Oscillating Microscopic Beads Used for Biochip

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

A team of scientists at Massachusetts Institute of Technology (MIT; Cambridge, MA, USA) 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 beads are placed in a biological sample, biomolecules attach to their surfaces, making the beads larger and this 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 technique, for the first time, allows these beads, which are each about one micrometer 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. The dual functionality of domain walls as both bead carriers and sensors is a promising platform for the development of lab-on-a-bead technologies.


Besides being potentially quicker and requiring a far smaller biological sample to produce a result, such a device would be more flexible than existing chip-based biomedical tests. While most such devices are specifically designed to detect one particular kind of protein or disease agent, this new device could be used for a wide variety of different tests, simply by inserting a fresh batch of fluid containing beads coated with the appropriate reactant. After the test, the material could be flushed out, and the same chip used for a completely different test by inserting a different type of magnetic beads.

There are dozens of types of magnetic beads commercially available that can be coated to react with many different biological materials; therefore, such a test device could have enormous flexibility. The team used magnetic beads of different sizes to demonstrate that their system is capable of detecting size differences corresponding to those between particles that are bound to biological molecules and those that are not. The study was published online on August 21, 2012, in the journal Lab on a Chip.

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