title: Simple photografting method to chemically modify and micropattern the surface of SU-8 photoresist.
abstract: SU-8 has gained widespread acceptance as a negative photoresist. It is also finding increasing use as a structural material in microanalytical devices. Consequently, methods to tailor the surface properties of SU-8 as well as to micropattern coatings on the surface of SU-8 are needed. The SU-8 photoresist consists of EPON SU-8 resin mixed with the photoacid generator triarylsulfonium hexafluoroantimonate. This photoacid generator can also serve as a photoinitiator generating free radicals when illuminated with UV light. Under the appropriate conditions, sufficient triarylsulfonium hexafluoroantimonate remains within cured SU-8 to act as a source of free radicals and initiate UV-mediated grafting of polymers onto the surface of the SU-8. UV-mediated grafting was used to coat SU-8 surfaces with poly(acrylic acid) and other water-soluble monomers. The SU-8 surface was chemically micropatterned by placing a mask between the UV light and SU-8. The X-Y spatial resolution of micropatterned poly(acrylic acid) on the SU-8 surface was 2 mum. Three applications of these chemically modified SU-8 surfaces were demonstrated. In the first, poly(ethylene glycol) was used to protect the SU-8 from interactions with proteins, yielding a surface resistant to biofouling. In the second demonstration, the SU-8 surface was micropatterned with a cell-resistant layer to guide cellular attachment and growth. In the final application, SU-8 micropallets were encoded with polymer lines. The bar codes were read by either absorbance or fluorescence measurements. Thus, UV-mediated graft polymerization is an efficient and effective method to micropattern coatings onto the surface of SU-8.
authors.affiliation: Integrated Nanosystems Research Facility, Department of Electrical Engineering and Computer Science, University of California, Irvine, California 92697, USA.
authors.forename: Yuli
authors.initials: Y
authors.lastname: Wang
authors.forename: Mark
authors.initials: M
authors.lastname: Bachman
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Sims
authors.forename: G P
authors.initials: GP
authors.lastname: Li
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Allbritton
mesh_terms: D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured; D018625:Microscopy, Atomic Force; D010777:Photochemistry; D051381:Rats; D012666:Semiconductors; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D014466:Ultraviolet Rays