Gel-tool Sensor Positioned by Optical Tweezers for Local pH Measurement in a Microchip

A local pH measurement method in a microchip using a functional gel-tool was developed. We used salting-out gel-tools impregnated with Bromothymol Blue (BTB), which is a pH indicator. The gel-tool is made of hydrophilic photo-crosslinkable resin. The primary constituent of this photo-crosslinkable resin is polyethyleneglycol. A solution mixed with photo-crosslinkable resin, BTB, high concentrations of an electrolytic solution are stirred, and gel beads impregnated with BTB are obtained. Gel-tools are cured by UV-ray and adhere to the glass plate, but we can manipulate them by the optical tweezers. We can measure pH value locally from the color of gel-tool using calibrated color information in YCrCb color space. We succeeded in measuring local pH value with the pH sensing gel-tool by manipulating and locating it at the desired point in the microchip.