Articles you may be interested inUnderstanding the nonfouling mechanism of surfaces through molecular simulations of sugar-based selfassembled monolayers Nanostructural and electrical properties of functionally terminated self-assembled monolayers on silicon surfacesSulfur-based molecules containing biotin and hydroxyl groups have been used to create a wide variety of self-assembled monolayers on gold surfaces. Surface plasmon resonance has been used to study in situ the binding of streptavidin to these monolayers from solution. The self-assembled monolayers allow a high degree of control over the surface properties. The choice of an appropriate biotin-containing molecule, with a spacer segment, and the dilution of this molecule within the monolayer by hydroxythiols, allows optimization of the binding properties of the monolayer-nonspecific interactions between streptavidin and the surface are below detection limits, and specific binding between the streptavidin and biotin groups can be maximized. EXPERIMENTAL SECTION MaterialsPrisms and slides used were either LaSFN9, or BK7 Schott glass.Biotin was purchased from Sigma. Solvents were of Chromasolv quality from Riedel de Haen. All chemicals were used as received. Water was purified using an ion exchange purification train (MilliQ system, Millipore). Synthesis of thiols, disulfides, and sulfidesThe sulfur-based compounds used are shown in Fig. 1. Compounds 1 and 2 were synthesized following Ref. 18. Compound 3 is a byproduct of the synthesis and can be 7012

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The assemblage of protein multilayers induced by molecular recognition, as seen, for example, in the immune cascade, has been mimicked by using streptavidin as a docking matrix. For these experiments, this protein matrix was organized on liposomes, monolayers at the air-water interface, and self-assembled layers on gold, all three containing biotin lipids. The docking of streptavidin to biotin at liposomal surfaces was confirmed by circular dichroism. Mixed double and triple layers of streptavidin, concanavalin A, antibody Fab fragments, and hormones are prepared at the air-water interface and on gold surfaces and were characterized by fluorescence microscopy and plasmon spectroscopy. With the use of biotin analogs that have lower binding constants it has been possible to achieve multiple formation and competitive replacement of the oriented protein assemblages.

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Neutron reflection and surface plasmon optical experiments have been performed to evaluate structural data of the interfacial binding reaction between the protein streptavidin and a solid-supported lipid monolayer partly functionalized by biotin moieties. Since both experimental techniques operate in a total internal reflection geometry at a substrate/solution interface, identical sample architectures allow for a direct comparison between the results obtained with these two recently developed methods. It is found that a monomolecular layer of dipalmitoyllecithin doped with 5 mol% of a biotinylated-phosphatidylethanolamine shows a thickness of d1 approximately (3.4 +/- 0.5) nm. Binding of streptavidin to the biotin groups results in an overall layer thickness of d = (5.9 + 0.5) nm that demonstrates the formation of a well-ordered protein monolayer with the (biotin+spacer) units of the functionalized lipids being fully embedded into the binding pocket of the proteins. It is demonstrated by model calculations that a more detailed picture of the internal structure of this supramolecular assembly can only be obtained if one uses deuterated lipid molecules, thus generating a high contrast between individual layers.