Explorations
As research matures, nanotechnology promises even more benefits to society
Stories by Charles Feigenoff, Photographs by Tom Cogill

A fluid approach to life
Joseph “pepe” Humphrey has rarely let his curiosity be checked by the formal boundaries separating academic disciplines. He began his career studying chemistry and chemical engineering, but his interest in the properties of liquids ultimately led him to fluid mechanics and a doctorate in mechanical engineering. And while Humphrey, who is the Wade Professor of Engineering and Applied Science and chairman of the Department of Mechanical and Aerospace Engineering, has continued to focus on fundamental problems in fluid mechanics, he also holds an appointment in the Department of Biology, thanks to groundbreaking research on the way arthropods like spiders and moths sense and respond to their environment.

Indeed, it is precisely Humphrey’s ability to transcend borders that makes his research so valuable. His knowledge of fluid mechanics provides his colleagues in biology with a new perspective on phenomena they had earlier observed. After all, most living creatures are immersed in a fluid of some sort, whether it is a gas or a liquid, and the laws of fluid mechanics shape their behavior and their adaptations to their surroundings.

At the same time, Humphrey’s colleagues in biology are helping him understand the variety of sensory and neural systems that organisms have evolved to flourish in their fluid environments. These systems, which enable them to respond to different kinds of motion in the fluid medium as well as various chemicals carried by it, far exceed artificial sensors in sensitivity, selectivity and minute size. As such, they provide successful models — refined through natural selection over hundreds of millions of years — that can guide engineers in their quest to produce ever more responsive and capable micro- and nano-sized machines.
“The relationship between biologists and engineers is both natural and highly productive,” Humphrey observes. “Biologists are trained to draw inferences from data, while engineers learn how to reduce complex data sets to their underlying principles.”

Research that Humphrey is conducting with colleagues at U.Va. and at the University of Vienna illustrates the process of using the natural world as a pattern for the artificial. “Using hair-like sensory structures, spiders can detect air motions as weak as 1 millimeter per second and are capable of registering their magnitude, direction and frequency,” he notes. “Similarly, a male moth can sense a female as far away as 1 kilometer from the chemodetection of as few as 10 to 20 pheromone molecules. Sensors with characteristics like these would be invaluable to industry.”

Humphrey and his colleagues are studying sensory systems in spiders, moths and crayfish to uncover the basic design principles that determine their performance. They distill these principles into a set of mathematical equations to create physical models of the systems. Both of these steps are extremely complex, involving the application of fluid mechanics to structures that are 1–10 micrometers in diameter and from 10–1,000 micrometers in length. Once the models are shown to replicate the response of these sensory hairs, they can be used as the basis for designing and fabricating artificial arrays to sense fluid motion and chemical transport.

Humphrey has established a Sensory and Neural Systems Group at the University to study problems like these and others that involve the intersection of fluid mechanics and sensory systems in animals. “We believe U.Va. has the necessary core group of researchers to emerge as a leader in this field,” he says. Among other projects, members of this group are shedding light on the feedback mechanisms used in animal locomotion — another field that can help scientists build more effective micro- and nano-sized machines — as well as studying the sensing mechanisms that enable certain types of brain tumor cells to disperse through their environment. The hope is to develop new techniques to prevent growth and metastasis of brain tumors.

Complex ethics of small changes
Small changes can produce large outcomes. that is the paradox of nanotechnology as well as its promise. As Rosalyn Berne observes, “Nanotechnology is likely to alter the social, psychological and spiritual dimensions of human life as well as its physical ones. It may impact our economic systems, our conception of justice and even our belief systems.”

It is precisely because of its tremendous power that Berne, an assistant professor in the engineering school’s Division of Technology, Culture and Communications, advocates exploring the ethical implications of nanotechnology while it is still in its formative stages. “There is too much at stake to stand passively by,” she asserts. “We need to actively decide how we want to proceed.”

