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March 30, 2007

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Study: Cells Selectively Absorb Short Nanotubes

Nanotube length threshold image

Nanotube length threshold: NIST experiments using human lung cells demonstrate that DNA-wrapped single-walled carbon nanotubes longer than about 200 nanometers are excluded from cells, while shorter lengths are able to penetrate the cell interior (dark lines in the fluorescence image above).

Credit: NIST
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DNA-wrapped single-walled carbon nanotubes (SWCNTs) shorter than about 200 nanometers readily enter into human lung cells and so may pose an increased risk to health, according to scientists at the National Institute of Standards and Technology (NIST). The results of their laboratory studies appear in an upcoming issue of Advanced Materials.*

Eyed for uses ranging from electronic displays to fuel cells to water filtration, SWCNTs are tiny cylinders—essentially single-sheet rolls of carbon atoms. They are many times stronger than steel and possess superlative thermal, optical and electronic properties, but safety and biocompatibility remain an open question.

“Published data citing in vitro (outside the body) toxicity are particularly inconsistent and widely disputed,” writes biomaterials scientist Matthew Becker and his NIST colleagues. Public concerns surrounding the environmental, health and safety impacts of SWCNTs could derail efforts to fast track the development of nanotubes for advanced technology applications. A significant hurdle in outlining the parameters contributing to nanotube toxicity is to prepare well-defined and characterized nanotube samples, as they typically contain a distribution of lengths, diameters, twists and impurities.

The team chose to isolate the effects of nanotube length. They first adsorbed short DNA molecules onto the nanotubes because this renders them soluble in water and allows them to be sorted and separated by length. The researchers then exposed human lung fibroblasts to solutions containing unsorted nanotubes. Regardless of the concentration levels, the cells did not absorb between about one-fourth and one-third of the SWCNTs in the solutions. Further examination of the results revealed that only short nanotubes made it into the cellular interior.

In the next phase of the research, the team exposed the cells to sorted nanotubes of controlled length. They found that tubes longer than about 200 nanometers were excluded from the cells and remained in solution. Cells exposed to the longer nanotube solutions did not undergo a decrease in metabolic activity, but cells exposed to nanotubes below that threshold absorbed them and, depending on the concentration level, died or showed other signs of toxicity. “Our results demonstrate that cellular uptake in these lung cells depends significantly on the length of the nanotubes,” Becker explains. “This is the first of many steps in the critical goal of reducing health risk by de novo engineering of the nanotubes themselves.”

*M.L. Becker, J.A. Fagan, N.D. Gallant, B.J. Bauer, V. Bajpai, E.K. Hobbie, S.H. Lacerda, K. B. Migler and J.P. Jakupciak. Length-dependent uptake of DNA-wrapped single-walled carbon nanotubes. Advanced Materials, published on-line : 20 March 2007.

Media Contact: Michael Baum, michael.baum@nist.gov, (301) 975-2763

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Titanium Dioxide: It Slices, It Dices …

illustration of the cleavage of proteins

Illustration of the cleavage of proteins near a titanium dioxide surface: when illuminated with ultraviolet light, hydroxyl radicals are formed in water near the semiconductor's surface and cut proteins at the location of the amino acid proline.

Credit: NIST
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Chemists from the National Institute of Standards and Technology (NIST) and Arizona State University have proposed an elegantly simple technique for cleaving proteins into convenient pieces for analysis. The prototype sample preparation method, detailed recently in Analytical Chemistry,* uses ultraviolet light and titanium dioxide and could be ideal for new microfluidic “lab-on-a-chip” devices designed to rapidly analyze minute amount of biological samples.

Because most proteins are very large, complex molecules made up of hundreds or thousands of amino acids, they usually must be cut up into more manageable pieces for analysis. Today, this most commonly is done by using special enzymes called “proteases” that sever the chains at well-known locations. The protease trypsin, for example, cuts proteins at the locations of the amino acids lysine and arginine. Analyzing the residual fragments can identify the original protein. But enzymes are notoriously fussy, demanding fairly tight control of temperature and acidity, and the enzymatic cutting process can be time-consuming, from a matter of hours to days.

