Development of an optical pumped gradiometric system to detect magnetic relaxation of magnetic nanoparticles

The investigation of magnetic nanoparticles for medical and biological applications is relatively recent and steadily growing. When properly functionalized, magnetic nanoparticles (MNPs) can target cancer cells and deliver a drug or heat to these cells. MNPs are being investigated in several applications in medicine such as hyperthermia, magnetic particle imaging, cell separation and magnetofection, in vitro and in vivo alternating current biosusceptibility, T1 and T2 magnetic resonance contrast agents, and magnetorelaxometry. In each of these applications, a specific physical property is measured. Magnetorelaxometry relies on the fact that when MNPs are magnetized they can relax by the Brownian and Néel mechanisms. Both mechanisms depend on the MNP size and for certain conditions can have a faster relaxation through the Brownian, compared to the Néel, mechanism. This can be exploited to target cells. For certain sizes, when an MNP is free to rotate in the biological fluids, they will relax faster than when attached to a cell. This can provide a high contrast for detection of magnetically-labelled cancer cells, making it possible to differentiate normal from cancer tissue. Until very recently SQUIDs were the main detectors employed to measure MNPs, but Optically Pumped Magnetometers (OPM) are now an attractive alternative. OPMs are smaller, do not need liquid helium, and are simpler to operate than SQUIDs. Here, we present the initial steps of the development of an OPM-based instrument to measure relaxation of MNP in vitro.