Biomedical subjects

Flemming Besenbacher

Publications and source records attributed to Flemming Besenbacher.

At least 19 recordsLinked to original sources

PubMed2007

The influence of polymeric properties on chitosan/siRNA nanoparticle formulation and gene silencing.

We have previously introduced the use of the biomaterial chitosan to form chitosan/siRNA nanoparticles for gene silencing protocols. This present study shows that the physicochemical properties (size, zeta potential, morphology and complex stability) and in vitro gene silencing of chitosan/siRNA nanoparticles are strongly dependent on chitosan molecular weight (Mw) and degree of deacetylation (DD). High Mw and DD chitosan resulted in the formation of discrete stable nanoparticles approximately 200 nm in size. Chitosan/siRNA formulations (N:P 50) prepared with low Mw (approximately 10 kDa) showed almost no knockdown of endogenous enhanced green fluorescent protein (EGFP) in H1299 human lung carcinoma cells, whereas those prepared from higher Mw (64.8-170 kDa) and DD (approximately 80%) showed greater gene silencing ranging between 45% and 65%. The highest gene silencing efficiency (80%) was achieved using chitosan/siRNA nanoparticles at N:P 150 using higher Mw (114 and 170 kDa) and DD (84%) that correlated with formation of stable nanoparticles of approximately 200 nm. In conclusion, this work confirms the application of chitosan as a non-viral carrier for siRNA and the importance of polymeric properties for the optimisation of gene silencing using chitosan/siRNA nanoparticles.

Cell Line, Tumor↗

PubMed2006

Cluster-support interactions and morphology of MoS2 nanoclusters in a graphite-supported hydrotreating model catalyst.

Supported MoS(2) nanoparticles constitute the active component of the important hydrotreating catalysts used for industrial upgrading and purification of the oil feedstock for the production of fossil fuels with a low environmental load. We have synthesized and studied a model system of the hydrotreating catalyst consisting of MoS(2) nanoclusters supported on a graphite surface in order to resolve a number of very fundamental questions related to the atomic-scale structure and morphology of the active clusters and in particular the effect of a substrate used in some types of hydrotreating catalysts. Scanning tunneling microscopy (STM) is used to image the atomic-scale structure of graphite-supported MoS(2) nanoclusters in real space. It is found that the pristine graphite (0001) surface does not support a high dispersion of MoS(2), but by introducing a small density of defects in the surface, highly dispersed MoS(2) nanoclusters could be synthesized on the graphite. From high-resolution STM images it is found that MoS(2) nanoclusters synthesized at low temperature in a sulfiding atmosphere preferentially grow as single-layer clusters, whereas clusters synthesized at 1200 K grow as multilayer slabs oriented with the MoS(2)(0001) basal plane parallel to the graphite surface. The morphology of both single-layer and multilayer MoS(2) nanoclusters is found to be preferentially hexagonal, and atom-resolved images of the top facet of the clusters provide new atomic-scale information on the MoS(2)-HOPG bonding. The structure of the two types of catalytically interesting edges terminating the hexagonal MoS(2) nanoclusters is also resolved in atomic detail in STM images, and from these images it is possible to reveal the atomic structure of both edges and the location and coverage of sulfur and hydrogen adsorbates.

Journal Article↗

PubMed2006

Supramolecular nanopatterns self-assembled by adenine-thymine quartets at the liquid/solid interface.

By means of scanning tunneling microscopy (STM), we have observed for the first time well-ordered supramolecular nanopatterns formed by mixing two complementary DNA bases: adenine (A) and thymine (T), respectively, at the liquid/solid interface. By mixing A and T at a specific mixing molar ratio, cyclic structures that were distinctly different from the structures observed by the individual base molecules separately were formed. From an interplay between the STM findings and self-consistent charge density-functional based tight-binding (SCC-DFTB) calculation method, we suggest formation of A-T-A-T quartets constructed on the basis of A-T base pairing. The formation of the A-T-A-T quartets opens new avenues to use DNA base pairing as a way to form nanoscale surface architecture and biocompatible patterned surfaces particularly via host-guest complexation that might be suitable for drug design, where the target can be trapped inside the cavities of the molecular containers.

