0000000000082710
AUTHOR
Heiko Bauer
Multifunctional superparamagnetic MnO@SiO2 core/shell nanoparticles and their application for optical and magnetic resonance imaging
Highly biocompatible multifunctional nanocomposites consisting of monodisperse manganese oxide nanoparticles with luminescent silica shells were synthesized by a combination of w/o-microemulsion techniques and common sol–gel procedures. The nanoparticles were characterized by TEM analysis, powder XRD, SQUID magnetometry, FT-IR, UV/vis and fluorescence spectroscopy and dynamic light scattering. Due to the presence of hydrophilic poly(ethylene glycol) (PEG) chains on the SiO2 surface, the nanocomposites are highly soluble and stable in various aqueous solutions, including physiological saline, buffer solutions and human blood serum. The average number of surface amino groups available for lig…
The “Needle in the Haystack” Makes the Difference: Linear and Hyperbranched Polyglycerols with a Single Catechol Moiety for Metal Oxide Nanoparticle Coating
Multifunctional linear (CA-linPG) and hyperbranched polyglycerols (CA-hbPG) bearing a single catechol unit were synthesized by use of an acetonide-protected catechol initiator for the anionic polymerization of ethoxyethyl glycidyl ether (EEGE) and glycidol, respectively. A key feature for the synthesis of the hyperbranched structures was a selective, partial acetal deprotection step. The single catechol unit among a large number of aliphatic 1,2- and 1,3-diol moieties (i.e., the “needle in the haystack”) in both linear and hyperbranched polyglycerols permits dispersion of transition metal oxide nanoparticles in brine, as demonstrated for manganese oxide (MnO) nanoparticles. Molecular weight…
Catechol-Initiated Polyethers: Multifunctional Hydrophilic Ligands for PEGylation and Functionalization of Metal Oxide Nanoparticles
Bifunctional CA-PEG (catechol-poly(ethylene glycol)) and multifunctional CA-PEG-PGA/PEVGE (poly(glycidyl amine)/poly(ethylene glycol vinyl glycidyl ether)) ligands for the functionalization and solubilization of nanoparticles are introduced. Tunable polymers with polydispersities1.25 and molecular weights in the range 500-7700 g mol(-1) containing a catechol moiety for conjugation to metal oxide nanoparticles were prepared. The functional PEG ligands were synthesized starting from the acetonide-protected catechol initiator 2,2-dimethyl-1,3-benzodioxole-5-propanol (CA-OH) for oxyanionic polymerization. CA-OH was used both for homopolymerization of ethylene oxide (EO) as well as copolymerizat…
Synthesis and Magnetic Properties of FePt@MnO Nano-heteroparticles
Monodisperse FePt@MnO nano-heteroparticles with different sizes and morphologies were prepared by a seed-mediated nucleation and growth technique. Both size and morphology of the individual domains could be controlled by adjustment of the synthetic parameters. As a consequence, different particle constructs, including dimers, dumbbell-like particles, and flowerlike particles, could be obtained by changing the polarity of the solvent. The FePt@MnO nano-heteroparticles were thoroughly characterized by high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) analyses and superconducting quantum interference device (SQUID) magnetometry. Due to a sufficient lattice m…
Highly soluble multifunctional MnO nanoparticles for simultaneous optical and MRI imaging and cancer treatment using photodynamic therapy
Superparamagnetic MnO nanoparticles were functionalized using a hydrophilic ligand containing protoporphyrin IX as photosensitizer. By virtue of their magnetic properties these nanoparticles may serve as contrast enhancing agents for magnetic resonance imaging (MRI), while the fluorescent target ligand protoporphyrin IX allows simultaneous tumor detection and treatment by photodynamic therapy (PDT). Caki-1 cells were incubated with these nanoparticles. Subsequent exposure to UV light lead to cell apoptosis due to photoactivation of the photosensitizer conjugated to the nanoparticles. This method offers great diagnostic potential for highly proliferative tissues, including tumors. In additio…
How do different surface modification strategies affect the properties of MnO nanoparticles for biomedical applications? Comparison of PEGylated and SiO2-coated MnO nanoparticles
ABSTRACTMnO nanoparticles (NPs) were surface functionalized by two different approaches, (1) using a dopamine-poly(ethylene glycol) (PEG) (DA-PEG) ligand and (2) by encapsulation within a thin silica shell applying a novel approach. Both MnO@DA-PEG and MnO@SiO2 NPs exhibited excellent long-term stability in physiological solutions. In addition, the cytotoxic potential of both materials was comparatively low. Furthermore, owing to the magnetic properties of MnO NPs, both MnO@DA-PEG and MnO@SiO2 lead to a shortening of the longitudinal relaxation time T1 in MRI. In comparison to the PEGylated MnO NPs, the presence of a thin silica shell led to a greater stability of the MnO core itself by pre…
Multifunctional two-photon active silica-coated Au@MnO Janus particles for selective dual functionalization and imaging.
Monodisperse multifunctional and nontoxic Au@MnO Janus particles with different sizes and morphologies were prepared by a seed-mediated nucleation and growth technique with precise control over domain sizes, surface functionalization, and dye labeling. The metal oxide domain could be coated selectively with a thin silica layer, leaving the metal domain untouched. In particular, size and morphology of the individual (metal and metal oxide) domains could be controlled by adjustment of the synthetic parameters. The SiO2 coating of the oxide domain allows biomolecule conjugation (e.g., antibodies, proteins) in a single step for converting the photoluminescent and superparamagnetic Janus nanopar…
Magnetism of monomer MnO and heterodimer FePt@MnO nanoparticles
We report about the magnetic properties of antiferromagnetic (AF) MnO nanoparticles (NPs) with different sizes (6--19 nm). Using a combination of polarized neutron scattering and magnetometry, we were able to resolve previously observed peculiarities. Magnetometry, on the one hand, reveals a peak in the zero-field-cooled (ZFC) magnetization curves at low temperatures $(\ensuremath{\sim}25$ K) but $no$ feature around the N\'eel temperature at 118 K. On the other hand, polarized neutron scattering shows the expected behavior of the AF order parameter vanishing around 118 K. Moreover, hysteresis curves measured at various temperatures reveal an exchange-bias effect, indicating a coupling of an…