Magnetic forces help to identify nanoparticles

The "nano-flower" is an extremely small particle made up of a gold core and iron oxide "petals." Source: The Schaak/Williams reasearch groups

A team of Penn State University scientists in the US has invented a new system that uses magnetism to purify hybrid nanoparticles -- structures that are composed of two or more kinds of materials in an extremely small particle that is visible only with an electron microscope. Team leaders Mary Beth Williams, an associate professor of chemistry, and Raymond Schaak, a professor of chemistry, explained that the never-before-tried method will not only help scientists to remove impurities from such particles, it also will help researchers to distinguish between hybrid nanoparticles that appear to be identical when viewed under an electron microscope, but that have different magnetism - a great challenge in recent nanoparticle research. The team combined forces to figure out a way to purify hybrid nanoparticles. The innovative technique uses the magnetic components of nanoparticles to tell them apart and to separate impurities from the target nanoparticle structures. "Our method uses magnetic fields to slow the flow of particles through tiny glass tubes called capillaries," Williams explained. "We use a magnet to pull magnetic particles against the wall of the tube and, when the magnetic field is reduced, the particles flow out of the capillary. Magnetism increases as particle volume increases, so small and gradual changes in the magnetic field let us slowly separate and distinguish between nanoparticles based on even minute magnetic and structural differences."