Self-assembled Monolayer Substrate Research Articles

Immobilization of Peptides with Distinct Biological Activities onto Stem Cell Culture Substrates Using Orthogonal Chemistries

We have used the orthogonal carbodiimide condensation and copper-catalyzed azide-alkyne "click" cycloaddition (CuAAC) reactions to prepare self-assembled monolayers that present distinct peptides to stem cells in a bioinert background. The approach involved first forming mixed SAMs with three components: (i) an azide-terminated hexaethylene glycol alkanethiolate (HS-EG6-N3), (ii) a carboxylate-terminated hexaethylene glycol alkanethiolate (HS-EG6-COOH), and (iii) a triethylene glycol alkanethiolate (HS-EG3). An acetylene-bearing peptide and an amine-terminated peptide were then immobilized to these substrates using a "click" CuAAC reaction and a carbodiimide condensation reaction, respectively. Polarization-modulated infrared reflectance-absorbance spectroscopic analysis demonstrated formation of well-ordered, close-packed self-assembled monolayers (SAMs), chemoselective conjugation of amine-terminated peptides to surface carboxylate groups, and subsequent conjugation of acetylene-terminated peptides to the azide groups on SAMs. Varying the mole fraction of HS-EG6-N3, HS-EG6-COOH, and HS-EG3 during SAM formation allowed for control over the densities of each peptide on the substrate. Substrates presenting varying surface densities of RGESP (a nonfunctional peptide), RGDSP (a cell adhesion peptide), or TYRSRKY (a heparin/heparan sulfate-binding peptide) were then used to characterize the relationship between peptide surface density and human mesenchymal stem cell (hMSC) adhesion. Results demonstrate that RGESP does not influence RGDSP-mediated adhesion of hMSCs, which indicates that a second peptide with distinct bioactivity can be immobilized alongside RGDSP to characterize the influence of two peptides on hMSC behavior. Our results also demonstrate that RGDSP and TYRSRKY act synergistically to promote hMSC adhesion in the absence of serum. Interestingly, heparin sequestered by TYRSRKY inhibits cell adhesion on substrates presenting RGDSP = 0.1% and > or = 0.1% TYRSRKY or RGDSP = 1% and > or = 0.5% TYRSRKY. Taken together, these results indicate that two peptides can be controllably presented to stem cells on the same otherwise bioinert SAM substrate, and that multiple, distinct extracellular moieties act in concert to regulate hMSC adhesion.

Effects of tip geometry on interfacial contact forces

Experimental techniques that utilize atomic force microscopy are routinely used to examine tribological properties of tip–sample interactions. While analysis of data obtained with these methods provides values for macroscale properties, such as interfacial shear strength, understanding nanoscale properties, such as contact radius, requires an atomic-scale approach. Molecular dynamics simulations provide the ability to numerically analyze the nanoscale origins of a wide-range of material and tribological properties. In this paper, the sliding contact between a self-assembled monolayer (SAM) and two countersurfaces (a nominally flat, amorphous carbon surface and a nearly spherical fullerene tip) is compared. By examining contact forces between the tip and monolayer atoms, large differences in monolayer behavior that occur due to tip geometry can be elucidated. The structure factor reveals that the fullerene tip creates a more disordered monolayer than the amorphous counterface. Friction forces were also studied using the atomic-level contact forces, which show that the depth at which the fullerene tip affects the SAMs substrate is much deeper than the amorphous counterface. The distribution of contact forces that contribute to friction and load were studied and show a difference in behavior between the two countersurfaces. Finally, while there are a large number of atoms that have a non-zero load during sliding, a smaller subset of 32 atoms carries ∼96% of the load. Using this subset of atoms to compute contact radius reveals a greater agreement with the continuum mechanics models than using all atoms with a non-zero load. This paper highlights how computer simulations can yield insight into tribological interactions at the atomic scale.

