  Controlled actuation of superparamagnetic beads (SPBs) within a microfluidic
environment using tailored dynamic magnetic field landscapes (MFLs) is a potent
approach for the realization of point-of-care diagnostics within Lab-on-a-chip
(LOC) systems. Making use of an engineered magnetic domain pattern as the MFL
source, a functional LOC-element with combined magnetophoretic funnel,
concentrator, and valve functions for micron-sized SPBs is presented. A
parallel-stripe domain pattern design with periodically increasing/decreasing
stripe lengths has been fabricated in a topographically flat continuous
exchange biased (EB) thin film system by ion bombardment induced magnetic
patterning (IBMP). It is demonstrated that, upon application of external
magnetic field pulses, a fully reversible concentration of SPBs at the domain
pattern focal point occurs. In addition, it is shown that this functionality
may be used as an SPB funnel, allowing only a maximum number of particles to
pass through the focal point. Adjusting the pulse time length, the focal point
can be clogged up for incoming SPBs, resembling an on-and-off switchable
particle valve. The observations are supported by quantitative theoretical
force considerations.
