| Abstract
| - Microfluidic networks (μFNs) are passive (self-filling) devices incorporating microchannels for guidingminute volumes of fluids over surfaces. μFNs can be employed to localize the deposition of proteins fromaqueous solutions onto substrates, for example. The walls of the channels must be hydrophilic for thispurpose and should ideally resist the adsorption of proteins. We made μFNs using poly(dimethylsiloxane)(PDMS), Si/SiO2, and Au-covered Si and derivatized them with poly(ethylene glycol)s (PEGs) to fulfill bothof these requirements. The grafting of the PEG molecules is optimized for either type of μFN: the networksfrom PDMS and silicon are derivatized using PEG-silanes and the Au-coated networks are derivatizedwith a thiolated PEG. Additionally, the zones of the Au-covered Si μFNs separating the channels areselectively covered with a hydrophobic thiol using microcontact printing. X-ray photoelectron spectroscopyand contact angle measurements indicate that all grafted layers have the expected chemical compositionand are thin, homogeneous, and hydrophilic where desired. Finally, using fluorescently labeled antibodieswe show that these μFNs are more effective for patterning, with high positional accuracy and edge resolutionon PDMS substrates, than conventional O2-plasma-treated μFNs made from PDMS. Overall, our approachshould help in making and using μFNs made from different materials but having similar surface properties.
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