Homogeneous Bioassays Based on the Manipulation of Magnetic Nanoparticles by Rotating and Alternating Magnetic Fields—A Comparison

The rotating magnetic field as a source of magnetic nanoparticle manipulation for the use in homogenous bioassays is presented and compared with the frequently used alternating magnetic field technique. For the investigation of the impact of the rotating and alternating field mode on the biomolecule detection, a fluxgate based measurement system has been used. This system detects the MNPs magnetization stray field and calculates the phase lag between the aligning field and the MNPs magnetization. By analyzing the phase lag, the analysis is not altered by changes in MNP concentration. The measured phase lag spectra show a significant difference between both magnetic field modes and agree well with simulations based on the Fokker-Planck equation. A modeling of binding experiments based on these simulations predicts a higher sensitivity for the rotating magnetic field manipulation.