Ferrofluids are colloidal solutions of magnetic nanoparticles in a carrier fluid. Ferrofluids are increasingly used for biological and medical applications, such as high gradient magnetic separation techniques, magnetic drug targeting, magnetic hyperthermia and contrast agents for Magnetic Resonance Imaging. In many of these medical and biological applications, the synthesis of uniformly sized magnetic nanoparticles has a key importance because their magnetic properties depend strongly on their dimensions. As a result of the difficulty of synthesizing monodisperse nanoparticles, a technique capable of fractionating nanoparticles in accordance with their dimensions should be generated.

In this study, we designed a novel microfluidic device which is capable of separating magnetic nanoparticles according to their particle sizes.

Device consists of a microfluidic channel in which ferrofluid will flow. The pumping of the ferrofluid from inlet to outlet is achieved by using spatially traveling, sinusoidally time-varying magnetic fields. To obtain such traveling fields parallel electrodes are built under the fluidic channel where the electrodes are perpendicular to the channel axis.

In addition to traveling magnetic fields, DC magnetic field gradients are used for the particle separation. Equal but opposite DC Magnetic fields are applied from the sides of the fluidic channel and they cancel each other along the axis of the channel. Thus, a region having a zero magnetic field is produced in the middle of the channel (Magnetic Field Free Region). While the bigger particles are attracted to the side walls of the channel, smaller particles reside in the middle of the channel and by the traveling magnetic field pumping only the smaller particles in the middle of the channel will be eluted.

Main advantage of this system among the current field flow fractionation systems is its very high efficiency. By just increasing the magnitude of the applied DC magnetic field, much narrower particle size distributions can easily be obtained.

The operation of the system was successfully proven by making both magnetic and fluidic simulations with Comsol Multiphysics Software. In addition, all the fabrication steps of the device are planned and device is ready for the fabrication.

We believe that by the help of this design, the fractionation of magnetic nanoparticles can be done more effectively compared to existing technology.