Microfluidic Networks made of Polydimethylsiloxane, Si and Au coated with Polyethylene Glycol for Patterning Proteins onto Surfaces

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 of 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 (XPS) 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 effective for the patterning with high positional accuracy and edge resolution on PDMS substrates than conventionally O2-plasma treated µFNs made from PDMS.