'Catch and release' program could improve nanoparticle safety assessment

ScienceDaily (June 8, 2011) — Depending on whom you ask, nanoparticles are, potentially, either one of the most promising or the most perilous creations of science. These tiny objects can deliver drugs efficiently and enhance the properties of many materials, but what if they also are hazardous to your health in some way? Now, scientists at the National Institute of Standards and Technology (NIST) have found a way to manipulate nanoparticles so that questions like this can be answered.

The team has developed a method of attracting and capturing metal-based nanoparticles on a surface and releasing them at the desired moment. The method, which uses a mild electric current to influence the particles' behavior, could allow scientists to expose cell cultures to nanoparticles so that any lurking hazards they might cause to living cells can be assessed effectively.

The method also has the advantage of collecting the particles in a layer only one particle thick, which allows them to be evenly dispersed into a fluid sample, thereby reducing clumping -- a common problem that can mask the properties they exhibit when they encounter living tissue. According to NIST physicist Darwin Reyes, these combined advantages should make the new method especially useful in toxicology studies.

"Many other methods of trapping require that you modify the surface of the nanoparticles in some way so that you can control them more easily," Reyes says. "We take nanoparticles as they are, so that you can explore what you've actually got. Using this method, you can release them into a cell culture and watch how the cells react, which can give you a better idea of how cells in the body will respond."

Other means of studying nanoparticle toxicity do not enable such precise delivery of the particles to the cells. In the NIST method, the particles can be released in a controlled fashion into a fluid stream that flows over a colony of cells, mimicking the way the particles would encounter cells inside the body -- allowing scientists to monitor how cells react over time, for example, or whether responses vary with changes in particle concentration.

For this particular study, the team used a gold surface covered by long, positively charged molecules, which stretch up from the gold like wheat in a field. The nanoparticles, which are also made of gold, are coated with citrate molecules that have a slight negative charge, which draws them to the surface covering, an attraction that can be broken with a slight electric current. Reyes says that because the surface covering can be designed to attract different materials, a variety of nanoparticles could be captured and released with the technique.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

Darwin R. Reyes, Geraldine I. Mijares, Brian Nablo, Kimberly A. Briggman, Michael Gaitan. Trapping and Release of Citrate-Capped Gold Nanoparticles. Applied Surface Science, 2011; DOI: 10.1016/j.apsusc.2011.04.030

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Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

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New material could improve safety for first responders to chemical hazards

ScienceDaily (May 2, 2011) — A new kind of sensor could warn emergency workers when carbon filters in the respirators they wear to avoid inhaling toxic fumes have become dangerously saturated.

In a recent issue of the journal Advanced Materials, a team of researchers from the University of California, San Diego and Tyco Electronics describe how they made the carbon nanostructures and demonstrate their potential use as microsensors for volatile organic compounds.

First responders protect themselves from such vapors, whose composition is often unknown, by breathing through a canister filled with activated charcoal -- a gas mask. Airborne toxins stick to the carbon in the filter, trapping the dangerous materials.

As the filters become saturated, chemicals will begin to pass through. The respirator can then do more harm than good by providing an illusion of safety. But there is no easy way to determine when the filter is spent. Current safety protocols base the timing of filter changes on how long the user has worn the mask.

"The new sensors would provide a more accurate reading of how much material the carbon in the filters has actually absorbed," said team leader Michael Sailor, professor of chemistry and biochemistry and bioengineering at UC San Diego. "Because these carbon nanofibers have the same chemical properties as the activated charcoal used in respirators, they have a similar ability to absorb organic pollutants."

Sailor's team assembled the nanofibers into repeating structures called photonic crystals that reflect specific wavelengths, or colors, of light. The wing scales of the Morpho butterfly, which give the insect its brilliant iridescent coloration, are natural examples of this kind of structure.

The sensors are an iridescent color too, rather than black like ordinary carbon. That color changes when the fibers absorb toxins -- a visible indication of their capacity for absorbing additional chemicals.

The agency that certifies respirators in the U.S., the National Institute of Occupational Safety and Health, has long sought such a sensor but the design requirements for a tiny, sensitive, inexpensive device that requires little power, have proved difficult to meet.

The materials that the team fabricated are very thin -- less than half the width of a human hair. Sailor's group has previously placed similar photonic sensors on the tips of optical fibers less than a millimeter across and shown that they can be inserted into respirator cartridges. And the crystals are sensitive enough to detect chemicals such as toluene at concentrations as low as one part per million.

Ting Gao, a senior researcher at the Polymers, Ceramics, and Technical Services Laboratories of Tyco Electronics in Menlo Park, California and Timothy L. Kelly, a NSERC post-doctoral fellow at UC San Diego co-authored the paper. The National Science Foundation, the Department of Homeland Security, the Natural Sciences and Engineering Research Council of Canada, and TYCO Electronics provided funding for the work.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - San Diego. The original article was written by Susan Brown.

Journal Reference:

Timothy L. Kelly, Ting Gao, Michael J. Sailor. Carbon Nanofiber Photonic Crystals: Carbon and Carbon/Silicon Composites Templated in Rugate Filters for the Adsorption and Detection of Organic Vapors (Adv. Mater. 15/2011). Advanced Materials, 2011; 23 (15): 1688 DOI: 10.1002/adma.201190052

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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