Magnetic immunoassay platform based on the planar frequency mixing magnetic technique

• 2D superparamagnetic imaging for magnetic immunoassay using the p-FMMD technique.
• Acquirement of sum-frequency components from the magnetically nonlinear nanoparticles.
• Ability to acquire planar images of magnetic NPs in microchannel as narrow as 30 µm.
• Spatial resolution enabling to distinguish two distinct microchannels 2 mm apart.

We represent the experimental results of our planar-frequency mixing magnetic detection (p-FMMD) technique to obtain 2D superparamagnetic images for magnetic immunoassay purpose. The imaging of magnetic beads is based on the nonlinear magnetic characteristics inherent in superparamagnetic materials. The p-FMMD records the sum-frequency components originating from both a high and a low frequency magnetic field incident on the magnetically nonlinear nanoparticles. In this study, we apply the p-FMMD technique to 2D scanning imaging of superparamagnetic iron oxide nanoparticles (SPIONs) in a microfluidic platform. Our p-FMMD system enables to acquire planar images of SPIONs filled in a microchannel as narrow as 30 µm in width. The minimum detectable amount is ~1.0×108 beads of 100 nm size. The system shows a spatial resolution enabling to distinguish between two distinct channels even 2 mm apart from each other. Our p-FMMD system as a magnetic immunoassaying system has permitted the detection of amyloid beta 42 (Aβ42), a promising biomarker of Alzheimer's disease, at the minimum concentration of 23.8 pg/ml. This may enable the identification of the Aβ42 levels for the early-stage of Alzheimer's disease with the assistance of the MPI using p-FMMD technique. The results show that the deployment of the p-FMMD can be an alternative to conventional biosensing analytical methods, and can be used as a fast and portable screening method.