For a “radically” different approach, the NIST group turned to a semiconductor material, titanium dioxide. Titanium dioxide is a photocatalyst—when exposed to ultraviolet light its surface becomes highly oxidizing, converting nearby water molecules into hydroxyl radicals, a short-lived, highly reactive chemical species.** In the NIST experiments, titanium dioxide coatings were applied to a variety of typical microanalysis devices, including microfluidic channels and silica beads in a microflow reactor. Shining a strong UV light on the area, in the presence of a protein solution, creates a small “cleavage zone” of hydroxyl radicals that rapidly cut nearby proteins at the locations of the amino acid proline.

Although development work remains to be done, according to the researchers, the NIST photocatalysis technique offers several advantages over conventional enzyme cleavage of proteins. It’s not particularly sensitive to temperature or acidity, and needs no additional reagents other than dissolved oxygen in the solution. It’s a simple arrangement, easy to incorporate into a wide range of instruments and devices, and titanium dioxide, an inorganic material, will last virtually forever in a broad range of conditions—enzymes have to be treated carefully and stored in temperature-controlled environments. The target amino acid, proline, is relatively sparse in most proteins, but it’s found at key locations, such as sharp turns in the molecule, that aid analysis. And it’s fast—in trials with the protein angiotensin I, the team obtained detectable cleavage patterns in as little as 10 seconds.

* B.J. Jones, M.J. Vergne, D.M. Bunk, L.E. Locascio and M.A. Hayes. Cleavage of peptides and proteins using light-generated radicals from titanium dioxide. Anal. Chem. 2007, 79, 1327-1332.

** A property that has been applied to a variety of sanitization tasks from wastewater treatment to self-cleaning surgical room tiles.

Media Contact: Michael Baum, michael.baum@nist.gov, (301) 975-2763

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Novel Experiments on Cement Yield Concrete Results

schematic drawing of nanoscale calcium silicate hydrate

Schematic drawing of nanoscale calcium silicate hydrate (C-S-H) particles in cement showing the multiple roles played by water as defined in the NIST/Northwestern experiments. Solid red areas are calcium silicate, pebbled areas in between show the water physically bound between the layers to form solid C-S-H. Dark blue halos around the C-S-H particles are water adsorbed on the surface; pale blue areas represent liquid water caught in nanopores.

Credit: NIST
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Using a brace of the most modern tools of materials research, a team from the National Institute of Standards and Technology (NIST) and Northwestern University has shed new light on one of mankind’s older construction materials—cement. Their refinements to our understanding of how cement and concrete actually work, reported this week in Nature Materials,* ultimately may make possible improvements in the formulation and use of cement that could save hundreds of millions of dollars in annual maintenance and repair costs for concrete structures and the country’s infrastructure.

Cement may be the world’s most widely used manufactured material—more than 11 billion metric tons are consumed each year—but it also is one of the more complex. And while it was known to the Romans, who used it to good effect in the Colosseum and Pantheon, questions still remain as to just how it works, in particular how it is structured at the nano- and microscale, and how this structure affects its performance.

Cement is something of a paradox. It requires just the right amount of water to form properly—technically it’s held together by a gel, a complex network of nanoparticles called calcium silicate hydrate (C-S-H) that binds a significant amount of water within its structure. But once the cement has set, the C-S-H structure retains a tough, unchanging integrity for centuries, even in contact with water. To date, attempts to pinpoint the amounts and different roles of water within the C-S-H in cement paste have required taking the water out, either by drying or chemical methods. The NIST/Northwestern researchers instead combined structural data from small-angle neutron scattering experiments at the NIST Center for Neutron Research and from an ultrasmall-angle X-ray scattering instrument built by NIST at the Advanced Photon Source at Argonne National Laboratory. Their experiments are the first to classify water by its location in the cured cement.

As a result, the researchers were able to distinguish—and measure—the difference between water physically bound within the internal structure of the solid C-S-H nanoparticles and adsorbed or liquid water between the nanoparticles. They also measured a nanoscale calcium hydroxide structure that co-exists with the C-S-H gel. The new data, which imply significantly different values for the formula and density of the C-S-H gel than previously supposed, have implications for defining the chemically active surface area within cement, and for predicting concrete properties. They also may lead to a better understanding of the contribution of the nanoscale structure of cement to its durability, and how to improve it.

* A.J. Allen, J.J. Thomas and H.M. Jennings. Composition and density of nanoscale calcium–silicate–hydrate in cement. Nature Materials, published online: 25 March 2007.

