Gold speck highlights molecules

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.