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Dive into the research topics where Nathan Kohler is active.

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Featured researches published by Nathan Kohler.


Biomaterials | 2002

Surface modification of superparamagnetic magnetite nanoparticles and their intracellular uptake

Yong Zhang; Nathan Kohler; Miqin Zhang

Superparamagnetic magnetite nanoparticles were surface-modified with poly (ethylene glycol) (PEG) and folic acid, respectively, to improve their intracellular uptake and ability to target specific cells. PEG and folic acid were successfully immobilized on the surfaces of magnetite nanoparticles and characterized using fourier transform infrared spectra. The nanoparticle internalization into mouse macrophage (RAW 264.7) and human breast cancer (BT20) cells was visualized using both fluorescence and confocal microscopy, and quantified by inductively coupled plasma emission spectroscopy (ICP). After the cells were cultured for 48 h in the medium containing the nanoparticles modified with PEG or folic acid, the results of fluorescence and confocal microscopy showed that the nanoparticles were internalized into the cells. The ICP measurements indicated that the uptake amount of PEG-modified nanoparticles into macrophage cells was much lower than that of unmodified nanoparticles. while folic acid modification did not change the amount of the uptake. However, for breast cancer cells, both PEG and folic acid modification facilitated the nanoparticle internalization into the cells. Therefore, PEG and folic acid modification of magnetite nanoparticles could be used to resist the protein adsorption and thus avoid the particle recognition by macrophage cells, and to facilitate the nanoparticle uptake to specific cancer cells for cancer therapy and diagnosis.


Journal of the American Chemical Society | 2009

FePt nanoparticles as an Fe reservoir for controlled Fe release and tumor inhibition.

Chenjie Xu; Zhenglong Yuan; Nathan Kohler; Jaemin Kim; Maureen A. Chung; Shouheng Sun

Chemically disordered face centered cubic (fcc) FePt nanoparticles (NPs) show the controlled release of Fe in low pH solution. The released Fe catalyzes H(2)O(2) decomposition into reactive oxygen species within cells, causing fast oxidation and deterioration of cellular membranes. Functionalized with luteinizing hormone-releasing hormone (LHRH) peptide via phospholipid, the fcc-FePt NPs can bind preferentially to the human ovarian cancer cell line (A2780) that overexpresses LHRH receptors and exhibit high toxicity to these tumor cells. In contrast, the fcc-FePt NPs pre-etched in the low pH (4.8) buffer solution show nonappreciable cytotoxicity. The work demonstrates that fcc-FePt NPs may function as a new type of agent for controlled cancer therapy.


Biomedical Microdevices | 2004

Self-assembled coatings on individual monodisperse magnetite nanoparticles for efficient intracellular uptake.

Yong Zhang; Conroy Sun; Nathan Kohler; Miqin Zhang

Monodispersed iron oxide superparamagnetic nanoparticles were prepared using a novel circulating system. A simple dialysis method was developed to immobilize nanoparticles with functional biopolymers and targeting agents, which avoids the use of the normal centrifugation process that may cause particle agglomeration during the coating process. To enhance the specific targeting capability of the nanoparticles, a new chemical scheme was introduced, in which folic acid (FA) was chosen as the targeting agent combined with PEG serving to improve biocompatibility of nanoparticles. The AFM characterization showed that the nanoparticles produced are well dispersed with a narrow size distribution. The FTIR and XPS spectrum analyses indicated that PEG and FA-PEG have been chemically/covalently bonded to nanoparticles using synthetic approach introduced in this study. Our biological study showed that coating nanoparticles with PEG-FA significantly enhanced the intracellular uptake of nanoparticles by target cells.


Chemistry-an Asian Journal | 2008

Monodisperse Magnetite Nanoparticles Coupled with Nuclear Localization Signal Peptide for Cell‐Nucleus Targeting

Chenjie Xu; Jin Xie; Nathan Kohler; Edward G. Walsh; Y. Eugene Chin; Shouheng Sun

Functionalization of monodisperse superparamagnetic magnetite (Fe(3)O(4)) nanoparticles for cell specific targeting is crucial for cancer diagnostics and therapeutics. Targeted magnetic nanoparticles can be used to enhance the tissue contrast in magnetic resonance imaging (MRI), to improve the efficiency in anticancer drug delivery, and to eliminate tumor cells by magnetic fluid hyperthermia. Herein we report the nucleus-targeting Fe(3)O(4) nanoparticles functionalized with protein and nuclear localization signal (NLS) peptide. These NLS-coated nanoparticles were introduced into the HeLa cell cytoplasm and nucleus, where the particles were monodispersed and non-aggregated. The success of labeling was examined and identified by fluorescence microscopy and MRI. The work demonstrates that monodisperse magnetic nanoparticles can be readily functionalized and stabilized for potential diagnostic and therapeutic applications.


