Tiny particles could light the way to improved cancer tests or drugs with fewer side effects
Jennifer Dionne, 35
To choose her research goals, Jennifer Dionne envisions conversations with hypothetical grandchildren, 50 years down the line. What would she want to tell them she had accomplished? Then, to chart a path to that future, “I work backward to figure out what are the milestones en route,” she says.
That long-term vision has led the 35-year-old materials scientist on a quest to wrangle light and convince it to do her bidding in interactions with nanoparticles and various materials. Already, Dionne has created new nanomaterials that steer light in ways that are impossible with natural substances. Her new projects could eventually lead to light-based technologies used to improve drugs or to create new tests to find cancerous cells. There are even applications for renewable energy, for example, designing materials that help solar cells absorb more light.
But the route to a scientific vision may not always be clear, so Dionne makes time for diversions. “A lot of the really amazing discoveries that we enjoy today came from just playing in the lab,” she says. Dionne encourages her team to let creativity be a guide, melding a serious sense of purpose with play.
“She’s a very curious person, so she’s always learning new things,” says Paul Alivisatos, the vice chancellor for research at the University of California, Berkeley, who mentored Dionne when she was a postdoc there. Plus, “she’s an extremely deep and rigorous thinker.”
Dionne, now at Stanford University, studies nanophotonics, the way that light interacts with matter on very small scales. Her interest in light and materials began in childhood, she recalls, when she was fascinated by the blue morpho butterfly.
The insect’s wings sport an azure hue that comes not from pigments, like most colors found in living things, but from tiny nanostructures on the wings’ surface (SN: 6/7/08, p. 26). When light reflects off the structures, blue wavelengths are amplified, while wavelengths corresponding to other colors are canceled out.
That early interest in tricks of light led Dionne to begin wielding it as a tool during graduate school at Caltech and then her postdoc at UC Berkeley. Then and now, says Alivisatos, “she has consistently done very beautiful work.”
Light rays bend as they pass from air into water, making a drinking straw look broken (illustrated in a computer-generated image, left). In materials with a negative index of refraction (right), light rays bend in the opposite direction they normally do, so that the straw appears flipped around.
At Caltech, Dionne and colleagues created a bizarre optical material in which light bends backward. As light passes from one material to another — say, from air to water — the rays are deflected due to a property called the index of refraction. (That’s why a straw in a drinking glass appears to be broken at the water’s surface.) In natural materials, light always bends in the same direction. But that rule gets flipped around in oddball nanomaterials with a negative index of refraction.
Dionne’s material, reported in Science in 2007, was the first that worked with visible light (SN: 3/24/07, p. 180). Because they can steer light around objects to hide the objects from view, such materials could be used to create rudimentary versions of invisibility cloaks — though so far all attempts are a far cry from Harry Potter’s version. Dionne is now working on a “squid skin” with an adjustable refractive index, which would mimic the shifting camouflage patterns of the stealthy cephalopod.
Another focal point of Dionne’s research is harnessing light to separate mixtures of mirror-image molecules. Right- and left-handed versions of these molecules are perfect reflections of each other, like a person’s right and left hands. The two types are so similar that scientists struggle to separate them, which can cause problems for drugmakers. In drugs, these molecules can be two-faced; one might relieve pain, while the other causes unwanted side effects.
To separate molecules and their mirror images, Dionne is developing techniques that use circularly polarized light, in which the light’s wiggling electromagnetic waves rotate over time. Such light can interact differently with right- and left-handed molecules, for example, breaking apart one version while leaving the other unscathed.
Normally, the light’s effect is very weak. But in a theoretical study published in ACS Photonics last December, Dionne and colleagues showed that adding nanoparticles to the mix could enhance the process. These tiny particles behave like antennas that concentrate the light onto nearby molecules, helping break them apart. Dionne is now working to implement the technique.
She and her colleagues have also created nanoparticles that, when illuminated with infrared light, emit visible light. The color of that light changes depending on how tightly the nanoparticle is squeezed, the team reported in Nano Letters in June. In keeping with her penchant for creative exploration in the lab, Dionne and colleagues fed these nanoparticles to roundworms, the nematode Caenorhabditis elegans, to study the forces exerted as a transparent worm squeezed a meal through its digestive tract.
“You can see the nanoparticles change colors throughout,” Dionne says. She plans to use the technique to reveal more sinister squeezing. Cancer cells exert stronger mechanical forces on their environment than healthy cells, so such nanoparticles could one day be used to test for cancer, she says. Dionne is now cooking up other creative ways to use these nanoparticles. In collaboration with other researchers, she hopes to marshal her color-changing nanoparticles to understand how jellyfish move and how plants take a drink.
Dionne’s work exploits light to reveal hidden forces — and as a force for good. “She’s done amazing work,” says materials scientist Prineha Narang of Harvard University. Narang was a graduate student at Caltech after Dionne left, and had heard chatter about Dionne before meeting her in person. “The legend of Jen Dionne was definitely all over,” Narang says. So Dionne has made a start at establishing her scientific legacy — even before that chat with her future grandchildren.
C.-S. Ho et al. Enhancing enantioselective absorption using dielectric nanospheres. ACS Photonics. Vol. 4, December 12, 2016, p. 197. doi: 10.1021/acsphotonics.6b00701.
A. Lay et al. Upconverting nanoparticles as optical sensors of nano- to micro-Newton forces. Nano Letters, Vol. 17, June 13, 2017, p. 4172. doi: 10.1021/acs.nanolett.7b00963.
H.J. Lezec, J.A. Dionne and H.A. Atwater. Negative refraction at visible frequencies. Science. Vol. 316, April 20, 2007, p. 430. doi: 10.1126/science.1139266.