1 Surface hydrophilisation of SU-8 for microfluidic applications Ferdinand Walther a , Tanja Drobek a , Alexander M. Gigler a , Marc Hennemeyer a , Michael Kaiser b , Helmut Herberg b , Tetsuji Shimitsu c , Gregor E. Morfill c , and Robert W. Stark a,* a Center for NanoScience (CeNS) and Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstraße 41, 80333 Munich, Germany b Munich University of Applied Sciences, FB-06, Lothstraße 34, 80335 Munich, Germany c Max-Planck-Institut für Extraterrestrische Physik, 85748 Garching, Germany * phone: +49 89 2180 4329, fax: +49 89 2180 4334 e-mail stark@lrz.uni-muenchen.de Abstract: For the fabrication of microfluidic devices based on SU-8, the wetting properties of the polymer surface need to be adjusted. We investigated the effects of wet chemical and plasma processes with respect to wetting properties, surface roughness, and surface chemistry. Wet chemical etching with ceric ammonium nitrate (CAN) rendered the SU-8 surface hydrophilic. CAN etching, however, also led to the accumulation of cerium species on the surface, which may interfere with biochemical reactions in the device. Surface activation was also achieved by treatment with an argon plasma torch at atmospheric pressure. This process resulted in an enhanced wettability, which could be attributed to an increase of C=O and COO groups at the surface. Treatment of SU-8 by oxygen plasma led to a stable hydrophilisation and induced an increased surface roughness. Directly after plasma processing, antimony species were accumulated that could be removed with a simple cleaning step. The cleaned SU-8 surface was coated with a protein resistant graft copolymer (PLL-g-PEG). The PLL-g- PEG coated surface maintained its hydrophilic properties through several wetting-drying cycles.