A Supramolecular Network as Sacrificial Mask for the Generation of a Nanopatterned Binary Self‐Assembled Monolayer

Supramolecular self-assembly on surfaces has become a straightforward and flexible route for the generation of extended nanoscale structures, with porous networks serving as templates to control the arrangement of metal clusters or guest molecules. The latter includes thiols, which are particularly interesting as they afford an enormous flexibility in surface functionalization. Recently we have shown that a supramolecular network of perylene-tetracarboxylic di-imide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (melamine), which involves a triple hydrogen bonding motif (Figure 1a), can be used as a template for an all-solution-based generation of periodic patterns of thiol self-assembled monolayer (SAM) nanoislands on Au(111) (Figure 1b). These network–SAM hybrid structures can be further processed in an electrochemical environment, as demonstrated by underpotential deposition (UPD) of Cu, where one atomic layer of the metal intercalates at the SAM–substrate interface but not between network and substrate (Figure 1c). While formation and modification of network–SAMhybrids demonstrate the robustness of the PTCDI–melamine network, it is nevertheless of limited stability as evidenced by its displacement upon prolonged exposure to a thiol solution. Since the formation of hybrid structures is a kinetically controlled process, substitution of the network by thiols different to those in the network pores is a potential way to produce binary SAMs (Figure 1d) over extended areas with resolution and pattern definition unmatched by other approaches such as random insertion,mixing, or lithographic techniques.However, the feasibility of this approach critically depends on the properties of the thiol islands filling the nanopores. One evident issue is their stability against replacement by the second thiol species that depends on a number of mutually dependent factors such as molecule–substrate bond strength, intermolecular interactions,

In-Situ Negatively Nanopatterning Alkylated Silicon (111) Surface by Conductive Atomic Force Microscope

Negative nanopatterns have been successfully in-situ fabricated on tetradecylated Si(111) surface via bias-dependent atomic force microscopy (AFM) lithography without wet chemical etching procedures. Alkyl self-assembled monolayers (SAMs) made of 1-tetradecene coupled to hydride-terminated Si(111) surface through robust silicon-carbon covalent bonds was employed as a resist layer. The SAM covered silicon substrate was then treated with dilute hydrofluoride, and subsequent used in AFM lithography. By varying the applied bias and pulse duration, both negative and positive patterns can be fabricated via this approach, such as Si pores and oxide dots. The results indicated that the HF-ethanol treatment of SAMs plays an important role in forming negative nanopatterns in situ. In particular, the Si pore structure formation was related to the reaction between F-buried inside the SAM and silicon substrate under the effect of tip electric field. A possible mechanism of Si pore formation based on the reaction of F- ions with silicon induced by the tip bias was proposed.

Using "click" chemistry to prepare SAM substrates to study stem cell adhesion.

We have used a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reaction to prepare self-assembled monolayers (SAMs) presenting the cell adhesion peptide Arg-Gly-Asp-Ser-Pro (RGDSP) in a bioinert background. The surface preparation approach involved first forming mixed SAMs with an azide-terminated hexa(ethylene glycol) alkanethiolate (HS---EG6---N3) and a tri(ethylene glycol) alkanethiolate (HS---EG3), then using the CuAAC reaction to immobilize an alkyne-terminated peptide. The mixed SAMs were classified as bioinert, as SAMs comprising 10 mol % HS---EG6---N3 and 90 mol % HS---EG3 showed minimal nonspecific protein adsorption in solutions of 1 mg/mL lysozyme or 10% fetal bovine serum. The reaction between an acetylene-terminated peptide and an azide-terminated SAM proceeded rapidly and quantitatively in the presence of a Cu(I)-TBTA complex, displaying pseudo-first-order kinetics with a rate constant of approximately 0.2 min(-1). Varying the ratio of HS---EG6---N3 to HS---EG3 during SAM formation allowed for control over the density of azide and, in turn, the density of RGDSP on the substrates. These substrates were therefore used to study the detailed relationship between RGDSP surface density and human mesenchymal stem cell (hMSC) adhesion, spreading, and focal adhesion complex formation, without interference from nonspecifically adsorbed serum proteins. Results indicate that an RGDSP intermolecular spacing of 36 nm or less (>or=0.01 mol % on the surface) is sufficient for hMSC adhesion and a spacing of 11 nm or less (>or=0.05 mol % on the surface) is sufficient for cell spreading and focal adhesion complex formation. In total, our results demonstrate that CuAAC is a suitable mechanism for conjugating peptides to otherwise bioinert SAMs and the resulting SAMs can be used to study the dependence of peptide density on stem cell behavior.

