The light-addressable potentiometric sensor (LAPS) is an ion-sensitive biosensor which can detect activity images of a group of cells . The biggest disadvantage of the conventional LAPS structure is the low spatial resolution. The conventional LAPS composes three flat layers: silicon, silicon dioxide, and silicon nitride from bottom to top. The spatial resolution issue is generated by minority carrier diffusion in the silicon. The new design patterns the silicon layer to form discrete pillars of LAPS on a flat conductive and transparent layer. The pillars block the carrier diffusion, leading to a better spatial resolution decided by the size of pillars.
The goal of this project is to build a single cell activity detection system composed of a microfluidic system, a LAPS, and a signal detection system. The minority carrier diffusion model is used to investigate the spatial resolution limitation for conventional LAPS, and it is improved to fit experimental results. The diffusion model under the short-base assumption is being researched to predict the photocurrent value of LAPS pillars. Fabrication processing is being discussed, and the experiment system is being built at the same time.