Nanotechnology researchers at Rice University have demonstrated the ability to precisely control the electromagnetic field around nanoparticles, opening the door for chemical screening techniques that could allow doctors, life scientists and chemists to routinely analyse samples as small as a single molecule.
The research is said to build upon Raman spectroscopy and capitalises on the tuneable optical properties of metal nanoshells, a type of nanoparticle invented at Rice.
‘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,’ said nanoshell inventor Naomi Halas, the Stanley C. Moore Professor of Electrical and Computer Engineering. ‘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.’
Scientists commonly use spectroscopy to discern detailed information about everything from distant galaxies to individual molecules. By studying the spectrum of light that an object emits, scientists can decipher which elements are present in the sample, and in some cases, how those elements relate to one another.
Raman spectroscopy, in particular, allows scientists to observe the vibrational states of molecules, giving clues about where and how much molecules bend and serves as a ‘fingerprint’ for the identification of specific molecules that may be of interest, such as environmental contaminants or chemical or biological toxins.
Scientists have long known that they could boost the Raman light emissions from a sample by a million times or more by placing the sample next to small particles of colloids. Scientists have even observed single molecules with this method, but they have never been able to precisely control the electromagnetic state of the metal colloids, so results and interpretations of such studies vary widely.
Rice’s research offers scientists a chance to precisely control ‘surface enhanced Raman scattering,’ or SERS. In the Rice experiments, Halas’s group was able to enhance the SERS effect, making it up to a billion times more powerful in some cases.
Nanoshells are layered colloids that consist of a core of non-conducting material covered by a thin metallic shell. By varying the thickness of the conducting shell, researchers in Halas’ group can precisely tune the electric and optical properties of nanoshells.
Nanoshells are useful for enhancing SERS and for other applications because of their size and precise structure. Nanoshells are just slightly larger than the size of molecules, measuring just a few tens of nanometers. Tuning the properties of nanoshells gives Halas’ group the ability to exert new forms of precision control at the molecular level.