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Dive into the research topics where Christopher Wolter is active.

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Featured researches published by Christopher Wolter.


Langmuir | 2014

Polymer-assisted self-assembly of superparamagnetic iron oxide nanoparticles into well-defined clusters: controlling the collective magnetic properties.

Christian Schmidtke; Robin Eggers; Robert Zierold; Artur Feld; Hauke Kloust; Christopher Wolter; Johannes Michael Ostermann; Jan-Philip Merkl; Theo Schotten; Kornelius Nielsch; Horst Weller

The combination of superstructure-forming amphiphilic block copolymers and superparamagnetic iron oxide nanoparticles produces new nano/microcomposites with unique size-dependent properties. Herein, we demonstrate the controlled clustering of superparamagnetic iron oxide nanoparticles (SPIOs) ranging from discretely encapsulated SPIOs to giant clusters, containing hundreds or even more particles, using an amphiphilic polyisoprene-block-poly(ethylene glycol) diblock copolymer. Within these clusters, the SPIOs interact with each other and show new collective properties, neither obtainable with singly encapsulated nor with the bulk material. We observed cluster-size-dependent magnetic properties, influencing the blocking temperature, the magnetoviscosity of the liquid suspension, and the r2 relaxivity for magnetic iron oxide nanoparticles. The clustering methodology can be expanded also to other nanoparticle materials [CdSe/CdS/ZnS core/shell/shell quantum dots (QDs), CdSe/CdS quantum dots/quantum rods (QDQRs), gold nanoparticles, and mixtures thereof].


Angewandte Chemie | 2015

A universal approach to ultrasmall magneto-fluorescent nanohybrids.

Artur Feld; Jan-Philip Merkl; Hauke Kloust; Sandra Flessau; Christian Schmidtke; Christopher Wolter; Johannes Michael Ostermann; Michael Kampferbeck; Robin Eggers; Alf Mews; Theo Schotten; Horst Weller

Seeded emulsion polymerization is a powerful universal method to produce ultrasmall multifunctional magnetic nanohybrids. In a two-step procedure, iron oxide nanocrystals were initially encapsulated in a polystyrene (PS) shell and subsequently used as beads for a controlled assembly of elongated quantum dots/quantum rods (QDQRs). The synthesis of a continuous PS shell allows the whole construct to be fixed and the composition of the nanohybrid to be tuned. The fluorescence of the QDQRs and magnetism of iron oxide were perfectly preserved, as confirmed by single-particle investigation, fluorescence decay measurements, and relaxometry. Bio-functionalization of the hybrids was straightforward, involving copolymerization of appropriate affinity ligands as shown by immunoblot analysis. Additionally, the universality of this method was shown by the embedment of a broad scale of NPs.


Beilstein Journal of Nanotechnology | 2015

Tailoring the ligand shell for the control of cellular uptake and optical properties of nanocrystals

Johannes Michael Ostermann; Christian Schmidtke; Christopher Wolter; Jan-Philip Merkl; Hauke Kloust; Horst Weller

Summary In this short review, the main challenges in the use of hydrophobic nanoparticles in biomedical application are addressed. It is shown how to overcome the different issues by the use of a polymeric encapsulation system, based on an amphiphilic polyisoprene-block-poly(ethylene glycol) diblock copolymer. On the basis of this simple molecule, the development of a versatile and powerful phase transfer strategy is summarized, focusing on the main advantages like the adjustable size, the retained properties, the excellent shielding and the diverse functionalization properties of the encapsulated nanoparticles. Finally, the extraordinary properties of these encapsulated nanoparticles in terms of toxicity and specificity in a broad in vitro test is demonstrated.


Langmuir | 2015

Clustering of CdSe/CdS Quantum Dot/Quantum Rods into Micelles Can Form Bright, Non-blinking, Stable, and Biocompatible Probes.

Mona Rafipoor; Christian Schmidtke; Christopher Wolter; Christian Strelow; Horst Weller; Holger Lange

We investigate clustered CdSe/CdS quantum dots/quantum rods, ranging from single to multiple encapsulated rods within amphiphilic diblock copolymer micelles, by time-resolved optical spectroscopy. The effect of the clustering and the cluster size on the optical properties is addressed. The clusters are bright and stable and show no blinking while retaining the fundamental optical properties of the individual quantum dots/quantum rods. Cell studies show neither unspecific uptake nor morphological changes of the cells, despite the increased sizes of the clusters.


