Polystyrene Coating of Microfluidic Devices to Reduce Hydrophobic

Polystyrene Coating of Microfluidic Devices to Reduce Hydrophobic Absorption Nathan A. Unterman, RET Fellows 2010, Glenbrook North High School Nilesh Kavthekar, IMSA Fellow 2010 RET Mentor: Dr. David T. Eddington NSF-RET Program Motivation PDMS is an inexpensive andiseasily Polydimethylsiloxane (PDMS) an inexpensive and moldable material used formed material for biofluidic micro-fluidic This material is experiments. Its hydrophobicity allows preferred due its transparency and gas for the absorption of hormones, permeability. Its hydrophobicity and structure pheromones, and similar substances, allows for the absorption of enzymes, thus inhibiting use oftesting pheromones, and controlled other hydrophobic materials. sub-stances, thus preventing controlled use of these materials 1. Consequences Hypothesis 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. Results (Continued) Device Characteristics Device Design and Fabrication Images at Different Stages of Measurement Using lithography techniques, a Y -channel master was fabricated with SU 8 photoresist. (Same sample in all pictures) 1 mm Master on Silicon With this master, testing devices were made using PDMS. Pre-filled Dye Filled 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. Coating (PS) Normalized Change in Mean Intensity % Mean Intensity vs. Spin Speed PDMS test device 50 Conclusions 30 20 10 0 Spin Speed (RPM) 60 Change in Intensity vs. PS Concentration 50 40 30 20 10 1600 RPM 2800 RPM 4000 RPM • 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 0 Concentration of Polystyrene in Toluene Solution (%) There was no significant difference among experimental groups of different spin speeds with the same PS concentration. Normalized Change in Mean Intensity (%) 60 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. 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. 40 This normalized the change in intensity for each device to itself. Normalized Change in Mean Intensity (%) Different concentrations and spin rates were chosen based on work done by Hall et al 2. 60 Control 0. 05% Conc 0. 5% Conc The normalized mean intensity was calculated by. Side View Top View Change in Intensity vs. Spin Speed 50 40 30 20 0. 05% 0. 5% 5% 10 0 0 1000 2000 Spin Speed (Rotations Per Minute) 3000 4000 There were significant differences among experimental groups with different PS concentrations and the same spin speed. Acknowledgements NSF Grant EEC-0743068 Flushed Results Master with PDMS The process for spin coating PDMS microfluidic channels with polystyrene (PS) solution can be optimized to minimize the absorption of small hydrophobic molecules. • 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. References 1 Toepke, Michael, and David Beebe, Lab Chip, 2006, 6, pp. 1484 -1486. 2 Hall, David, Patrick Underhill, and John Torkelson, Polymer Dr. David J. Beebe, Dr. Eric Hagedorn for answering questions in their work. Dr. Andreas Linninger, Director of the RET-IMSA summer internship program. Engineering and Science, Volume 38 Number 12, pp 2039 -2045. August 2010