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One-step synthesis of sub 5 nm sized manganese oxide based nanoparticles
Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
Division of Solid State Physics, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
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2013 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Sub 5 nm sized manganese oxide nanoparticles; MnOx (1 ≤ x ≤ 2), were synthesized via a short time room temperature synthesis route. The nanoparticles are crystalline, spherically shaped and in the size range of 2-4 nm as shown by transmission electron microscopy studies. Selected area electron diffraction patterns were collected and their appearance indicated that the nanoparticle cores are composed of MnO. Also, co-existence of the (II) and (III) oxidation states at the nanoparticle surface was verified by results achieved from infrared spectroscopy and X-ray photoelectron spectroscopy. These measurements also supported presence of a minor amount of acetate groups as well as a negligible fraction of carbonate groups at the nanoparticle surfaces. The interpretation of the IR spectra was confirmed by quantum chemical calculations using the high spin manganese nanoparticle Mn12O12(OAc)16(H2O)4, as a model system for the MnOx nanoparticle surface. Bulk MnO and Mn2O3 are known to be antiferromagnetic. The magnetic properties are however somewhat dependent of the crystallite size and changes when scaling down to the nanoregion. The MnOx (1 ≤ x ≤ 2) nanoparticles investigated in this work show a superparamagnetic behavior with a blocking temperature of approximately 12 K proven by means of SQUID measurements. The relaxivities of the nanoparticles and the Mn(OAc)2 precursors were studied with a bench top NMR analyzer verifying nanoparticle r1 and r2 of 0.5 and 6 mMs-1 respectively. The r1 relaxivity is lower than what is earlier reported for Gd based contrast agent, but improvements are expected by further surface modification, due to increased rotational time and higher water dispersability.

Place, publisher, year, edition, pages
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-98692OAI: diva2:655347
Available from: 2013-10-11 Created: 2013-10-11 Last updated: 2015-05-29Bibliographically approved
In thesis
1. Metal Oxide Nanoparticles for Contrast Enhancement in Magnetic Resonance Imaging: Synthesis, Functionalization and Characterization
Open this publication in new window or tab >>Metal Oxide Nanoparticles for Contrast Enhancement in Magnetic Resonance Imaging: Synthesis, Functionalization and Characterization
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis work focuses on the design and production of nanoparticle based contrast agents for signal enhancement in magnetic resonance imaging (MRI). Three different synthesis routes are explored, primarily to produce crystalline gadolinium oxide (Gd2O3) nanoparticles, and surface modification is done to obtain stable, dispersible, biocompatible probes inducing high proton relaxivities.

In Paper I and II we utilized the polyol synthesis method and nanoparticle purification was performed with dialysis. Active surface functionalization was achieved by an innermost layer of 3-mercaptopropyl trimetoxy silanes (MPTS) and an outer layer of bifunctional PEG. Surface capping was shown to greatly affect the water proton relaxation to a degree which is strongly dependent on the purification time. PEGylation also induced stabilizing effects and the ability to provide the nanoparticles with luminescent properties was proven by linking the fluorescent dye Rhodamine to the bifunctional PEG.

In Paper III the magnetic behavior of yttrium (Y) alloyed Gd2O3 nanoparticles was investigated as a function of Y concentration. This was done by performing magnetic measurements and by studying the signal line width in electron paramagnetic resonance spectroscopy for Gd2O3, Y2O3 and a series of (GdxY1-x)2O3 samples produced using the combustion synthesis. The results verified that the signal line width is dependent on the percent of yttrium dilution. This is considered as an indication of that yttrium dilution changes the electron spin relaxation time in Gd2O3.

Paper IV and V present a novel precipitation synthesis method for Gd2O3 nanoparticles. Acetate molecular groups were found to coordinate the nanoparticle surface increasing the water dispersability. The Gd2O3 nanoparticles induce a twice as high relaxivity per gadolinium atom, as compared to the commercially available contrast agent Magnevist. Incorporation of luminescent europium (Eu3+) ions into the Gd2O3 nanoparticles in combination with surface modification with a fluorescent branched carboxyl terminated TEG, produced dual probes with tunable luminescence, maintained relaxivity and thus a bright contrast in MRI.

In Paper VI, a new approach to accomplish a dual probe was investigated. Luminescent ZnO nanoparticles decorated with Gd ions bound in an organic matrix were evaluated for MR signal enhancement and ability to function as fluorescent probes. Interestingly, these nanoprobes did show an enhanced capability to both strengthen the MR signal and increase the fluorescent quantum yield, as compared to the pure oxides.

In Paper VII we investigate sub 5 nm crystalline manganese based nanoparticles produced by the precipitation synthesis used for Gd2O3 nanoparticles. Manganese oxide was chosen as another candidate for MRI contrast enhancement as it is expected to have a straight forward surface coupling chemistry. Characterization of the crystal structure and chemical composition indicated nanoparticles with a MnO core and presence of manganese species of higher valences at the nanoparticle surface. The MnO nanomaterial showed a superparamagnetic behavior and less capability to increase the MR signal as compared to Gd2O3.

Characterization of the nanoparticle crystal structure and size is, throughout the work, performed by means of transmission electron microscopy, X-ray diffraction and dynamic light scattering. The chemical composition is studied with X-ray photoelectron spectroscopy, infrared spectroscopy and near edge X-ray absorption fine structure spectroscopy and the fluorescence characteristics are evaluated with fluorescence spectroscopy. In addition, theoretical models and calculated IR spectroscopy and near edge X-ray absorption fine structure spectroscopy data have been used for evaluation of experimental results.

To conclude, the aim of this work is the design, production and characterization of ultrasmall rare earth based nanoparticles for signal enhancement in biomedical imaging. Surface modification clearly increases the colloidal stability and biocompatibility of the nanoparticles. Compared to the agents in clinical use today, these nanoprobes have a higher capability to enhance the MR-signal, and they will in the near future be equipped with tags for specific targeting.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 82 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1541
National Category
Natural Sciences
urn:nbn:se:liu:diva-98693 (URN)10.3384/diss.diva-98693 (DOI)978-91-7519-522-3 (print) (ISBN)
Public defence
2013-11-15, Brillouin, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Available from: 2013-10-11 Created: 2013-10-11 Last updated: 2015-06-03Bibliographically approved

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