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 incorpora ting microchannels for guiding minute volumes of fluids over surfaces. mu F Ns can be employed to localize the deposition of proteins from aqueous solu tions onto substrates, for example. The walls of tile channels must he hydr ophilic for this purpose and should ideally resist the adsorption of protei ns. We made mu FNs using poly(dimethylsiloxane) (PDMS), Si/SiO2, and Au-cov ered 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: tile networks from PDMS and silicon are derivatiz ed using PEG-silanes and the Au-coated networks are derivatized with a thio lated PEG. Additionally, the zones of the Au-covered Si mu FNs separating t ile channels are selectively covered with a hydrophobic thiol using microco ntact printing. X-ray photoelectron spectroscopy and contact angle measurem ents indicate that all grafted layers have the expected chemical compositio n and are thin, homogeneous, and hydrophilic where desired. Finally, using fluorescently labeled antibodies we show that these mu FNs are more effecti ve for patterning, with high positional accuracy and edge resolution on PDM S substrates, than conventional O-2-plasma-treated mu FNs made from PDMS. O verall, our approach should help in making and using mu FNs made from diffe rent materials but having similar surface properties.