A simple and convenient set-up of light addressable potentiometric sensors (LAPS) for chemical imaging using a commercially available projector as a light source

Light addressable potentiometric sensors (LAPS) are important semiconductor based label free sensing tools that are useful for visualizing the 2-D distribution of chemical species because of their light addressing capability at measurement sites. However, the expense and complexity of the LAPS light modulation set-up is highly inconvenient. To address this issue, we demonstrate a simple and convenient LAPS set-up that uses a commercially available projector as a programmable scanning light source. In the proposed set-up, an illuminated light spot used to excite electron-hole pairs in silicon was generated from a projector and an objective lens with the aid of commercially available computer software. Using a projector is an easy and flexible method of controlling the shape, size, movement, and the modulation frequency of the measurement spot in a user defined manner through a computer software interface. This approach avoids the complexity associated with using an X-Y stage or multiple light sources for scanning the LAPS surface. In addition, it reduces the setup time for the optical system and language programming for the control of digital micro-mirror device by using ARM-based processor. Using the set-up developed here, a minimum measurement spot of size 22x22 m2 was achieved. Additionally, the photoresponse-voltage characteristics, constant bias measurement and the pH sensitivity were successfully studied with this set-up. Finally, the pH imaging ability of this setup was successfully demonstrated.