title: On-chip pH measurement using functionalized gel-microbeads positioned by optical tweezers.
abstract: This paper demonstrates local pH measurement in a microchip using a pH-sensing gel-microbead. To achieve this, the gel-microbead made of a hydrophilic photo-crosslinkable resin was functionalized with the pH indicator bromothymol blue (BTB). The primary constituent of this photo-crosslinkable resin is poly(ethylene glycol). Gel-microbeads impregnated with BTB were obtained by stirring the mixture solution, which was composed of the resin, BTB, and an electrolyte solution. The gel-microbead is polymerized by UV illumination. The polymerized gel-microbead can be manipulated by optical tweezers and made to adhere to a glass surface. The local pH was measured from the color of the gel-microbead impregnated with BTB by calibrated color information in the YCrCb color space. We succeeded in measuring the local pH value using the pH-sensing gel-microbead by manipulating and positioning it at the desired point in the microchip.
authors.affiliation: Department of Micro-Nano Systems Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. maruyama@robo.mein.nagoya-u.ac.jp
authors.forename: Hisataka
authors.initials: H
authors.lastname: Maruyama
authors.forename: Fumihito
authors.initials: F
authors.lastname: Arai
authors.forename: Toshio
authors.initials: T
authors.lastname: Fukuda
mesh_terms: D001979:Bromthymol Blue / Q000737:chemistry; D005782:Gels; D006863:Hydrogen-Ion Concentration; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation* / Q000379:methods*; D008863:Microspheres; D052898:Optical Tweezers; D011092:Polyethylene Glycols / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013499:Surface Properties; D013997:Time Factors
chemical_list: D005782:Gels; D011092:Polyethylene Glycols; D001979:Bromthymol Blue