On-chip pH measurement using functionalized gel-microbeads positioned by optical tweezers

Area of Science:

• Materials Science
• Analytical Chemistry
• Microfluidics

Background:

• Accurate local pH measurement is crucial for microfluidic systems.
• Existing methods can be complex or lack spatial resolution.
• Development of novel pH sensors for microscale applications is needed.

Purpose of the Study:

• To demonstrate local pH measurement in a microchip using a pH-sensing gel-microbead.
• To develop a method for creating and manipulating pH-sensitive microbeads.
• To validate the accuracy of the microbead-based pH sensing technique.

Main Methods:

• Fabrication of gel-microbeads from a poly(ethylene glycol)-based photo-crosslinkable resin.
• Functionalization of microbeads with bromothymol blue (BTB) pH indicator.
• Polymerization using UV illumination, manipulation with optical tweezers, and adhesion to a glass surface.
• Local pH measurement based on colorimetric analysis of the BTB-impregnated microbead in the YCrCb color space.

Main Results:

• Successfully created pH-sensing gel-microbeads.
• Demonstrated precise manipulation and positioning of microbeads within a microchip using optical tweezers.
• Achieved accurate local pH measurements by correlating microbead color changes to calibrated pH values.

Conclusions:

• The developed pH-sensing gel-microbead provides an effective tool for local pH measurement in microchips.
• This technique offers a promising approach for real-time monitoring in microfluidic devices.
• The combination of materials science and optical manipulation enables advanced microanalytical applications.