Using light to reveal hidden molecular information

Alison Ballance - Senior Producer

Detecting art forgeries. Helping conserve valuable art works. Finger printing milk. What these all have in common is Michél Nieuwoudt, a researcher at the University of Auckland who uses light to uncover hidden information in different kinds of material.

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Michél Nieuwoudt works in the Photon Factory in the School of Chemical Sciences at the University of Auckland.

“My job,” she says, “is to try and extract information about materials from the molecules that are in them – using light.”

“What we’re hoping to do is uncover hidden information about these materials.”

In scientific terms her work involves vibrational spectroscopy. She uses two different techniques, known as FTIR and Raman spectroscopies.

Michél has been working with the Auckland Art Gallery Toi o Tāmaki to investigate aging paint on valuable artworks, to “understand why paint deteriorates, why paints flake off.”

She has also been called on by other galleries to help determine if a particular artwork is genuine – or fake. And she can do this without damaging the painting in any way, as her method is non-invasive and non-destructive.

If the painting of doubtful origin is small enough, Michél simply puts the whole work under the microscope, shines a light on it and examines a tiny one to two micron area in great detail.

She can identify exactly what pigments were used by comparing what she finds against known standards. Then Michél works with the art curator to find out whether these pigments match what would have been available in the period when the painting was said to have been made.

“We actually managed to identify a fake Lindauer,” says Michél. “Lindauer ceased painting around 1920, and before that all the white pigments in paint were mostly lead carbonates. Whereas this painting had titanium dioxide and that was only used after 1941.”

Michél explains that the reason she can differentiate between materials is that molecules are always vibrating, but they all vibrate at different frequencies. This gives each molecule its own vibration signature.

“The set of frequencies that a molecule vibrates at is determined by what it’s made of,” says Michél, so lead carbonate, for instance, has a different pattern of vibration to titanium dioxide.

“We can measure those frequencies,” Michél says, “by letting it interact with light.”

The method is so precise that it can differentiate between different crystal forms of the same material, because they have a different energy environment and therefore interact with light differently.

Fingerprinting milk

Michél is now looking for hidden properties in milk that the usual lab testing won’t reveal. This work is part of the Primary Growth Partnership Programme with Fonterra.

Fonterra already uses infrared spectroscopy to routinely test for fat, lactose and protein in milk. Michél hopes she will able to reveal more information about the different types of fat and protein that are present in the milk, by more closely analysing these infrared spectra.

These individual milk fngerprints might identify, for example, that milk from a particular farm is particularly well suited to cheese making, while milk from somewhere else would make a healthy milk drink with unique characteristics.

Michél says the value of spectroscopy as a technique is that it is a very fast and cheap way of generating a lot of information, although she points out that the key is to be able to accurately extract and analyse that information.

Our Changing World previously reported on the Photon Factory’s Milk on a Disc project, which analyses the quality of milk from individual cows using spectroscopy.

Michél’s latest project has funding from a MBIE Smart Ideas grant to develop a hand-held scanner to detect melanoma and other skin cancers.

Using light to reveal hidden molecular information
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