Observing pH changes in electro-osmotic flow in a micro-channel

• Main Author: Fung, Kiu Yan
• Other Authors: Lam Yee Cheong
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/68311
• Institution: Nanyang Technological University

Electroosmotic flow (EOF) is the transport of fluid under applied electric field across a microfluidic channel. Undesirable pH change in the fluid occurs due to the electrolysis of water at the electrodes. The objective of this project is to investigate on the pH change during electroosmotic flow (EOF) in a micro-channel. Disodium fluorescein dye which is a pH-sensitive probe, was added to unbuffered (potassium chloride, KCl) and buffered (sodium bicarbonate, NaHCO3) solutions. An epi-fluorescent microscope was employed to observe the flow of the solution in the micro-channel under EOF. An electron multiplying charge coupled device (EMCCD) camera is used to record fluorescent images in the micro-channel during EOF. Various experimental parameters were varied to investigate their effect on the pH change during EOF, namely the locations of observation along the micro-channel, type of dyes (fluorescent & Rh6G), type of electrolytes (buffered and unbuffered solution) and volume of electrolyte in the reservoirs. The spatial and temporal changes for the fluorescent intensity during EOF were analysed. The experimental results show that electrolysis of water at the electrodes in the reservoirs is the cause for the formation of a peak fluorescent intensity which originates at the exit of the micro-channel, near the cathode. Joule heating in the micro-channel also causes significant temperature variation which affects the fluorescent intensity of the dyes.