OPM magnetorelaxometry in the presence of a DC bias field

Abstract

Spatial quantitative information about magnetic nanoparticle (MNP) distributions is a prerequisite for biomedical applications like magnetic hyperthermia and magnetic drug targeting. This information can be gathered by means of magnetorelaxometry (MRX) imaging, where the relaxation of previously aligned MNP’s magnetic moments is measured by sensitive magnetometers and an inverse problem is solved. To remove or minimize the magnetic shielding in which MRX imaging is carried out today, the knowledge of the influence of background magnetic fields on the MNP’s relaxation is a prerequisite. We show MRX measurements using an intensity-modulated optically pumped magnetometer (OPM) in background magnetic fields of up to $100~\upmu \mbox{T}$ 100 μ T . We show that the relaxation parameters alter or may be intentionally altered significantly by applying static fields parallel or antiparallel to the MNP’s alignment direction. Further, not only the relaxation process of the MNP’s magnetic moments could be measured with OPM, but also their alignment due to the MRX excitation field.

Perspective: magnetic nanoparticles in theranostic applications

“…Turning our attention again to nonzero fields, Jaufenthaler et al 87 showed how the relaxation time was already affected by small DC fields (< 100 µT) and their applied direction 87 . Similarly, the measured phase lag in MSI is also related to these relaxation time constants and could provide information on changes in particle dynamics and interactions for the case of small AMFs.…”

Monitoring magnetic nanoparticle clustering and immobilization with thermal noise magnetometry using optically pumped magnetometers

“…Today, there are many different OPM configurations, covering a broad range of applications 36,[45][46][47][48] . Comparisons have been made with SQUID systems [49][50][51] and the magnetometers have also found their way into applications such as MNP detection, characterization and imaging [52][53][54][55][56][57] .…”

“…36,[45][46][47][48] Comparisons have been made with SQUID systems [49][50][51] and the magnetometers have also found their way into applications such as MNP detection, characterization, and imaging. [52][53][54][55][56][57] The developed tabletop setup (Fig. 3a) consists of two Gen-2 QuSpin zero-eld magnetometers (QZFMs) (QuSpin Inc., CO, USA) 58 that are operated in single-axis mode.…”

Pulsed Optically Pumped Magnetometers: Addressing Dead Time and Bandwidth for the Unshielded Magnetorelaxometry of Magnetic Nanoparticles

“…The remanent magnetization can be exploited in MRX imaging [ 60 ]. In this respect it is worth noting that in unshielded experiments, the Earth’s field (or any other bias field) contributes non-neglectably to the remanent magnetization and to the relaxation behavior of the MNP [ 64 , 65 ].…”