Showing papers by "Stefan Zauscher published in 2008"

Distance-Dependent Plasmon Resonant Coupling between a Gold Nanoparticle and Gold Film

Abstract: We present an experimental analysis of the plasmonic scattering properties of gold nanoparticles controllably placed nanometers away from a gold metal film. We show that the spectral response of this system results from the interplay between the localized plasmon resonance of the nanoparticle and the surface plasmon polaritons of the gold film, as previously predicted by theoretical studies. In addition, we report that the metal film induces a polarization to the single nanoparticle light scattering, resulting in a doughnut-shaped point spread function when imaged in the far-field. Both the spectral response and the polarization effects are highly sensitive to the nanoparticle−film separation distance. Such a system shows promise in potential biometrology and diagnostic devices.

Bimaterial Microcantilevers as a Hybrid Sensing Platform

Abstract: : Microcantilevers, one of the most common MEMS structures, have been introduced as a novel sensing paradigm nearly a decade ago. Ever since, the technology has emerged to find important applications in chemical, biological and physical sensing areas. Today the technology stands at the verge of providing the next generation of sophisticated sensors (such as artificial nose, artificial tongue) with extremely high sensitivity and miniature size. The article provides an overview of the modes of detection, theory behind the transduction mechanisms, materials employed as active layers, and some of the important applications. Emphasizing the material design aspects, the review underscores the most important findings, current trends, key challenges and future directions of the microcantilever based sensor technology.

Conformational mechanics, adsorption, and normal force interactions of lubricin and hyaluronic acid on model surfaces.

Abstract: Glycoproteins, such as lubricin, and hyaluronic acid (HA) play a prominent role in the boundary lubrication mechanism in diarthrodial joints Although many studies have tried to elucidate the lubrication mechanisms of articular cartilage, the molecular details of how lubricin and HA interact with cartilage surfaces and mediate their interaction still remain poorly understood Here we used model substrates, functionalized with self-assembled monolayers terminating in hydroxyl or methyl groups, (1) to determine the effect of surface chemistry on lubricin and HA adsorption using surface plasmon resonance (SPR) and (2) to study normal force interactions between these surfaces as a function of lubricin and HA concentration using colloidal probe microscopy We found that lubricin is amphiphilic and adsorbed strongly onto both methyl- and hydroxyl-terminated surfaces On hydrophobic surfaces, lubricin likely adopts a compact, looplike conformation in which its hydrophobic domains at the N and C termini serve as surface anchors On hydrophilic surfaces, lubricin likely adsorbs anywhere along its hydrophilic central domain and adopts, with increasing solution concentration, an extended tail-like conformation Overall, lubricin develops strong repulsive interactions when compressing two surfaces into contact Furthermore, upon surface separation, adhesion occurs between the surfaces as a result of molecular bridging and chain disentanglement This behavior is in contrast to that of HA, which does not adsorb appreciably on either of the model surfaces and does not develop significant repulsive interactions Adhesive forces, particularly between the hydrophobic surfaces, are large and not appreciably affected by HA For a mixture of lubricin and HA, we observed slightly larger adsorptions and repulsions than those found for lubricin alone Our experiments suggest that this interaction depends on unspecific physical rather than chemical interactions between lubricin and HA We speculate that in mediating interactions at the cartilage surface, an important role of lubricin, possibly in conjunction with HA, is one of providing a protective coating on cartilage surfaces that maintains the contacting surfaces in a sterically repulsive state

Polymeric and biomacromolecular brush nanostructures: progress in synthesis, patterning and characterization

Abstract: A significant scientific and engineering challenge of recent years has been the fabrication of patterned polymeric and biomacromolecular brush nanostructures on surfaces. These structures provide researchers with a rich platform on which to exploit and observe nanoscale phenomena. In this review we present an overview of the field and highlight, through selected examples, recent advances in the nanostructuring of polymer and biomacromolecular brushes. This includes a brief overview of polymer brush synthesis techniques and how these are integrated with nanolithographic and templating approaches. We discuss the characterization of polymeric nanostructures and its associated difficulties, and we provide some perspective of how we see the future direction of the field evolving.

