Device Design and Fabrication

1. Polystyrene Coating of Microfluidic Devices to Reduce Hydrophobic Absorption Nathan A. Unterman, RET Fellows 2010, Glenbrook North High School NileshKavthekar, IMSA Fellow 2010 RET Mentor: Dr. David T. Eddington NSF-RET Program Motivation PDMS is an inexpensive and easily formed material for biofluidic experiments. Its hydrophobicity allows for the absorption of hormones, pheromones, and similar substances, thus inhibiting controlled use of hydrophobic materials. Motivation Polydimethylsiloxane(PDMS) is an inexpensive and moldable material used for micro-fluidic experiments. This material is preferred due its transparency and gas permeability. Its hydrophobicityand structure allows for the absorption of enzymes, pheromones, and other hydrophobic testing sub-stances, thus preventing controlled use of these materials1. Consequences Inexpensive and simple thin film coating of PDMS is necessary to create a barrier to prevent absorption of hydrophobic molecules in device channels for biological and other applications. Hypothesis The process for spin coating PDMS microfluidic channels with polystyrene (PS) solution can be optimized to minimize the absorption of small hydrophobic molecules. • Results (Continued) • Potential errors included: • The formation of bubbles in channels that would cause variation of mean intensity. • Variation of coatings in devices, including cracking and deformations in the imaged areas possibly due to handling. • Non-uniform coating due to evaporation of solvent before completion of spin cycle. • Conclusions • The 0.05% and 0.5% concentrations of PS did not minimize hydrophobic absorption when compared to the control devices. • Spin rate does not significantly affect hydrophobic absorption. • The least penetrable concentration was the 5% PS in toluene. • The 5% solution created coatings that made noticeable changes in the channel geometry of the devices. • Future Work • Testing coating capabilities with different channel geometries. • Optimize with more precision in the 0.5% to 5% range. • Consider other materials than PS that will coat PDMS. • Utilize other coating techniques such as vapor deposition, flushing/evaporation, atomizer spray, etc. • Testing humidity, temperature, and pressure variations when coating the PS. Device Characteristics Images at Different Stages of Measurement (Same sample in all pictures) Pre-filled Dye Filled Flushed Results The normalized mean intensity was calculated by . This normalized the change in intensity for each device to itself. There was no significant difference among experimental groups of different spin speeds with the same PS concentration. There were significant differences among experimental groups with different PS concentrations and the same spin speed. • Device Design and Fabrication • Using lithography techniques, a Y-channel master was fabricated with SU8 photoresist. • Master on Silicon • With this master, testing devices were made using PDMS. • Master with PDMS • PDMS test device • Inlet and outlet holes were bored in the cured PDMS. Employing • plasma treatment, the • PDMS was attached to a • glass slide. • Polystyrene (PS) was chosen as the channel coating material. • Different concentrations and spin rates were chosen based on work done by Hall et al2. • Intensities were measured as follows: • Pre-fill • Rhodamine B dye fill (soak for one hour) • De-ionized water flush (flush, one hour soak, flush). • The intensity measurements were normalized and plotted. 1 mm 1 mm 1 mm Coating (PS) PDMS Side View Top View References 1Toepke, Michael, and David Beebe, Lab Chip, 2006, 6, pp. 1484-1486. 2Hall, David, Patrick Underhill, and John Torkelson, Polymer Engineering and Science, Volume 38 Number 12, pp 2039-2045. Acknowledgements Dr. David J. Beebe, Dr. Eric Hagedorn for answering questions in their work. Dr. Andreas Linninger, Director of the RET-IMSA summer internship program. August 2010 NSF Grant EEC-0743068