Development, synthesis and characterization of multifunctional nanomaterials

To achieve the societal and technological ambitions set for nanotechnology in general, multifunctional magnetic-plasmonic nanostructures can be a great asset. Such multifunctional materials, in which magnetic and plasmonic functionalities are combined at the nanoscale, can be used to unravel fundamental interactions between light and magnetism at that same scale. Further, they can also be applied in e.g. biomedicine for cancer therapy, catalysis for improved reaction rates at lower temperatures, sensors for magnetic field strength and miniaturized optical components such as optical isolators.In the first part of this work we present the calculated optical properties of core-shell magnetic-plasmonic nanospheres and nanorods as a function of nanostructure composition, size, and shape with a focus on biomedical applications. With this knowledge it is possible to rationally design and synthesize structures that possess a plasmon band in the advantageous biomedical near-infrared spectral window region and other optical properties such as scattering and absorption cross sections as desired for potential application in life sciences.To deal with the disadvantages of previously used synthesis protocols for nanoparticle-based thin film magnetic-plasmonic materials, a novel synthetic protocol was devised. The protocol itself, the resulting materials and their linear, nonlinear and magneto-optical properties are described in the second part of this work.Using short bifunctional molecular linkers, we produced magnetic-plasmonic nanoparticle multilayers by a novel layer-by-layer (LbL) synthesis on glass substrates. No polymers or polyelectrolytes were required during synthesis. Resulting nanocomposites, incorporating gold, silver and magnetite nanoparticles were homogeneous over a large area, had large nanoparticle filling fractions and showed tunability of the plasmon wavelength over a very broad spectral range by changing composite thickness through the number of added nanoparticle layers.Theoretical calculations were performed to verify and explain the observed optical properties of these magnetic-plasmonic assemblies. The calculations and the comparison with experimental observations lead us to a more nuanced view of the LbL self-assembly process as a function of layers. Nonlinear optical microscopy images confirmed homogeneity of the sample and the generated nonlinear optical signals. Spectral nonlinear optical measurements showed that gold-magnetite nanoparticle multilayers combine and simultaneously enhances second and third order nonlinear optical processes. Large magneto-optical responses were measured for gold-magnetite composites and the influence of the plasmonic gold nanoparticles was established.These results show that the developed layer-by-layer synthesis protocol can be used to produce homogeneous thin films of good quality. Advantageous and tuneable optical properties, large magneto-optical responses and the observed nonlinear optical resonance enhancements of such thin films make them attractive candidates for further fundamental research into e.g. magnetoplasmonics and for application in sensors or optical components.status: publishe

Optical properties of magnetic-plasmonic nanoparticle multilayers

Magnetic-plasmonic materials are an interesting class of materials for both fundamental and applied research. Knowledge of the optical properties and their origin in the materials is a must. Using a layer-by-layer method, we fabricated magnetic-plasmonic nanoparticle multilayers and measured their optical properties. Discrete dipole approximation calculations to model the optical properties of such materials allow us to understand the observed optical features. Comparing experimental and theoretical results provides us with a detailed insight in the build-up of the nanoparticle multilayers and shows that nanoparticles of the added layers fill holes in previous layers and improve the quality of the sample.status: publishe

Switching Faraday rotation on a molecular level

In this work we present measurements of the switching of the Faraday effect in metal-organic compounds. Faraday rotation is the rotation of the plane of polarization of linearly polarized light under the influence of a magnetic field in the direction of propagation of the light. It is the magnetic equivalent of circular birefringence and is related to magnetic circular dichroism via the Kramers-Kronig transformation. The Faraday effect is used in optical isolators and magnetic sensors.status: publishe

Core-shell nanoparticles as enhanced probes for imaging applications

The development of highly specific markers for fluorescent microscopy has become a very popular research topic. Organic fluorophores have several drawbacks, such as photobleaching and autofluorescence. Therefore increasing interest in inorganic nanoparticles has been observed because of their unseen photostability, chemical robustness and straightforward synthesis. The surface of iron oxide nanoparticles was coated with trialkoxy silanes, which introduced functional groups for possible subsequent coupling reactions. An additional gold layer was added to the surface of the particle to show the enhanced contrast improvement. The nanoparticles were imaged by an optical microscope, in dark field mode, on a glass substrate and inside microorganisms. This proved that the reported method could have great potential as a labelling technique, since it combines the non-photobleaching, photostable nanoparticles with a straightforward and rapid imaging technique. © 2012 SPIE.status: publishe

Magnetically induced Suzuki and Sonogashira reaction performed using recyclable, palladium-functionalized magnetite nanoparticles

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Two-Step Directional Surface Modification of Iron Oxide Nanoparticles with Protected Siloxanes

Successful surface modification of iron oxide nanoparticles is crucial for their usage in applications. However, ligand exchange methods introducing siloxanes have several drawbacks. Presented here is a novel approach for the surface modification of iron oxide nanoparticles by making use of siloxanes, synthesized by thiol-ene click chemistry, with protected functional groups. Afterwards the ligands are deprotected to liberate their functionality. This approach solves the issues related to ligand orientation and colloidal stability during surface modification.status: publishe