Although so tiny they are invisible, it’s easy to see that nanomaterials are becoming a big thing. There are odor-fighting socks and antibacterial dishrags impregnated with silver nanoparticles. Nano-sized titanium dioxide can be found in a long list of food and consumer products, including salad dressing, cake frosting, toothpaste and sunscreen. The vibrantly colored screen of the Kindle Fire can be attributed to quantum dots, a.k.a. nano-scale crystals of cadmium selenide. And the list goes on.
Nanomaterials are tiny by definition, measuring between 1–100 nanometers along one or more dimension. (By comparison, a human hair is approximately 100,000 nanometers in width.) At this scale, they possess unique physical and chemical properties that make them useful for a wide array of applications, including consumer products, environmental remediation and medicine. Yet there are many unanswered questions about their safety.
“We don’t know a lot about the toxicity of nanomaterials, and we have much to learn about the potential risks associated with the release of these materials into the environment,” says Joel Pedersen, Rothermel Bascom Professor of Soil Science at UW-Madison.
Pedersen is part of a collaborative, multidisciplinary research team exploring these unknowns as part of the UW-Madison-based Center for Sustainable Nanotechnology, which was founded in 2012 with support from the National Science Foundation. Center scientists are working to understand how nanomaterials interact with living systems and the environment, with the practical goal of developing the insights needed to start creating nanomaterials that are environmentally “benign by design.” This includes re-engineering them to make them safer, if needed.
With expertise in chemistry, biology and engineering, Pedersen is in charge of the Center’s efforts to develop laboratory models to assess the biological impacts of nanomaterials. While he has done some experiments in zebrafish, Pedersen’s work for the Center focuses on innovative, non-biological approaches, including creating “artificial cell surfaces” in the lab.
“Our intent is to get down to the molecular level,” Pedersen explains. “What are the rules that govern how these materials interact with biological systems? In particular, how do these particles interact with a cell membrane?”
One way Pedersen’s group makes artificial cell surfaces is by depositing lipid vesicles on a special quartz crystal sensor, until the vesicles spontaneously rupture and then fuse to form a lipid bilayer—the basic structure of a cell membrane—on the sensor’s surface.
When electricity is applied to the sensor, it causes the system to vibrate at a particular frequency. Next, Pedersen’s team applies nanomaterials to the artificial cell surface. The sensor can detect subtle changes in the frequency of the vibration, yielding clues about the interaction between the material and the membrane.
By combining the results of this approach with others, Pedersen is finding that some nanoparticles, by virtue of their unique physical and chemical properties, seem to be able to extract lipids from the cell surface.
“Our results are consistent with the idea that these nanoparticles are grabbing lipids out of the membrane and acquiring a lipid coating when they come in contact with a cell,” explains Pedersen.
This cell membrane-disrupting behavior is a concern for the health of humans and animals. And while Pedersen’s team hasn’t observed this behavior in models of bacterial cell surfaces, there are other, broader concerns about the impacts of nanomaterials on microbial communities in the environment.
“Eukaryotes are our main focus, but there is some concern that nanomaterials in the environment can alter microbial community compositions. At present, we don’t know to what extent such changes are deleterious,” says Pedersen.
The information gained from Pedersen’s research will help inform the work of other scientists in the Center for Sustainable Nanotechnology who focus on tweaking nanoparticles to make them safer.
“Ultimately, the goal is to redesign nanomaterials to minimize their adverse effects, or find better ways to embed them in materials so they aren’t released into the environment,” he says.