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Synthesis and Characterization of Colloidal Superparamagnetic Iron Oxide and Iron/Iron Oxide Nanoparticles as MRI Contrast Agent

Masoudi, Afshin | 2012

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 43685 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Madaah Hosseini, Hamid Reza; Seyed Reyhani, Morteza
  7. Abstract:
  8. As contrast enhancement agent, two different structures of superparamagnetic nanoparticles were synthesized. Iron oxide nanoparticles were prepared through an alkaline coprecipitation method of Iron (II) and (III) ions. PEG-6000 was used as biocapping material and its effect on particle size, colloidal stability and cytotoxicity was evaluated. On the other hand, novel core/shell structures were produced by NaBH4 reduction process of iron (III) in an aqueous media following by further oxidation by two different methods using (CH3)3NO oxygen transferring agent and exposure to oxygen flow. In both cases, structural examinations were conducted via X-ray diffraction, electron microscopy and Mössbauer spectroscopy methods. The coprecipitation products were dominantly composed of 38 wt.% Fe3O4 and 62 wt.% γFe2O3.The resulting crystallitesreachednear 6 nm diameter in pre-grafting (in-situ) procedure rather independent of anchoring concentration up to 5:1 weight ratio of PEG:nanoparticles. This value was very similar to the size of crystallites obtaining from post-grafting (ex-situ) manner. However, with adding more PEG the crystallite sizes of in-situ process were reduced ~1 nm. Microscopy results indicated that nanoparticles produced by in-situ process had comparable size with the crystallite dimensions which implying that the particles were single-crystalline. Nevertheless, coating nanoparticles with ex-situ procedure encapsulated at least two particles in separated polymeric shells and consequently produced coated nanoparticles with the average diameter of about 16 nm. Despite the lower size of individual particles taking from in-situ coating process, the nanoparticles agglomeration would not be inevitable and bigger nanoparticles were achieved compared to ex-situ process. FTIR and TG results also confirmed the formation of PEG on the surface of oxide nanoparticles. The reduction and oxidation with oxygen gas flow yielded nanoparticles with 9.4 nm α-Fe in core and 2.3 nm amorphous oxide in shell. By (CH3)3NO, deeper layers of the core could be oxidized and crystalline oxide phases of 4.5 nm thicknesscould be attained. Saturation magnetization values of Fe/Fe-oxide nanoparticles were greater than conventional oxide phases. Among core/shell structures, saturation was reduced from 115 to 92 emu/g with increasing oxide shell thickness. Nanoparticles’ toxicity was behaved in a same direction as colloidal stability trend. For fresh nanopartilces, the higher the coating amount the higher viability. But, in post 4-months examinations, more stable samples demonstrated lower viability. Oxidenanoparticles showed acceptable viability (>50%) up to 400 μg [Fe], while this values was 300 μg [Fe] in the case of Fe/Fe-oxide samples. T1 and T2 relaxation times measurements verified that ex-situ coated nanoparticles hadbetter effect on T1 and T2, due to their coagulated core structure and higher magnetic properties, respectively.In-vitro MR signal reduction and corresponding relaxometry parameters, especially r2/r1>2, assure that most of nanoparticles can be administrated for negative contrast enhancement. Nanoparticles uptake and accumulation in lymph nodes were supported by MR imaging of Wistar rats. Higher saturation of Fe/Fe-oxide samples led to more powerful influence on signal reduction of MR images.Accumulation of core/shell nanoparticles in axillary and brachial lymph nodes of examined rats and minimum contrast enhancement of 20% regarding to pure iron oxide implies the efficacy of these materials as potential contrast agent. Although some critical charateristics of core/shell nanoparticles were decreased after 4 months of post preparation due to imperfect protection of oxide shells, r2/r1>2 rendered suitable conditions for using nanoparticles as MRI contrast agent.


  9. Keywords:
  10. Co-Precipitation ; Superparamagnetic Nanoparticles ; Iron Oxide Nanoparticles ; Core-Shell Nanostructure ; Magnetic Resonance Imagin (MRI)Contrast Agent ; Relaxation Time ; Colloidal Stability ; Lymph Nodes

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