Detection of low-concentration superparamagnetic nanoparticles using an integrated radio frequency magnetic biosensor

Improving the sensitivity of existing biosensors for highly sensitive detection of magnetic nanoparticles as biomarkers in biological systems is an important and challenging task. Here, we propose a method of combining the magneto-resistance (MR), magneto-reactance (MX), and magneto-impedance (MI) effects to develop an integrated magnetic biosensor with tunable and enhanced sensitivity. A systematic study of the 7 nm Fe3O4 nanoparticle concentration dependence of MR, MX, and MI ratios of a soft ferromagnetic amorphous ribbon shows that these ratios first increase sharply with increase in particle concentration (0-124 nM) and then remain almost unchanged for higher concentrations (124nM-1240 nM). The MX-based biosensor shows the highest sensitivity. With this biosensor, similar to 2.1 x 101(17) nm Fe3O4 nanoparticles can be detected over a detection area of 2.0 x 10(5) mu m 2, which is comparable to a superconducting quantum interference device biosensor that detects the presence of similar to 1 x 10(8) 11 nm Fe3O4 nanoparticles over a detection area of 6.8 x 10(4)l mu m(2). The proposed biosensor can detect low and various concentrations of superparamagnetic nanoparticles (below 10 nm in size), which is of practical importance in biosensing applications. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795134]