Emilie Ringe

In 2018, Emilie Ringe had a pivotal year in her work with plasmonic nanoparticles. These tiny specks of matter act like antennas for light, gathering and concentrating energy that can be used to trigger chemical reactions or kill cancerous cells. The nanoparticles are often made from expensive metals like gold and silver, but Ringe discovered a way to use cheap and abundant magnesium in their place. “It was the start of most of the things we do now,” says Ringe, a lecturer at the University of Cambridge.

A plasmonic nanoparticle is a stiff lattice of positive ions in a sea of electrons, she explains. When light of just the right frequency hits the particle, it sets the electrons in resonant motion—like a parent pushing a child higher and higher on a playground swing. “These electrons sloshing backwards and forwards are super­efficient at capturing light,” Ringe says. The particles focus energy so they can drive chemical reactions and other processes at their surface. “You can boil water with these particles just by shining light on them,” she says.

Very few elements in the periodic table possess this plasmonic prowess, and the usual suspects have some disadvantages. For many industrial applications, gold nanoparticles are still considered far too pricey, silver degrades too quickly, and aluminum resonates well only in response to ultraviolet light.

Ringe showed that magnesium could form effective plasmonic nanoparticles. Different sizes and shapes of magnesium particles absorb light from different parts of the spectrum from UV to visible and infrared, making them versatile as well as cheap.

Other researchers have taken some convincing that nanoparticles of a reactive element are stable. “Everyone always tells us, ‘It’s going to blow up in your face,’ ” Ringe says. Fortunately, the particles form a thin oxide layer that makes them stable in air for weeks. Her team is already decorating the plasmonic magnesium nanoparticles with other metals to test their photocatalytic abilities. Since the energy harvested by the nanoparticles eventually turns into heat, the particles could also be used to kill tumor cells in a strategy known as photothermal therapy.

Research at a glance

Ringe uses magnesium plasmonic nanoparticles (gray hexagon) to harvest light and concentrate that energy into metal catalysts. These metal-decorated nanoparticles can potentially catalyze useful reactions, such as the conversion of acetylene to ethylene.

Credit: Yang H. Ku/C&EN/Shutterstock

Ringe grew up in Quebec and first worked on plasmonic nanoparticles during her PhD at Northwestern University, where she combined electron microscopy and spectroscopy to understand how the particles’ shapes affected their plasmonic properties. “She had an amazing number of publications, and awards all over the place,” says Laurence Marks of Northwestern, one of her PhD supervisors. He adds that her work already stands out in the field of nanoplasmonics. “She’s certainly one of the young stars,” he says. After a postdoc at Cambridge, Ringe moved to an assistant professorship at Rice University, where she made her magnesium discovery.

Back at Cambridge since 2018, Ringe has a dual appointment in materials science and earth sciences and is involved in microscopy and spectroscopy at every scale from millimeters to nanometers, studying natural and synthetic materials. While she hopes to forge links with industry to develop applications for her magnesium nanoparticles in the coming years, she is still prospecting for other elements that could expand the nanoplasmonic toolbox. “The periodic table is not quite done yet,” she says.