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Monodisperse Magnetic Nano/Microspheres: Preparation, Characterization and Biomedical Applications

Author: ShiRuoBing
Tutor: WanQianHong
School: Tianjin University
Course: Applied Chemistry
Keywords: Magnetic microspheres Genetically modified organism detection Identification of Chinese medicinal herbs Cell separation Monodiperse magnetic nanocrystals
CLC: TB383.1
Type: PhD thesis
Year: 2012
Downloads: 544
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Abstract

Magnetically assisted separation is a novel separation technique based on the magnetophoretic movement of magnetic particles under the influence of external magnetic field. Being highly efficient, rapid, non-staining, and versatile with separation and enrichment, the technique has been widely used in immunoassay, nucleic acid extraction, gene sequencing, cell separation, enzyme immobilization and chiral separation. Recent efforts in development of bio-magnetic separation technology are focused on miniaturization, parallelism and automation. One of the key problems to overcome is facile preparation of magnetic microspheres with uniform particle size, excellent dispensability, high responsiveness and superparamagnetic behavior. These properties are important to ensure the efficiency,reproducibility and controllability of the magnetic separation process. Magnetic nanoparticles have generated much interest because they show some potential in diagnosis and treatment of a variety of human diseases. Although nano/micro magnetic particles can be prepared by a variety of methods such as chemical co-precipitation and monomer polymerization, these methods all show some shortcomings, for example, the product with highly uneven particle size distribution, complex and tedious process, expensive raw materials and toxic solvents used. It is therefore of both academic and practical interests to develop methods for the preparation of high-quality monodisperse magnetic nano/microspheres and explore their applications in biomedical fields. In this thesis, the work aimed at development of methods for preparation of magnetic nano/micro particles with improved properties is described, which starts with the in-situ synthesis of magnetic silica composite microspheres using porous silica microspheres as templates. The magnetic microspheres obtained were used to extract DNA templates from soybeans and foodstuffs followed by PCR amplification for detection of genomic modified organisms in soy products. Because of their relatively weak response to magnetic field, they are less ideal for application in extraction of DNA from viscous solutions. Efforts were made to prepare magnetic Fe₃O₄ microspheres with strong magnetization and to explore their application in extraction of DNA from traditional Chinese medicinal herbs for identification and authentication. Application of magnetic particles to cell sorting requires the particles of good dispensability. Therefore core-shell polystyrene composite magnetic microspheres with low density and good suspension were prepared and conjugated with avidin for capturing specific cells from a cell mixture. Finally, to overcome the shortcoming with chemical precipitation for preparation of magnetic nanoparticles, a new thermolysis procedure was introduced in which a non-toxic ferric oleate complex was used as precurcor and the highly monodiperse magnetic nanoparticles produced were then converted to hydrophilic nanoparticles which are essential for using as contract agents for MRI/MPI.The details of this thesis are outlined as follows:1. A facile method for the preparation of such magnetic composite particles was developed, which entails impregnation of porous silica microspheres with iron salts, followed by calcination and reduction treatments. The samples were characterized using powder X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, nitrogen adsorption/desorption isotherms, and vibrating sample magnetometry （VSM）. The magnetic silica composite microspheres coated with silica shells were tested as adsorbents for rapid extraction of genomic DNA from soybean-derived products. The purified DNA templates were amplified by PCR for screening of genetically modified organisms （GMOs）. The preliminary results confirm that the DNA extraction protocols using magnetite-loaded silica microspheres are capable of producing DNA templates which are inhibitor-free and ready for downstream analysis.2. Using ethylene glycol as solvent, a variety of nitrogen-containing substances as ligands, Fe₃O₄ magnetic microspheres of high magnetic responsiveness were prepared by solvothermal method. The as-prepared Fe₃O₄ magnetic microspheres show quick response for applied magnetic field even in a relatively viscous solution, which made them ideal separation tool for plant cell nucleic acid sample separation and enrichment. The Fe₃O₄ magnetic microspheres of high magnetic responsiveness were applied in DNA extraction of Chinese medical herbs and the possibility of identification and species identification.was discussed.3. Magnetic nanoparticles prepared by chemical precipitation method were modified and coated on the surface of polystyrene microspheres to form core-shell polystyrene magnetic composite microspheres by layer-by-layer method. The as-prepared magnetic composite microspheres are characterized of lower density and better suspension in aqueous solution compared with as-prepared magnetic silica composite microspheres and Fe₃O₄ magnetic microspheres. The effects of methods of surface modification on subsequent biological applications were discussed. The magnetic composite microspheres were modified with avidin protein to form new separation carriers for specific cells. The ability of specific capture of cells was studied and shown to produce good results.4. In order to obtain monodisperse superparamagnetic nano-magnetic crystals to be used for medical testing and treatment, monodisperse Fe₃O₄ nanoparticles by pyrolysis, using non-toxic Fe oleate complex as precursor. The ratio of oleic acid to Fe oleate complex were studied on the effects in particle size. The oil-soluble magnetic nanoparticles were dispersed in aqueous solution by ligand exchange. The resulting water-soluble magnetic nanoparticles showed good stability in aqueous solution and were considered to be ideal candidate as contrast agent to be used in magnetic resonance and magnetic particle imaging.

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