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Posted: Mar 21, 2006
Device monitors airborne nanoparticles
(Nanowerk News) With a deep interest in the effects of air pollution on human health and global climate change, a University of Delaware researcher has developed a nanoaerosol mass spectrometer that can characterize microscopic airborne particles.
A primary use of the device, which was developed by Murray V. Johnston III, University of Delaware professor of chemistry and biochemistry, in cooperation with postdoctoral fellow Shenyi Wang and graduate student Christopher A. Zordan, is to characterize human exposure to such nanoparticles.
"As all of us go through our daily activities, we breathe in millions of these particles a day," Johnston said. "Those of us who work in nanotechnology laboratories are exposed to additional particles not found in ambient air. Through chemical analysis, we gain an understanding of where these particles come from and what their likely effects are on the human body."
Other uses of the nanoaerosol mass spectrometer, or NAMS, are to study the chemistry associated with particle formation and transformation in air, and also to study the dispersion of virus particles in air, Johnston said.
The research project is of much interest because there has been little work done in determining the chemical composition of nanoparticles as a result of the difficulty associated with finding a way to measure them.
Johnston said the first major challenge faced by the researchers in undertaking the research project was simply finding a way to sample the nanoparticles. To do that, they designed an instrument capable of capturing the particles, and their nanoaerosol mass spectrometer combines an aerodynamic inlet, an ion trap and a time-of-flight mass analyzer to characterize individual particles.
"There's no way of knowing exactly when a particle will be drawn into the instrument from air and when it does enter the instrument, we've got less than a second to complete the analysis," Johnston said. "We met this challenge by putting a charge on the particle and then using electric fields to steer and trap it inside the instrument. We don't know when a particle will come into the instrument, but when it does, we're able to capture it and put it in the precise location for analysis."
The second challenge, Johnston said, was the chemical analysis itself, which involves a sample that is less than one billionth of a billionth of a gram, or about the size of a single protein molecule. “We do this by completely disintegrating the particle into individual atoms,” he said. “We typically generate tens of thousands of atoms from a single particle, which is sufficient to detect a signal and at the same time determine the elemental composition, in other words determine the relative amounts of carbon, oxygen, nitrogen, and so forth, in the particle.”
Johnston said the technique was developed over a long period of time. "We have been working on this type of technology on and off for over eight years," he said. "Along the way, we learned much about what works and what doesn't. Finally, everything came together. This is an excellent example of how patience and persistence pay off in the end."
The researchers have mounted the NAMS on wheels so that it can be used in a variety of environments. "An instrument of this type can be used as an air quality monitor in the environment or the workplace," Johnston said. "While it is mounted on wheels and can be transported from site to site, it is still rather large, about the size of an office desk, so it will likely be used for specialized, targeted applications rather than routine monitoring."
Johnston said part of what drew him to an interest in airborne nanoparticles was the challenge. "At the most basic level, I am an analytical chemist, which means that I enjoy the challenge of finding a way to characterize a sample that simply could not be done in the past," he said. "With regard to airborne nanoparticles, the analytical challenge is great. There is an incredibly small amount of material to work with and many constraints on how we can go about it."
Johnston said he is drawn to the study of the effects of air pollution on human health and global climate change and so working with airborne nanoparticles combines several of his interests.
The UD team's work was featured recently in Chemical & Engineering News and will be highlighted in March 15 issue of Analytical Chemistry.