On-Chip pH Sensing with Gel Microbead Positioned by Optical Tweezers

1. PME MAPS On-Chip pH Sensing with Gel Microbead Positioned by Optical Tweezers Hisataka Maruyama1, Fumihito Arai2 and Toshio Fukuda1 1Department of Micro-Nano Systems Engineering, Nagoya University, Japan 2Department of Bioengineering and Robotics, Tohoku University, Japan Ref: μTAS2006 9633584 黃紫郁

2. PME MAPS Outline • Introduction • Gel-Tool Contained a pH Indicator • Experimental • Conclusions • References

3. PME MAPS Introduction • Environment measurement in a microchip is important to the on-chip experiment. • Conventionally, microsphere’s surface is modified by fluorescent reagents and indicators. • A local pH sensing method in a microchip using a functional gel-tool was developed. • Gel-tools are UV curing and adhere to the glass, but we can manipulate them by the optical tweezers. • Measure pH value locally from the color of gel-tool using calibrated color information in YCrCb color.

4. PME MAPS Gel-Tool Contained a pH Indicator • Gel-tool is made bysalting-outof ENT-3400 (polyethyleneglycol, PEG) which is hydrophilic resin. • Manipulate gel-tool by optical tweezers in a water because the relative refractive index of PEG (1.42) is higher than that of water (1.33). Fig.1 Optical tweezer Fig.2 Active pH sensing Fig.3 pH sensing gel-tool pattern

5. PME MAPS Gel-Tool Contained a pH Indicator 20 wt% KCl Gel-tool Fig.4 A schematic of generation of pH sensing gel-tool Fig.5 Photograph of salting-out gel-tool

6. PME MAPS Gel-Tool Contained a pH Indicator • Fabrication of gel-tools takes a few minutes and is shorter than that of the surface modification. • Gel-tools can be used as a carrier of cells because the tool adheres to cells by attaching. • Color information on gel-tools acquired by CCD camera is converted from RGB to YCrCb by eq(1). Y = 0.299R + 0.587G + 0.114B Cr = 0.5000R - 0.419G - 0.081B (1) Cb = -0.169R - 0.419G + 0.500B

7. PME MAPS Experimental • Applied Cr value for calculating pH value and pH value is calculated by eq.(2). pH = - 0.17 × Cr + 7.1 (2) pH = 0.13 × Cb + 8.0 (3) • Adhered gel-tools did not removed from glass even by 894 mm/s flow speed. Fig.6 Relation between pH and Cr Fig.7 Relation between pH and Cb

8. PME MAPS Experimental Fig.9 Change of pH value Fig.8 A schematic of active pH sensing (a) Start point (d) Return to start point (b) 100 μm moved (c) 200 μm moved Fig.10 Active pH sensing

9. PME MAPS Experimental (c) Fixation of gel-tool (a) Manipulation of gel -tool (b) Size adjustment (d) Gel-tool pattern (pH 6) (e) pH 7 (f) pH 9 Fig.10 On-chip pH sensing using pH sensing gel-tool

10. PME MAPS Conclusions • Proposed the pH sensing gel-tool for local environ-ment sensing in a microchip. • Demonstrate active pH sensing and arrangement of pH sensing gel-toolpattern. • Make the on-chip measurement easy. • Make great contributions for cell biology.

11. PME MAPS References [1] H. Maruyama, F. Arai, and T. Fukuda, Proc. of μTAS2006, pp. 1247-1249, 2006 [2] H. Maruyama, F. Arai, and T. Fukuda, Proc. of IEEE2007, pp. 806-811, 2007 [3] 林世傑, 光學嵌住之技術探討