No abstract

An increasing number of biomedical applications requires detailed knowledge of the magnetic susceptibility of individual particles. With conventional techniques it is very difficult to analyze individual particles smaller than 1μm. The authors demonstrate how the susceptibility of individual nanoparticles can be determined in an efficient way by optically analyzing the confined Brownian motion of a nanoparticle trapped in a known magnetic potential well on a chip. A setup is introduced that has a controllable two-dimensional magnetic potential well, which is defined by an integrated microscopic current wire. Susceptibility measurements have been performed on 150–450nm superparamagnetic beads. They found differences in bead susceptibility of an order of magnitude and differences in volumetric susceptibility of more than a factor of 2.

We describe an analysis of the dynamics of individual superparamagnetic micro-and nanoparticles in order to quantify their magnetic properties and mobility near a chip surface. The particles are attracted to the chip surface by integrated microscopic current wires. We show that it is possible to accurately analyze particles with a diameter of about 1 m by the magnetophoretic movement between current wires because of the very high field gradients. This reveals distinct differences in volume susceptibilities of particles with the same outer diameter. Smaller particles are characterized using the technique of confined Brownian motion analysis. By capturing 300 nm particles on a current wire with surface barriers or a focused shape, the magnetization of the particles can be measured with an accuracy better than 10%.