Imaging and Linking Spatial Magnetic Nanoparticle Distribution to Microbead Torques Using Soft X‐Ray Laminography

ABSTRACT The introduction of magnetic microbeads has greatly advanced biomedical research by enabling high‐precision methods for cell sorting, biomolecule transport, and cell force analysis. Applications extend to molecular isolation, diagnostic assays, and targeted drug delivery. Torques observed on superparamagnetic microbeads during cell experiments indicate spatial variations in the microbead properties. A high degree of internal magnetic structure complexity is revealed by nanoscale 3D imaging of superparamagnetic microbeads via soft X‐ray laminography. Microbeads are found to have an uneven distribution of magnetic magnetite nanoparticles. The effects of this on the hydrodynamic behavior of the microbeads are analyzed by semi‐numerical simulations using the laminography data. The calculated magnitudes of magnetic torque are consistent with the data from microbead transport experiments, involving fibroblast cells. By this, a structural basis for magnetic torques observed in experiments with superparamagnetic microbeads has been identified. Soft X‐ray laminography is proven to be a powerful technique for revealing structural details important to lab‐on‐a‐chip technologies. The findings indicate that magnetic microbeads deviate considerably from the theoretical model of uniform spheres. The identified structural heterogeneities hold significant implications for lab‐on‐chip experiments.