The new technique selectively separates
tiny magnetic particles using an array
of metal disks © Purdue
Because different pathogens could be attracted to specific-size magnetic particles and the new technique 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.
The micron-size magnetic particles have been coated with antibodies that attract certain pathogens and are then mixed with blood samples from patients. A critical piece of the technology is a microchip containing an array of metal disks as wide as 5 microns, or millionths of a meter. The magnetic particles are dispersed in a liquid placed in a container housing 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, Lee said.
In recent experiments, samples containing magnetic particles attached to yeast were placed inside the rotating magnetic field and separated from the rest of the samples. The technique, called non-linear magnetophoretic separation, works using an array of disks made of cobalt and coated with chromium to prevent corrosion. The disks are regularly, or periodically, spaced on the surface of the silicon chip.
An advantage of the non-linear magnetophoresis technique is that it can be used to simultaneously separate and identify pathogens with a sensitivity up to a million times higher than the "solid phase immunoassays" commonly used today for human diagnostics.
The new approach, however, aims to use the particles not for research but for medical diagnostics or possibly to detect biological materials in environmental samples.
COMPAMED.de; Source: Purdue University