31 research outputs found
Tailored Optical Properties on the Macroscale by Template-Assisted Self-Assembly of Plasmonic Nanoparticles
Template-assisted colloidal self-assembly of macroscopic magnetic metasurfaces
We demonstrate a template-assisted colloidal self-assembly approach for magnetic metasurfaces on macroscopic areas. The choice of anisotropic colloidal particle geometry, assembly pattern and metallic film is based on rational design criteria, taking advantage of mirror-charge effects for gold nanorods placed on gold film. Monodisperse gold nanorods prepared utilizing wet-chemistry are arranged with high precision on wrinkled templates to form linear array-type assemblies and subsequently transferred to a thin gold film. Due to the obtained particle-to-film distance of 1.1 nm, the plasmonic mode of the nanorod is able to couple efficiently with the supporting metallic film, giving rise to a magnetic mode in the visible spectrum (721 nm). Conventional UV-vis-NIR measurements in close correlation with electromagnetic simulations provide evidence for the presence of a magnetic resonance on the macroscopic area. The herein presented scalable lithography-free fabrication process paves the road towards colloidal functional metasurfaces with an optical response in the effective magnetic permeability
Colloidally Stable and Surfactant-Free Protein-Coated Gold Nanorods in Biological Media
In this work, we investigate the ligand exchange of cetyltrimethylammonium bromide (CTAB) with bovine serum albumin for gold nanorods. We demonstrate by surface-enhanced Raman scattering measurements that CTAB, which is used as a shape-directing agent in the particle synthesis, is completely removed from solution and particle surface. Thus, the protein-coated nanorods are suitable for bioapplications, where cationic surfactants must be avoided. At the same time, the colloidal stability of the system is significantly increased, as evidenced by spectroscopic investigation of the particle longitudinal surface plasmon resonance, which is sensitive to aggregation. Particles are stable at very high concentrations (cAu 20 mg/mL) in biological media such as phosphate buffer saline or Dulbeccoâs Modified Eagleâs Medium and over a large pH range (2â12). Particles can even be freeze-dried (lyophilized) and redispersed. The protocol was applied to gold nanoparticles with a large range of aspect ratios and sizes with main absorption frequencies covering the visible and the near-IR spectral range from 600 to 1100 nm. Thus, these colloidally stable and surfactant-free protein-coated nanoparticles are of great interest for various plasmonic and biomedical applications.ISSN:1944-8244ISSN:1944-825
Nucleotide-amino acid Ï-stacking interactions initiate photo cross-linking in RNA-protein complexes
Photo-induced cross-linking is a mainstay technique to characterize RNA-protein interactions. However, UV-induced cross-linking between RNA and proteins at âzero-distanceâ is poorly understood. Here, we investigate cross-linking of the RBFOX alternative splicing factor with its hepta-ribonucleotide binding element as a model system. We examine the influence of nucleobase, nucleotide position and amino acid composition using CLIR-MS technology (crosslinking-of-isotope-labelled-RNA-and-tandem-mass-spectrometry), that locates cross-links on RNA and protein with site-specific resolution. Surprisingly, cross-linking occurs only at nucleotides that are Ï-stacked to phenylalanines. Notably, this Ï-stacking interaction is also necessary for the amino-acids flanking phenylalanines to partake in UV-cross-linking. We confirmed these observations in several published datasets where cross-linking sites could be mapped to a high resolution structure. We hypothesize that Ï-stacking to aromatic amino acids activates cross-linking in RNA-protein complexes, whereafter nucleotide and peptide radicals recombine. These findings will facilitate interpretation of cross-linking data from structural studies and from genome-wide datasets generated using CLIP (cross-linking-and-immunoprecipitation) methods
Colloidally Stable and Surfactant-Free Protein-Coated Gold Nanorods in Biological Media
In this work, we investigate the
ligand exchange of cetyltrimethylammonium bromide (CTAB) with bovine
serum albumin for gold nanorods. We demonstrate by surface-enhanced
Raman scattering measurements that CTAB, which is used as a shape-directing
agent in the particle synthesis, is completely removed from solution
and particle surface. Thus, the protein-coated nanorods are suitable
for bioapplications, where cationic surfactants must be avoided. At
the same time, the colloidal stability of the system is significantly
increased, as evidenced by spectroscopic investigation of the particle
longitudinal surface plasmon resonance, which is sensitive to aggregation.
Particles are stable at very high concentrations (<i>c</i><sub>Au</sub> 20 mg/mL) in biological media such as phosphate buffer
saline or Dulbeccoâs Modified Eagleâs Medium and over
a large pH range (2â12). Particles can even be freeze-dried
(lyophilized) and redispersed. The protocol was applied to gold nanoparticles
with a large range of aspect ratios and sizes with main absorption
frequencies covering the visible and the near-IR spectral range from
600 to 1100 nm. Thus, these colloidally stable and surfactant-free
protein-coated nanoparticles are of great interest for various plasmonic
and biomedical applications
Colloidally Stable and Surfactant-Free Protein-Coated Gold Nanorods in Biological Media
In this work, we investigate the
ligand exchange of cetyltrimethylammonium bromide (CTAB) with bovine
serum albumin for gold nanorods. We demonstrate by surface-enhanced
Raman scattering measurements that CTAB, which is used as a shape-directing
agent in the particle synthesis, is completely removed from solution
and particle surface. Thus, the protein-coated nanorods are suitable
for bioapplications, where cationic surfactants must be avoided. At
the same time, the colloidal stability of the system is significantly
increased, as evidenced by spectroscopic investigation of the particle
longitudinal surface plasmon resonance, which is sensitive to aggregation.
