The beauty of it, said Martel, is that the phenomenon is generalized, and many types of dyes can be used to make nanoprobes or tags, whose "bar codes" are all different. "So far, more than 10 different tags have been made, and it seems the sky's the limit," he said. "We could, in theory, create as many of these tags as there are bacteria and use this principle to identify them with a microscope operating in Raman mode."
The story of Raman signals
Raman scattering mode is an optical phenomenon discovered in 1928 by the physicist Chandrasekhara Venkata Raman. The effect involves the inelastic scattering of photons, i.e. the physical phenomenon by which a medium can modify the frequency of the light impinging on it.
The difference corresponds to an exchange of energy (wavelength) between the light beam and the medium. In this way, scattered light does not have the same wavelength as incidental light. The technique has become widely used since the advent of the laser in the industry and for research .
But until now, molecular Raman signals have been too weak to serve the needs of optical imaging effectively. So researchers have used other more sensitive techniques but which are less specific because they have no "bar code." "It is technically possible, however, to enhance the Raman signals of molecules using rough metallic surfaces," said Martel. "But their sizes limit the applications of Raman spectroscopy and imaging."
By aligning dye molecules encapsulated in carbon nanotubes, the researchers were able to amplify the Raman signals of these molecules, which until now have not been strong enough to detect. The article presents experimental evidence of extraordinary scattering of visible light on a nanoparticle.
|Contact: Julie Gazaille|
University of Montreal