Quantitative detection of DNA labeled with magnetic nanoparticles using arrays of MTJ sensors

Fall River, MA - July 23, 2008 - Physicists at Brown University and Micro Magnetics, Inc. have developed a new technique that could revolutionize medical diagnosis techniques by using magnetic nanoparticles that bind to specific biological molecules found in the body. The research was published in the journal of Applied Physics Letters on July 22, 2008, entitled "Quantitative detection of DNA labeled with magnetic nanoparticles using arrays of MgO-based magnetic tunnel junction sensors".

These scientists are now able to measure the concentrations of specific biomolecules in a fluid purely by analyzing the magnetic signal produced by nanoparticles bound to these molecules. The importance of these results is immense, as "the future technology would be noon-invasive, much more accurate and faster than current techniques involving detection of biomolecules in a fluid (immunoassay)", Dr. Weifeng Shen, the lead author of the publication, commented.

How the new technique works is relatively simple. For each given biomolecule, there is one kind of magnetic nanoparticle which binds to it. These molecule-nanoparticle combinations are then introduced to the magnetic sensor. Once the specific nanoparticle bonds to this molecule in a fluid, it is forever stuck.

The surface of the magnetic sensor is coated with a special chemical which "captures" the biomolecule and the magnetic nanoparticle. Only those biomolecules that match the sensor will be bound to it. Because the molecules that bind to the sensor already are bound to magnetic nanoparticles, the sensor then detects these nanoparticles, producing an electrical signal confirming their presence. All other molecules which have not bonded to the sensor can then be washed away from the sensor area. The strength of the signal produced is directly related to the concentration of the biomolecule of interest. Therefore, the concentration of all these molecules in the body can be measured to a degree of accuracy previously unachieved.

The physical phenomenon behind this process is a property that certain magnetic materials have called magnetoresistance (MR). MR is the property that the resistivity, or charge carrying capacity, of a material changes with the strength of an external magnetic field. MR materials transmit more or less current depending on the strength of the magnetic field, and by measuring this current, the strength of the field can be calculated. MR technology is currently used in modern hard drive heads for reading stored data, as well as in extremely sensitive magnetic field sensors.

Micro Magnetics, Inc. is currently producing some of the world's most powerful magnetoresistive magnetic sensors, known as Magnetic Tunneling Junctions (MTJs). MTJ is a nanoscale quantum mechanical device, belonging to a special kind of electronics - spintronics, where the electron spin plays a significant role in the operation of the device.

The research was sponsored by the National Science Foundation.