Ralph Nuzzo’s job interview did not go smoothly.
“I’d recently broken my finger,” he recalls. “During my talk, all I was thinking about was how hard it was to write with my left hand because I couldn’t hold the chalk in my right. It was a train wreck. I was sure there was no way they were ever going to hire me.”
But Nuzzo, who was fresh out of grad school, soon found himself treading the hallowed halls of Bell Laboratories, wondering what to do next.
With its focus on microchips and electronics, Bell Labs was interested in Nuzzo’s work on organic interfaces—how polymer surfaces behave when they come in contact with various materials, including water, living matter, or each other. To explore the chemistry of these surfaces, Nuzzo soon decided to assemble and study thin films, which are essentially all surface.
“The first experiment was actually pretty easy,” he says. Nuzzo took a gold wafer and suspended it in a solution containing his molecule of choice—a long chain of hydrocarbon with a sulfur on one end. The sulfur stuck to the metal, driving the formation of a single layer of hydrocarbon molecules that jut from the wafer's surface like bristles from a toothbrush.
That film—Nuzzo’s first self-assembled monolayer, or "SAM"—had the ability to reject wetting. “I would dip it in a solvent and it would come out completely dry,” he says. That physical property suggested there was “something cool going on,” says Nuzzo. “But understanding what was happening microscopically was a deeply challenging analytical question.”
Nuzzo wanted to know how tightly the bristle-like molecules were packed, and in which orientation, as well as how the molecules changed shape and shifted in space as conditions changed.
Enter David Allara, an expert on analytics and all manner of spectroscopic techniques. “Dave had the vision, skills, and quantitative capabilities to make characterization of SAMs doable,” Nuzzo says.
Together, Nuzzo, Allara, George Whitesides, and Jacob Sagiv share the 2022 Kavli Prize in Nanoscience for the development and characterization of self-assembled monolayers with an amazing array of properties.
“What we learned from SAMs about complex interfacial dynamics and surface-related phenomenon were foundational,” says Nuzzo. They laid the groundwork for the production of polymer coatings that are used in everything from electronics and semiconductors to medical diagnostics and implantable devices.
Here, Nuzzo describes how today’s nanoscience could spawn quantum electronics, nanostructures that interact with living systems, and four-dimensional structures that evolve over time.
What innovations will drive the next generation of electronics?
For decades, transistors have been assembled on thin wafers. This strategy was transformational, but we’re at the limits of what can be done in 2D. So the world is starting to lift semiconductors into three-dimensional topologies.
Another approach that’s receiving intense interest is quantum IT, where you can code more bits per unit real estate because things operate not on charge alone, but on charge and spin. Also deeply interesting is integration using photons rather than electrons.
I can’t imagine today’s electronics being supplanted by anything less than a highly integrated, high-performance structure of almost unimaginable complexity.
Can we design nanostructures that interact with living matter?
The frontiers of nanoscience are in applications related to medicine. There’s a huge distance to traverse before we can approach the interfacial complexity of biological systems. Developing materials that interact with living matter in medically relevant ways is a vibrant area of study.
For example, toward the end of my time at the University of Illinois, my collaborators and I started making scaffolds that can support cells and allow them to survive and maintain their phenotype in 3D microcultures. We took explants from the dorsal root ganglion, which has five different cell types, and fabricated 3D scaffolds that allow these cells to reorganize into structures that mimic those in the peripheral nervous system.
Those experiments were enormously complex and hard to do. But things like that point toward approaches for doing nerve repair. If I had another career to invest, I think I might focus less on semiconductors and a lot more on interacting with living systems.
Illustration by Alisdair Macdonald
What are the potential benefits and challenges of engineering systems that change over time?
Four-dimensional printing is where you design systems whose form and structure can morph. This is a new frontier. People are making sophisticated structures that fold, origami-like, in response to changes in osmotic forces, and they’re using them to make things like actuators that operate like an artificial muscle. Part of what’s necessary are materials that change their form and function in response to things they sense, feel and encounter in their environment.
I also like the idea of transient structures or functions, such as an adhesive property that lasts for a certain period and then goes away—like a soft material used for tissue repair or implantable devices that perform their function and then disappear. People like John Rogers, who is a Mozart in this area of engineering, have explored making things as enormously complex as an absorbable pacemaker, which does its work for 30 days and then goes away. We already have absorbable sutures. So we just need to extrapolate that approach to a level of sophistication maybe 15,000 orders of magnitude greater.
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