Characterization of SU-8 for electrokinetic microfluidic applications

Area of Science:

• Materials Science
• Chemical Engineering
• Microfluidics

Background:

• SU-8 is a common negative photoresist used in microfabrication.
• Microfluidic devices rely on controlled fluid flow, often driven by electrokinetic phenomena.
• Understanding SU-8 microchannel properties is crucial for optimizing microfluidic applications.

Purpose of the Study:

• To characterize SU-8 microchannels for electrokinetic microfluidic applications.
• To investigate the electroosmotic (EO) mobility in SU-8 microchannels as a function of pH and ionic strength.
• To assess the stability and repeatability of SU-8 microchannels for long-term use.

Main Methods:

• Current monitoring method to determine electroosmotic mobility.
• Utilizing lithographically defined SU-8 microparticles to measure zeta-potential.
• Testing microchannels across a range of pH and ionic strengths.

Main Results:

• SU-8 microchannels demonstrated extensive electroosmotic flow (EOF) comparable to glass microchannels for pH >= 4.
• The highest EO mobility (5.8 x 10^-4 cm^2 V^-1 s^-1) was observed at pH >= 7 in 10 mM phosphate buffer.
• A reversed EOF towards the anode was observed at pH <= 3, reaching 1.8 x 10^-4 cm^2 V^-1 s^-1 at pH 2.
• Zeta-potential measurements on SU-8 microparticles showed similar pH dependence.
• SU-8 microchannels exhibited repeatable performance and no aging effects over time.

Conclusions:

• SU-8 microchannels are a viable and stable material for electrokinetic microfluidic applications.
• The electroosmotic flow in SU-8 microchannels can be effectively controlled by adjusting the pH.
• The consistent performance and lack of aging make SU-8 microchannels suitable for demanding, long-term microfluidic operations.