| 1. |
- Augulis, R, et al.
(författare)
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Atomic force microscopy of self-assembled nanostructures of TPPS4 on SAM substrates
- 2004
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Ingår i: Solid State Phenomena. - 1012-0394 .- 1662-9779. ; 97-98, s. 195-200
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of organic molecules on solid surfaces is one of the fundamental processes for the development of molecular-based nanodevices. Here we focus on the adsorption and ordering of the TPPS4-based J-aggregates on silicon and gold as well as on self-assembled monolayer (SAM) surfaces. The SAMs used for the experiments were based on the chemisorption of thiol containing compounds onto gold. Long omega-substituted alkanethiols are spontaneously assembled on gold to form highly ordered and densely packed layers with controllable chemical and physical properties. TPPS4 J-aggregates were dispersed on SAM surfaces, and on plain gold and silicon substrates for comparison. The dimensions of aggregates, measured by means of atomic force microscopy, varied depending on the type of substrate. Long stripe-like aggregates were flattened on the substrate surface, and the height and width of aggregates highly correlated with the polarity of surface groups. For example, the J-aggregates were narrower on hydrophobic substrates (with non-polar groups) and wider on hydrophilic substrates (with polar groups). These observations support the hypothesis, that TPPS4 forms,soft" cylindrical aggregates, that appear flattened on the substrate.
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| 2. |
- Ederth, Thomas, et al.
(författare)
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Force measurements between semifluorinated thiolate self-assembled monolayers : Long-range hydrophobic interactions and surface charge
- 2001
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 235:2, s. 391-397
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Tidskriftsartikel (refereegranskat)abstract
- Long-range interactions between self-assembled monolayers (SAMs) of semifluorinated alkanethiols have been studied by direct force measurements in water and aqueous NaCl solutions. SAMs prepared from three different thiols, with identical fluorinated head groups but varying hydrocarbon spacer lengths, were investigated: CF3(CF2)(9)(CH2)(x)SH, where x = 2, 11, or 17. Force measurements show that the interactions in water and electrolyte solutions are composed of both double-layer interactions emerging from what appears to be charges adsorbed onto the surfaces and long-range "hydrophobic" attractions, in excess of the expected van der Waals forces. The three investigated thiols produce similar results in force measurements, though the contact angles with water are slightly different, The "hydrophobic" attraction has the form of step-like attractive discontinuities in the force profiles at separations ranging from 20 to 40 nm, caused by bridging of microscopic bubbles residing at the surfaces, The shape or range of these discontinuities are not significantly affected by replacement of the water with either 1 mM or 1 M NaCl solutions. The origin of the charges causing the electrostatic double-layer interaction is unclear, but some possible causes are discussed.
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| 3. |
- Eimont, R., et al.
(författare)
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Extracellular matrix mimetics by crosslinked peptide hydrogels: application to neural 3D cell cultures
- 2018
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Ingår i: International conference Vita Scientia Conference book. ; , s. 59-59
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Self-supporting, shapeable hydrogels that consist of self-assembling synthetic peptides mimic the structural blocks of the extracellular matrix (ECM). Although they have been developed for regenerative medicine purposes, with a potential of grafting into patients without transplantation from organ donors, this class of materials are attractive as scaffolds for advanced cell culture/ in vitro tissue applications. In the present study, we have combined a series of peptides with functional motives (collagen, fibronectin, and laminin-like) for promoting granule layer-like organization of primary cerebellar cells and for controlling the cell attachment, neuritogenesis, cluster size and organization. We show that the micro/nanofabricated hydrogel scaffolds are applicable as multiwell plate inserts helping to analyse cell migration, differentiation, proliferation, adhesion, ultimately forming organotypic cell culture and artificial tissue structures.
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| 4. |
- Rotomskis, R, et al.
