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

Microfluidic networks (mu FNs) are passive (self-filling) devices incorporating microchannels for guiding minute volumes of fluids over surfaces. mu FNs can be employed to localize the deposition of proteins from aqueous solutions onto substrates, for example. The walls of the channels must he hydrophilic for this purpose and should ideally resist the adsorption of proteins. We made mu FNs 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 of mu FN: 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 mu FNs 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 mu FNs are more effective for patterning, with high positional accuracy and edge resolution on PDMS substrates, than conventional O-2-plasma-treated mu FNs made from PDMS. Overall, our approach should help in making and using mu FNs made from different materials but having similar surface properties.