To study the function behind the molecular arrangement of single integrins in cell adhesion, we designed a hexagonally close-packed rigid template of cell-adhesive gold nanodots coated with cyclic RGDfK peptide by using block-copolymer micelle nanolithography. The diameter of the adhesive dots is < 8 nm, which allows the binding of one integrin per dot. These dots are positioned with high precision at 28, 58, 73, and 85 nm spacing at interfaces. A separation of > or = 73 nm between the adhesive dots results in limited cell attachment and spreading, and dramatically reduces the formation of focal adhesion and actin stress fibers. We attribute these cellular responses to restricted integrin clustering rather than insufficient number of ligand molecules in the cell-matrix interface since "micro-nanopatterned" substrates consisting of alternating fields with dense and no nanodots do support cell adhesion. We propose that the range between 58-73 nm is a universal length scale for integrin clustering and activation, since these properties are shared by a variety of cultured cells.

Protein resistance of oligoether self-assembled monolayers (SAMs) on gold and silver surfaces has been investigated systematically to elucidate structural factors that determine whether a SAM will be able to resist protein adsorption. Oligo(ethylene glycol) (OEG)-, oligo(propylene glycol)-, and oligo(trimethylene glycol)-terminated alkanethiols with different chain lengths and alkyl termination were synthesized as monolayer constituents. The packing density and chemical composition of the SAMs were examined by XPS spectroscopy; the terminal hydrophilicity was characterized by contact angle measurements. IRRAS spectroscopy gave information about the chain conformation of specific monolayers; the amount of adsorbed protein as compared to alkanethiol monolayers was determined by ellipsometry. We found several factors that in combination or by themselves suppress the protein resistance of oligoether monolayers. Monolayers with a hydrophobic interior, such as those containing oligo(propylene glycol), show no protein resistance. The lateral compression of oligo(ethylene glycol) monolayers on silver generates more highly ordered monolayers and may cause decreased protein resistance, but does not necessarily lead to an all-trans chain conformation of the OEG moieties. Water contact angles higher than 70 degrees on gold or 65 degrees on silver reduce full protein resistance. We conclude that both internal and terminal hydrophilicity favor the protein resistance of an oligoether monolayer. It is suggested that the penetration of water molecules in the interior of the SAM is a necessary prerequisite for protein resistance. We discuss and summarize the various factors which are critical for the functionality of "inert" organic films.

Self-assembled monolayers (SAMs) formed from thiophenol, 1,1′-biphenyl-4-thiol, 1,1′;4′,1′′-terphenyl-4-thiol, and anthracene-2-thiol on polycrystalline Au and Ag were characterized by X-ray photoelectron spectroscopy and angle-resolved near-edge X-ray absorption fine structure spectroscopy. With the exception of the poorly defined thiophenol film on Au, all thioaromatic molecules were found to form highly oriented and densely packed SAMs on both substrates. The molecular orientation and orientational order of the adsorbed thioaromatic molecules depends on the number of aromatic rings, the substrate, and the rigidity of the aromatic system. The molecules, which on average are slightly inclined with respect to the surface normal, show a less tilted orientation with increasing length of the aromatic chain, and as observed for aliphatic SAMs, they exhibit smaller tilt angles on Ag than on Au. However, the difference in the tilt angles for aromatic SAMs on Au and Ag is smaller than that observed in the aliphatic films. A comparison of the monolayers formed from p-terphenylthiol and anthracenethiol films suggests that a higher molecular rigidity has only a slight effect on the final molecular orientation within the respective SAMs.

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Chemically defined surface patterning has been achieved via irradiation with low‐energy electrons. Irradiation of nitro‐arene‐thiol monolayers leads to the reduction of the nitro groups to amino groups, which can then be further chemically modified. The Figure shows such a monolayer that was irradiated through a copper grid followed by acylation with trifluoroacetic acid anhydride.