Proceedings of SPIE | 2014

Shielding of quantum dots using diblock copolymers: implementing copper catalyzed click chemistry to fluorescent quantum dots

Jan-Philip Merkl; Johannes Michael Ostermann; Christian Schmidtke; Hauke Kloust; Robin Eggers; Artur Feld; Christopher Wolter; Anna-Marlena Kreuziger; Sandra Flessau; Hedi Mattoussi; Horst Weller

We describe the design and optimization of an amphiphilic diblock copolymer and its use to provide surface functionalization of colloidal semiconductor nanoparticles (quantum dots, QDs). This polymer coating promotes hydrophilicity of the nanocrystals while providing numerous functional groups ideally suited for biofunctionalization of the QDs using copper-catalyzed azide alkyne Husigen 1,3-cyloaddition (i.e., cupper catalyzed “click” reaction). Copper ions are known to quench the fluorescence of QDs in solution. Thus effective shielding of the nanocrystal surface is essential to apply copper-catalyzed reactions to luminescent QDs without drastically quenching their emission. We have applied a strategy based on micellar encapsulation within poly(isoprene-block- ethylene oxide) diblock-copolymers (PI-b-PEO), where three critical factors promote and control the effectiveness of the shielding of copper ion penetration: 1) The excess of PI-b-PEO, 2) the size of PI-b-PEO and 3) insertion of an additional PS-shell grown via seeded emulsion polymerization (EP) reaction. Due to the amphiphilic character of the block-copolymer, this approach provides a shielding layer surrounding the particles, preventing metal ions from reaching the QD surfaces and maintaining high photoluminescence. The effective shielding allowed the use of copper-catalyzed azide-alkyne 1,3-cycloaddition (CuAAC) to hydrophilic and highly fluorescent QDs, opening up great possibilities for the bio functionalization of QDs.


VIII INTERNATIONAL CONFERENCE ON “TIMES OF POLYMERS AND COMPOSITES”: From Aerospace to Nanotechnology | 2016

Seeded emulsion polymerization as a powerful tool for the biofunctionalization of quantum dots

Lasse Habercorn; Jan-Philip Merkl; Hauke Kloust; Artur Feld; Johannes Michael Ostermann; Christian Schmidtke; Christopher Wolter; Marcus Janschel; Horst Weller

With the polymer encapsulation of quantum dots via seeded emulsion polymerization we present a powerful tool for the preparation of fluorescent nanoparticles with an extraordinary stability in aqueous solution. The method of the seeded emulsion polymerization allows a straightforward and simple in situ functionalization of the polymer shell under preserving the optical properties of the quantum dots. These requirements are inevitable for the application of semiconductor nanoparticles as markers for biomedical applications. Polymer encapsulated quantum dots have shown only a marginal loss of quantum yields when they were exposed to copper(II)-ions. Under normal conditions the quantum dots were totally quenched in presence of copper(II)-ions. Furthermore, a broad range of in situ functionalized polymer-coated quantum dots were obtained by addition of functional monomers or surfactants like fluorescent dye molecules, antibodies or specific DNA aptamers. Furthermore the emulsion polymerization can be used to ...


ACS Nano | 2013

Controlling the Physical and Biological Properties of Highly Fluorescent Aqueous Quantum Dots Using Block Copolymers of Different Size and Shape

Johannes Michael Ostermann; Jan-Philip Merkl; Sandra Flessau; Christopher Wolter; Andreas Kornowksi; Christian Schmidtke; Andrea Pietsch; Hauke Kloust; Artur Feld; Horst Weller


Nanoscale | 2014

CdSe/CdS-quantum rods: fluorescent probes for in vivo two-photon laser scanning microscopy

Jelena Dimitrijevic; Lisa Krapf; Christopher Wolter; Christian Schmidtke; Jan-Philip Merkl; Tobias Jochum; Andreas Kornowski; Anna Schüth; Andreas Gebert; Gereon Hüttmann; Tobias Vossmeyer; Horst Weller


Physical Chemistry Chemical Physics | 2017

Excitation wavelength dependence of the photoluminescence quantum yield and decay behavior of CdSe/CdS quantum dot/quantum rods with different aspect ratios

Daniel Geißler; Christian Würth; Christopher Wolter; Horst Weller; Ute Resch-Genger


Nanoscale | 2016

Investigations of ion transport through nanoscale polymer membranes by fluorescence quenching of CdSe/CdS quantum dot/quantum rods

Jan-Philip Merkl; Christopher Wolter; Sandra Flessau; Christian Schmidtke; Johannes Michael Ostermann; Artur Feld; Alf Mews; Horst Weller

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Alf Mews

University of Hamburg

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