Fluxgate gradiometer for magnetic nanoparticle magnetorelaxometry in unshielded environment

The detection of magnetic nanoparticles (MNPs) is essential for applications in biomedicine, specifically in the detection of biological targets such as disease-related proteins and cells, known as magnetic immunoassay [1]. The size of the MNPs varies within a few to tens of nanometers; hence, their sizes are comparable to cells, viruses and proteins. This means that, with proper treatment, MNPs (magnetic markers) can provide a method of `marking´ or addressing specific biological entities. With the use of magnetic immunoassay, we can perform immunoassays in the liquid phase; where the bound and unbound markers can be magnetically distinguished by exploiting the difference in the Brownian relaxation time between bound and unbound markers without needing to perform a time-consuming washing process [2].