Berne is going to the heart of the problem by learning more about the attitudes of those who are playing a leading role in creating nanotechnology. With the help of a prestigious Career Award from the National Science Foundation, Berne has undertaken a five-year study to understand the myths and metaphors contained in the narratives that key nanoscientists use to describe their work. Meeting one-on-one with 35 researchers twice a year, Berne is asking about their hopes and dreams for nanotechnology, their sense of the ethical issues it raises, as well as their responsibility as scientists and engineers to address these issues. “I began with a list of questions that I wanted to ask them,” she says, “but increasingly our conversations are open-ended. I want to open the door to discussion and see where we end up.”

Once she returns from her meetings, Berne examines the transcripts of her interviews, using tools from psychology, linguistics, anthropology and religious studies to understand the largely tacit moral and ethical frameworks that inform the researchers’ sense of their work. “One idea that researchers bring up over and over again is the betterment of humanity,” she observes. “I go back to them and try to get them to pinpoint more exactly what they mean. Is it improved access? Freedom of choice? Control over their lives?”

Although changing the perceptions of individual scientists is not the goal of her research, Berne is finding that the opportunity to talk to her — and the kinds of questions she asks — affects the way they think. A number of her subjects have told her that their conversations are the only time they have to step back and think about the implications of their discoveries. From Berne’s point of view, this is all to the good. “They are an extraordinarily influential group of people,” she says. “An infinitesimal fraction of all the people on the planet possess the knowledge and the intellectual resources they have — and thus the power to change our lives. It is extremely important that they themselves understand the ethical implications of the choices they make.”

Next-generation catalysts 
Catalysts make things happen without getting involved themselves. The catalytic converter in your car, for instance, promotes the breakdown of nitrogen oxides, carbon monoxide and hydrocarbons into materials that are less harmful to the environment. Taken all together, catalysts, in the form of nanometer-sized metal, oxide, sulfide particles and other substances, add about $2.4 trillion in value to raw materials, according to the U.S. government, and have made possible advances in virtually every industry, from sporting goods to textiles to food production.

Chemical engineering professor Matthew Neurock has developed and applied a suite of atomistic simulation tools and other techniques associated with nanotechnology to help aid the design of next-generation catalysts. By understanding the relationship between their atomic and subatomic properties, he hopes to create catalysts that can improve the yields of existing processes, reduce our dependency on nonrenewable resources like petroleum, decrease pollution and make promising technologies such as fuel cells commercially viable.

The challenges are considerable. Catalysis involves simultaneously tracking a complex myriad of chemical reactions along with other kinetic phenomena that occur over very disparate time scales ranging from picoseconds to years. “In our work, we must consider the electronic interactions between the atoms in the molecules we wish to convert and atoms at the surface of the catalytic nanoparticles,” Neurock says. His models, which incorporate such factors as the electronic structure of the catalyst surface along with the specific reaction environment, give him the ability to simulate the kinetic behavior of specific materials and thus conduct virtual experiments. This sets the stage for the atomic design of more efficient catalytic materials.

Neurock’s work has led to a number of productive partnerships with industry and the government. His research has led to suggestions in new catalyst formulations for the synthesis of tetrahydrofuran, a key intermediate in manufacturing spandex; the reduction of nitrogen oxide emissions from lead-burning gasoline engines; and the synthesis of vinyl acetate, an important constituent in both paints and adhesives. In this last system, he found that by atomically engineering the amount as well as the spatial position of gold atoms within the catalytic nanoparticle, he could theoretically increase the catalytic activity by 1,000 percent while also increasing selectivity.

Neurock’s extensive collaboration with other faculty at U.Va. highlights the need for atomic-scale engineering of materials. He has worked closely with chemical engineer Robert Davis over the past eight years to establish a joint theory/experimental catalysis program at U.Va. In addition, he has collaborated closely with materials scientist Haydn Wadley in the design of surfactants to control the growth of thin films in manufacturing spintronics devices and with another materials scientist, Robert Kelly, in elucidating the atomistic processes that lead to corrosion. He is also part of a research team led by Lloyd Harriott looking at molecular electrical circuits that could self-assemble on more traditional semiconductor surfaces. His work demonstrates that as our demands on technology increase, the ability to atomically engineer materials with specific properties and performance will increase.