Optical Magnetometry of Single Biocompatible Micromagnets for Quantitative Magnetogenetic and Magnetomechanical Assays

Abstract

The mechanical manipulation of magnetic nanoparticles is a powerful approach to probing and actuating biological processes in living systems. Implementing this technique in high-throughput assays can be achieved using biocompatible micromagnet arrays. However, the magnetic properties of these arrays are usually indirectly inferred from simulations or Stokes drag measurements, leaving unresolved questions about the actual profile of the magnetic fields at the micrometer scale and the exact magnetic forces that are applied. Here, we exploit the magnetic field sensitivity of nitrogenvacancy color centers in diamond to map the 3D stray magnetic field produced by a single soft ferromagnetic microstructure. By combining this wide-field optical magnetometry technique with magneto-optic Kerr effect microscopy, we fully analyze the properties of the micromagnets, including their magnetization saturation and their size-dependent magnetic susceptibility. We further show that the high magnetic field gradients produced by the micromagnets, greater than 10 4 T•m −1 under an applied magnetic field of about 100 mT, enables the manipulation of magnetic nanoparticles smaller than 10 nm inside living cells. This work paves the way for quantitative and parallelized experiments in magnetogenetics and magnetomechanics in cell biology.

Parallelized manipulation of adherent living cells by magnetic nanoparticles-mediated forces

“…The micro-magnetic array (MMA) was designed by our group (Fig. 1a-d), specifically for the manipulation of small MNPs (magnetic core of <10 nm) inside living cells, by engineering micromagnets able to promote high magnetic field gradients (10 3 to 10 4 T/m) on ~50 µm spatial length scales (Toraille et al, 2018). Following characterization of both the micro-magnetic pillars ( Fig.…”

“…However, these prior convincing studies lack real-time observations of live cell where the movement of MNPs inside cells can be correlated with the cell displacement or neurite outgrowth over several hours or days. To fill this gap, we utilized a recently developed parallelized magnetic system (Toraille et al 2018) in order to simultaneously manipulate and image hundreds of living cells over extended periods of time (0-48 hours). We were able to remotely control force-induced processes such as cellular migration and neurite outgrowth, by applying mechanical tensions on endosomes filled with MNPs.…”

Parallelized Manipulation of Adherent Living Cells by Magnetic Nanoparticles-Mediated Forces

“…However, these prior convincing studies lack real-time observations of live cells, in which the movement of MNPs inside cells can be correlated with the cell displacement or neurite outgrowth over several hours or days. To fill this gap, we utilized a recently developed parallelized magnetic system [ 36 ] in order to simultaneously manipulate and image hundreds of living cells over extended periods of time (0–48 h). We were able to remotely control force-induced processes such as cellular migration and neurite outgrowth, by applying mechanical tensions on endosomes filled with MNPs.…”

Magnetic measurements on micrometer-sized samples under high pressure using designed NV centers

“…The detailed analysis focuses on one of the iron beads (see Supporting Information for the signals associated to the other samples). A magnetic field B 0 ≈ 11 mT, created by a permanent magnet, is applied to magnetize the iron samples and to split and resolve the resonances associated to the four orientations of the NV centers existing in a [100]-oriented diamond (17).…”