A novel magnetophoretic-based device for magnetometry and separation of single magnetic particles and magnetized cells

The use of magnetic micro- and nanoparticles in medicine and biology is expanding. One important example is the transport of magnetic microparticles and magnetized cells in lab-on-a-chip systems. The magnetic susceptibility of the particles is a key factor in determining their response to the externally applied magnetic field. Typically, to measure this parameter, their magnetophoretic mobility is studied. However, the particle tracking system for accurately determining the traveled distance in a certain time may be too complicated. Here, we introduce a lithographically fabricated chip composed of an array of thin magnetic micro-disks for evaluating the magnetic susceptibility of numerous individual magnetic particles simultaneously. The proposed novel magnetometer works based on the phase change in the trajectory of microparticles circulating around the disks in a rotating in-plane magnetic field. We explain that the easily detectable transition between the phase-locked and the phase-slipping regimes and the frequency at which it happens are appropriate parameters for measuring the magnetic susceptibility of the magnetic particles at the single-particle level. We show that this high-throughput (i.e., similar to ten thousand particles on a 1 cm(2) area) single-particle magnetometry method has various crucial applications, including i) magnetic characterization of magnetic beads as well as magnetically labeled living cells, ii) determining the magnetization rate of the cells taking up magnetic nanoparticles with respect to time, iii) evaluating the rate of degradation of magnetic nanoparticles in cells over time, iv) detecting the number of target cells in a sample, and v) separating particles based on their size and magnetic susceptibility.

Automated summary

The use of magnetic micro- and nanoparticles in medicine and biology is expanding, with one important example being the transport of these particles in lab-on-a-chip systems. This study introduces a novel magnetometer using magnetic micro-disks to evaluate the magnetic susceptibility of numerous individual particles simultaneously. The method has various crucial applications, including magnetic characterization of beads and living cells, determining magnetization rate of cells, evaluating degradation rate of nanoparticles in cells, detecting target cells in samples, and separating particles based on size and magnetic susceptibility.