R&D DIGEST

Magnets could play a heightened role in diagnosing pathogens. Micron-sized magnetic particles are coated with antibodies that attract certain pathogens and are mixed with patients' blood samples. The sensitive technique, developed by researchers at Purdue and Duke universities, can selectively separate particles by size so that several diseases can be detected in a single sample.

Gil Lee, a professor of chemical and biomedical engineering at Purdue, explains that the technology relies on a microchip containing an array of metal disks as wide as 5 µm. The magnetic particles are dispersed in a liquid and put in a container that also houses the chip. The container is surrounded by three electromagnets energized in sequence to produce a rotating magnetic field.

As the magnetic field rotates, the particles move from one disk to another until they are separated 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, said researchers.

The technique, called nonlinear magnetophoretic separation, works using an array of disks made of cobalt and coated with chromium to prevent corrosion. The advantage of the technique is that it can be used to simultaneously separate and identify pathogens with sensitivity up to a million times higher than the immunoassays commonly used today for human diagnostics, explains Hao Shang, from Purdue's School of Chemical Engineering and Weldon School of Biomedical Engineering.

Shang's company, MagSense Life Sciences Inc., is developing a method to produce the magnetic particles. The micron-sized particles are made from thousands of nano-sized particles. These particles are unique because they are superparamagnets, meaning that they are not magnetic unless they are in a magnetic field. The particles can be mixed in a solution without attracting each other or clumping together, which is critical for them to be distributed uniformly throughout the solution. When the rotating magnetic field is applied, the particles become magnetic.

“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 says. “The doctor[s] 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.”

Lee's work is based at the Birck Nanotechnology Center at Purdue's Discovery Park. The research has been supported by the Institute for Nanoelectronics and Computing, and funded by NASA.

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