Raman-detectable nanoparticles give anti-counterfeit signal

Researchers in Canada have developed a nanoparticle-based fingerprinting technology that can be detected using Raman spectroscopy down to the level of a single particle.

The discovery entails the use of carbon nanotubes that can be loaded with a range of dyes in such a way as to provide a unique fingerprint that can be linked to an item. The nanoparticles can be detected in "infinitely small" quantities using, which marks a major leap forward in the capabilities of the technology.

Raman - which involves harnessing visible light to acquire vibrational fingerprints of molecules - is already used to analyse a wide range of chemical media. Its potential for optical imaging at high resolution is however limited by the fact that the Raman effect is weak, which means that quite a large amount of material needs to be present in a sample.

The key discovery by the team at the Department of Chemistry of the Université de Montréal is that Raman scattering of the dye-nanotube particles is so large that a single particle of this type can be located and identified. All that is needed is an optical scanner capable of detecting this particle.

The particles are about one nanometre in diameter and 500nm long, yet they send a Raman signal one million times stronger than the other molecules in the surrounding, say the researchers in the journal Nature Photonics.

The technology could be suitable for a range of applications, including detection of counterfeits and document security applications such as passports, according to lead researcher Richard Martel, who said: "By incorporating these nanoparticles in an object, you can make it perfectly traceable."

The beauty of it, said Martel, is that the phenomenon is generalised, and many types of dyes can be used to make nanoprobes or tags with different fingerprints.

"So far, more than 10 different tags have been made, and it seems the sky’s the limit," said Martel.