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Giant Magnetoimpedance Effect In Meander-shaped Sandwich Films And Its Applications For Biosensing

Posted on:2016-12-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:T WangFull Text:PDF
GTID:1108330503993809Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Giant magnetoimpedance(GMI) effect has attracted much attention due to its potential for the development of high-performance magnetic sensor, namely GMI sensor. GMI sensors have found a wide range of potential applications in areas of magnetic-field sensors, current sensors, stress sensors and biosensors since they offer many advantages such as high sensitivity, quick response, small size, low consumption, etc. Until now, considerable efforts have been put into the basic research of GMI effect, while less attention has been paid to the application research of GMI effect, particularly in the field of magnetic-field sensing and biosensing. Based on this, this thesis focuses on the development of GMI sensors for detection of magnetic beads and biomarkers, the aim of this thesis is to explore the application value of the GMI sensors in the field of magnetic-field sensing and biosensing, and lay the foundations for practical application of GMI sensors. This thesis presents a systematic study formed by both theories and experiments, which mainly includes theoretical GMI model of the meander-shaped sandwich films, fabrication of the miniature GMI sensors by Micro-Electro-Mechanical System(MEMS) technology, investigation of GMI effect in films, detection of superparamagnetic beads, detection of Alpha-fetoprotein(AFP) antigens and carcinoembryonic antigens(CEA), involving Scanning electron microscope, X-ray photoelectron spectroscopy, Vibrating sample magnetometer, Atomic force microscope and Energy dispersive spectrometer characterizations. The major results are as follows:1. The miniature GMI biosensor based on multilayered films(Cr/Cu/NiFe/Cu/NiFe/Al2O3/Cr/Au) was fabricated by MEMS technology. The GMI sensor of integrating Au film and soft magnetic films has made it feasible to perform in-situ bioassay. A practical GMI sensor of integrating a micro-plane spiral coil and sandwich films was fabricated by MEMS technology. By applying the small perpendicular bias magnetic field provided by the spiral coil on the GMI sensor, the field-operating point can be regulated, the magnetic field direction can be determined, and the low-field hysteresis can be suppressed.2. The theoretical analytical GMI model of meander-shaped sandwich films was established. High-frequency impedance expression was derived from Maxwell equations and magnetization motion equations, and it was found that the magnetoimpedance of soft magnetic films can be solved by using effective permeability of films eventually. In this thesis, the magnetoimpedance of films was calculated from the contribution of both resistance and inductance, and the magnetic mutual-inductive effect was taken into account in the GMI model. Experimental measurements are consistent with theoretical calculations, which confirms the correctness of this model, this mathematical model can provide theoretic guides for the design of high-performance GMI sensors.3. Quantitative and ultrasensitive detection of the Dynabeads(Dynabeads? protein A and Dynabeads? MyOne? Streptavidin C1) was achieved by using the separated-type measuring method and the in-situ measuring method based on the GMI sensors. The separated-type measuring method can be used to quantitatively detect Dynabeads? protein A in the concentration range of 0.1 μg/mL-5 μg/mL and Dynabeads? MyOne? Streptavidin C1 in the concentration range of 0.02 μg/mL-5 μg/mL. The detection limits of the separated-type measuring method for Dynabeads? protein A and Dynabeads? MyOne? Streptavidin C1 can be as low as 90 and 200 particles, respectively. The in-situ measuring method is able to quantitatively detect Dynabeads? protein A in the concentration range of 0.1 μg/mL-10 μg/mL and Dynabeads? MyOne? Streptavidin C1 in the concentration range of 0.01 μg/mL-2.5 μg/mL. The detection limits of the in-situ measuring method for Dynabeads? protein A and Dynabeads? MyOne? Streptavidin C1 can be 90 and 100 particles, respectively. Experimental results indicate that the GMI sensors based on sandwich films are capable of quantifying the low-concentration Dynabeads, which has laid the foundation for detection of magnetically labeled biomolecules.4. Ultrasensitive detection of the biomarkers was achieved by the GMI sensors. Detection of AFP antigens and CEA antigens by the GMI sensors combined with magnetically labeled sandwich immunoassay has been deeply studied, including the investigation of sensitivity, specificity, reproducibility and linear range for detection of biomarkers. Based on the in-situ measuring method, the GMI sensors were able to qualitatively detect AFP antigens(1 ng/mL, 3 ng/mL and 10 ng/mL). Quantitative detection of AFP antigens and CEA antigens was realized by the separated-type measuring method, showing a high linearity in the concentration range of 1 pg/mL-1 ng/mL for AFP antigens and in the concentration range of 1 pg/mL-10 ng/mL for CEA antigens, respectively. The lower detection limits for both AFP antigens and CEA antigens can be 1 pg/mL. In addition, Bovine serum albumin(BSA), AFP antigens and CEA antigens were respectively employed as non-specific targets for immunoassay, and it was found there were no positive signals detected in the tests. Hence, the magnetic immunoassay based on GMI effect possesses high sensitivity, high linearity and good specificity.5. An interesting physical phenomenon has been found in the detection of magnetic beads and biomarkers: The target signals dropped off sharply when high-concentration magnetic beads or antigens were detected by GMI sensors. It was found that the high-concentration magnetic beads or antigens could cause the high-density accumulation and clusters of magnetic beads, thereby resulting in canceling out the opposing dipole fields among the magnetic beads, and reducing the intensity of whole stray magnetic field and thus the target signals.
Keywords/Search Tags:giant magnetoimpedance, stray magnetic field, magnetic beads, detection, alpha-fetoprotein, carcinoembryonic antigen
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