Media Contact: Michael Baum, michael.baum@nist.gov, (301) 975-2763

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Traces of Nanobubbles Determine Nano-boiling

ultra-highspeed photographs

Ultra-highspeed photographs of microbubbles forming on a microheater show the effect of residual nanobubbles between heating pulses. The first pulse of a two-pulse sequence (a) produces nearly identical microbubbles time after time, but the second pulse (b) produces a random assortment of bubbles of varying sizes. Vertical bar shows a distance of 15 micrometers.

Credit: NIST
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View video clips of microbubble formation.

Using a microscope and some extreme “snapshot” photography with shutter speeds only a few nanoseconds long, researchers from the National Institute of Standards and Technology (NIST) and Cornell University have uncovered the traces of ephemeral “nanobubbles” formed in boiling water on a microheater. Their observations* suggest an added complexity to the everyday phenomenon of boiling, and may affect technologies as diverse as inkjet printers and some proposed cancer therapies.

You might think that the science of boiling had been worked out some time ago, but it still has some mysteries, particularly at the nanometer scale. As water and other fluids change from their liquid state to a vapor, bubbles of the vapor form. The bubbles usually form at “nucleation sites,” which can be small surface irregularities on the container or tiny suspended particles in the fluid. The exact onset of boiling depends on the presence and nature of these sites.

To observe the process, the NIST/Cornell team used a unique ultrafast laser strobe microscopy technique with an effective shutter speed of eight nanoseconds to photograph bubbles growing on a microheater surface about 15 micrometers wide. At this scale, a voltage pulse of only five microseconds superheats the water to nearly 300 C, creating a microbubble tens of microns in diameter. When the pulse ends, the microbubble collapses as the water cools. What the team found was that if a second voltage pulse follows closely enough, the second microbubble forms earlier during the pulse and at a lower temperature apparently, as conjectured by the team, because nanobubbles formed by the collapse of the first bubble become new nucleation sites for the growth of later bubbles. The nanobubbles themselves are too small to observe, but by changing the timing between voltage pulses and observing how long it takes the second microbubble to form, the researchers were able to estimate the lifetime of the nanobubbles—roughly 100 microseconds.

These experiments are believed to be the first evidence that nanoscale bubbles can form on hydrophilic surfaces (previous evidence of nanobubbles was found only for hydrophobic surfaces like oilcloth) and the method for measuring nanobubble lifetimes may improve models for optimal heat transfer design in nanostructures. The work has immediate implications for inkjet printing, in which a metal film is heated with a voltage pulse to create a bubble that is used to eject a droplet of ink through a nozzle. If inkjet printing is pushed to higher speeds (repetition rates above about 10 kilohertz), the work suggests, nanobubbles on the heater surface between pulses will make it difficult or impossible to control bubble formation properly.

The findings also may impact proposed thermal cancer therapies in which nanoscale objects are designed to accumulate in tumors and are subsequently heated remotely by infrared radiation or alternating magnetic fields. Each particle acts as a nanoscale heater, with nanobubbles being created if the applied radiation is sufficient. The bubbles may have a therapeutic effect through additional heat delivered and mechanical stresses they may impart to the surrounding tissue.

* R. E. Cavicchi and C.T. Avedisian. Bubble nucleation and growth anomaly for a hydrophilic microheater attributed to metastable nanobubbles. Phys. Rev. Lett. 98, 124501 (2007).

Media Contact: Michael Baum, michael.baum@nist.gov, (301) 975-2763

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How Long Does It Take to Take 10 Fingerprints?

The Department of Homeland Security (DHS) and the United States Visitor and Immigrant Status Indicator Technology (US-VISIT) program are migrating from a process that captures fingerprints from two fingers (left and right index fingers) of U.S. visitors to a process that captures prints from all 10 fingers. Researchers at the National Institute of Standards and Technology (NIST) conducted a study for DHS to determine the amount of time it might take to successfully capture 10 fingerprint images. As part of the study, the NIST researchers also examined how different types of instructions given to visitors affected the fingerprint-capturing time.

