Monitoring Minute Changes of Magnetic Markers´ Susceptibility by SV-GMR Needle-Type Probe

The aim of this study is to present the novel methodology for magnetic markers immunoassay measurements by spin valve giant magnetoresistive (SV-GMR) needle probe. Extremely small size and specific construction of this probe type allow detecting the changes of complex susceptibility directly from the sample. The needle-type probe consists of four SV-GMR elements connected in a Wheatstone bridge and it has sensitivity of 11 μV/μT. The SV-GMR sensing element has dimensions of 40 μm × 75 μm. This paper presents a setup feasible to perform spectroscopic magnetic markers measurement. It includes data related to signal changes caused by the magnetic markers dilution. It shows the influence of particle size changes (120 nm, 1 μm, 3.5 μm, 6.5 μm) on real and imaginary parts of the complex susceptibility of the specimen. While performing measurements, probe sensing elements were placed inside the sample. Monitoring changes of samples susceptibility allows performing homogenous immunoassay measurements in a liquid phase by SV-GMR probe. Based on the measurement results, analytical model of changes of complex susceptibility is derived and described.