(författare)
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Hierarchical structure of TPPS4 J-aggregates on substrate revealed by atomic force microscopy
- 2004
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:9, s. 2833-2838
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Tidskriftsartikel (refereegranskat)abstract
- The spatial structure of the J-aggregates of meso-tetra(4-sulfonatophenyl)porphine (TPPS4) formed in acidic aqueous solutions and coated on silicon substrates was analyzed by means of atomic force microscopy (AFM). The AFM experiments indicate the presence of the stripelike J-aggregate structures on the surface. The size of the individual stripes ranged from 4.5 x 40 x 200 to 4.5 x 40 x 1000 nm(3) (height x width x length). The length of the stripelike structures varied, whereas stripe width and thickness remained unchanged. The stripes stacked into larger domains, "fibers", containing typically 2-20 stripes aligned parallel with a longitudinal shift with respect to each other. The size of individual stripes remained the same when interacting side-by-side in fibers. At lower magnification it is clearly seen that fibers form a network-like structure. The J-aggregates assemble into large (up to several millimeters) bushlike structures. It takes several weeks to form such structures in acidic aqueous solutions. On the basis of our experimental findings, it is also suggested that the stripes consist of rings that form nanotube-like TPPS4 J-aggregates, which are flattened as a result of attractive interactions with the substrate.
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| 5. |
- Valiokas, R., et al.
(författare)
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Self-assembled monolayers containing terminal mono-, bis-, and tris-nitrilotriacetic acid groups : Characterization and application
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:9, s. 4959-4967
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Tidskriftsartikel (refereegranskat)abstract
- We have undertaken a structural and functional study of self-assembled monolayers (SAMs) formed on gold from a series of alkylthiol compounds containing terminal multivalent chelators (MCHs) composed of mono-, bis-, and tris-nitrilotriacetic acid (NTA) moieties. SAMs were formed from single-component solutions of the mono-, bis-, and tris-NTA compounds, as well as from mixtures with a tri(ethylene glycol)-terminated alkylthiol (EG3). Contact angle goniometry, null ellipsometry, and infrared spectroscopy were used to explore the structural characteristics of the MCH SAMs. Ellipsometric measurements show that the amount of the MCH groups on surfaces increases with increasing mol % of the MCH thiols in the loading solution up to about 80 mol %. We also conclude that mixed SAMs, prepared in the solution composition regime 0-30 mol % of the MCH thiols, consist of a densely packed alkyl layer, an amorphous ethylene glycol layer, and an outermost layer of MCH groups exposed toward the ambient. Above 30 mol %, a significant degree of disorder is observed in the SAMs. Finally, functional evaluation of the three MCH SAMs prepared at 0-30 mol% reveals a consistent increase in binding strengdi with increasing multivalency. The tris-NTA SAM, in particular, is enabled for stable and functional immobilization of a His6-tagged extracellular receptor subunit, even at low chelator surface concentrations, which makes it suitable for applications when a low surface density of capturing sites is desirable, e.g., in kinetic analyses. © 2008 American Chemical Society.
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| 6. |
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| 7. |
- Malysheva, L., et al.
(författare)
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Conformation-dependent molecular orientation deduced from first-principles modeling of oligo(ethylene glycol)-terminated and amide group containing alkanethiolates self-assembled on gold
- 2005
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Ingår i: Electronic properties of novel nanostructures. - Melville, NY : American Institute of Physics (AIP). - 0735402752 ; , s. 456-460
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Konferensbidrag (refereegranskat)abstract
- We report orientation angles for the alkyl chain, amide group, and oligo(ethylene glycol) (OEG) portion within self-assembled monolayers (SAMs) of OEG-terminated and amide containing alkanethiolates which, depending on the OEG length and substrate temperature, display unique conformations - all-trans or helical. Optimized geometries of the molecular constituents, characteristic vibration frequencies and transition dipole moments are obtained by using DFT methods with gradient corrections. These ab initio data are subsequently used to simulate infrared reflection-absorption (RA) spectra associated with different conformations and orientations. The obtained results have generated a deeper knowledge of the internal SAM structure, which is crucial for understanding phase and folding characteristics, interaction with water and ultimately the protein repellent properties of OEG-containing SAMs.
