The effect of the particle size and magnetic moment of the Fe3O4 superparamagnetic beads on the sensitivity of biodetection

In recent years, the quantitative detection of biomolecules based on Giant magnetoresistive (GMR) sensors and magnetic nanoparticles have received continuous attention. Researchers try to improve the accuracy of detection by various methods, including using a more sensitive sensor, designing circuit to reduce system noise, and so on. In which, the intrinsic properties of magnetic labels, such as the particle size of labels is a vital aspect for the GMR biosensing technology. In this work, a series of Fe3O4 particles with average particle sizes from 80 to 580 nm were prepared for exploring the effect of particle size on the limit of detection (LOD). An ultra-low LOD of 0.1 ng/mL was obtained for small particles with average sizes from 80 to 200 nm detected by our home-made biodetection device. However, for the ones with large sizes from 330 to 580 nm, the LOD increases with the increase of particle size. The total magnetic moments of all particles attached on the sensor surface Σmm are calculated theoretically and compared with the experimental data of the normalized voltage ratio (Vnvr=|ΔV|/V0×100%) over particle size. It is found that not only the particle size but also the magnetic moment of particles affect the LOD of the concentration.