Moment-Based Separation of Magnetic Nanoparticles with an Inverted Halbach Array

Science Center, Bent Corridor

Magnetic nanoparticles have a variety of applications in medicine and technology that require particle uniformity, both in size and in magnetic moment. Because of synthesis difficulties, effective sorting methods are necessary to ensure this uniformity. Here, we describe a relatively new method for sorting magnetic nanoparticles. Our approach relies on an unusual magnet design known as an inverted linear Halbach array, its properties of low magnetic field and high field gradient, and its resulting ability to cause selective agglomeration of the particles, creating an effective method of separation by magnetic moment. Previously, our method has been shown to give promising results when used on particles of different sizes that were mostly suspended in toluene. Recently, however, we have been separating particles that were suspended in water, as is typical for biomedical applications. These new particles are also of similar sizes (around 20 nm) but different magnetizations (around 30-90 emu/g), showing that this method is not just size-dependent but can be done on the basis of magnetic moment alone.