Figure 1.

Magnetic ratcheting utilizes arrays of electroplated permalloy micro-pillars, of pitch P, to create dynamic potential energy wells which can be used to trap and manipulate superparamagnetic particles. (a)The magnetic ratcheting system is comprised of a mechatronic instrument driving a rotating magnetic wheel as well as a microchip composed of permalloy micro-pillar arrays, with each pillar having a 1:1 aspect ratio. When proximal to the magnetic wheel, the micro-pillars magnetize in alignment to the bulk field; modifying the magnetic potential energy landscape and introducing potential wells in which superparamagnetic particles migrate. (b)As the wheel is cycled at frequency f, particles will follow the potential wells and ratchet through the pillars based on size and iron oxide content. Using a chip consisting of micro-pillar arrays with gradient horizontal pitch (c), particles will traverse the array until reaching their critical pitch, P_crit, where they will collect and oscillate. Particles with increasing magnetic content will have correspondingly higher critical pitches and can therefore be separated.