New Magnetic Herding Technique Proposed to Manipulate the Very Small

Interesting research out of Duke with possible future applications in medicine:

Engineers have introduced a new magnetic shepherding approach for deftly moving or positioning the kinds of tiny floating objects found within organisms, in order to advance potential applications in fields ranging from medicine to nanotechnology.
The authors of a new research article said their method avoids pitfalls of using tiny light beams, electric currents or even a competing magnetic approach to micromanipulate so-called “colloidal” objects.
“Biology is composed primarily of colloidal materials, things larger than a few billionths of a meter that are suspended in solution and don’t settle rapidly,” said Benjamin Yellen, who developed this “magnetic nanoparticle assembler” technique while obtaining his doctorate at Drexel University.
“They could be cells or large molecules; they are also being investigated for a variety of new devices, such as miniature lasers or semiconducting components,” added Yellen, who in September will become an assistant professor of mechanical engineering and materials science at Duke University’s Pratt School of Engineering.
Yellen is first author of a research paper on the method, already available on-line and to be published in print in the Tuesday, June 21, 2005, issue of Proceedings of the National Academy of Sciences (PNAS)…
The PNAS authors’ paper described how they demonstrated their technique by first patterning permanent rectangular and circular “magnetic traps,” each with millionths of a meter dimensions, on silicon or glass wafers. Each trap was made of cobalt, an element that, like iron, is magnetic.
Over those trap-patterned wafers the authors then added a fluid containing swarms of suspended magnetic iron oxide nanoparticles, with each particle measuring only about 10 billionths of a meter (“nano” means “billionths”).
Into this “ferrofluid” (the prefix “ferro” refers to “iron”) they then floated non-magnetic microscopic beads of the colloid latex, each bead measuring between 90 and 5,000 nanometers.
Finally, the researchers set up an additional switchable external magnetic field that, when switched on, could alter the magnetic field surrounding the permanent magnetic traps.
This arrangement allowed the non-magnetic latex beads to be herded around, even arranged into a variety of complex patterns, by varying how the dueling magnetic fields influenced the shepherding swarms of magnetic iron oxide nanoparticles.
Under the direction of changeable magnetic fields, the particle swarms acted collectively like nano-scale tugboats to push and pull the comparatively large beads of colloids. The beads themselves were color-labeled so their movements could be traced under microscopic observation.
“In a way, bead movement is analogous to the movement of a train along a railroad track,” wrote the authors in their PNAS paper.

Duke University press release…
Magnetic Microsystems Group @ Drexel University…