(471b) Fast Magnetophoresis Using Low Magnetic Gradients

An essential step in the development of scientific and clinical applications of magnetic carriers is the control of particle behaviour. Control of particle trajectory in drug delivery applications or extraction from dispersion in immunoassay applications using externally applied magnetic gradients are typical examples. However, the magnetic gradients required to produce a significant magnetophoretic drift in a magnetic carrier are very high, even in the case of superparamagnetic particles. For example, gradients of the order of 10⁴ T/m could be found in typical separation columns using a packed bed of magnetically susceptible wires (diameter 50µm) placed inside an electromagnet.

Here, we present new experimental and theoretical results showing that low gradient magnetic separation (LGMS) is also possible. The key step in this LGMS process is the reversible aggregation of magnetic carriers induced by the magnetic field. We report fast separation (a few minutes for a 25 mL sample) of dispersions of superparamagnetic particles with different concentrations (0.01 g/L to 10 g/L) using a 30 T/m uniform magnetic gradient. The interplay between the different factors determining low gradient magnetophoresis (magnetization of particles, size, ...) is consistently described by a magnetic analogous to the Bjerrum length concept [1,2]. We formulate a simple criterion predicting the onset of low gradient magnetophoresis separation as a function of the sample properties (e.g., minimum particle radius). The separation times of samples with different concentrations and different particles seem to be described by a unique curve depending on the ratio between the magnetic Bjerrum length and the particle separation (depending on concentration).

References

[1] G. De Las Cuevas, J. Faraudo and J. Camacho, J. Phys. Chem. C (2008), 112, 945-950

[2] J. Faraudo and J. Camacho, Colloid. Polym. Sci. (2010), 288, 207?215