New study turns gold into magnets

While it’s well known in scientific circles that the properties of metals are fairly fixed, a team of nanoscience researchers has made a surprising innovation when it comes to the properties of one of the most coveted and precious metals — gold.

In its elemental form, gold is one of the least reactive chemical elements; it's always been considered to be non-magnetic. This year, Dr. Simon Trudel, PhD, associate professor in the Department of Chemistry and director of the Nanoscience Multidisciplinary Program in the Faculty of Science, UCalgary graduate student Dr. Pengcheng Dong, PhD, and co-investigators from Mount Allison University, applied the study of nanoscale materials to manipulate gold nanoparticles to become magnetic.

Nanoscience is the study of particles on the nanoscale. The nanoscale is measured in nanometres (nm), which is a billionth of a metre. The particles are usually cited as being one to100 nanometres in size.

The gold nanoparticles this team studied are 2nm. In Trudel’s latest paper, published in the journal Nanoscale, the research team demonstrated how to tune (increase/decrease) the magnetism of gold nanoparticles by choosing the correct non-magnetic organic molecule attached to their surfaces. The study achieved the most tuneablity ever demonstrated.

“You can think of the nanoparticles as a small ball of metal — gold, in this case — that is coated with a single layer of molecule. Both, individually, are non-magnetic,” says Trudel.

“We have changed the magnetization, or how 'strong' a magnet it is, by changing the organic molecules that are attached to the surface of the gold nanoparticles. We can increase the magnetization seven-fold, a control that had yet to be demonstrated before now.”

Possible applications include chemistry research, health care

Trudel says this new discovery can be put to work in practical settings in the future, but emphasizes that the findings need to be kept in context.

“We show the highest relative control over the magnetization; however, we do not have the highest magnetization ever shown. This is a key challenge in this field. The reported magnetizations are all over the place, varying by as much as 10,000 times,” he says. “Our own nanoparticles are mid-range. At this point, the magnetization is still too low for practical applications, but we did understand how to control it.”

Should researchers be able to reproducibly achieve high magnetization that can be tuned, Trudel expects many possible applications for magnetic gold nanoparticles.

Although gold is an inert metal (which is why gold jewelry doesn’t tarnish or rust), it's been found that gold nanoparticles can be active as catalysts to speed up chemical reactions. However, gold is not cheap, and recovering nanoparticles is challenging. Applying a magnet to the side of the flask, one could recover the nanoparticles easily.

Further, nanoparticles are already used in medical imaging and drug delivery. With suitable magnetic properties, Trudel says, gold nanoparticles could be used for magnetic resonance imaging.

“New useful properties can emerge in unexpected places when studying new nanoscale materials," he says. “Building our understanding of these new properties is a challenging but necessary step in the pursuit of new applications. This is really a great example of driving innovation through fundamental science.”

This research was funded by a Discovery Grant from the Natural Sciences and Engineering Research Council to Trudel.