Low molecular weight poly(ethylene glycol) silanes (PEG silanes) have been grafted onto the surface of silicon wafers in a one-step procedure yielding ultrathin and stable PEG monolayers. Structural investigation by means of X-ray reflectivity provided data on the thickness of the PEG monolayers. The layer thickness varied between 10 and 17 Å depending on the PEG silane concentration applied. These results have been confirmed by X-ray photoelectron spectroscopy measurements. Atomic force microscopy data indicate very smooth and homogeneous coverages with roughnesses of less than 3 Å. The PEG layers are hydrophilic as determined with advancing water contact angles between 36 and 39°.

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 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.

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In this article, we describe the synthesis of polypeptides onto the whole specific surface of poly(ethylene terephthalate) particle track membranes. In this case, initial functionalization is necessary. It had been done by an optimized surface oxidation in accordance with the method of Marchant-Brynaert, J.; Deldime, M.; Dupont, I.; Dewez, J.-L.; Schneider, Y.-J. (J Colloid Interface Sci 1995, 173, 236). Subsequent activation with carbodiimide and reaction with multifunctional amines yielded an aminated surface. The synthesis of peptides was carried out by two different means: first, by the coupling of single amino acids analogous to the method of Merrifield, and second, by coupling of presynthesized polypeptides consisting of 18 helix-forming amino acids. Analytical characterization was carried out by fluorescence spectroscopy by using the label Fluram and confirmed by the results of X-ray photoelectron (XP) spectroscopy. Only the stepwise synthesis led to a dense surface functionalization with peptides, whereas the coupling of fragments resulted in lower yields of coupling.

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