Measuring molecular interactions

A simple instrument that uses the principle of back-scattering interferometry (BSI) has been developed by chemists at Vanderbilt University to measure the interactions between free-floating, unlabelled molecules including proteins, sugars, antibodies, DNA and RNA.

By shining a red laser into a microscopic, liquid-filled chamber where two kinds of molecules are mixed, the instrument can measure the strength with which they react, even when the interactions are extremely weak. In fact, the researchers have demonstrated that it is sensitive enough to detect the process of protein folding.

'Pharmaceuticals depend on reactions between proteins and small molecules or between pairs of proteins, or interactions between RNA and DNA or pairs of DNA molecules. So the ability to measure how that happens is very advantageous,' said Darryl J. Bornhop, the Prof of Chemistry who headed the 12-year development process.

The equipment required for the sensor is surprisingly modest: a helium-neon laser, a mirror, a CCD detector like those used in digital cameras and a special glass microfluidic chip. The chip contains a channel about one-fiftieth the size of a human hair. There is a "Y" at one end of this channel that allows the researchers to inject two solutions simultaneously, each containing a different kind of molecule. It is followed by a serpentine section that mixes the two.