The XacPro-E101 system measures the mixed-frequency ac magnetic susceptibility of materials. The probing port of the system consists two shells of coaxial solenoids, so-called excitation coils, as well as a so-called pick-up coil located inside these two solenoids. The pick-up coil is composed of two in-series but opposite wiring sections. Two independent electric circuits drive the two separated excitation coils to generate two ac magnetic fields having frequencies of the f1 and f2.

A detected sample posited in either section of the pick-up coil is magnetized to generate magnetization at a mixed frequency. The magnetization at a target frequency is detected via the pick-up coil and magnified with an amplifier and a fast Fourier transformation circuit.

Here gives an example to demonstrate the feasibility of assaying c-reactive protein using XacPro-E101.

When tissues are damaged during the course of infectious and non-infectious diseases, cytokine is produced and induces c-reactive proteins (CRP) (MW = 1440000 g). Due to the fact that CRP levels increase dramatically in the event of injury, infection, or inflammation CRP levels have become key indicators of infectious/non-infectious disease or of acute tissues. Furthermore, CRP is also an indicator for heart attack. The required sensitivity for evaluate the risk of heart attack is 1 mg/l, i.e. 1 ppm. Hence, high-sensitivity and quantitative immunoassay tests for CRP are important tools in clinical diagnosis.

To magnetically label CRP, anti-CRP is bound to magnetic beads. After incubating the immuno-complex of CRP-anti-CRP- magnetic-beads, the / of magnetic reagents added with various amounts of CRP are probed by using the XacPro-E101. The characteristic relationship between the /and the CRP concentration for pure CRP solutions is shown with green crosses. The sensitivity is 0.01 ppm or 0.001 mg/dl. The ImmunoMagnetic Reduction (IMR) is also done for clinical samples such as serum, which results are shown with blue dots. The blue dots follows the same behavior as red crosses. Since serum contains many kinds of proteins, not only CRP. The similar trend between green crosses and blue dots demonstrates the high specificity of IMR using XacPro-E101 and anti-CRP coated magnetic beads. Furthermore, the sensitivity of IMR on CRP/hsCRP is higher than those of turbidimetry, nephelometry, and ELISA.

Ref.: "Magnetic susceptibility reduction method for magnetically labeled immunoassay", Appl. Phys. Lett, 88, 212512 (2006).