Oscillating microscopic beads could be key to biolab on a chip

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 is based on work by graduate student Elizabeth Rapoport and assistant professor Geoffrey Beach, of MIT’s Department of Materials Science and Engineering (DMSE).
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.
This new technique, for the first time, allows these beads — each about one micrometer, or millionth of a meter, in diameter — to be used for precise measurements of tiny quantities of materials. This could, for example, lead to tests for disease agents that would need just a tiny droplet of blood and could deliver results instantly, instead of requiring laboratory analysis. MIT