Hydration and conformational mechanics of single, end-tethered elastin-like polypeptides.

Abstract: We investigated the effect of temperature, ionic strength, solvent polarity, and type of guest residue on the force−extension behavior of single, end-tethered elastin-like polypeptides (ELPs), using single molecule force spectroscopy (SMFS). ELPs are stimulus-responsive polypeptides that contain repeats of the five amino acids Val-Pro-Gly-Xaa-Gly (VPGXG), where Xaa is a guest residue that can be any amino acid with the exception of proline. We fitted the force−extension data with a freely jointed chain (FJC) model which allowed us to resolve small differences in the effective Kuhn segment length distributions that largely arise from differences in the hydrophobic hydration behavior of ELP. Our results agree qualitatively with predictions from recent molecular dynamics simulations and demonstrate that hydrophobic hydration modulates the molecular elasticity for ELPs. Furthermore, our results show that SMFS, when combined with our approach for data analysis, can be used to study the subtleties of polypeptid...

Quantitative biological surface science: challenges and recent advances.

Abstract: Biological surface science is a broad, interdisciplinary subfield of surface science, where properties and processes at biological and synthetic surfaces and interfaces are investigated, and where biofunctional surfaces are fabricated The need to study and to understand biological surfaces and interfaces in liquid environments provides sizable challenges M, as well as fascinating opportunities Here, we report on recent progress in biological surface E science that was described within the program assembled by the Biomaterial Interface Division of the Science and Technology of Materials, Interfaces and Processes (wwwavsorg) during their 55th International Symposium and Exhibition held in Boston, October 19-24, 2008 The selected examples show that the rapid progress in nanoscience and nanotechnology, hand-in-hand with theory and simulation, provides increasingly sophisticated methods and tools to unravel the mechanisms and details of complex processes at biological surfaces and in-depth understanding of biomolecular surface interactions

Novel evaluation method of neutron reflectivity data applied to stimulus-responsive polymer brushes

Abstract: Neutron reflectivity (NR) measurements have been performed on stimulus-responsive polymer brushes containing N-isopropylacrylamide (NIPAAM) at different temperatures and contrasts using two different brush samples of roughly the same grafting density and layer thickness. The NR data were analyzed using a novel method employing polymer density profiles predicted from lattice mean-field theory augmented with a polymer model to describe polymer solubility that decreases with increasing temperature. The predicted density profiles at the different temperatures were self-consistent with the experimentally observed profiles; hence the experimental data lend credibility to the theory. We found that the brush thickness decreased from 220 to 160 nm and the polymer volume fraction increased from 55 to 75% when increasing temperature from 293 to 328 K. The new evaluation approach involved significantly fewer independent fitting parameters than methods involving layers of uniform densities. Furthermore, the approach can straightforwardly be extended to analyze neutron reflectivity data of grafted, weakly charged polymers that display pH-sensitive behaviour and also to block copolymers and to surfaces with adsorbed polymers. We propose that such accurate model calculations provide a tool to interpret results from NR experiments more effectively and design neutron reflectivity experiments for optimal outcome.

Biomechanical and Biochemical Cellular Response Due to Shock Waves

Abstract: : Our research provides a first step towards a systematic, cell-level study of the effects of shock waves on the mechanical and biochemical properties of cells on solid supports. Motivated to better understand the relationship between shock exposure and heterotopic ossification (HO), a type of soft tissue injury, we designed an experimental setup to expose cell sheets of adipose derived stem cells to shock waves. A key guideline in the experimental design was to suppress cavitation. To this end we built a spark transducer and used a pressurized sample chamber. Cell viability tests and cytoskeletal staining showed little difference between shock-exposed cells and controls. We attribute this to the absence of cavitation. Time-resolved gene expression revealed that a large number of genes were affected by the shock wave exposure. Importantly, the experimental setup and the procedures we developed provide a basis for further studies of shock wave effects on a broad range of other cells. Specifically, they could be adopted to gain further understanding of cellular level causes of traumatic brain injury.