Macroscopic Tribological Testing of Alkanethiol Self-assembled Monolayers (SAMs): Pin-on-disk Tribometry with Elastomeric Sliding Contacts

We demonstrate that the frictional properties of alkanethiol self-assembled monolayers (SAMs) with various surface-chemical and structural features can be investigated on a macroscopic scale by employing an elastomer as the sliding partner in pin-on-disk tribometry. The mild contact conditions at the elastomeric tribological interface allow the SAM films to remain virtually intact despite the tribological stress. Sliding contact between SAMs and elastomers over the speed range available from an ordinary tribometer in a liquid environment induced a broad range of lubrication mechanisms, ranging from boundary to fluid-film lubrication regimes. Thus, the impact of both the chemical and structural characteristics of SAMs on the formation of fluid films and interfacial friction forces could be probed in the absence of wear processes. Given the large SAM "toolbox” that is readily available for the modification of surface-chemical characteristics, this approach provides an opportunity to investigate the influence of surface chemistry on the frictional properties of elastomeric tribological contact

Construction of Cell-Resistant Surfaces by Immobilization of Poly(ethylene glycol) on Gold

Considerable effort has been expended in efforts to create surfaces that resist the adsorption of proteins and cells for biomedical applications. The majority of such work has focused on surfaces constructed from bulk polymers or thin polymer films. However, the fabrication of surfaces via self-assembled monolayers (SAMs) has attracted considerable interest because of the robustness, versatility, and wide-ranging applicability of these materials. SAMs are particularly appealing for biological systems where well-defined surface chemistries can be created to facilitate coupling, biorecognition, or cell adhesion along with a host of other applications in biochemistry and biotechnology

Bioinspired catechol-terminated self-assembled monolayers with enhanced adhesion properties

The role of the catechol moiety in the adhesive properties of mussel proteins and related synthetic materials has been extensively studied in the last years but still remains elusive. Here, a simplified model approach is presented based on a self-assembled monolayer (SAM) of upward-facing catechols thiol-bound to epitaxial gold substrates. The orientation of the catechol moieties is confirmed by spectroscopy, which also showed lack of significant amounts of interfering o-quinones. Local force-distance curves on the SAM measured by atomic force microscopy (AFM) shows an average adhesion force of 45 nN, stronger than that of a reference polydopamine coating, along with higher reproducibility and less statistical dispersion. This is attributed to the superior chemical and topographical homogeneity of the SAM coating. Catechol-terminated SAMs are also obtained on high-roughness gold substrates that show the ability to assemble magnetic nanoparticles, despite their lack of enhanced adhesion at the molecular level. Finally, the influence of the catechol group on the formation and quality of the SAM is explored both theoretically (molecular dynamics simulations) and experimentally using direct-write AFM lithography.This work was supported by MICINN through projects MAT2012–38318-C03–02, MAT2012–38319-C02–01, CTQ2010–15380 and CONSOLIDER NANOSELECT CSD 2007–00041. M. G. thanks the CSIC for a predoctoral grant.Peer Reviewe

Study of the interactions of a major rubber particle protein (REF1) with synthetic phospholipids in Langmuir monolayers

Rubber Elongation Factor (REF1) protein is located on the surface of rubber particles (RPs). As a RP-bound and hydrophobic protein, REF1 is suspected to be only partially eliminated by the water washing occurring during latex processing into raw natural rubber (NR) in the form of unsmoked rubber sheet (USS) and could thus affect raw NR properties. In this work, REF1 was identified as an abundant protein of raw NR and bio physical methods were used to describe the organization/structure of REF1 at the surface of RPs interacting with the lipid monolayer surrounding the poly-isoprene core. Therefore, an approach in Langmuir film was implemented to investigate the interactions between recombinant REF1 and synthetic phospholipids (POPC, POPG and POPA) by fluorescence (calcein-leakage measurements), ellipsometry, Brewster angle microscopy, and PM-IRRAS spectroscopy. REF1 was shown to interact differently depending on lipid headgroup type: no interaction with POPC, intermediate interactions with POPG and strong interactions associated to a conformational switch from α-helices to β-sheets with POPA. (Résumé d'auteur

Antibody mimetics for the detection of small organic compounds using a quartz crystal microbalance

Conventional immunoassays rely on antibodies that provide high affinity, specificity and selectivity against a target analyte. However, the use of antibodies for the detection of small-sized, non-immunogenic targets, such as pharmaceuticals and environmental contaminants presents a number of challenges. Recent advances in protein engineering have led to the emergence of antibody mimetics that offer the high affinity and specificity associated with antibodies but with reduced batch-to- batch variability, high stability and in vitro selection to ensure rapid discovery of binders against a wide range of targets. In this work we explore the potential of Affimers, a recent example of antibody mimetics, as suitable bio-receptors for the detection of small organic target compounds, here methylene blue. Target immobilisation for Affimer characterisation was achieved using long-chained alkanethiol linkers coupled with oligoethyleneglycol (LCAT-OEG). Using quartz crystal microbalance with dissipation monitoring (QCM-D), we determine the affinity constant, KD , of the methylene blue Affimer to be comparable to that of antibodies. Further, we demonstrate the high selectivity of Affimers for its target in complex matrices, here a limnetic sample. Finally, we demonstrate an Affimer-based competition assay, illustrating the potential of Affimers as bioreceptors in immunoassays for the detection of small-sized, non-immunogenic compounds

Ethynylbenzene monolayers on gold: A metal-molecule binding motif derived from a hydrocarbon

Exposure of a Au(111) surface to ethynylbenzene in solution leads to the formation of a bound monolayer. A chemisorption process occurs to give a stable layer consisting of oxygen-containing hydrocarbon species. Ethynylbenzene itself does not oxidize under the deposition conditions indicating that the gold surface facilitates the oxidation process. Calculations show that ethynylbenzene and its oxidation products phenylacetic acid and phenyloxirane have positive binding energies to the gold surface. 1,4-Diethynylbenzene also binds to Au(111) and anchors gold nanoparticles deposited from solution to form dense, semiregular arrays. © 2007 American Chemical Society