Fabrication of magnetic microfiltration systems using soft lithography

Arrays of nickel posts were used as magnetic elements in a microfiltration device that is compatible with microfluidic systems. The combination of microtransfer molding-a soft lithography technique-and electrodeposition generated nickel posts similar to7 mum in height and similar to15 mum in diameter inside a microfluidic channel. Once magnetized by a magnetic field from an external, permanent, neodymium-iron-boron magnet, these nickel posts generated strong magnetic field gradients and efficiently trapped superparamagnetic beads moving past them in a flowing stream of water. These nickel post arrays were also used to separate magnetic beads from nonmagnetic beads. (C) 2002 American Institute of Physics.