(71c) Multiparameter Paramagnetic Particle Characterization By Dark-Field Imaging

Magnetic particles widely varying in composition, size and magnetization are currently in use in ferrofluids, biochemical separations, cell purification, cell labeling, cell physiology, endocytosis, endosome research, drug targeting, analytical biochemistry, environmental analysis, magnetic resonance imaging, hyperthermia, in vivo diagnostics and others. Most producers, whether research or commercial, are most interested in particle size uniformity and colloidal stability, but magnetization is never specified and is typically mentioned only in terms of per cent iron oxide. Bulk measurements of magnetic susceptibility, using a squid magnetometer, vibrating sample magnetometer, Guoy’s scale, Faraday’s scale, inductive method or MR method provide an average value at best and do not account for the distributed nature of this variable or for particles with zero or very low susceptibility.

By particle tracking velocimetry in dark field illumination we have been able to measure multiple characteristics of several thousand individual particles per sample. The Hyperflux^TM velocimeter is utilized to provide the quantitative video analysis of cells and particles using high definition camera/microscope and capture the images of the particle trajectories in an isodynamic field, the image analysis software converts the image data to the parameters of interest based on velocimetry calculations. By measuring calibrated magnetophoretic mobility and calibrated diameter of every particle we report magnetic susceptibility on a particle-by-particle basis and provide susceptibility distributions for numerous commercial products. Limitations of the method include the size of the particles, currently providing good results for particles in the micrometer size range. In conclusion, the simultaneous determination of distributions of diameter, magnetophoretic mobility, and susceptibility using the commercial velocimeter provide good scope to know the detailed analysis of the sample on a particle-by-particle basis in different fields of science.

Key words: paramagnetic particles, magnetophoretic mobility, particle characterization and quantification, dark field imaging, magnetic susceptibility distribution