Northwestern scientists assess safety of nanoparticles

By Zachary Vasile

Nanoparticles are revolutionizing the way the world works, offering an enticing commercial formula: better, more novel results with less material. Since achieving widespread commercial popularity in the 1990s and early 2000s, nanoparticles have transformed technology that can be engineered starting with the molecules that make virtually any material.

But one of the most fundamental questions surrounding nanoparticles remains conspicuously unanswered: is the use of nanoparticles sustainable and safe?

Merve Doğangün, a Northwestern graduate student in the nanotechnology program, prepares an experiment for continuing research on the safety  and sustainability of nanoparticles.
Merve Doğangün, a Northwestern graduate student in the nanotechnology program, prepares an experiment for continuing research on the safety and sustainability of nanoparticles.

This question, and others like it, drives the research of the multi-institutional Center for Sustainable Nanotechnology, an organization funded by the National Science Foundation’s Center for Chemical Innovation.

“The idea is to find nanomaterials that are environmentally benign,” says Dr. Franz Geiger, a Northwestern University chemistry professor and head of the “Geiger group” here.

Though there haven’t been any recalls of nanoparticle-related technology, Geiger hopes his research can head off any problems. “We want to take a proactive stance so that when these nanoparticles are being used, the companies using them don’t have to do a massive recall in five years,” Geiger said.

Most simply defined as particles with at least one dimension between 1 and 100 nanometers (one-billionth of a meter), nanoparticles have become so popular in recent years because they often possess unexpected properties not seen in their larger bulk equivalents. For instance, zinc oxide nanoparticles are far more effective at blocking ultraviolet light than larger versions of the same compound; as a result. Zinc oxide nanoparticles are now widely used in commercial sunscreens. The benefit for commercial interests is two-fold: a more effective product made with less principal material.

But no one knows with any certainty how safe nanoparticles are when it comes to interaction with biological material.

“There are a number of nanoparticles used in diagnostics that are touted as perfectly safe, but they can break down,” says Geiger. “They can end up in your liver, your kidneys. At that point they’ll be broken down further and there’s been little work about what happens to them then. Could they cross the blood-brain barrier? Could this material make it into the food chain and then back into me?”

Dr. Robert J. Hamers, a professor at the University of Wisconsin-Madison and the leader of the larger CSN network, voiced similar concerns. Hamers pointed to mixed metal oxide nanoparticles as an example.

“The complexity is so high that there’s a lot of variability,” Hamers said. “The number of nanoparticles that are well-understood is very small, and that raises red flags.”

The center at Northwestern – composed of four full-time graduate students- has started to unlock the secrets of nanoparticle interactions with biological membranes. In the cavernous basement of a sprawling university tech building, the team runs several experiments per week, each involving meticulous preparation and planning. Though the group has explored endless iterations and variants, the basic setup is the same: nanoparticles are run across the surface of a silica-supported lipid bilayer, a lab-constructed synthetic membrane designed to model aspects of the lining of actual cells. A special high-powered laser records how the nanoparticles interact with the bilayer, if the two interact at all. Thus far, the project has focused primarily on four different types of widely used and researched nanoparticles: nano-gold (primarily used in research and medical diagnostics), oxidized carbon nanotubes (energy storage and thin-film electronics), nano-diamond (metalworking), and lithium cobalt oxide (fuel cell layers and batteries).

Such experiments alone cannot definitively tell whether a given nanoparticle is safe and sustainable, but they do constitute an important first step.

The Northwestern group itself is just one cog in the much larger machinery of the center’s umbrella, which includes teams at the University of Wisconsin-Madison, the University of Wisconsin-Milwaukee, the University of Minnesota, the University of Illinois at Urbana-Champaign, the University of Iowa, Pacific Northwest National Laboratory, Johns Hopkins University, and Georgia Institute of Technology. Working together offers the advantage of sharing not only equipment but knowledge.

“It’s like a very big Swiss Army knife,” says Geiger of the project. “There are groups that work with biology, with multicellular organisms. We get the entire ten thousand-foot view.”

“We are only one piece of a much larger puzzle,” adds Alicia McGeachy, a graduate student in the Northwestern group. “Together, the pieces mean a lot more than any one piece in isolation.”

In the two years since its founding, the Geiger group at Northwestern has had much success. Geiger refers to one important discovery with evident enthusiasm.

“We discovered that nanoparticles can pull out the contents of a lipid membrane and destroy it, to the point that the membrane wraps itself around the nanoparticles. And this may connect to the death of multicellular organisms exposed to the same nanoparticle formulation but not others. That’s an insight we hadn’t had before,” Geiger said. Lipids, or fats, include cholesterol and triglycerides.

The center’s mission at Northwestern is slated to continue until next fall. However, the group has already submitted a proposal for a grant from the National Science Foundation’s Division of Chemistry that, if accepted, will allow them to continue past that date. Geiger sees the federal investment in the center’s work as more than worthwhile.

“The nanotechnology field is so interesting because we are seeing things no one has ever seen before,” says Geiger.