Small Particles Can Pose a Large Problem


By Josh Wilkinson

 

What are nanomaterials?

Nanomaterials are small – very small. They are so small, in fact, that it is difficult to truly appreciate their size. The smallest nanomaterials are called nanoparticles. What is the average size of a nanoparticle as compared to, for example, a soccer ball? Well, first imagine that the nanoparticle is the size of that soccer ball. Now compare that soccer ball to the size of the Earth! Despite their small size, nanomaterials have gained enormous attention due to their application in nanotechnology across myriad industries. So what makes nanomaterials so special and different from other materials?  To quote physicist Richard Feynman from one of his lectures, “Atoms on a small scale behave like nothing on a large scale” (Feynman 1959). One might assume that the unique characteristics and properties of nanomaterials are due to their small size. Because nanomaterials are so small, they operate at a quantum level, giving a nanomaterial completely different characteristics and properties compared to their counterparts on a larger scale. For example, when we look at a piece of gold at a regular scale, it will have the traditional yellow color. However, when looking at a mixture containing gold nanoparticles at the nanoscale level, the nanoparticles will appear to have a deep red color. This occurs because the quantum effects on nanoparticles change the optic, or visual, properties of the gold atoms when they reach the nanoscale. Engineered nanomaterials can be designed to have a wide range of unique properties just by simply tweaking their size, making them very attractive for novel applications.

Nanomaterials and the environment

The use of nanotechnology in consumer products is only becoming more prominent, so it is inevitable that various nanomaterials are going to end up in our environment. Nanomaterials might enter our environment through accidental industrial spills, release from product use, or breakdown and release in landfills. Whenever we release substances into the environment that may be potentially harmful it tends to draw the concern of regulators, toxicologists, and ecologists alike, and nanomaterials are no exception. Previous research was directed toward studying the harmful effects of various nanomaterials on living organisms. However, much less research has been conducted on how nanomaterials interact with and travel through the environment. Our lack of understanding of nanomaterial fate and transport makes it difficult to properly assess the ecological risk that engineered nanomaterials may present. When a new pollutant is evaluated for environmental toxicity, scientists typically can measure certain properties of the pollutant as a method to predict how it will travel through the environment. Unfortunately, nanomaterials do not obey the traditional mechanisms that most non-nanomaterial chemicals do. To properly assess the risk of nanomaterials, scientists need to better understand and agree upon how to describe the ways in which nanomaterials interact and move through the environment.

What are we doing

This summer, I am working in the Wiesner lab under Dr. Geitner with Project 4 of the Duke Superfund Research Center. For our project we are attempting to better describe the fate of nanoparticles as they enter the environment. To describe the fate of a nanoparticle we are using a concept called surface attachment efficiency, also known as “alpha”. Alpha can be defined as the probability of a particle sticking to a surface after collision. So essentially we can think of alpha as a way to describe how “sticky” a nanoparticle is relative to a surface. To determine alpha, I conduct mixing studies in which I essentially measure the rate at which nanoparticles attach to background (non-nanomaterial) surfaces. Alpha is an ideal fate descriptor for nanoparticles because it can help predict which compartments of the environment the nanoparticle would end up in by giving insight into what the nanoparticle would attach to, and ultimately effect. For example, we could predict if a type of nanoparticle be more likely to stick to algae in a body of water, stick to clays and be confined to soils, or stick to grains of sand and end up on the banks of rivers.

What we would like to accomplish

 A major goal for our project is to fill out a chart of alpha values to quantify the interaction of several nanoparticles with various surface properties with specific background surfaces that nanoparticles are likely to encounter in the environment. This chart would allow us to see the level of stickiness nanoparticles have with common environmental surfaces. Some of the background surfaces we are using include, algae, clay, and glass beads. Once we complete the chart of alpha values, we can evaluate trends in alpha values based on the properties of the nanoparticle and the background surface it’s coming in contact with. By observing trends and conducting further mixing studies, we hope to learn which factors affect alpha and how alpha can be used to better understand the fate and transport of nanoparticles. Ultimately, we would like to make a convincing argument for using alpha as an appropriate descriptor in regards to the environmental fate of nanoparticles, predicting how nanoparticles move through and interact with the environment.

My personal experience

My experience interning with the scientists of Project 4 of the Duke Superfund Research Center has been one of the most impactful summers I have had. Combining the hands on experience in the lab along with the relationships I’ve built with Ph.D. students and post-docs has given me an incredible amount of insight into the direction I may take for further education. From this experience I will walk away with a deeper understanding of how to conduct research and a few new friends.