"This is the first time that anyone has designed and engineered a nanosensor specifically for obtaining chemical information," said Naomi Halas of Rice University. "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."
Raman spectroscopy allows scientists to observe the vibrational states of molecules, and serves as a "fingerprint" for the identification of specific molecules. Researchers can boost the Raman light emissions from a sample by a factor of more than a million by placing the sample next to a metal colloid. This has enabled the observation of single molecules, but scientists have not been able to precisely control the electromagnetic state of the colloid particles.
In place of the colloid, the Rice scientists used metal nanoshells consisting of a dielectric silica core with a silver coating. They employed 65 or 79 nm diameter cores with silver layers between 5 and 20 nm thick. Changing the geometry of the shells enabled tuning of the particles' electrical and optical properties. In this way, the scientists were able to control the local electromagnetic field at the nanoparticle surface, and hence control the SERS of molecules attached to the nanoshells.
The scientists reported their work in Applied Physics Letters.