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Nanocrystals could help prevent forgery

Nanocrystal markers A new kind of fluorescent marker made from nanocrystals could help improve medical research and document security, according to a new study.

Called 'tau-dots', the new generation fluorescent markers may also pave the way for higher density data storage, says lead author Dr Yiqing Lu of Macquarie University.

The research is published today in the journal Nature photonics,

Fluorescent markers are commonly used in medical research to diagnose or track such targets as pathogens or drugs, and to study their interaction with other target molecules in the body.

Researchers use markers that fluoresce with different colours, depending on the frequency of the light shined on them, to identify different targets.

The problem is, when two targets are close together, it can be hard to distinguish them and this limits the number of targets researchers can study at the same time.

"Conventional fluorescence markers use colours which can overlap or even blend into each other, and so cannot be resolved properly," says Lu.

To address this problem Lu and colleagues have engineered fluorescent markers out of nanocrystals that can fluoresce for different durations ('lifetimes'), depending on wavelength of light used, quite independent of the particle's colour and intensity.

"Our tau-dots add a temporal or lifetime dimension, providing an additional way of separating targets," says Lu.

"It's like tuning in to different radio frequencies to listen to different stations."

He says this could help speed up diagnositc times by allowing more targets on a single sample, and make it easier for researchers to analyse the interaction of thousands of different molecules at the same time.

"What we've done is work out how to control the length of the fluorescence at the single nanocrystal level," says fellow author Dr Dayong Jin, also from Macquarie University.

"We can vary the lifetimes to whatever length we want, from a few microseconds to hundreds of microseconds."

Lu says the next step towards using the nanocrystals in medical applications is to make them biocompatible.

"Also when it comes to clinical and medical usage we need to prove that it's safe for humans," he says.

Security and data storage

Lu says the nanocrystals could also help provide additional levels of document and product security against forgery above and beyond the fluorescent colour watermarks currently used.

The different lifetimes represent a unique code for each tau-dot, he says.

"The fluorescent colours can be replicated, but the lifetime has to be measured by a dedicated scanner, so we can assign different markers with different lifetimes to different products," he says.

"Only the product's producer knows which lifetime markers they use, so when they scan the product, they can determine whether it's genuine or a fake."

The researchers say tau-dots could be mixed in with conventional inks and applied by regular ink jet printers for documents.

The ability to layer tau-dots on top of each other could also help create higher density data storage than was previously possible. Each tau-dot with a specific 'lifetime' would represent one bit of information, says Lu.