Magnetic immunoassay system utilizing magnetic marker and SQUID sensor

免疫测定法广泛用于医学诊断中疾病相关蛋白的检测。这些蛋白质一般被称为抗原，抗原和抗体之间的所谓结合反应用于免疫测定。为了提高免疫分析的性能，我们开发了一种利用磁性标记和SQUID传感器的新检测系统。本研究的主要结果如下：(1)阐明了磁性纳米颗粒的大小对磁性性能的影响。结果表明，公称直径为25 nm的颗粒可以保持剩余物，并能产生较大的磁信号。因此，该颗粒适用于磁免疫分析。我们开发了一种用聚合物覆盖磁性颗粒的涂层工艺。利用这一工艺，我们制备了一种聚合物包覆的磁性纳米粒子，在液体中表现出良好的分散性。(3)研制了用于检测标记体磁信号的高Tc SQUID系统。由于信号在空间中衰减很快，我们实现了冷却后的SQUID与室温样品之间的距离很近。(4)研制了无磁污染反应室和消除环境噪声的方法，以检测极弱信号。我们的系统可以在几分钟的短测量时间内检测12个样品，现场分辨率约为10 pT。(5)我们进行了一种名为IgE的蛋白质检测。我们证明了检测到的IgE低至0.3 pg，这表明了磁性方法的高灵敏度。我们还演示了在人血清中检测IgE，这显示了实际诊断的可能性。

Immunoassays are widely used to detect disease-related proteins for medical diagnostics. These proteins are generically called antigens, and the so-called binding reaction between antigen and its antibody is used for the immunoassay. In order to improve the performance of the immunoassay, we have developed a new detection system utilizing a magnetic marker and a SQUID sensor. The main results obtained in this study are as follows.(1)We clarified the dependence of the magnetic properties on the size of the magnetic nanoparticle. We showed that the particle with nominal diameter of 25 nm can keep remanence, and can generate large magnetic signal. This particle is, therefore, suitable for magnetic immunoassay.(2)We developed a coating process to cover the magnetic particle with polymer. With this process, we fabricated a polymer-coated magnetic nanoparticle that shows good dispersion in liquid.(3)We developed the high Tc SQUID system for detecting magnetic signal from the marker. Since the signal decays rapidly in space, we realized a close distance between the cooled SQUID and the room temperature sample.(4)We developed a magnetic-contamination free reaction chamber and a method to cancel environmental noise in order to detect very weak signal. Our system can detect 12 samples in a short measurement time of a few minutes with a field resolution of about 10 pT.(5)We conducted a detection of protein called IgE. We demonstrated the detection of IgE down to 0.3 pg, which shows the high sensitivity of the present magnetic method. We also demonstrated the detection of IgE in human serum, which shows the possibility to practical diagnosis.