo conditions. This sensor has a pixel configuration that can be fabricated via a modified CMOS process technology, and it achieved a pixel size of
$5.65\times 4.39\ \mu \mathrm{m}^{2}$
. The proposed image sensor is the highest-definition implantable ion image sensor among other conventional image sensors. For in vivo implantation, the sensor's shape was modified to a needle structure of
$9.88\times 1.10\ \text{mm}^{2}$
with a thickness of
$100\ \mu \mathrm{m}$
. From the measurement results, we verified that the sensor exhibits a high spatiotemporal resolution with a pH sensitivity, pH resolution, and temporal resolution of 56.4 mV/pH, 0.015 pH, and 14.1 fps, respectively. In addition, we detected pH changes in the brain of the experimented mouse during neural hyperexcitation, and successfully reproduced the measured data as 2-D images in real time.