Controlling Biomolecules With Magnetic 'Tweezers'

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 applied, each particle is attracted to the closest nickel-iron "trap."

So far, the research team has demonstrated that the traps attract individual particles and that the microscope tip can gently drag particles with piconewton forces. (One piconewton is about a trillionth the force required to hold an apple against Earth's gravity.) The next step is to attach particles to both ends of biomolecules such as DNA. The trapping stations then can be used to hold one end of a molecule while the microscope tip gently pulls on the other end. By applying magnetic fields in different directions, the researchers hope to ultimately rotate the magnetic particles to produce complex single molecule motions for genomic studies.