In this work, a highly balanced ac susceptometer was designed and implemented for magnetic immunoassays for sensing human C-reactive proteins (CRP). It is known that CRPs are used mainly as a biomarker for inflammation or acute diseases. Monitoring CRP values in blood can help medical doctors understand disease progression or the effectiveness of treatments. We characterize magnetic properties of the ac susceptometer as the human CRPs are associated with Fe3O4-antiCRP. In the design, the pickup coil and the excitation coil are positioned side-by-side with their coil axis parallel and separated at a distance of ∼1.5 cm. The pick-up coil consists of two coils wound in opposite direction with a compensation coil to improve balance. We use the Fe3O4-antiCRP-CRP magnetic clusters as the bio-target and study the effects of magnetic clustering on the changes of magnetization. The magnetic clusters are CRPs conjugated onto the Fe3O4-antiCRP and can be observed directly with SEM. The Fe3O4-antiCRP is the anti-C-reactive protein (antiCRP) coated onto dextran-coated magnetic nanoparticles (MNPs), also called the bio-functionalized magnetic nanoparticles (BMNs).
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