With a sticky coating and other tricks, materials self-assemble in the lab
L. Brian Stauffer/Univ. of Illinois News Bureau
Qian Chen, 30
University of Illinois
In a darkened room, bathed in the glow of green light, materials scientist Qian Chen watches gold nanorods dance. They wiggle across a computer screen displaying real-time video from a gigantic microscope — a tall, beige tube about as wide as a telephone pole.
Chen has observed these and other minuscule specks of matter swimming, bumping into one another and sometimes organizing into orderly structures, just like molecules in cells do. By pioneering the design of new biologically inspired materials, she’s exploring what it means to be “alive.” Next, Chen wants to get an up-close and personal view of cellular molecules themselves: the nimble, multitasking proteins that work day and night to keep living organisms running.
At age 30, Chen is already racking up high-profile publications and turning some far-out ideas into reality. Her ultimate goal: To mimic the machinery that living cells have already perfected. To create life, or something like it, out of nonliving materials.
“If you can see it, you can start to understand it,” Chen said when I visited her lab at the University of Illinois at Urbana-Champaign earlier this year. “And if you understand it, you can start to control it.”
Chen didn’t always want to be a scientist. Growing up in China, she imagined one day becoming a writer. In middle school, she wrote an award-winning story about a girl who figures out how to repair the ozone layer. “My idea was to get some material that can be stretched, like the skin of the balloon,” Chen says.
If you can see it, you can start to understand it. And if you understand it, you can start to control it.
— Qian Chen
Her interest in inventing new and unusual materials took off years later, in the United States. After graduating from college in China in 2007 — Chen was the first in her family to do so — she headed to Illinois to work with materials scientist Steve Granick.
From the start, Chen stood out. “She made hard things look easy,” says Granick, now at the Ulsan National Institute of Science and Technology in South Korea. He recalls one experiment in particular, when Chen performed a feat some scientists thought impossible: She got thousands of tiny beads to form an open and orderly two-dimensional structure — all by themselves.
Chen had been studying colloidal particles, microscopic specks roughly a micrometer in size. People normally think of these particles as a component of paint, not all that interesting.
But Chen had the idea to cover the particles with a kind of sticky coating that acted something like Velcro. When the particles bumped into one another, they stuck together. At first, “It looked like a mess, like a failed experiment,” says Granick. “Most graduate students would have just chalked it up to a mistake and gone home.”
After a day of knocking around in solution, sticking together and tearing apart, the particles finally settled into something stable. The special coating and the way Chen applied it (capping the top and bottom of each particle) led to a “kagome lattice,” something sort of like a honeycomb. Never before had scientists coaxed colloidal particles into such an open, porous framework. Usually, the particles pack together more tightly, like apples stacked on the shelf at a grocery store, Chen says.
After a sticky coating was applied, colloidal particles came together in what’s known as a kagome lattice (below, left). The striped pattern of the coating led to a specific particle orientation (particles in white box are illustrated at right).
That work led in 2011 to a publication in Nature: “Directed self-assembly of a colloidal kagome lattice.” A week earlier, Chen and Granick had published a different paper in Science, “Supracolloidal reaction kinetics of Janus spheres,” about particles that self-assemble into a twisting chain, or helix. At the time, Chen was 24.
“Her work is at the leading edge,” says Penn State chemist Christine Keating. “She’s so full of enthusiasm for science, and energy and creative ideas.”
Exactly how such particles might one day be used is still anybody’s guess. Some researchers envision self-assembling materials building smart water filters or adaptable solar panels that change shape in response to the sun. But the full range of possibilities is hard to fathom. Chen is “trying to invent the rules of the game,” Granick says. “She’s laying the groundwork for future technologies.”
Her next big focus will take her field from self-assembly 101 to the master class level, by mimicking how biological molecules behave. But first she has to see them in action.
Into the cell
In 2012, Chen traveled west to the University of California, Berkeley to work with National Medal of Science winner Paul Alivisatos on a new microscopy technique.
Scientists today can view the details of proteins and DNA close up under a microscope, but the results are typically still-life images, frozen in time. It’s harder to get action shots of proteins morphing in their natural, fluid world. That view could unveil what roles different protein parts play.
Even a technique that won its developers a Nobel Prize in 2014 (SN: 11/2/14, p. 15) — it relies on fluorescent molecules to illuminate a cell’s moving parts — can’t always reveal the intricacies of proteins, Chen says. They’re just glowing dots under the microscope. Imagine, for example, looking at a dump truck from an airplane window. You can’t see how the truck actually works, how the pistons help lift the bed and the hinges open the tailgate.
“I use this as inspiration,” Chen says, grabbing her laptop and starting up a video that may well be the fantasy of anyone exploring biology’s secret world. The computer animation shows molecules whizzing and whirling deep inside a cell. Gray-green blobs snap together in long chains and proteins haul giant, gelatinous bags along skinny tracks. No one yet has gotten a view as clear as this hypothetical one, but a technique Chen is now helping to develop at Illinois could change that.
It’s called liquid-phase transmission electron microscopy, and it’s a slick twist on an old method. In standard TEM, researchers create subnanometer-scale images by shooting an electron beam through samples placed in a vacuum. But samples have to be solid — still as stone — because liquids would evaporate.
By sandwiching beads of liquid between thin sheets of graphene, though, Chen gets around the problem. It’s like putting droplets of water in a plastic baggie. The liquid doesn’t dry up, so researchers can observe the particles inside jittering around. Chen has used the technique to see gold nanorods assembling tip-to-tip and DNA-linked nanocrystals moving and rotating in 3-D. Now, she may be on the verge of a big advance.
With liquid-phase microscopy, Chen is attempting to see cellular machinery with a clarity no scientist has achieved before. She is cautious about revealing too many details. But if Chen succeeds, she may be on her way to cracking the code that links biological structure to function — figuring out the parts of a protein, the pistons and hinges, that let it do its specific job. Knowing the structural building blocks of life, she says, will help scientists create them — and everything they can do — out of artificial materials.
“We’re not there yet,” Chen says, “but that’s the big dream.”
Q. Chen et al. Supracolloidal reaction kinetics of Janus spheres. Science. Vol. 331, January 14, 2011, p. 199. doi:10.1126/science.1197451.
Q. Chen et al. Directed self-assembly of a colloidal kagome lattice. Nature. Vol. 469, January 20, 2011, p. 381. doi: 10.1038/nature09713.
Q. Chen et al. 3D motion of DNA-Au nanoconjugates in graphene liquid cell EM. Nano Letters. Vol. 13, August 14, 2013, p. 4556. doi: 10.1021/nl402694n.
J. Park et al. 3D structure of individual nanocrystals in solution by electron microscopy. Science. Vol. 349, July 17, 2015, p. 290. doi:10.1126/science.aab1343.
T.H. Saey. New microscope techniques give deepest view yet of living cells. Science News Online, August 31, 2015.
M. Rosen. New microscope gives clear view inside cells. Science News. Vol. 186, December 13, 2014, p. 4.
B. Mole and M. Rosen. Microscopy providing ‘window into the cell’ wins chemistry Nobel. Science News Online, October 8, 2014.