Superparamagnetic iron oxide nanoparticles (SPIO-NPs) are highly relevant for many biological and medical applications. Iron oxide nanoparticles are biocompatible and can be used for hyperthermia in cancer treatment, to harvest specific cells from a cell mixture and to enhance the contrast, e.g. of tumour tissue in magnetic resonance imaging (MRI). MRI is a very cost-intensive technique that requires a huge investment. Magnetic particle imaging (MPI), another imaging method for SPIO-NPs, requires high magnetic field gradients for a good spatial resolution.
Besides these drawbacks, neither MRI nor MPI are able to determine whether the SPIO-NPs are bound or unbound. This differentiation is possible in magnetorelaxometry (MRX) of SPIO-NPs due to their different relaxation time constants. The cause for this relaxation is that superparamagnetic particles only show a magnetization if they are inside a magnetic field. After switching off this field, the magnetisation vanishes over time due to thermodynamic effects. The time constant of this decay is dependent on the binding state of the SPIO-NPs.
Here we will show whether it is possible to measure magneto relaxation with a sensor that is under investigation in the CRC 1261 – “Magnetoelectric Sensors: From Composite Materials to Biomagnetic Diagnostics”. This tiny, highly sensitive sensor is able to detect small magnetic fields at low frequencies. It consists of a magnetostrictive and piezoelectric layer on a cantilever. There are several applications where such a setup would be highly interesting, ranging from the detection of the proliferation of cells in 3D printed biomaterials to the testing of the homing capability of magnetically labelled macrophages to tumour sites.