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Lighting Up Nanoparticles in Complex Samples: ES&T’s Top Technology Article 2012 Sarah Webb
generating visible and near-infrared spectra. Each spectrum serves as a chemical fingerprint for the material that exists in each pixel of the sample. Hyperspectral imaging is best known for its use in military surveillance to map out land surface features. When Badireddy first used the instrument, he was blown away by what he saw: The dark field technique, as the name suggests, leaves a black background, but the scattered light from silver nanoparticles paint a “multicolor starscape” in the foreground. In the ES&T paper, the researchers first characterized more than a dozen types of engineered nanoparticles, including carbon nanotubes, as well as silver, gold, and titanium dioxide nanoparticles. They then used this library of spectra to examine nanoparticle mixtures in ultrapure water and observed changes in the coatings on silver nanoparticles. The team also mapped the locations of and estimated abundances of silver nanoparticles from one of their mesocosm samples and a wastewater field sample. These tests demonstrated that the technique was sensitive enough to analyze complex environmental samples containing nanomaterials. The method’s sample preparation is minimal, Wiesner says. Acquiring microscopy images for a single sample can take as little as 10 to 15 min, Badireddy adds. The image processing of a complex sample takes longer, about half a day. But before researchers can even start to work on complex samples, they have to build a spectral database of known materials that they can use to identify them in the samples. A complete hyperspectral imaging system costs approximately $150,000, according to CytoViva. Though the technique requires less sample preparation than others such as transmission electron microscopy, hyperspectral imaging is not trivial to carry out, PNNL’s Baer says. Still the technique fills a niche where there are not many options. “You need to apply an armada of techniques,” he says, to really understand the changes in nanoparticles. “And this has the potential of being one of those techniques.” Wiesner says he and his co-workers at Duke are using this technique to study the uptake of nanomaterials in various organisms. In another ES&T paper, Badireddy, Wiesner, and their colleagues used the technique to observe the inactivation of viruses using fullerene nanoparticles exposed to ultraviolet light (Environ. Sci. Technol., DOI: 10.1021/es300340u). “Raju Badireddy has been the genius behind making this apparatus work,” Wiesner says. Other researchers want to pick his brain, he adds.
Environ. Sci. Technol.
s materials scientists find new ways to use nanotechnology in electronics and medicine, environmental researchers want to understand the fate and impact of these engineered materials after they leach into the environment. In ES&T’s Best Technology Paper of 2012, researchers from Duke University describe a microscopy technique that can detect and characterize nanoparticles at biologically relevant concentrations and under conditions that mimic surface and ground waters (Environ. Sci. Technol., DOI: 10.1021/es204140s). At Duke’s Center for the Environmental Implications of NanoTechnology (CEINT), environmental scientists study 30 mesocosms, controlled systems that mimic natural ecosystems such as groundwater. Researchers seed each mesocosm with nanoparticles to try to understand the changes in these materials over time and how the materials affect their environments. A major challenge in these experiments, and in field studies, is to detect and characterize the chemical makeup of nanoparticles in complex environmental samples that contain myriad types of molecules, says Mark R. Wiesner, CEINT’s director. While techniques such as transmission electron microscopy, scanning electron microscopy, and inductively coupled plasma mass spectrometry have sufficient sensitivity to identify nanomaterials, the sample preparation involved with those techniques is labor-intensive and can potentially alter the materials researchers would like to study. As a result of these analytical limitations, researchers struggle to fully characterize nanomaterials, says Donald Baer of Pacific Northwest National Laboratory, who was not involved in this research. So Wiesner and his colleagues turned to other techniques to characterize the materials. In 2010, postdoctoral researcher Appala Raju Badireddy started working with a microscopy instrument called a CytoViva Hyperspectral Imaging System. The instrument is a dark field microscope, which characterizes samples by shining light on them and then capturing only light scattered from the samples. The instrument then analyzes the scattered light using hyperspectral imaging, a process that characterizes light from individual pixels of the sample,
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© 2013 American Chemical Society
Received: February 28, 2013 Accepted: March 7, 2013 Published: March 22, 2013 3021
dx.doi.org/10.1021/es400922g | Environ. Sci. Technol. 2013, 47, 3021−3022
Environmental Science & Technology
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Perspective
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
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dx.doi.org/10.1021/es400922g | Environ. Sci. Technol. 2013, 47, 3021−3022