1-Octanol↗

PubMed2006

RNA interference in vitro and in vivo using a novel chitosan/siRNA nanoparticle system.

This work introduces a novel chitosan-based siRNA nanoparticle delivery system for RNA interference in vitro and in vivo. The formation of interpolyelectrolyte complexes between siRNA duplexes (21-mers) and chitosan polymer into nanoparticles, ranging from 40 to 600 nm, was shown using atomic force microscopy and photon correlation spectroscopy. Rapid uptake (1 h) of Cy5-labeled nanoparticles into NIH 3T3 cells, followed by accumulation over a 24 h period, was visualized using fluorescence microscopy. Nanoparticle-mediated knockdown of endogenous enhanced green fluorescent protein (EGFP) was demonstrated in both H1299 human lung carcinoma cells and murine peritoneal macrophages (77.9% and 89.3% reduction in EGFP fluorescence, respectively). In addition, Western analysis showed approximately 90% reduced expression of BCR/ABL-1 leukemia fusion protein while BCR expression was unaffected in K562 (Ph(+)) cells after transfection using nanoparticles containing siRNA specific to the BCR/ABL-1 junction sequence. Effective in vivo RNA interference was achieved in bronchiole epithelial cells of transgenic EGFP mice after nasal administration of chitosan/siRNA formulations (37% and 43% reduction compared to mismatch and untreated control, respectively). These findings highlight the potential application of this novel chitosan-based system in RNA-mediated therapy of systemic and mucosal disease.

Animals↗

PubMed2006

Chiral close-packing of achiral star-shaped molecules on solid surfaces.

From the interplay of scanning tunneling microscopy and theoretical calculations, we study the chiral self-assembly of achiral HtB-HBC molecules upon adsorption on the Cu(110) surface. We find that chirality is expressed at two different levels: a +/-5 degrees rotation of the molecular axis with respect to the close-packed direction of the Cu(110) substrate and a chiral close-packed arrangement expected for star-shaped molecules in 2D. Out of the four possible chiral expressions, only two are found to exist due the effect of van der Waals (vdW) interactions forcing the molecules to simultaneously adjust to the atomic template of the substrate geometry and self-assemble in a close-packed geometry.

Stereoisomerism↗

PubMed2006

Nanostructure of the neurocentral growth plate: Insight from scanning small angle X-ray scattering, atomic force microscopy and scanning electron microscopy.

In this study, the experimental techniques scanning electron microscopy (SEM) including energy-dispersive X-ray analysis, atomic force microscopy (AFM) and scanning small angle X-ray scattering (SAXS) have been exploited to characterize the organization of large molecules and nanocrystallites in and around the neurocentral growth plate (NGP) of a pig vertebrae L4. The techniques offer unique complementary information on the nano- to micrometer length scale and provide new insight in the changes in the matrix structure during endochondral bone formation. AFM and SEM imaging of the NGP reveal a fibrous network likely to consist of collagen type II and proteoglycans. High-resolution AFM imaging shows that the fibers have a diameter of approximately 100 nm and periodic features along the fibers with a periodicity of 50-70 nm. This is consistent with the SAXS analysis that yields a cross-sectional diameter of the fibers in the range of 90 to 112 nm and a predominant orientation in the longitudinal direction of the NGP. Furthermore, we find inhomogeneities around 7 nm in the NGP by SAXS analysis. Moving towards the bone in the direction perpendicular to the growth plate, a systematic change in apparent thickness is observed, while the large-scale structural features remain constant. In the region of bone, the apparent thickness equals the mean mineral thickness and increases from 2 nm to approximately 3.5 nm as a function distance from the NGP. The mineral particles are organized as plates in a rather compact network structure. We have demonstrated that SEM, AFM and SAXS are valuable tools for the investigation of the organization of large molecules and nanocrystallites in the NGP and adjacent trabecular bone. Our findings will be an important basis for future work into identifying the defects on nanometer length scale responsible for idiopathic scoliosis and other growth-plate-related diseases.

