Gold speck highlights molecules

September 10/17, 2003

How do you sense what is happening at the scale of molecules, which are thousands of times smaller than microscopic objects like red blood cells?

Researchers from Ludwig-Maximilians University in Germany have found a way to detect the very small spectral shifts that occur when the light scattering off a single gold nanoparticle interacts with molecules.

The device makes it possible to detect molecular changes in real-time. The method could eventually be used to make arrays of devices that very quickly sense many types of molecules at once.

The researchers used a 40-nanometer nanoparticle coated with biotin, which combines with a second molecule -- streptavidin. They were able to sense the slight change in red light -- a red shift -- caused when the molecules bound together and changed the way the light around the nanoparticle refracted, or bent. Forty nanometers is more than 100 times smaller than a red blood cell, and is the span of 400 hydrogen atoms.

This is sensitive enough to detect fewer than fifty molecules undergoing a binding process, according to the researchers.

The work appeared in the May 30, 2003 issue of July 9, 2003 Nano Letters.

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