(118b) Sedimentation and Magnetophoretic Velocity of Plain and Functionalized Magnetic Nanoparticles By in Situ Visualization of Separation Behavior in Superposed Gravity and Magnetic Fields (Invited)

Magnetic micro- and nanoparticles (MNP) have increasingly wide applications in information technology, magnetic fluids, selective separation, and nanomedicine. Their magnetic susceptibility (responsiveness) and magnetization has to be analysed during the particle design, optimization of application and quality control of production process. To this end, comprehensive characterization is demanded for both of the MP themselves and of the state of intermediate as well as final application ready dispersion.

The contribution introduces a recently developed measuring method characterizing magnetic MNP of particles and magnetic nanoparticles laden objects. Basically, gravity fields are superposed by parallel or orthogonal magnetic fields. Strength and direction of fields determine the acceleration of MNP and their direction of movement. Terminal velocity depends on field strength/gradient, buoyancy and hydrodynamic frictional coefficient of particles. Velocity can be determined with high precision and no assumption/material parameters by STEP-Technology^® (1), recording instantaneously space and time resolved extinction profiles over the entire sample. Based on these profiles migration velocity is determined by software package SEPView^®. A LUMiReader^® adapted with permanent magnets of different field directions regarding gravity field was used. If cell holders with no magnets are used, particles can be analyzed regarding sedimentation velocity and particle size distribution as well as stability of the particle dispersion (1).

In a first study, magnets were positioned sidewise (orthogonal field) and applicability of the new approach investigated for a broad field of magnetic objects (MNP, assemblies of MNPs, siRNA-MNP, pDNA-MNP, virus-MNP, micro bubbles, labelled cells). Mean magnetophoretic velocity of analyzed particles amount to some tens µm/s up to over 100 µm/s.

On the other hand, we report in more detail on magnetophoretic mobility for monodisperse particles and magnetic viral complexes that were prepared via self-assembling of PEI-Mag2 or SO-Mag6-12 nanoparticles with adenoviral (Ad) or VSV-particles (VSV). We employed holders equipped with two disk neodymium-iron-boron magnets positioned underneath optical cell (magnetic flux density and gradient averaged over vertical sample height: 0.16 T and 33.5 T/m, respectively). Magnetophoretic velocity ν was calculated based on integral normalized extinction, E/E₀, for different wavelengths, versus time t (2). No sedimentation of MNP was detected within time frame with no magnetic field application. A significant decline of E/E₀ (clarification) was observed with the magnetic field indicating a decrease of MNP concentration. From E/E₀ magnetophoretic velocity distribution was calculated for each wavelength. In case of monodisperse MNP magnetophoretic velocity distribution is independent on wavelength. In contrast, for polydisperse magnetic particles differences can be measured indicating that size classes have a different magnetic responsiveness (2). The newly developed STEP‐MAG technology for in situ visualization and analysis of magnetophoretic velocity of MNP and micro-/ nanomagnetic assemblies has potential applications in design of advanced materials, molecule and cell separation, tissue engineering and drug/nucleic acid targeting.

[1] Lerche D., Comprehensive characterization of nano- and microparticles by in-situ visualization of particle movement using advanced sedimentation techniques. KONA Powder Particle J. (34) 2017 (open access)

[2] Mykhaylyk, O. et. al., Magnetophoretic mobility: Determination by space and time resolved extinction profiles (in-situ visualization). IEEE MAGNETICS LETTERS (6) 2015 (open access)