Animals↗

PubMed2006

Monitoring cell adhesion on tantalum and oxidised polystyrene using a quartz crystal microbalance with dissipation.

The quartz crystal microbalance with dissipation (QCM-D) (Q-Sense AB, Sweden) has been established as a useful tool for evaluating interactions between various biological and non-biological systems, and there has been increasing interest in using the QCM-D technique for cell monitoring applications. This study investigated the potential of the QCM-D to characterise the initial adhesion and spreading of cells in contact with protein precoated biocompatible surfaces. The QCM-D technique is attractive for monitoring cell adhesion and spreading as it allows in situ real-time measurements. The adhesion of NIH3T3 (EGFP) fibroblasts to tantalum (Ta) and oxidised polystyrene (PS(ox)) surfaces precoated with serum proteins was examined using the QCM-D for a period of either 2 or 4 h. Time-lapse photography was performed at 30 min intervals to visually examine cell adhesion and spreading in order to relate cell morphology to the QCM-D response. Following adsorption of albumin, fibronectin or newborn calf serum onto the surfaces, QCM-D measurements showed that cells adhered and spread on the fibronectin and serum coated surfaces, while few cells adhered to the albumin coated surfaces. Cells adhered to albumin coated surfaces had a rounded morphology. The responses to fibronectin and serum precoated surfaces were quite different for each of the underlying substrates indicating that the process of cell adhesion and spreading elicits different responses depending on both the protein coating composition and the influence of the underlying substrate. The different response may be due to extracellular matrix remodelling as well as cytoskeletal changes. Frequency (f) and dissipation (D) changes associated with cell adhesion were less than would be expected from the Sauerbrey relation due to the viscoelastic properties of the cells.

Absorption↗

PubMed2006

Azobenzene on Cu(110): adsorption site-dependent diffusion.

Azobenzene and its derivatives can undergo reversible trans-cis isomerizations when irradiated with light, making them potential candidates for optically sensitive materials and devices. The adsorption and diffusion of azobenzene on the Cu(110) surface was investigated with a variable-temperature scanning tunneling microscope. The trans-isomer was observed and found to occupy two adsorption geometries-an energetically stable and a metastable state. Diffusion occurred along the closed-packed [1 -1 0] direction of the surface, and the diffusivity for the two adsorption states was found to differ by approximately 1 order of magnitude.

Journal Article↗

PubMed2006

L-cysteine adsorption structures on Au(111) investigated by scanning tunneling microscopy under ultrahigh vacuum conditions.

Adsorption structures formed upon vapor deposition of the natural amino acid L-cysteine onto the (111) surface of gold have been investigated by scanning tunneling microscopy under ultrahigh vacuum conditions. Following deposition at room temperature and at cysteine coverages well below saturation of the first monolayer, we found coexistence of unordered molecular islands and extended domains of a highly ordered molecular overlayer of quadratic symmetry. As the coverage was increased, a number of other structures with local hexagonal order emerged and became dominant. Neither of the room temperature, as-deposited, ordered structures showed any fixed rotational relationship to the underlying gold substrate, suggesting a comparatively weak and nonspecific molecule-substrate interaction. Annealing of the cysteine-covered substrate to 380 K lead to marked changes in the observed adsorption structures. At low coverages, the unordered islands developed internal order and their presence started to perturb the appearance of the surrounding Au(111) herringbone reconstruction. At coverages beyond saturation of the first monolayer, annealing led to development of a ( radical3 x radical3)R30 degrees superstructure accompanied by the formation of characteristic monatomically deep etch pits, i.e., the behavior typically observed for alkanethiol self-assembled monolayers on Au(111). The data thus show that as-deposited and thermally annealed cysteine adsorption structures are quite different and suggest that thermal activation is required before vacuum deposited cysteine becomes covalently bound to single crystalline Au(111).