Theranostics | 2012

Penetration of endothelial cell coated multicellular tumor spheroids by iron oxide nanoparticles

Don N. Ho; Nathan Kohler; Aruna Sigdel; Raghu Kalluri; Jeffrey R. Morgan; Chenjie Xu; Shouheng Sun

Iron oxide nanoparticles are a useful diagnostic contrast agent and have great potential for therapeutic applications. Multiple emerging diagnostic and therapeutic applications and the numerous versatile parameters of the nanoparticle platform require a robust biological model for characterization and assessment. Here we investigate the use of iron oxide nanoparticles that target tumor vasculature, via the tumstatin peptide, in a novel three-dimensional tissue culture model. The developed tissue culture model more closely mimics the in vivo environment with a leaky endothelium coating around a glioma tumor mass. Tumstatin-iron oxide nanoparticles showed penetration and selective targeting to endothelial cell coating on the tumor in the three-dimensional model, and had approximately 2 times greater uptake in vitro and 2.7 times tumor neo-vascularization inhibition. Tumstatin provides targeting and therapeutic capabilities to the iron oxide nanoparticle diagnostic contrast agent platform. And the novel endothelial cell-coated tumor model provides an in vitro microtissue environment to evaluate nanoparticles without moving into costly and time-consuming animal models.


MRS Proceedings | 2001

Intracellular uptake of poly(ethylene glycol) and folic acid modified magnetite nanoparticles

Yong Zhang; Nathan Kohler; Miqin Zhang

Superparamagnetic magnetite nanoparticles were surface-modified with poly (ethylene glycol) (PEG) or folic acid, to resist the protein adsorption and avoid their recognition by macrophage cells, and to improve their cell internalization and ability to target specific cells. The nanoparticle uptake into human osteosarcoma cells, MG63, was visualized using both fluorescence and confocal microscopy, and quantified using inductively coupled plasma emission spectroscopy (ICP) measurement. Fluorescence and confocal microscopy results showed that the nanoparticles were internalized into the cells after the cells were cultured for 48h in the medium containing the nanoparticles modified with PEG or folic acid. ICP measurements indicated that both the PEG and folic acid modification increased the amount of the nanoparticle uptake into the cells, in comparison with that of unmodified nanoparticles.


International Symposium on Optical Science and Technology | 2002

Synthesis and surface modification of superparamagnetic nanoparticles for biomedical applications

Nathan Kohler; Yong Zhang; Brad Busche; Miqin Zhang

Monodispersed superparamagnetic nanoparticles were synthesized from aqueous iron chloride solutions and were modified with poly(ethylene glycol) self assembled monolayers to improve their dispersion, biocompatibility and intracellular uptake for biomedical applications. Transmission electron micrographs (TEM) and atomic force microscopy (AFM) showed an average particle size of 10-30 nm and confirmed particle dispersion following surface modification with PEG. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of PEG on the nanoparticle surface and the particles were further characterized with electron energy loss spectroscopy (EELS).


Advanced Materials | 2007

Controlled PEGylation of Monodisperse Fe3O4 Nanoparticles for Reduced Non-Specific Uptake by Macrophage Cells†

Jin Xie; Chenjie Xu; Nathan Kohler; Yanglong Hou; Shouheng Sun


Nano Letters | 2005

Optical and MRI multifunctional nanoprobe for targeting gliomas.

Omid Veiseh; Conroy Sun; Jonathan Gunn; Nathan Kohler; Patrik Gabikian; Donghoon Lee; Narayan Bhattarai; Richard G. Ellenbogen; Raymond W. Sze; Andrew Hallahan; James M. Olson; Miqin Zhang


Langmuir | 2005

Methotrexate-modified superparamagnetic nanoparticles and their intracellular uptake into human cancer cells.

Nathan Kohler; Conroy Sun; Jassy Wang; Miqin Zhang

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Miqin Zhang

University of Washington

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Jonathan Gunn

University of Washington

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Yong Zhang

University of Washington

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Chenjie Xu

Nanyang Technological University

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Glen E. Fryxell

Battelle Memorial Institute

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Jin Xie

University of Georgia

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Christopher A. Coyle

Pacific Northwest National Laboratory

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