Self-Assembled Monolayers of Metal-Assembling Dendron Thiolate Formed from Dendrimers with a Disulfide Core

Novel phenylazomethine dendrimers with a disulfide core (SS-DPA G1-4) were synthesized in nearly quantitative yields. Although the disulfide core is shielded by the rigid dendron shell, direct formation of the self-assembled monolayers of metal-assembling dendron thiolate was observed by XPS and electrochemical reduction of the self-assembled monolayer substrates. The dendrimers showed a similar metal-assembling manner with other derivatives. The metal assembly to the self-assembled monolayers of metal-assembling dendron thiolate was also confirmed.

Covalent Nanoparticle Assembly onto Random Copolymer Films

We present a novel class of nanoparticle-decorated surfaces: amine-functionalized silica nanoparticles covalently attached to poly(styrene-random-acrylic acid) films and carboxylic acid-terminated self-assembled monolayers (SAMs). The dependence of the particle attachment kinetics on the concentration of particles in solution and acrylic acid moieties in the polymer backbone was investigated and was compared to the observed kinetics with SAM substrates. The kinetics on the polymer films included three distinct stages, which were governed by the acrylic acid concentration-dependent morphological changes of the films under the reaction conditions. The first stage was an induction period with little change in the particle coverage with time, followed by a rapid rise in the coverage, and finally a plateau. The maximum coverage achieved for the polymer films, 70%, was nearly twice that of the SAM substrates, which followed diffusion-limited coverage kinetics prior to reaching saturation. This enhanced coverage is attributed to the swelling of the acrylic acid groups at the film surface in the reaction solvent, which increases the surface area and roughness of the substrate. This approach is a reproducible way of preparing nanoparticle-decorated, chemically robust surfaces with controlled coverages and have potential applications for controlling surface wettability, optical properties, and cellular adhesion.

Langmuir Adsorption Study of the Interaction of CdSe/ZnS Quantum Dots with Model Substrates: Influence of Substrate Surface Chemistry and pH

We investigate the utility of Langmuir adsorption measurements for characterizing nanoparticle-substrate interactions. Spherical CdSe/ZnS core-shell nanoparticles were chosen as representative particles because of their widespread use in biological labeling measurements and their relatively monodisperse dimensions. In particular, the quantum dots were functionalized with 11-mercaptoundecanoic acid, and we utilized an amine-terminated self-assembled monolayer (SAM) as a model substrate. SAMs with different end-groups (-CH(3) and -COOH) were also considered to contrast with the adsorption behavior on the amine-terminated SAM substrates. We followed the kinetics of nanoparticle adsorption on the aminosilane layer by quartz crystal microgravimetry (QCM) over a range of particle concentrations and determined the corresponding Langmuir adsorption isotherms. Analysis of both equilibrium adsorption and kinetic adsorption data allowed us to determine a consistent value of the Langmuir adsorption equilibrium constant for the amine-terminated SAM at room temperature (K(L) approximately 2.7 (micromol/L)(-1)), providing a useful characterization of the nanoparticle-substrate interaction. The effect of varying solution pH on Langmuir adsorption was also investigated in order to gain insight into the role of electrostatic interactions on nanoparticle adsorption. The equilibrium extent of adsorption was found to be maximum at about pH 7. These changes of nanoparticle adsorption were further quantified and validated by X-ray photoelectron spectroscopy (XPS) and confocal fluorescence microscopy measurements. We conclude that Langmuir adsorption measurements provide a promising approach for quantifying nanoparticle-substrate interactions.

Nano/Micro Patterning of Inorganic Thin Films

Abstract The present review is focused on the site-selective deposition of inorganic thin films on self-assembled monolayer (SAM) templates. SAMs were used to modify the substrate surface with chemical functional groups. The patterned SAM substrate was prepared by exposing the SAM substrate to UV light through photomasks for photocleavage. The patterned SAM was used as the templates for deposition of ceramic thin films in aqueous solutions. The preparation and characterization methods of SAMs, and the preparation of the patterned SAM templates are explained. Solution chemistry for the deposition of ceramic oxides and the physics and chemistry of interfaces are described. Experimental examples are given to explain how these aspects influence the formation of films and their properties. Various examples of site-selective deposition of ceramic oxides on SAM templates are explained with classification into three categories: patterning by site-selective attachment of homogeneously nucleated particles, patterning by surface-selective heterogeneous nucleation and growth, and patterning by catalyst-induced heterogeneous nucleation. We also describe pattern-deposition on flexible substrates and future views to improve the pattern resolution.

