AVS 51st International Symposium
    Plasma Science and Technology Friday Sessions
       Session PS+BI-FrM

Paper PS+BI-FrM7
Novel Plasma Modification of Microfluidic Devices for Control of Electroosmotic Flow

Friday, November 19, 2004, 10:20 am, Room 213C

Session: Plasmas in Bioscience
Presenter: E.R. Fisher, Colorado State University
Authors: E.R. Fisher, Colorado State University
C.S. Henry, Colorado State University
M.A. Boggs, Colorado State University
I.T. Martin, Colorado State University
Y. Liu, Colorado State University
C.D. Garcia, Colorado State University
Correspondent: Click to Email
Microchip capillary electrophoresis (CE) is a widely used separation technique that combines the efficiency of CE with the portability of a microchip. Poly(dimethylsiloxane), PDMS, is often used to fabricate these microfluidic devices because it is inexpensive, has good optical properties, and the fabrication of complicated channel geometries is straightforward. Separations that occur in PDMS are based on the electroosmotic flow (EOF) within the channel. This, in turn, depends on the density of negatively charged groups on the PDMS surface, which is sensitive to both the pH of the solution and the sealing method (air plasma treatment, methanol). An additional issue is the hydrophobicity of the PDMS, which leads to the adsorption of hydrophobic analytes such as proteins during separations. The goal of this work is to treat PDMS with both non-depositing and depositing plasmas and fully characterize the altered surface chemistry, and its effects on EOF and separations. We have used depositing plasma systems to alter preassembled PDMS microchips, yielding novel surface chemistries. Plasma treated PDMS has been characterized using various surface analysis techniques, including contact angle measurements and XPS. XPS mapping shows that fluorocarbon (FC) plasma treatments permeate the channel via the reservoirs, not through the porous PDMS. Consequently, the reservoirs and channel are selectively coated with a FC film, resulting in reduced EOF. Conversely, plasma deposition of a hydrophilic hydrocarbon film yielded an increase in EOF. Selected coatings are stable over multiple EOF measurements. Separations conducted with treated chips evaluate biomolecule fouling characteristics. This is the first report of the modification of these devices via depositing plasma systems; plasma treatment of PDMS microchips has essentially been limited to O@sub 2@ or air plasmas to oxidize or cure the PDMS, for the enhancement of adhesion of PDMS to PDMS/glass.