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Browsing by Subject "biosensor"

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    Developmentof High Sensitivity Magnetic Biosensors for Biomedical Applications
    (2020-02) Feng, Yinglong
    As a very important subgroup of biosensors, magnetic biosensor is known to possess major advantages over its competitors due to low cost, rapid detection, low background signal in biological tissue and magnetic sensing system has met the requirements to be a portable point-of-care medical system. Providing a useful supplement or alternative for various applications in areas such as diagnosis and cognation study. Detection and quantification of specific biomolecules become increasingly important since the statistical results provide insightful correlation with specific diseases. In the area of disease diagnosis, disease early detection is critical since exposing diseases at early stage will lead to more effective treatments. Biological analytes are low abundance in number or concentration, as a result, many new methods of biosensing are primarily targeting on high sensitivity. One of the promising candidates uses a physical phenomenon called “giant magnetoresistance” (GMR). In GMR element, the electrical resistance changes in response to an applied magnetic field. This technology has been developed and utilized in the hard disk drive industry for decades. Unlike the mature design of GMR biosensor, this dissertation presents a novel GMR magnetic biosensing system with unique particle sensing scheme of localized interaction between particles and sensors. This may provide an alternative path to design GMR sensor with higher sensitivity to truly meet the challenge of detecting low abundance biomolecules in disease early detection. Magnetic sensor can be used in more than assay-based disease detection, it can also be used as a magnetic field sensor to detect magnetic field generated by neuronal electrical activities. Magnetic field generated from neuronal electrical signal is small and it degrades over distance. Great challenge is made for the sensing system to be very sensitive in response to magnetic field, in the same time, to maintain very low overall system noise. We built a Tunnel magnetoresistance (TMR) based magnetic sensing system to address these challenges. TMR stacks and sensor design are optimized to achieve high “zero” field sensitivity, soft magnetic material is sputtered and ion milled to build an integrated magnetic flux concentrator. Sputtering condition and the geometric dimensions of the flux concentrator is also optimized. Low noise analog circuit and different noise reduction methods are utilized to minimize the overall system noise. At last, we have preliminarily demonstrated using our magnetic sensing system to detect brain signals from a rat, Electroencephalography (EEG) sensor is used to verify our magnetic sensor.
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    Magnetic Biosensing System
    (2015-05) Li, Yuanpeng
    Biosensing systems that detect and quantify biomolecules at ultra-low concentration, with point of care settings, are of great need in many fields, including diagnostics, disease control, general health monitoring and fundamental research. Over the past decade, detection of biomolecule using magnetic biosensing system, which combines giant magnetoresistive (GMR) sensors and magnetic particles, has been attracting a lot of attention in biosensing area, due to the potential advantages on portability, low cost and rapid detection. This dissertation presents a novel magnetic biosensing system, consisting of highly sensitive GMR sensor and high-moment FeCo magnetic nanoparticle. Based on competition-based detection scheme, this system successfully demonstrates the quantification of ultralow concentration of biomarkers under a small magnetic field in real human serum/urine samples, and differentiates the patients with different grades of cancers. One of the key factors to achieve detection of biomarkers in ultralow concentration is the sensitivity of the GMR biosensor. We designed and fabricated a GMR sensor with a near 0-degree ground state for the magnetization directions between pinned layer and free layer. This configuration enables three times greater sensitivity than any reported traditional GMR biosensor design, and requires much smaller polarization working field (10 Oe) which is more suitable for lab-on-chip and portable diagnostics. Another key factor to increase the system sensitivity is to enhance the magnetic signal of magnetic label. High-magnetic-moment FeCo nanoparticles with great homogeneity, is proposed and synthesized for biomedical application. The net magnetic moment of a FeCo nanoparticle is seven times higher than that of a commercial available Fe3O4 nanoparticle with an applied field of 10 Oe, assuming the same particle size. Moreover, the high homogeneity of FeCo nanoparticle enables the accurate quantification of low-abundance biomarkers. Combining the novel GMR biosensor and high-moment FeCo magnetic nanoparticle, the accurate quantification of various biomarkers in real human serum/urine sample is demonstrated. To assist the high sensitivity quantification, two-layer/three-layer based competition detection schemes are developed. The low concentration interleukin-6 in unprocessed human sera, down to 200 copies, has been detected in only 5 minutes processing time. Based on the results, normal individuals and lung cancer patients were nicely identified. Moreover, the detection of as few as 1000 copies of endoglin is demonstrated in human urine samples. Based on the endoglin concentrations, the patients with different grades of prostate cancer are successfully differentiated.