Research On The Design And Performance Of Magnetic Tags Based On Giant Magnetoresistance (GMR) Biosensors

In recent years,the quantitative detection of biomolecules has been extensively applied in many fields,including environment monitoring,medicine,biology and drug discovery,and so on.Various ultra-sensitive biosensors have been designed and developed,in which the chip-based detection using giant magnetoresistive?GMR?sensors and magnetic labels gains increasing interest due to the merits of low cost,portability,high sensitivity,low background signal and real-time electronic readout.The GMR sensor determines the number of biomolecules through capturing the magnetic fringing fields introduced by the magnetic particles attached on the sensor surface.Therefore,the property of the particles will directly affect the detection result.The magnetic labels of GMR biodetection should havelarge magnetization,suitable particle size,narrow size distribution and good dispersiveness.In order to realized ultra-low concentration and high throughput detection of GMR biosensor,researchers attempted to choose different particles as the labels to improve the detection performances,such as LOD,linear range and signal-to-noise ratio.Therefore,this thesis focuses on design and performance research of magnetic label based on giant magnetoresistance?GMR?biosensor:?1?We synthesized four kinds of ferrite magnetic labels??-Fe₂O₃,NiFe₂O₄,CoFe₂O₄ and NiZnFe₂O₄?by calcination for the ultra-low concentration biodetections.These ferrite magnetic labels showed excellent performances for the ultra-low concentration biodetections.This can be explained that,the large bias magnetization of nanoparticles will introduce the large diffusion field which is beneficial to improve the limit of detection.The limit of detection of the four ferrite magnetic labels were 0.1 ng/mL,and the limit of detection wrer significantly reduced.?2?A series of Fe₃O₄ particles with average particle sizes from 80 to 580 nm were prepared for high-throughput detection.An ultra-low LOD of 0.1 ng/mL and a six orders of magnitude wide linear range from 0.1 ng/mL to 10?g/mL were obtained for the samples with 80 nm particle size which showed excellent performances for high-throughput detection.A detailed analysis about the effect of particles'size and magnetic properties were given and the theoretical calculated results are well consistent with the experimental data.It was found that not only the particle size but also the magnetic moment of particles affect the LOD essential.?3?Surface-modified of GMR biosensors used silane coupling agent APTES,at the same time,PEI-modified magnetic labels was prepared.The fixation of the magnetic label on the sensor surface is achieved by using glutaraldehyde as a coupling agent.Through detection and data analysis,it was found that binding process and the distance increased between magnetic label and sensor surface reducing sensitivity of sensor.?4?The repeatability of the self-made GMR biosensor system was tested.Firstly,based on the detection results of different concentrations of magnetic labels,the standard empirical formula of the sensor is fitted.The magnetic label of known concentration is then measured and the test results are processed.Finally,the test concentration was analyzed by mathematical calculation,and the difference between the test concentration and the actual concentration was compared to verify the accuracy of the test results of the self-made GMR biosensor...