Nanoshell Sensor Opens Door for New Methods to Examine Single Molecules

Scientists commonly use spectroscopy to discern detailed information about everything from distant galaxies to individual molecules.

Raman spectroscopy, in particular, allows scientists to observe the vibrational states of molecules and to identify specific molecules that may be of interest, such as environmental contaminants or chemical or biological toxins. The problem is that readings from single molecules are very weak. Although scientists can boost the Raman light emissions from a sample by a million times or more by placing the sample next to small particles of metal called colloids, they have never been able to precisely control the electromagnetic state of the colloids. This means that the results and interpretations of such studies vary widely.

New work with nanoshells by a Rice nanotechnology research group may solve that problem. Led by nanoshell inventor Naomi Halas, the Stanley C. Moore Professor of Electrical and Computer Engineering, the group has demonstrated the ability to precisely control the electromagnetic field around nanoshells, opening the door for chemical screening techniques that could allow doctors, life scientists, and chemists to routinely and accurately analyze samples as small as a single molecule.

The precision is possible because of the structure of nanoshells, which consist of a core of nonconducting material covered by a thin metallic shell. Because the researchers can control the thickness of the conducting shell, they can precisely tune the electric and optical properties of the nanoshells to dramatically enhance the Raman light emissions—up to a billion times in some cases.

“This result is extremely important because it is the first time that anyone has actually designed and engineered a nanosensor specifically for obtaining chemical information,” says Halas. “There are widespread applications for this technology in environmental science, chemistry, and biosensing, and it may have very important applications in the early detection of cancer.”

The research is described in Applied Physics Letters in a paper titled “Controlling the Surface Enhanced Raman Effect via the Nanoshell Geometry,” by J. B. Jackson, S. L. Westcott, L. R. Hirsch, J. L. West, and N. J. Halas. It is available online at http://ojps.aip.org/aplo/.