Effect of fluorescent dye on zeta potential in electroosomotic flow

• Main Author: Wong, Jonathan Tze Hou
• Other Authors: Lam Yee Cheong
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/60155
• Institution: Nanyang Technological University

Fluorescent dyes are widely used in the area of microfluidic studies. However, few studies have been conducted to determine whether these fluorescent dyes affect the zeta potential and the electroosomotic flow (EOF) of the fluids used in experiments. This project aims to investigate the effect of fluorescent dyes on zeta potential in EOF, which is induced by an electric field. Sodium bicarbonate (NaHCO3) is used as the buffer solution in this project as it is stable in all the substrates used; providing a good baseline on which the behaviors of the fluorescent dyes can be analysed. The dyes used are disodium fluorescein (Fl), Rhodamine B (RhB) and Rhodamine 6G (Rh6G). Current monitoring method was utilized to measure the time taken for the fluid to be transported through straight microchannels made from three different materials, namely glass, polydimethylsiloxane (PDMS) and polyurethane (PU). Linear curve fitting is performed to determine the time taken for the fluid to be transported through the channel from the current-time plot. Subsequently, the zeta potential can be determined. Finally, statistical tests are conducted to examine the effect of fluorescent dyes on zeta potential of various microchannels. From the experimental result, it can be observed that Fl dye which is a negatively charged dye increases the zeta potential for flow in PU microchannels. This phenomenon is potentially useful and can be exploited to increase the flow velocity in PU microchannels. RhB which is a neutral dye has no effect on the zeta potential of a fluid when it is added to the buffer solution. Rh6G which is a positive dye does not support any EOF in glass, PDMS and PU microchannels. This effect is potentially useful to suppress EOF in certain applications. For example, during the measurement of ion mobility, EOF is typically not desirable and should be suppressed.