Mad Scientists: Nontoxic Nanoparticles with Lee Bishop
Post by Christie Taylor on 7/30/2012 1:30pm
Mad Scientists is a new regular feature, presenting local science researchers. We’ll talk to them about their research, why it’s interesting, and why you should care.
For our inaugural post, we talked to Lee Bishop, a postdoctoral scholar (“postdoc”) working in chemistry and environmental chemistry and technology. Lee works with nanoparticles, which are particles (groups of atoms and molecules that behave as a single unit) between 1 and 100 nanometers in size. At that size, the properties of particles can vary greatly (and unpredictably) from larger versions of the same materials. Nanoparticles are used in everything from making crack-resistant paints and scratch-proof sunglasses to casting lighter, stronger metal alloys.
D101: First things first; what exactly do you do?
Lee: I make titanium dioxide nanoparticles with different surface coatings and study their properties. The goal is to be able to predict where they will travel in the environment and what toxicity risks they might pose.
D101: What's the point of coating nanoparticles?
Lee: Usually people will coat nanoparticles or other nanomaterials with organic (carbon-containing) molecules or polymers. They can also coat them with other inorganic chemicals, like silicon dioxide (sand). In the case of titanium dioxide nanoparticles, they will coat them in polymers so that they mix well with whatever application they are being used in. Often whatever they are being added to is an organic, oily mixture, and titanium dioxide is an inorganic, rock-like chemical. So by coating the nanoparticle you assure that the nanoparticle doesn't separate from the mixture. This is just one reason someone would coat a nanoparticle with something, there are TONS of others.
D101: So you’re putting a coating on something that’s already really small. How is that even possible?
Lee: That's simple; coat it with something smaller! Most molecules that organic chemists (like myself) know how to make are SUPER small, often smaller than 1 nanometer. It's often as simple as making a solution of the molecules you want to coat your nanoparticles with and add that to your nanoparticles. The molecules eventually find the nanoparticles and assemble themselves on the surface.
D101: Isn’t titanium dioxide pretty harmless? Why would toxicity be a concern?
Lee: The main way nanoparticles are hazardous to humans is if you inhale the dry powder. They are so small that they can reach all the way into the depths of your lungs, get stuck there, and cause all sorts of harm. We usually don't work with dry powder nanoparticles, but instead work with them in water. The main way we have discovered that titanium dioxide nanoparticles can be harmful is by creating things known as “reactive oxygen species” when the nanoparticles are exposed to light. These reactive oxygen species perform reactions with almost anything they encounter (such as DNA). We perform our studies using zebrafish embryos, which turn out to be decent model for human health. We have shown that reactive oxygen species are formed inside the zebrafish, and that zebrafish exposed to these reactive oxygen species develop all sorts of deformities as they grow. But unlike humans, the zebrafish are nearly transparent, so when a nanoparticle gets inside them, sunlight can penetrate all the way through them, reaching the nanoparticles and creating these reactive oxygen species. It is very unlikely titanium dioxide nanoparticles would be toxic to humans in the same ways they are toxic to our zebrafish. A lot more research needs to be done before we have any clear understanding about the types and severity of risks nanoparticles pose to human health and the environment.
D101: I am pretty opaque, but that still worries me. How can chemists make safer nanoparticles?
Lee: One way we’ve reduced the toxicity of titanium dioxide nanoparticles is designing molecules that are greasy (water-hating) near the nanoparticle surface, but are water-loving towards the exterior. In order to produce reactive oxygen species, water molecules need to penetrate the surface of the titanium dioxide nanoparticles. With this setup, the water-loving portion makes the nanoparticles mix well with water so we can study them easily, while the water-hating portion keeps water away from the actual surface of the nanoparticle. We’ve found that nanoparticles coated with these molecules produce fewer dangerous reactive oxygen species than other nanoparticles.
D101: So, is there a gadget we might see down the road based on your work?
Lee: The chemical industry is doing a fine job of making products from titanium dioxide nanoparticles (sunscreens, paints, toothpaste, so much stuff!). In these various products, companies often alter the nanoparticle surface coatings. My goal is to try and understand how changing the nanoparticle surface coatings changes the associated environmental and human health risks. The only gadget that will come out of my research is KNOWLEDGE.
D101: What’s most misunderstood about nanoparticles? What do you wish more people knew?
Lee: I once had a conversation with my uncle, who asked "So what's the deal with this nano stuff? Is it good or bad?" I'm not sure how common that conception is, but having worked in this field for two years I can now say that there are no easy answers. "Nanotechnology" is incredibly diverse. The variety of shapes, sizes, compositions, and surface coatings that can be made is stupendous. Compound that complexity with the complexity of the environment, and that shows you that there can be no easy answers to my uncle's questions. That being said, the research that has gone into this has made lots of progress. We have shown that even fairly innocuous materials like titanium dioxide, when in nano form, can enter into organisms under certain conditions and cause damage. With an understanding of how this damage occurs, one of my colleagues has even been able to design nanoparticles that are less hazardous from that standpoint.
D101: Why is this research exciting to you? Why should we care?
Lee: Nanoscience is really interesting in that we have known how to make super small things (less than one nanometer) for around a century, and pretty small things (less than 1000 nanometers) for a few decades, but the size range in between has been totally off limits until recently. This particular research is exciting to me because I am very interested in green chemistry. The more we know about the risks posed by certain materials, the better equipped chemists are to design products that are "benign by design."
Bishop’s main hobby, aside from research, is being “an amateur science enthusiast.” He writes a blog, Science Minus Details, and helps organize Madison's Nerd Nite, which convenes about monthly at the High Noon Saloon to bring nerds together to learn new things and drink beer together.
A film of nanoparticles from Bishop's lab. Particles and picture by Joe Yeager.
Christie Taylor (@ctaylsaurus) covers science, environment, and, depending on the season, state politics for dane101. She verbs a lot of nouns, including rollerskates, radio, and Kurt Vonnegut. A Madison native, she's not sure she'll ever quite manage to leave Wisconsin, and that's just fine by her. Contact her at firstname.lastname@example.org.