Browsing by Subject "Magnetic"

Now showing 1 - 3 of 3
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    Constricted current perpendicular to plane (CPP) magnetic sensor via electroplating.
    (2011-01) Huang, Xiaobo
    Electrochemically deposited magnetic nanowires have gained increasing attention since current perpendicular to the plane giant magnetoresistance (CPP-GMR) was observed in multilayered nanowires. Magnetic nanowires have potential for fundamental studies, including measuring spin diffusion lengths and understanding the mechanisms of the electron spin transfer. They also have great potential technological applications as CPP-GMR sensors, magnetic random access memory (MRAM), and next generation magnetic recording heads. Small diameter nanowires are desired in order to have large current density per device and a high areal density for device arrays, for example, 2 Tb/in2 media. In this research, E-beam lithography, nano-imprinting, and self-assembled nanoporous alumina templates (AAO) were studied to achieve as small diameter nanopores as possible. AAO templates with 10 nm diameter were fabricated using both Al foils and Al thin films. Very small diameter (10 nm) CPP-GMR Co/Cu nanowires were fabricated into AAO templates using electrochemical deposition. The magnetic transport properties of these multilayered and trilayered Co/Cu nanowires were investigated. It was found that nanowire anisotropies parallel and perpendicular to the nanowires were dependent on the thicknesses of Co and Cu layers. GMR of 19% was achieved with 10 nm diameter nanowires at room temperature. The magnetic free layers were as thin as 4.5 nm with GMR of 18%. Spin transfer torque switching current densities were measured to be 106 - 108A/cm2. The measurement of spin transfer torque was conducted numerous times with high repeatability in the critical switching currents from parallel to antiparallel alignment (JP-AP) and slight variations in back (JAP-P). Small resistance area products (RA) of 0.003 ohmµm2 were achieved with trilayers that had 40ohm total resistance. All of results in this study show that nanowires with 10 nm diameters have potential application as next generation CCP-GMR sensors and spin transfer torque MRAM.
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    Magnetic Biosensing Technologies and Applications
    (2021-01) Su, Diqing
    Magnetoresistance (MR) biosensors have been widely employed in the detection of small molecules, proteins, and nucleic acids. The major contribution of this thesis is the development of novel giant magnetoresistance (GMR) biosensing technologies to improve the portability, sensitivity, and flexibility of the detection process through both modeling and experimental studies. The work in this thesis can be divided into two major parts, i.e., the development of novel GMR sensors and the development of novel magnetic nanolabels as the labels for the target analytes. The possibility of employing spintronic structures for neuron stimulation is also explored.The optimization of the GMR sensors are from three different aspects. Firstly, GMR biosensors are successfully integrated with a handheld biosensing system, which is capable of fast, accurate, and onsite disease diagnosis. The detection of influenza A virus in swine nasal swab samples is demonstrated with comparable sensitivity to the enzyme-linked immunosorbent assay (ELISA), which is a lab-based golden standard technology for protein detection. Secondly, flexible GMR sensors with a bending radius lower than 1 mm and similar magnetic properties to their rigid counterparts are fabricated with a two-step thinning process. A lab-on-a-needle detection platform is used for cell detection with a LOD of 200 cells in the testing sample, exhibiting great potential in the onsite biopsy at the tumor site, as well as in drug delivery efficacy monitoring as an implanted device. Thirdly, a large-area GMR biosensing scheme based on the reverse nucleation mechanism is proposed, modeled, and demonstrated, which leads to a sensitivity 20 times higher than traditional GMR biosensors. In addition, magnetic nanowires (MNWs) are employed as the magnetic labels for the first time in the cell detection process. The MNWs can be readily internalized into cells without inducing much cytotoxicity. The distance, angular, and concentration dependence of sensor signal generated by the MNWs are studied. Single-cell detection has been successfully realized in the GMR biosensors when the cells are in direct contact with the sensor surface.
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    Microfluidic chips for cellular heterogeneity studies.
    (2009-10) Chung, Jaehoon
    In recent years several studies have found significant heterogeneity among even purified cells that were previously treated as if all cells were essentially identical. But since many measurements have been reported as averages over large numbers of cells, assuming that all cells are same when they might really be a mixture of different cell subtypes, this can lead to incorrect or at least imprecise and harder to replicate results. There is a macroscopic technique for single cell analysis known as dilution method: diluting and depositing cells in a conventional platform such as a 96 well plate. However, it is very labor-intensive, low-throughput, low single-cell loading efficiency, and poor reproducibility and thus is rarely performed. We have designed a high-throughput microfluidic chip which solves these problems and is superior to existing devices in allowing heterogeneous cell studies at scales and accuracies not previously possible and with minimum labor and cost. This chip performs 1) single-cell capture and culture to generate their colonies, and 2) sorting multiple specific target cells. Hydrodynamic force and magnetic force were studied to position or to sort cells in pre-determined locations precisely. We designed a novel hydrodynamic guiding structure which can automatically capture and position single cells into each microwell with high capturing efficiency, using only gravity flow, with which we could capture 80% of cells at a single cell resolution from all the injected cells (~ 2 orders of magnitude improvement, comparing to the state-of-art and widely adopted passive weir structures for single cell trapping). This hydrodynamic guiding scheme was applied to a high-throughput microfluidic array chip, which is the first chip capable of culturing single cells into their clonal colonies inside individual microwells and introducing test-reagents to their clones. To track cells carefully over time and ensure clonal outgrowth from single cells, we should prevent cell migration between neighbouring microwells, which can generally happen in other reported single cell culture chips. We integrated a surface patterning technique into a microwell, which effectively confines cells' movement inside each microwell. In addition, we utilized a gravity flow caused by pressure difference between inlet and out reservoir, which allows us a simple and easy operation without the necessity of external equipments. Using this chip we can detect heterogeneity of cells identify subtypes of clones and monitor drug responsiveness. We observed three different subtypes grown from a prostate cancer cell line, PC3 cells. These distinctive subtypes have different morphologies and proliferation rate, as well as different drug responsiveness. This single cell clonal chip can be extended to a larger array as well as used for multiple reagents by integrating pneumatic valves. An alternative method of cell sorting for heterogeneity studies has been explored where the objective cells have well-known identifiable surface markers. It is also desirable to collect cells at a specific target size especially for effective drug screening purpose. A macro magnetic sorter can separate target cells; however, the screened cells are not 100% pure and their sizes vary in a wide range. We devised a novel magnetic sorter which can separate multiple target cells into corresponding microwells. We have designed a magnetic sorter based on the phenomenon that magnetic particles move towards the minima of field and flowing electrical current generates controllable magnetic field. The magnetic sorter could separate different-sized cells by generating a local magnetic field gradient with the integrated current-carrying lines. We successfully demonstrated three different sizes of magnetic beads can be sorted under the different electrical current through the embedded current-carrying lines in three successive sorting units. More unit stages can be added and the number of stages can be determined to meet the sorting purpose.