MAGNETIC NANOPARTICLES: SYNTHESIS, CHARACTERIZATION AND APPLICATIONS

Open Access
Author:
Latham, Andrew Howard
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 08, 2008
Committee Members:
  • Mary Elizabeth Williams, Committee Chair
  • Thomas E Mallouk, Committee Member
  • Ayusman Sen, Committee Member
  • Peter E Schiffer, Committee Member
Keywords:
  • Microfluidics
  • Magnetism
  • Nanoparticles
  • Iron Oxide
  • TEM
Abstract:
A wide range of metal, magnetic, semiconductor, and polymer nanoparticles with tunable sizes and properties can be synthesized by straightforward wet-chemical techniques. Magnetic nanoparticles are particularly attractive because their inherent superparamagnetic properties make them highly desirable for medical imaging, magnetic field assisted transport, and separations and analyses. With such applications on the horizon, synthetic routes for quickly and reliably rendering the surfaces of magnetic nanoparticles chemically functional have become an increasingly important focus. This dissertation describes synthetic routes for making and functionalizing magnetic nanoparticles and also discusses their characterization and initial applications in magnetic field induced separations. Herein, the synthesis of a trifluoroethylester-PEG-thiol ligand (TFEE-PEG-SH) and its use to create water soluble, chemically functional Au metal and FePt magnetic nanoparticles is discussed in Chapter 2. The trifluoroethylester terminus facilitates attachment of any primary amine containing molecule via amide bond formation at room temperature without the use of coupling agents. Three possible routes of nanoparticle functionalization are demonstrated: synthesis of Au nanoparticles in the presence of functionalized R-PEG-SH; ligand exchange of R-PEG-SH onto both Au and FePt nanoparticles; and exchange of TFEE-PEG-SH onto Au nanoparticles, followed by subsequent amide condensation. A series of primary amine containing molecules, including biotin and fluorescamine, are easily attached to the water soluble particles and the resulting materials are characterized by NMR, UV Visible absorption and emission spectroscopies. In terms of characterization, significant changes to the morphology of amorphous metal oxide (Fe, Co, and Ni) nanoparticles caused by exposure to the high energy electron beam of a transmission electron microscope (TEM) are reported in Chapters 3 and 4. The studied particles were synthesized via literature methods and fully characterized by X-ray powder diffraction and time-resolved TEM. As a result of electron beam irradiation, these particles are observed to transform from an initially solid particle to one with a core/void/shell structure eventually leading to a hollow nanoparticle. These results indicate that TEM-induced structural evolution is a general observation and not unique to one specific system. These data have significant implications for the structural analysis of nanomaterials via TEM. The purification and analysis of magnetic nanoparticles using capillary magnetic field flow fractionation, which utilizes an applied magnetic field oriented orthogonal to the capillary flow, is also discussed in Chapter 5. To validate this approach as a separation method for nanometer-scale particles, samples of magnetic nanoparticles composed of either γ-Fe2O3 (maghemite) or CoFe2O4 with average diameters ranging from 4 to 13 nm were prepared and characterized by transmission electron microscopy and SQUID magnetometry. Retention of the samples on the capillary was investigated as a function of solvent flow rate and the nanoparticle size and composition; the elution times of the nanoparticles are strongly dependent on their magnetic moments. The use of this method to separate a mixture of nanoparticles into size monodisperse fractions is demonstrated. The magnetic moments of the particles are calculated based on analysis of the retention parameters and are compared to values obtained in separate SQUID magnetometry measurements. Finally, the manipulation of magnetic nanoparticles between microfluidic channels by the application of an external magnet is discussed in Chapter 6. Two orthogonal channels were prepared using standard PDMS techniques with pressure driven flow used to deliver the mobile phase. To study the ability to control magnetic nanoparticles within micrometer-sized channels, Fe2O3, MnFe2O4, and Au nanoparticle samples were compared. For the magnetic particles, transfer between flow streams is greatly increased by placing a permanent magnet beneath the intersection of the channels, but no change is observed for the nonmagnetic Au particles. More nanoparticles are magnetically transferred into the orthogonal channel as the solvent flow rate decreases. The ability to use this technique to perform multiple injections of plugs of magnetic particles by periodic application of a magnetic field is also demonstrated.