Soft-landing Isolation of Gas-phase-synthesized Transition Metal−Benzene Complexes into a Fluorinated Self-assembled Monolayer Matrix

Gas-phase-synthesized chromium−benzene 1:2 sandwich cation complexes [Cr+(benzene)2] were soft-landed on a self-assembled monolayer (SAM) of fluorinated alkanethiol (C10F-SAM) at a hyperthermal collision energy of ∼20 eV. The adsorption properties and thermal stability of the soft-landed complexes were studied with infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The landed complexes were neutralized due to charge transfer from the SAM substrate, but their native sandwich structure remained intact. The hyperthermal collision event resulted in the penetration of the incoming complexes into the C10F-SAM matrix. The embedded complexes then tended to orient their molecular axes approximately along the surface normal. This orientational preference is measurably different from that of complexes isolated in alkanethiol SAM matrices, a discrepancy that might be caused by a repulsive interaction between the π cloud of the capping benzene rings of the complex and the side-chain CF2 groups of the fluorocarbon chains in the C10F-SAM matrix. The thermal desorption study showed that the complexes supported inside the C10F-SAM could resist thermal desorption until the high-temperature region of ∼320 K, a persistence revealing a large desorption activation energy (∼190 kJ/mol).

Multifunctional Mixed SAMs That Promote Both Cell Adhesion and Noncovalent DNA Immobilization

The ability of DNA strands to influence cellular gene expression directly and to bind with high affinity and specificity to other biological molecules (e.g., proteins and target DNA strands) makes them a potentially attractive component of cell culture substrates. On the basis of the potential importance of immobilized DNA in cell culture and the well-defined characteristics of alkanethiol self-assembled monolayers (SAMs), the current study was designed to create multifunctional SAMs upon which cell adhesion and DNA immobilization can be independently modulated. The approach immobilizes the fibronectin-derived cell adhesion ligand Arg-Gly-Asp-Ser-Pro (RGDSP) using carbodiimide activation chemistry and immobilizes DNA strands on the same surface via cDNA-DNA interactions. The surface density of hexanethiol-terminated DNA strands on alkanethiol monolayers (30.2-69.2 pmol/cm2) was controlled using a backfill method, and specific target DNA binding on cDNA-containing SAMs was regulated by varying the soluble target DNA concentration and buffer characteristics. The fibronectin-derived cell adhesion ligand GGRGDSP was covalently linked to carboxylate groups on DNA-containing SAM substrates, and peptide density was proportional to the amount of carboxylate present during SAM preparation. C166-GFP endothelial cells attached and spread on mixed SAM substrates and cell adhesion and spreading were specifically mediated by the immobilized GGRGDSP peptide. The ability to control the characteristics of noncovalent DNA immobilization and cell adhesion on a cell culture substrate suggests that these mixed SAMs could be a useful platform for studying the interaction between cells and DNA.

Enhanced Fluorescence Detection on Homogeneous Gold Colloid Self-Assembled Monolayer Substrates

We report the observation of appreciable enhancement of fluorescence induced by large Au colloids on a solid support. Au colloids 40, 59, and 81 nm in radius were homogeneously deposited on glass substrates with varying average particle distances and interparticle coupling. The fluorescence enhancement was examined by using self-assembled monolayers of two different fluorophore−protein conjugates: fluorescein isothiocyanate−human serum albumin (FITC-HSA) and epicocconone (Deep Purple)−bovine serum albumin (DP-BSA). We demonstrated strong variations of fluorescence enhancement with both interparticle distance and particle size. The highest observed fluorescence enhancement for DP-BSA was 15 times with the 162 nm Au colloid and an average interparticle distance of 67 nm, estimated from the particle density in the SEM images. We analyzed the origin of such large enhancement observed for optimized nanoparticle size and distance. To this aim, we separated the effect of the increased excitation rate from the el...

