Contamination of PDMS microchannels by lithographic molds

Area of Science:

• Materials Science
• Microfluidics
• Surface Chemistry

Background:

• Polydimethylsiloxane (PDMS) is a common material for microfluidic devices.
• SU-8 is a widely used negative photoresist for microfabrication.
• Contamination during microfabrication can impact device performance.

Purpose of the Study:

• To investigate the potential contamination of PDMS by the SU-8 soft lithography process.
• To identify the source and nature of any contamination.
• To understand the impact of contamination on PDMS microfluidic device performance, specifically electroosmotic flow.

Main Methods:

• Synchrotron X-ray fluorescence (SXRF) was used to detect elemental composition.
• Rutherford backscattering spectrometry (RBS) was employed for surface analysis.
• Characterization of PDMS surface properties and electroosmotic flow (EOF) was performed.

Main Results:

• The SU-8 soft lithography process was found to contaminate PDMS surfaces.
• Residues of an antimony-containing photoinitiator were identified on the PDMS surface.
• This contamination led to uncontrolled intensification of the surface potential.
• Variable electroosmotic flow was observed in the contaminated PDMS microfluidic devices.

Conclusions:

• The SU-8 soft lithography process introduces contaminants to PDMS.
• Antimony-containing photoinitiator residues are responsible for surface potential changes.
• This contamination compromises the reliability of PDMS microfluidic devices by causing electroosmotic flow variability.