Journal Article↗

PubMed2006

Enantiospecific adsorption of cysteine at chiral kink sites on Au(110)-(1 x 2).

Enantiospecific adsorption of cysteine molecules onto chiral kink sites on the Au(110)-(1x2) surface was observed by scanning tunneling microscopy. l- and d-cysteine dimers were found to adopt distinctly different adsorption geometries at S kinks, which can be understood from the need to reach specific, optimum molecule-substrate interaction points. Extended, homochiral domains of l/d-cysteine were furthermore observed to grow preferentially from R/S kinks. The results constitute the first direct, microscopic observation of enantiospecific molecular interaction with chiral sites on a metal single-crystal surface.

Adsorption↗

PubMed2006

Chiral switching by spontaneous conformational change in adsorbed organic molecules.

Self-assembly of adsorbed organic molecules is a promising route towards functional surface nano-architectures, and our understanding of associated dynamic processes has been significantly advanced by several scanning tunnelling microscopy (STM) investigations. Intramolecular degrees of freedom are widely accepted to influence ordering of complex adsorbates, but although molecular conformation has been identified and even manipulated by STM, the detailed dynamics of spontaneous conformational change in adsorbed molecules has hitherto not been addressed. Molecular surface structures often show important stereochemical effects as, aside from truly chiral molecules, a large class of so-called prochiral molecules become chiral once confined on a surface with an associated loss of symmetry. Here, we investigate a model system in which adsorbed molecules surprisingly switch between enantiomeric forms as they undergo thermally induced conformational changes. The associated kinetic parameters are quantified from time-resolved STM data whereas mechanistic insight is obtained from theoretical modelling. The chiral switching is demonstrated to enable an efficient channel towards formation of extended homochiral surface domains. Our results imply that appropriate prochiral molecules may be induced (for example, by seeding) to assume only one enantiomeric form in surface assemblies, which is of relevance for chiral amplification and asymmetric heterogenous catalysis.

Journal Article↗

PubMed2006

Coadsorption of guanine and cytosine on graphite: ordered structure based on GC pairing.

Nanostructures formed by coadsorption of the complementary DNA bases guanine (G) and cytosine (C) at a graphite surface in 1-octanol solvent were investigated by in situ scanning tunneling microscopy. The high-resolution observations showed for the first time a well-ordered coadsorption structure, attributed to rows formed from Watson-Crick G-C pairs, which was distinctly different from the structures observed for the individual G/C components. The observed coadsorption structure has been modeled by self-consistent charge density-functional-based tight-binding (SCC-DFTB) calculations, providing information on the intermolecular interactions underlying its formation.

Adsorption↗

PubMed2006

Scanning tunneling microscopy manipulation of complex organic molecules on solid surfaces.

Organic molecules adsorbed on solid surfaces display a fascinating variety of new physical and chemical phenomena ranging from self-assembly and molecular recognition to nonlinear optical properties and current rectification. Both the fundamental interest in these systems and the promise of technological applications have motivated a strong research effort in understanding and controlling these properties. Scanning tunneling microscopy (STM) and, in particular, its ability to manipulate individual adsorbed molecules, has become a powerful tool for studying the adsorption geometry and the conformation and dynamics of single molecules and molecular aggregates. Here we review selected case studies demonstrating the enormous capabilities of STM manipulations to explore basic physiochemical properties of adsorbed molecules. In particular, we emphasize the role of STM manipulations in studying the coupling between the multiple degrees of freedom of adsorbed molecules, the phenomenon of molecular molding, and the possibility of creating and breaking individual chemical bonds in a controlled manner, i.e., the concept of single-molecule chemistry.

Journal Article↗

PubMed2005

QCM-D studies of attachment and differential spreading of pre-osteoblastic cells on Ta and Cr surfaces.