Effect of polarity of self-assembled monolayers on morphology and magnetic properties of a deposited magnetic material

With the decreasing size of devices, the ability to organize materials and control their physical properties through spatial and morphology manipulation becomes critical. Here, we show that the nature of the organic functional group at the top surface of the self-assembled monolayers can strongly influence the growth of a metallic thin film on the monolayer, as a chemical reaction may occur at the interface. We have sputtered Permalloy (Ni79Fe21) on patterned templates of polar and nonpolar self-assembled monolayers. Uniform film formation is observed on polar regions, and cluster/dropletlike structures are formed on the nonpolar regions. A similar behavior in morphology is observed for the deposition of Permalloy on a substrate having single component self-assembled monolayers. Magnetic measurements reveal that Permalloy exhibits a superparamagnetic behavior when deposited on a nonpolar self-assembled monolayer substrate, whereas a ferromagnetic behavior is observed for Permalloy deposited on a polar self-assembled monolayer substrate. Thus, a systematic deposition of Permalloy on polar and nonpolar self-assembled monolayers allows a control on morphology and the magnetic properties due to the difference in wettability of the terminal organic functional groups of the self-assembled monolayers.

Electron Beam and Soft X-ray Lithography with a Monomolecular Resist

This contribution reviews current state of electron beam and soft X-ray lithography with a monomolecular resist. Self-assembled monolayers (SAMs) represent versatile resist materials for such a lithography. Depending on the architecture of the SAM constituents, they can serve as both positive and negative resists within framework of conventional lithography, but also be used as multi-purpose templates for Chemical Lithography. The latter technique exploits either selective modification of specific tail groups at the SAM-ambient interface (in the case of aromatic backbone) or irradiation-promoted exchange reaction between the primary SAM and potential molecular substituents (in the case of aliphatic backbone). Due to the monolayer thickness of SAM resists and molecular size of their structural building blocks, patterning down to few nanometers is in principle possible. Currently, the lateral resolution is limited by the grain character of the SAM substrates and parameters of the lithographic setup, with the latter being especially important in the case of soft X-ray lithography.

Electrochemically Deposited Palladium as a Substrate for Self-Assembled Monolayers

The vast majority of reports of self-assembled monolayers (SAMs) on metals focus on the use of gold. However, other metals, such as palladium, platinum, and silver offer advantages over gold as a substrate. In this work, palladium is electrochemically deposited from PdCl2 solutions on glassy carbon electrodes to form a substrate for alkanethiol SAMs. The conditions for deposition are optimized with respect to the electrolyte, pH, and electrochemical parameters. The palladium surfaces have been characterized by scanning electron microscopy (SEM) and the surface roughness has been estimated by chronocoulometry. SAMs of alkane thiols have been formed on the palladium surfaces, and their ability to suppress a Faradaic process is used as an indication for palladium coverage on the glassy carbon. The morphology of the Pd deposit as characterized by SEM and the blocking behavior of the SAM formed on deposited Pd delivers a consistent picture of the Pd surface. It has been clearly demonstrated that, via selection of experimental conditions for the electrochemical deposition, the morphology of the palladium surface and its ability to support SAMs can be controlled. The work will be applied to create a mixed monolayer of metals, which can subsequently be used to create a mixed SAM of a biocomponent and an alkanethiol for biosensing applications.

Si/SiO2-Templated Formation of Ultraflat Metal Surfaces on Glass, Polymer, and Solder Supports: Their Use as Substrates for Self-Assembled Monolayers

This paper describes the use of several methods of template stripping (TS) to produce ultraflat films of silver, gold, palladium, and platinum on both rigid and polymeric mechanical supports: a composite of glass and ultraviolet (UV)-curable adhesive (optical adhesive, OA), solder, a composite of poly(dimethyl siloxane) (PDMS) and OA, and bare OA. Silicon supporting its native oxide layer (Si/SiO2) serves as a template for both mechanical template stripping (mTS), in which the metal film is mechanically cleaved from the template, and chemical template stripping (cTS), in which the film-template composite is immersed in a solution of thiols, and the formation of the SAM on the metal film causes the film to separate from the template. Films formed on all supports have lower root-mean-square (rms) roughness (as measured by atomic force microscopy, AFM) than films used as-deposited (AS-DEP) by electron-beam evaporation. Monolayers of n-dodecanethiolate formed by the mTS and cTS methods are effectively indistinguishable by scanning tunneling microscopy (STM); molecularly resolved images could be obtained using both types of surfaces. The metal surfaces, before being cleaved, are completely protected from contact with the atmosphere. This protection allows metal surfaces intended to support SAMs to be prepared in large batch lots, stored, and then used as needed. Template stripping thus eliminates the requirement for evaporation of the film immediately before use and is a significant extension and simplification of the technology of SAMs and other areas of materials science requiring clean metal surfaces.

