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Author: Müller, Robert × Has files: Yes ×

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Now showing 1 - 6 of 6
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    Different storage conditions influence biocompatibility and physicochemical properties of iron oxide nanoparticles
    (Basel : Molecular Diversity Preservation International (MDPI), 2015) Zaloga, Jan; Janko, Christina; Agarwal, Rohit; Nowak, Johannes; Müller, Robert; Boccaccini, Aldo R.; Lee, Geoffrey; Odenbach, Stefan; Lyer, Stefan; Alexiou, Christoph
    Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted increasing attention in many biomedical fields. In magnetic drug targeting SPIONs are injected into a tumour supplying artery and accumulated inside the tumour with a magnet. The effectiveness of this therapy is thus dependent on magnetic properties, stability and biocompatibility of the particles. A good knowledge of the effect of storage conditions on those parameters is of utmost importance for the translation of the therapy concept into the clinic and for reproducibility in preclinical studies. Here, core shell SPIONs with a hybrid coating consisting of lauric acid and albumin were stored at different temperatures from 4 to 45 °C over twelve weeks and periodically tested for their physicochemical properties over time. Surprisingly, even at the highest storage temperature we did not observe denaturation of the protein or colloidal instability. However, the saturation magnetisation decreased by maximally 28.8% with clear correlation to time and storage temperature. Furthermore, the biocompatibility was clearly affected, as cellular uptake of the SPIONs into human T-lymphoma cells was crucially dependent on the storage conditions. Taken together, the results show that the particle properties undergo significant changes over time depending on the way they are stored.
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    Time-resolved study of site-specific corrosion in a single crystalline silver nanoparticle
    (Berlin : SpringerOpen, 2019) Trautmann, Steffen; Dathe, André; Csáki, Andrea; Thiele, Matthias; Müller, Robert; Fritzsche, Wolfgang; Stranik, Ondrej
    We followed over 24 h a corrosion process in monocrystalline triangular-shaped nanoparticles at a single-particle level by atomic force microscopy and optical spectroscopy techniques under ambient laboratory conditions. The triangular-shaped form of the particles was selected, because the crystallographic orientation of the particles is well defined upon their deposition on a substrate. We observed that the particles already start to alter within this time frame. Surprisingly, the corrosion starts predominantly from the tips of the particles and it creates within few hours large protrusions, which strongly suppress the plasmon character of the particles. These observations support the crystallographic model of these particles consisting of a high-defect hexagonal closed packed layer, and they could help material scientists to design more stable silver nanoparticles. Moreover, this described technique can be used to reveal kinetics of the corrosion in the nanoscale of other materials.
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    Wet-chemical Passivation of Anisotropic Plasmonic Nanoparticles for LSPR-sensing by a Silica Shell
    (Amsterdam [u.a.] : Elsevier, 2015) Thiele, Matthias; Götz, Isabell; Trautmann, Steffen; Müller, Robert; Csáki, Andrea; Henkel, Thomas; Fritzsche, Wolfgang
    Metal nanoparticles showing the effect of localized surface plasmon resonance (LSPR), a collective oscillation of the conduction electrons upon interaction with light, represent an interesting tool for bioanalytics. This resonance is influenced by changes in the environment, and can be therefore used for the detection of molecular layers. The sensitivity, this means the extent of wavelength resonance shift per change in refractive index in the environment, represents an important performance parameter. It is higher for silver compared to gold particles, and is also increased for anisotropic particles. So silver triangles show a high potential for highly sensitive plasmonic nanoparticles. However, the stability under ambient conditions is rather poor. The paper demonstrates the passivation of silver triangles by silica coating using a wet-chemical approach. It compares the sensitivity for particles with and without passivation, and visualizes the passivation effect in a high resolution, single particle TEM study.
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    Studies on the Controlled Release of Drugs from Magnetic Nanobiocomposites
    (Palembang : Sriwijaya University, 2019) Heinze, Thomas; Müller, Robert; Zhou, Mengbo; Rabel, Martin; Warncke, Paul; Fischer, Dagmar
    Magnetic nanocomposites are a class of smart materials that have attracted recent interest as drug delivery systems or as medical implants. In this study, meltable nanobiocomposites (NBC) composed of biocompatible dextran fatty acid ester and magnetic nanoparticles (MNPs) melting close to human body temperature were prepared and loaded with Rhodamine B (RhB) or green fluorescent protein (GFP) as model drugs to evaluate their potential use as drug delivery system. The release of the model drugs from the magnetic NBC investigated under the influence of a high frequent alternating magnetic field (AMF, 20 kA/m at 400 kHz) showed that on-demand release is realized applying the external AMF. The NBC showed a long-term stability (28 d) of the incorporated iron oxide particles after incubation in artificial body fluids. This work reveals the potential of the NBC as a drug carrier.
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    (INVITED)Tm:YAG crystal-derived double-clad fibers – A hybrid approach towards high gain and high efficiency Tm lasers
    (Amsterdam : Elsevier, 2022) Leich, Martin; Müller, Robert; Unger, Sonja; Schwuchow, Anka; Dellith, Jan; Lorenz, Adrian; Kobelke, Jens; Jäger, Matthias
    The hybrid approach of combining a Tm:YAG laser crystal with an amorphous fused silica tube is investigated to evaluate the suitability of the resulting crystal-derived fibers for efficient double-clad fiber lasers. The fabrication process and fiber properties of these Tm fibers are investigated, focusing on the dependence of the active fiber properties on the incorporated Tm3+ concentration. Crystal rods with different doping concentrations (TmxY1-x)3Al5O12 (x = 0.02, 0.05 and 0.08) were used as starting core material for fiber drawing. The investigated fibers are mechanically stable and result in a fairly homogenous and amorphous core glass with optical absorption and emission spectra that are similar to conventional Tm:Al doped silica fibers. Regarding laser properties with 790 nm cladding pumping, we could achieve a maximum slope efficiency of 47% with an output power of 4 W. The fiber laser results are compared to a conventionally fabricated double-clad Tm fiber prepared by Modified Chemical Vapor Deposition and solution doping. To the best of our knowledge, we demonstrate the highest laser output and the highest efficiency obtained from a Tm:YAG crystal-derived fiber.
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