Magnetic Particle-Transport Microchip Could Be Suitable for Diagnostic Applications

Researchers at the National Institute of Standards and Technology (NIST; Gaithersburg, MD) and the University of Colorado Boulder (CU) have developed a low-power microchip that uses a combination of microfluidics and magnetic switches to trap and transport magnetic beads. Incorporating magnetic switches such as those used in computer random access memory, the chip traps, releases, and transports magnetic beads that potentially could be used as transport vehicles for biomolecules such as DNA. The chip could eventually be suitable for use in biotechnology and medical diagnostic applications.

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 eliminates these drawbacks, while offering the possibility for random access 2-D 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, which are commonly used as magnetic sensors in read heads of high-density computer disk drives. In this case, the spin valves have been optimized 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, thereby moving 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.

The chip demonstration provides a conceptual foundation for using magnetic random access memory (MRAM) for molecular and cellular manipulation. For example, programmable microfluidic MRAM chips might simultaneously control a large number of beads, and the attached molecules or cells, to assemble 'smart' tags with specified properties, such as an affinity for a given protein at a specific position in the array. NIST is also interested in developing cellular and molecular tags for MRI studies in which individual cells, such as cancer cells or stem cells, would be tagged with a smart magnetic biomarker that can be tracked remotely in an MRI scanner. Automated spin valve chips might also be used in portable instruments for rapid medical diagnosis or DNA sequencing.