Microfluidic networks made of poly(dimethylsiloxane), Si, and Au coated with polyethylene glycol for patterning proteins onto surfaces

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Microfluidic networks (μFNs) are passive (self-filling) devices incorporating microchannels for guiding minute volumes of fluids over surfaces. μFNs can be employed to localize the deposition of proteins from aqueous solutions onto substrates, for example. The walls of the channels must be hydrophilic for this purpose 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 both of these requirements. The grafting of the PEG molecules is optimized for either type μFN: the networks from PDMS and silicon are derivatized using PEG-silanes and the Au-coated networks are derivatized with a thiolated PEG. Additionally, the zones of the Au-covered Si μFNs separating the channels are selectively covered with a hydrophobic thiol using microcontact printing. X-ray photoelectron spectroscopy and contact angle measurements indicate that all grafted layers have the expected chemical composition and are thin, homogeneous, and hydrophilic where desired. Finally, using fluorescently labeled antibodies we show that these μFNs are more effective for patterning, with high positional accuracy and edge resolution on PDMS substrates, than conventional O2-plasma-treated μFNs made from PDMS. Overall, our approach should help in making and using μFNs made from different materials but having similar surface properties.