Interfacial bridge-mediated electron transfer: mechanistic analysis based on electrochemical kinetics and theoretical modelling

Understanding the physical and chemical factors that control the kinetics of interfacial electron-transfer (ET) reactions is important for a large number of technological applications. The present article describes electrochemical kinetic studies of these factors, in which standard interfacial ET rate constants (k(0)(l)) have been measured for ET between substrate Au electrodes and various redox couples attached to the electrode surfaces by variable lengths (l) of oligomethylene (OM), oligophenylenevinylene (OPV) and oligophenyleneethynylene (OPE) bridges, which were constituents of mixed self-assembled monolayers (SAMs). The k(0)(l) measurements employed the indirect laser-induced temperature jump (ILIT) technique, which permits the measurement of interfacial ET rates that are orders of magnitude faster than those measurable by conventional techniques using the macroelectrodes that are the most convenient substrates for the mixed SAMs. The robustness of the measured rate constants (k(0)(l)), together with the Arrhenius activation energies (E(a)(l)) and preexponential factors (A(l)), is demonstrated by their invariance with respect to several experimental system parameters (including the chemical nature and length of the diluent component of the mixed SAM). Analysis of the kinetic results demonstrates that all of the observed interfacial ET processes proceed through a common type of transition state (predominantly associated with solvent reorganization around the redox moiety) and that the actual ET step involves direct electronic tunnelling between the Au electrode and the redox moiety. However, for the full range of l investigated, a global exponential decay of A(l) is not found for any of the three types of bridges. Possible reasons for this behavior, including the role of rate determining steps associated with adiabatic mechanisms within or beyond the transition state theory framework, are discussed, and comparisons with related conductance measurements are presented.

Calcite shape modulation through the lattice mismatch between the self-assembled monolayer template and the nucleated crystal face

The shapes of biologically formed calcite crystals are extremely versatile. Numerous studies have addressed the possible biological mechanism of crystal shape regulation. Synthetic assays have shown that the shape and morphology of calcite crystals can be modulated by inorganic or organic solution additives. Hardly any studies have to date discussed the concept of controlling the shape of these crystals by organic nucleating surfaces. We show in this paper that self-assembled monolayers (SAMs) that template calcite nucleation have two pronounced effects: in addition to inducing the highly oriented crystal growth (the phenomenon that we have extensively described in our previous studies), each SAM induces a clear modification of the calcite shape from its equilibrium rhombohedron. We demonstrate that this change in shape originates from the anisotropy of lattice mismatches that develop between the nucleating crystal face and the organic SAM in different directions. We present a model that gives qualitative predictions for the shape of crystals grown on a variety of SAM substrates, as a function of lattice mismatch, and show that these shapes correlate extremely well with the experimental results. We believe that this mechanism might be utilized by organisms in the biomineralization process.

Using scaling laws to understand the growth mechanism of atomic layer deposited WNxCy films on methyl-terminated surfaces

Atomic layer deposition (ALD) of tungsten nitride carbide (WNxCy) on methyl-terminated self-assembled monolayers (SAMs) is investigated. SAM substrates provide extended transient regimes of different lengths, during which the WNxCy film growth is nonlinear. The extent of this offset from linear growth depends on the alkyl chain length. The film morphology is characterized by atomic force microscopy, which reveals island growth and fractal behavior. During the transient regime, WNxCy deposition shows nonconservative growth, as revealed by the low film density and a roughness exponent α of ∼0.4–0.5. During the linear growth regime, a conservative mechanism is observed, characterized by a higher, constant film density and α∼0.7. These observations do not apply to all ALD deposited films. In particular, ALD HfO2 films follow a conservative-type mechanism during the entire range of growth.

Switching On Cell Adhesion with Microelectrodes

Stick it! A microelectrochemical method was developed for in situ manipulation of the cell-adhesive property of an oligo(ethylene glycol)-terminated self-assembled monolayer substrate (OEG SAM) and subsequent cell adhesion and growth. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2006/z601151_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.