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| 8. |
- Nilebäck, Erik, 1984, et al.
(författare)
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Characterization and application of a surface modification designed for QCM-D studies of biotinylated biomolecules
- 2011
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Ingår i: Biosensors and Bioelectronics. - : Elsevier BV. - 0956-5663 .- 1873-4235. ; 28:1, s. 407-413
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Tidskriftsartikel (refereegranskat)abstract
- The rapid development of surface sensitive biosensor technologies, especially towards nanoscale devices, requires increasing control of surface chemistry to provide reliable and reproducible results, but also to take full advantage of the sensing opportunities. Here, we present a surface modification strategy to allow biotinylated biomolecules to be immobilized to gold coated sensor crystals for quartz crystal microbalance with dissipation monitoring (QCM-D) sensing. The unique feature of QCM-D is its sensitivity to nanomechanical (viscoelastic) properties at the sensing interface. The surface modification was based on mixed monolayers of oligo(ethylene glycol) (OEG) disulfides, with terminal -OH or biotin groups, on gold. Mixtures containing 1% of the biotin disulfide were concluded to be the most appropriate based on the performance when streptavidin was immobilized to biotinylated sensors and the subsequent biotinylated bovine serum albumin (BSA) interaction was studied. The OEG background kept the unspecific protein binding to a minimum, even when subjected to serum solutions with a high protein concentration. Based on characterization by contact angle goniometry, ellipsometry, and infrared spectroscopy, the monolayers were shown to be well-ordered, with the OEG chains predominantly adopting a helical conformation but also partly an amorphous structure. Storage stability was concluded to depend mainly on light exposure while almost all streptavidin binding activity was retained when storing the sensors cold and dark for 8 weeks. The surface modification was also tested for repeated antibody-antigen interactions between BSA and anti-BSA (immobilized to biotinylated protein A) in QCM-D measurements lasting for >10 h with intermediate basic regeneration. This proved an excellent stability of the coating and good reproducibility was obtained for 5 interaction cycles. With this kind of generic surface modification QCM-D can be used in a variety of biosensing applications to provide not only mass but also relevant information of the structural properties of adlayers.
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| 9. |
- Rakickas, T., et al.
(författare)
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Protein-Protein Interactions in Reversibly Assembled Nanopatterns
- 2008
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 8:10, s. 3369-3375
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Tidskriftsartikel (refereegranskat)abstract
- We describe herein a platform to study protein-protein interactions and to form functional protein complexes in nanoscopic surface domains. For this purpose, we employed multivalent chelator (MCh) templates, which were fabricated in a stepwise procedure combining dip-pen nanolithography (DPN) and molecular recognition-directed assembly. First, we demonstrated that an atomic force microscope (AFM) tip inked with an oligo(ethylene glycol) (OEG) disulfide compound bearing terminal biotin groups can be used to generate biotin patterns on gold achieving line widths below 100 nm, a generic platform for fabrication of functional nanostructures via the highly specific biotin-streptavidin recognition. Subsequently, we converted such biotin/streptavidin patterns into functional MCh patterns for reversible assembly of histidine- tagged (His-tagged) proteins via the attachment of a tris-nitriloacetic acid (trisNTA) biotin derivative. Fluorescence microscopy confirmed reversible immobilization of the receptor subunit ifnar2-His10 and its interaction with interferon-a2 labeled with fluorescent quantum dots in a 7 × 7 dot array consisting of trisNTA spots with a diameter of ~230 nm. Moreover, we carried out characterization of the specificity, stability, and reversibility as well as quantitative real-time analysis of protein-protein interactions at the fabricated nanopatterns by imaging surface plasmon resonance. Our work offers a route for construction and analysis of functional protein-based nanoarchitectures. © 2008 American Chemical Society.
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| 10. |
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