Detection of magnetic biomarkers using a single giant magneto-impedance microwire*

A combination of magnetic sensors and superparamagnetic nanoparticles provides a novel biosensing platform for detection of cancer cells and biomolecules. In this study, we demonstrate the excellent capacity of detecting 10 nm iron oxide nanoparticles at various concentrations up to 40 mg using a single microwire (Co_69.25Fe_4.25Si₁₃B_12.5Nb₁; d=60 µm) based sensor. The change in impedance of the microwire was measured using an impedance analyzer (1 MHz – 1 GHz) when exposed to the stray magnetic field from the nanoparticles. The detection sensitivity of the sensor is greatly enhanced by supplying a small DC field just below the anisotropy field of the microwire (H_K = 3.5 Oe). The external field dependence of the detection demonstrates the microwire as a tunable RF magnetic sensor for small magnetic fields. In addition, we utilize the linear low-field impedance response as a new method for determination of the stray field strength of the detected nanoparticles.