Oscillating microscopic beads could be key to biolab on a chip

MIT team finds way to manipulate and measure magnetic particles without contact, potentially enabling multiple medical tests on a tiny device.

If you throw a ball underwater, you'll find that the smaller it is, the faster it moves: A larger cross-section greatly increases the water's resistance. Now, a team of MIT researchers has figured out a way to use this basic principle, on a microscopic scale, to carry out biomedical tests that could eventually lead to fast, compact and versatile medical-testing devices.

The results, based on work by graduate student Elizabeth Rapoport and assistant professor Geoffrey Beach, of MIT's Department of Materials Science and Engineering (DMSE), are described in a paper published in the journal Lab on a Chip. MIT graduate student Daniel Montana '11 also contributed to the research as an undergraduate.

The balls used here are microscopic magnetic beads that can be ''decorated'' with biomolecules such as antibodies that cause them to bind to specific proteins or cells; such beads are widely used in biomedical research.

The key to this new work was finding a way to capture individual beads and set them oscillating by applying a variable magnetic field. The rate of their oscillation can then be measured to assess the size of the beads.

When these beads are placed in a biological sample, biomolecules attach to their surfaces, making the beads larger - a change that can then be detected through the biomolecules effect on the beads' oscillation. This would provide a way to detect exactly how much of a target biomolecule is present in a sample, and provide a way to give a virtually instantaneous electronic readout of that information.