Graduation date: 1996

No description available.

Compared with traditional radioimmunoassay and fluoroimmunoassay for early diseases detection, the magnetic immunoassay utilizing magnetic nanoparticles as bio-labels and magnetic signal sensors as detectors has remarkable advantages because most biological samples exhibit no magnetic background and highly sensitive measurements can be performed. This thesis presents the development of biodetection platform taking advantage of the physical-and chemical-stability, low-toxicity, and environmentally-safety of magnetic iron oxide nanoparticles (IONPs) and the high-sensitivity, low-cost, and portable capabilities of magnetoresistive (MR) sensors. The first part explained why a magnetic biodetection platform is desirable, and what advantages it possesses. Then the magnetism of IONPs utilized in this detection system was introduced, followed by the introduction of main synthesis methods to obtain the desirable IONPs. The working principle of MR sensor was explained, and the recent advances about the biodetection platforms with various magnetoresistive sensors and magnetic IONPs labeling was reviewed. A brief summary of new contributions reported in this thesis was summarized. Then the establishment of home-made measurement setups for the characterization of MR sensor was described. The MR loops of MR sensors can be obtained with the instrument using two-point probe measurement, four-point probe measurement, or Wheatstone bridge measurement. The single MTJ sensor, MTJs array sensor, and the GMR spin valve sensor in Wheatstone bridge were characterized here. The magnetic IONPs were prepared through co-precipitation method and thermal decomposition method, and then surface-functionalized using citric acid and fatty acids to acquire carboxyl groups for the binding ability with biomolecules. The physical and chemical properties, sterilizing-treatment tolerability and biocompatibility of nanoparticles were studied. Furthermore, two new synthesis methods were developed to obtain novel magnetic gold/iron oxide nanocomposites for their potential use as magnetic bio-labels. A magnetic detection platform was built, and the detection of 10-nm superparamagnetic IONPs with MR sensor was first realized here. The output signal of the giant magnetoresistive (GMR) sensor in Wheatstone bridge exhibited log-linear function of the concentration of IONPs, making our sensing system suitable for use when ultra-small bio-labels are needed. The biodetection platform with MR sensor and IONPs was successfully developed and applied for the detection of antigen biomolecules. The feasibility of magnetic biodetection system, based on magnetic tunneling junction (MTJ) sensors and carboxyl-group functionalized IONPs, to detect AFP antigens (liver cancer biomarker) and p24 antigens (HIV biomarker) was demonstrated here for the first time. By taking advantages of its high sensitivity, low power consumption, low cost, and feasibility to be miniaturized, the development of magnetoresistive biodetection platform will bring revolutionary impact on the biodetection techniques for clinical early diseases diagnosis. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

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Thesis (Ph. D.)--University of Hawaii at Manoa, 1996. / Includes bibliographical references (leaves 227-232). / Microfiche. / xiii, 232 leaves, bound ill. (some col.) 29 cm

Carbon nanotubes (CNTs) functionalized/embedded with ferromagnetic particles have several important advantages as materials for magnetic applications. The presence of ferromagnetic particles in a carbon matrix can substantially change the magnetic properties of CNT-based composites. For example, iron filled CNTs have been used as probes in magnetic force microscopy (MFM), and have potential in magnetic data storage applications. In addition, encapsulation in nanotubes provides iron nanoparticles with resistance to oxidation and mechanical damage. Chemical vapor deposition (CVD) is one of the most common single-step processes for the fabrication of high quality carbon nanotubes containing varying amounts of embedded ferromagnetic particles. This process results in the effective magnetic functionalization of CNTs and opens the door to numerous new applications. However, in order to optimize these materials for any application, their properties need to be understood. This study explores the ferromagnetic properties of carbon nanotubes containing nano-scaled iron particles which were derived from thermal decomposition of ferrocene. Both room temperature as well as low-temperature magnetic measurements will be presented and the results analyzed in the light of available theory.

The magnetic recording media used for hard disks in laptops and PC's is constantly being improved, leading to rapid increases in data rate and storage density. However, by the year 2010, it is predicted that the superparamagnetic limit will be reached, which is potentially insufficient for data storage. At the beginning of this century, CoCr -based alloys are used in longitudinal media since cobalt has a high magnetocrystalline anisotropy. In this thesis, the static and dynamic properties of longitudinal recording thin films were investigated in order to explain and correlate their magnetic characteristics to their recording properties. The samples in question were test samples and some were in commercial use. Magnetic techniques such as high field ferromagnetic resonance and torque magnetometry were used to determine accurately the crystalline anisotropy field. High field ferromagnetic resonance is an ideal tool to determine the crystalline anisotropy, magnetisation, Lande g-factor and the gyromagnetic damping factor. In contrast to previous work, there are no FMR simulations and so all the relevant parameters were determined directly from measurement. Ideally, there should be no exchange interactions between the neighbouring cobalt grains; however, interactions between the grains within the CoCr-alloy recording layer exist. Previous work on the measurements of interactions in recording media involves measuring the sample's magnetisation. In this thesis, an alternative novel method involves torque magnetometry. Another technique that was used in this thesis is small angle neutron scattering, which aims to determine the size of the magnetic grains and compare that with the physical size determined from TEM, by Seagate. There is an extended section on CoxAg1-x granular thin films, which involves determining the sample's g-factor, effective anisotropy, grain size, exchange constant and comparing the FMR lineshapes at 9.5 and 92GHz.

M.Sc. (Physics) / Please refer to full text to view abstract

D.Phil. (Physics) / Please refer to full text to view abstract

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