Researchers develop microchip to transport magnetic beads

A low-power microchip that uses a combination of microfluidics and magnetic switches to trap and transport magnetic beads has been developed in the US.

The novel transport chip, developed by a team from the US National Institute of Standards and Technology (NIST) and University of Colorado Boulder (CU), may have applications in biotechnology and medical diagnostics.

According to a statement, a key innovation in the chip is the use of magnetic switches like those in a computer random access memory.

The NIST/CU team used the chip to trap, release and transport magnetic beads that potentially could be used as transport vehicles for biomolecules such as DNA.

Conventional microfluidics systems use pumps and valves to move particles and liquids through channels. Magnetic particle transport microchips offer a new approach to microfluidics but generally require continuous power and in some cases cooling to avoid sample damage from excessive heating. The NIST/CU technology is said to eliminate these drawbacks while offering the possibility for random access two-dimensional control and a memory that lasts even with the power off.

The demo chip features two adjacent lines of 12 thin-film magnet switches called spin valves, commonly used as magnetic sensors in read heads of high-density computer disk drives.

In this instance, the spin valves have been optimised for magnetic trapping. Pulses of electric current are used to switch individual spin valve magnets ‘on’ to trap a bead, or ‘off’ to release it, and thereby move the bead down a ladder formed by the two lines. The beads start out suspended in salt water above the valves before being trapped in the array.

‘It’s a whole new way of thinking about microfluidics,’ said NIST physicist John Moreland. ‘The cool thing is it’s a switchable permanent magnet — after it’s turned on it requires no power. You beat heat by switching things quickly, so you only need power for less than a microsecond.’

NIST researchers previously demonstrated that spin valves could be used to trap and rotate particles, and recently were awarded two patents related to the idea of a magnetic chip.

Magnetic tags are used in bioassays such as protein and DNA purification, and cell breakdown and separation. The chip demonstration provides a conceptual foundation for a more complex magnetic random access memory (MRAM) for molecular and cellular manipulation.