Particles are stable at very high concentrations (<i>c</i><sub>Au</sub> 20 mg/mL) in biological media such as phosphate buffer
saline or Dulbeccoâs Modified Eagleâs Medium and over
a large pH range (2â12). Particles can even be freeze-dried
(lyophilized) and redispersed. The protocol was applied to gold nanoparticles
with a large range of aspect ratios and sizes with main absorption
frequencies covering the visible and the near-IR spectral range from
600 to 1100 nm. Thus, these colloidally stable and surfactant-free
protein-coated nanoparticles are of great interest for various plasmonic
and biomedical applications
Photochemical Synthesis of Polymeric Fiber Coatings and Their Embedding in Matrix Material: Morphology and Nanomechanical Properties at the FiberâMatrix Interface
In this contribution, we present a three-step pathway
to produce
a novel fiber coating, study its embedding in epoxy resin and characterize
its nanomechanical properties at the interface between fiber and matrix.
Inorganic surfaces were sulfhydrylated for subsequent use in thiol-initiated
ene photopolymerization. The influence of water on the sulfhydrylation
process was studied to find conditions allowing monomolecular deposition.
Surface morphology as well as SH-content were evaluated by UV/vis
spectroscopy, atomic force microscopy and spectroscopic ellipsometry.
Brush-like polymer layers (PS and PMMA) were introduced by UV-light
initiated surface polymerization of vinyl monomers. Polymer growth
and morphology were studied. After embedding, the nanomechanics of
the interfacial region of the fibers was studied. AFM force spectroscopy
allowed the mapping of the stiffness distribution at the cross-section
of the composite with high spatial resolution. Elastic moduli were
determined by Hertzian contact mechanics. The individual phases of
the composite material (fiber, interphase, and matrix) can be clearly
distinguished based on their mechanical response. The synthesis, morphology,
and mechanical properties of an interphase based on a polymeric graft-film
swollen with matrix material are shown, and perspectives of these
novel coatings for improved matrixâfiber compatibility and
interfacial adhesion are discussed
Strongly Coupled Plasmonic Modes on Macroscopic Areas via Template-Assisted Colloidal Self-Assembly
We present ensembles of surface-ordered nanoparticle arrangements, which are formed by template-assisted self-assembly of monodisperse, protein-coated gold nanoparticles in wrinkle templates. Centimeter-squared areas of highly regular, linear assemblies with tunable line width are fabricated and their extinction cross sections can be characterized by conventional UV/vis/NIR spectroscopy. Modeling based on electrodynamic simulations shows a clear signature of strong plasmonic coupling with an interparticle spacing of 1â2 nm. We find evidence for well-defined plasmonic modes of quasi-infinite chains, such as resonance splitting and multiple radiant modes. Beyond elementary simulations on the individual chain level, we introduce an advanced model, which considers the chain length distribution as well as disorder. The step toward macroscopic sample areas not only opens perspectives for a range of applications in sensing, plasmonic light harvesting, surface enhanced spectroscopy, and information technology but also eases the investigation of hybridization and metamaterial effects fundamentally.ISSN:1530-6984ISSN:1530-699
Structural requirements for photo-induced RNA-protein cross-linking
Understanding structure-function relationships of RNA-binding proteins requires knowledge of how they bind RNAs in vivo. RNA-protein interactions are studied using light-induced cross-linking at âzero-distanceâ, yielding nucleotide/amino-acid adducts for mass-spectrometry (MS)-based characterization. However, prerequisites for cross-linking are poorly understood, limiting interpretation of cross-linking data. Here, we report novel insights on cross-linking requirements from studying RBFOX-RRM domain bound to 13C-labeled variants of its heptaribonucleotide binding element as a model. We probed the influence of nucleotide identity, sequence position and amino-acid composition using tandem-MS to assign cross-links at site-specific resolution. We observed cross-linking at three nucleotides, which were stacked onto phenylalanines. Surprisingly, this stacking was required for neighbouring amino-acids to cross-link, and is apparent in published RNA-protein datasets. We hypothesize that Ï-stacking activates cross-linking via electron transfer, whereafter nucleotide- and peptide radicals, possibly stabilized by capto-dative effects, recombine. These findings should facilitate interpretation of cross-linking data from structural studies and genome-wide datasets
Injectable Shear-Thinning Fluorescent Hydrogel Formed by Cellulose Nanocrystals and Graphene Quantum Dots
In
the search for new building blocks of nanofibrillar hydrogels,
cellulose nanocrystals (CNCs) have attracted great interest because
of their sustainability, biocompatibility, ease of surface functionalization,
and mechanical strength. Making these hydrogels fluorescent extends
the range of their applications in tissue engineering, bioimaging,
and biosensing. We report the preparation and properties of a multifunctional
hydrogel formed by CNCs and graphene quantum dots (GQDs). We show
that although CNCs and GQDs are both negatively charged, hydrogen
bonding and hydrophobic interactions overcome the electrostatic repulsion
between these nanoparticles and yield a physically cross-linked hydrogel
with tunable mechanical properties. Owing to their shear-thinning
behavior, the CNC-GQD hydrogels were used as an injectable material
in 3D printing. The hydrogels were fluorescent and had an anisotropic
nanofibrillar structure. The combination of these advantageous properties
makes this hybrid hydrogel a promising material and fosters the development
of new manufacturing methods such as 3D printing