The quartz crystal microbalance with dissipation (QCM-D) technique was employed to characterize initial cell adhesion in terms of attachment and spreading of pre-osteoblastic MC3T3-E1 cells on Ta and Cr surfaces. Evaluation of initial cell adhesion established a correlation between input cell number and the shifts in frequency (f) and dissipation (D). The f-shift was found to be much larger in serum-free medium as compared to a medium including serum; hence, initial cell adhesion was subsequently evaluated in serum-free medium. During the first hour of adhesion, we found a positive correlation between the QCM-D f-shift and the average area of the spread cells, as measured by cryo-scanning electron microscopy (cryo-SEM). Finally, the QCM-D technique was used to study cell adhesion on different metal oxide surfaces. Initial cell adhesion on Ta was found to induce a larger f-shift as compared to Cr, indicating larger spreading of cells on Ta. Cryo-SEM data confirmed that spreading of cells on Cr was on average only two-thirds the spreading on Ta. Our results demonstrate that the QCM-D technique is a versatile technique to quickly distinguish initial cell-surface interactions on different biomaterials.

Animals↗

PubMed2005

Adsorbate-induced alloy phase separation: a direct view by high-pressure scanning tunneling microscopy.

The influence of high pressures of carbon monoxide (CO) on the stability of a Au/Ni(111) surface alloy has been studied by high-pressure scanning tunneling microscopy. We show that CO induces a phase separation of the surface alloy at high pressures, and by means of time-lapsed STM movies we find that Ni atoms are removed from the surface layer during the process. Density functional theory calculations reveal the thermodynamic driving force for the phase separation to be the Au-induced compression of the CO overlayer with a resulting CO-CO repulsion. Furthermore, the atomistic mechanism of the process is shown to be kink-site carbonyl formation and evaporation which is found to be enhanced by the presence of Au.

Journal Article↗

PubMed2005

The adsorption structure of NO on Pd(111) at high pressures studied by STM and DFT.

Using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we study the adsorption structure of NO on Pd(111) at pressures of up to 720 Torr. From atomically resolved STM images, we identify, at high pressures, only the (2 x 2)-3NO structure, which is identical with the highest NO-coverage structure found at low pressure and low temperature. DFT calculations confirm that the (2 x 2)-3NO structure is indeed the most stable adsorption structure at high pressures. Contrary to recent suggestions in the literature, we therefore conclude that we find no evidence for a (3 x 3)-7NO structure on Pd(111) at high NO pressure.

Letter↗

PubMed2005

Adsorption of fibrinogen on tantalum oxide, titanium oxide and gold studied by the QCM-D technique.

The adsorption of human fibrinogen on tantalum oxide, titanium oxide and gold surfaces has been studied by quartz crystal microbalance with dissipation (QCM-D) at 37 degrees C. Two different protein concentrations have been used, one close to physiological concentration (1 mg/ml) and one significantly lower (0.033 mg/ml). To further characterize the adsorbed fibrinogen layer, the subsequent binding of both polyclonal and monoclonal antibodies of fibrinogen is studied. We found that the viscoelastic properties of the fibrinogen layer depends strongly on the initial protein concentration. The trend is generally seen for all three surfaces. The fibrinogen layer on gold and tantalum oxide is found to have the same viscoelastic properties, which are different from those found for the fibrinogen layer adsorbed on titanium oxide. The dependency of the surface chemistry on the viscoelastic properties of the fibrinogen layer is observed directly for the 0.033 mg/ml solution, and indirectly through the antibody response for the 1 mg/ml solution. From this we conclude that the orientation and/or denaturation of fibrinogen on a surface depends on the surface chemistry and the protein concentration in the solution, and that the binding of antibodies is a useful way to detect this difference.

Adsorption↗

PubMed2005

Quantum size effects in adatom island decay.

The decay of hexagonal Ag adatom islands on top of larger Ag adatom islands on a Ag(111) surface is followed by a fast-scanning tunneling microscope. Islands do not always show the expected increase in decay rate with decreasing island size. Rather, distinct quantum size effects are observed where the decay rate decreases significantly for islands with diameters of 6, 9.3, 12.6, and 15.6 nm. We show that electron confinement of the surface state electrons is responsible for this enhancement of the detachment barrier for adatoms from the island edge.

Journal Article↗