Nonmagnetic particle separation using ferrofluids controlled by magnetic fields

Abstract

The ability to manipulate and control small particles is important in many biomedical applications including cell sorting for diagnosis and cancer detection. Several commonly used cell isolation techniques include flow cytometry, magnetic labeling, and electrophoresis. Recently, research has focused on sized based methods such as deterministic lateral displacement, and ferrofluid methods utilizing time and spatially traveling magnetic fields. Here a new sized based method of nonmagnetic particle separation is presented and investigated. This new method utilizes magnetic separation in combination with ferrofluids. The separation is accomplished without magnetic labeling and with the application of a time uniform magnetic field which can be contrasted with the complicated field dynamics required by other methods. In this technique, nonmagnetic particles are submerged in a ferrofluid which is subjected to a magnetic field. In this way the fluidic environment is controlled rather than the nonmagnetic particle directly. The resulting body forces on the fluid give rise to forces on the nonmagnetic particles. These resulting forces are similar to familiar buoyant forces. Like the buoyant force, this magnetic force is dependent on particle volume. Analysis shows that the nonmagnetic particles can be separated through a combination of magnetic forces in the direction of particle motion and drag forces that oppose this motion. This combination results in different position profiles in time for nonmagnetic particles of different sizes. Governing magnetic field and particle dynamics equations are developed and analytic solutions are obtained. Solution methods utilize numerical time integration tools to overcome difficulties associated with nonlinear governing dynamics. Experimentation is performed to validate the model developed. This technology will have direct impacts in cell separation and sorting for use in biomedical applications. It opens possibilities for the development of a point-of-care device that is disposable and does not require complicated equipment. Such a device would not require extensively trained technicians or a laboratory setting. Separation time scales are very short compared to currently available methods.