New system uses rotating magnetic field to detect pathogens

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A new technique that uses a magnetic field to selectively separate tiny magnetic particles may have the potential to diagnose many diseases from a single testing sample, providing medical diagnostics with a powerful new tool, according to research published in the Oct. 17 online issue of Lab on a Chip magazine.

Different pathogens can be attracted to specific-size magnetic particles and since the new technique, called non-linear magnetophoretic separation can selectively separate particles by size, the method could be used to diagnose the presence of many diseases in a single sample, said Gil Lee, a professor of chemical and biomedical engineering at Purdue University. The research was conducted at the Birck Nanotechnology Center at Purdue's Discovery Park.

The micron-size magnetic particles have been coated with antibodies that attract certain pathogens and are then mixed with blood samples from patients. The magnetic particles are dispersed in a liquid in a container housing a microchip that contains metal disks as wide as 5 microns, or millionths of a meter. The container is surrounded by three electromagnets energized in sequence to produce a rotating magnetic field.

The technique uses an array of disks made of cobalt and coated with chromium to prevent corrosion. The disks are periodically spaced on the surface of the silicon chip. As the magnetic field rotates, the particles move from one disk to another until they separate from the rest of the sample. Rotating the magnetic field at specific speeds separates only particles of certain sizes, meaning pathogens attached to those particles would be separated from the sample by varying the rotation speed, Lee said.

An advantage of the technique is that it can be used for medical diagnostics or possibly to detect biological materials in environmental samples, he added.

"When you walk into a doctor's office, the problem is that it could be one of five or six different pathogens giving you the symptoms," Lee said. "The doctor cannot determine which pathogen you have, so they simply give you a broad-spectrum antibiotic or tell you to go home and get some rest. There clearly is a need for technology that can recognize multiple pathogens simultaneously and at very low levels. It is likely they will be chip-based technologies that are easy to implement in medical environments."

The research has been supported by the Institute for Nanoelectronics and Computing and funded by NASA. The findings will be available in print in the December issue of Lab on a Chip.