An array of magnetic traps designed for manipulating individual
biomolecules and measuring the ultrasmall forces that affect
their behavior has been demonstrated by scientists at the
National Institute of Standards and Technology (NIST). Described
in a recent issue of Applied Physics Letters, the chip-scale,
microfluidic device works in conjunction with a magnetic force
microscope. It's intended to serve as magnetic "tweezers" that
can stretch, twist and uncoil individual biomolecules such as
strands of DNA. The device should help scientists study folding
patterns and other biochemical details important in medical,
forensic and other research areas. The new NIST device works
like drawing toys that use a magnetized stylus to pick up and
drag magnetic particles. Magnetic particles 2 to 3 micrometers
across are suspended in a fluid and injected into the device.
The surface of a thin membrane enclosing the fluid is dotted
with an array of thin film pads made of a nickel-iron alloy.
When a magnetic field is applie