Wu, Kai2018-07-262018-07-262017-08https://hdl.handle.net/11299/198407University of Minnesota Ph.D. dissertation. August 2017. Major: Electrical Engineering. Advisor: Jian-Ping Wang. 1 computer file (PDF); xxviii, 199 pages.In recent years, magnetic nanoparticles (MNPs) have been widely used in clinical and medical applications. MNPs are used as contrast agents in magnetic particle imaging (MPI) [1-6] and magnetic resonance imaging (MRI)[7, 8], carriers for drug delivery[9-12], tiny heating sources for hyperthermia cancer treatments[13-15], labels for magnetic biosensing[16-23], etc. MNPs-based biosensing strategies have received considerable attention because of their unique advantages over other techniques. For example, iron oxide MNPs are biocompatible, nontoxic, inexpensive to produce, environmentally safe, physically and chemically stable. In addition, most biological samples exhibit diamagnetism or paramagnetism properties, and thus highly sensitive measurements can be performed in visually obscured samples without further processing[24]. This thesis will focus on the use of MNPs for biosensing applications based on two detection platforms: search coil-based biosensor (volumetric based biosensing platform) and giant magnetoresistance (GMR) biosensor (surface based biosensing platform). The volumetric based biosensing platforms measure analytical signals that come from the entire detection volume, which makes assays simple and fast[25]. Representative examples of volumetric sensors include nuclear magnetic resonance (NMR) devices[26, 27], magnetic susceptometers[25, 28], and conventional superconducting-quantuminterference devices (SQUIDs)[29, 30]. In this thesis, the magnetic dynamics of ferrofluids are investigated, the Brownian and Néel relaxation models of MNPs are revisited and optimized, the energy barrier model and dipolar interaction model are taken into consideration in predicting magnetic responses of MNP suspensions. Based on these mathematic models, the hyperthermia performances of MNPs under different alternating magnetic fields (AMF) are evaluated. A search coil-based biosensor system is built up, MNPs have been used for the rapid in vitro human serum viscosity measurement, which successfully measured human serum viscosity in less than 1.5 minutes with an error rate lower than 5%. Furthermore, this search coil system has been used to characterize the physical properties of MNPs in liquid phase. By analyzing the phase lag and harmonic ratios in the MNPs, it is possible to predict the saturation magnetization, the average hydrodynamic size, the dominating relaxation processes of MNPs, and the distinction between single- and multicore nanoparticles. It is feasible to use search coil as a method to characterize physical and magnetic properties of MNPs, which may be applied as building blocks in nanoparticle characterization devices. The surface based biosensing platforms directly detect individual magnetic objects near the sensing elements. These sensors generally achieve higher sensitivity and finer resolution than volumetric ones; however, they require target samples to be placed in close proximity to the sensor surface. Such an arrangement limits the assay configuration, and typically causes the assays to be more time-consuming [16, 31]. To date, many different types of magnetometers (i.e., GMR sensors, Hall effect sensors) have been developed as surface based biosensors. In this thesis, a portable and quantitative immunoassay platform, Z-Lab, based on GMR sensors, is used for the detection of Influenza A virus (IAV) and its nucleoprotein (NP). This portable device Z-Lab displays quantitative results in less than 10 minutes with sensitivities down to 15 ng/mL and 125 TCID50/mL for IAV NP and purified IAV, respectively. This platform allows lab-testing to be performed outdoors and opens up the applications of immunoassays in non-clinical settings.enBrownian and Néel relaxationgiant magnetoresistance biosensorimmunoassayInfluenza A virusmagnetic nanoparticlessearch coilThesis or Dissertation