On average, the time to capture 10 fingerprints without operator assistance ranged from 48 to 64 seconds; with operator assistance, the time ranged from 50 to 54 seconds for the specific fingerprint system configuration used. The researchers also found that when an operator helped guide the process, 98 percent were able to leave a 10-print image to successfully complete the collection process. Participants who received oral instructions or video instructions with no audio component performed equally well; 93 percent were able to successfully complete the fingerprinting process with minimal errors in approximately 50 seconds. Participants getting instructions from a poster with no text had the most difficulty performing the fingerprinting task. Only 56 percent were able to successfully complete the fingerprinting process; they took significantly longer (64 seconds) and made more errors. A follow-up report will provide the details of the fingerprint image quality associated with the instructional modes. A report on the study, Usability Testing of Ten-Print Fingerprint Capture (NISTIR 7403), is available at http://zing.ncsl.nist.gov/biousa/.

Media Contact: Michael E. Newman, michael.newman@nist.gov, (301) 975-3025

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New Standard Protocol for Suspicious Powder Sampling

Through a special arrangement with the Department of Homeland Security (DHS), a recently developed methodology standard for collecting, containing and transporting small samples of unknown powders suspected of being hazardous biological agents is being made available, free of charge, to state and local emergency first responder teams and other interested parties. The new standard, issued by ASTM International, was developed for DHS by a multiagency team, including federal, state and local organizations, coordinated by the National Institute of Standards and Technology (NIST) and AOAC International.

The standard details a tested protocol to be used when emergency first responders are confronted with an unknown powdered substance that is suspected of being a biological threat after an initial assessment for explosive, radiological or chemical hazards. The protocol is designed to minimize exposure risks to the public and the first responders as much as possible while ensuring that unadulterated samples are collected for later biochemical and forensic analysis by public health and law enforcement organizations.

The first such nationally validated standard of its kind, ASTM E 2458, Standard Practices for Bulk Sample Collection and Swab Sample Collection of Visible Powders Suspected of Being Biological Agents from Nonporous Surfaces, is a two-stage process that covers, first, the bulk collection and packaging of a suspicious powder from a solid, non-porous surface, and, second, the collection of swab samples of residual powder from the surface for immediate on-site tests and biological screening. (Bulk sample collection is done first to minimize the dispersion of the powder.)

The standard was issued under the auspices of ASTM Committee E54 on Homeland Security. To ensure the widest possible dissemination and use of these procedures, DHS has secured a special unlimited license for ASTM E 2458, allowing it to be downloaded by interested groups and individuals free of charge from the E54 home page: www.astm.org/COMMIT/E54.htm.

In addition to NIST and AOAC International, a not-for-profit scientific association dedicated to the development and use of scientific analytical methods and laboratory quality assurance programs, participants in the original program to develop the suspicious powder sampling protocol included the Centers for Disease Control and Prevention, the Federal Bureau of Investigation, the Department of Defense, the Environmental Protection Agency, the U.S. Army Dugway Proving Ground, the DHS Center for Domestic Preparedness and the U.S. National Guard. State and local organizations on the team included the New York State Department of Health, State of Florida, and the International Association of Fire Chiefs.

Media Contact: Michael Baum, michael.baum@nist.gov, (301) 975-2763

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Quick Links

‘Interoperability Week’ Conference April 23-25

“Interoperability” is the catchword and a high-priority in today’s manufacturing sector. Yet few Computer-Aided Design/Computer-Aided Manufacturing programs can really share information with dissimilar systems. The 2006 Kubotek Computer-Aided Design and Computer-aided Manufacturing (CAD/CAM) Interoperability Survey, for instance, reveals 72 percent of CAD users, using different systems, must frequently redraw 3D designs from scratch and 11 percent must always recreate the earlier work. A National Institute of Standards and Technology (NIST) study found that economic costs of incompatibility data in the automobile industry alone exceed $1 billion a year.

NIST's second annual Interoperability Week in Gaithersburg, MD April 23-25, 2007, will spotlight manufacturing sector interoperability problems as well as advances being made to resolve these productivity roadblocks. The meeting brings together workshops in a broad range of information technology application areas to discuss open standards that enable different information systems to share and exchange data. Conference participants from manufacturing, business, security and science sectors will compare issues and share solutions to interoperability problems in their particular domains. Conference session topics cover manufacturing systems integration, long-term data retention, development, digital image search, sensor integration and federal enterprise integration.

A plenary session on April 24 will feature talks by Jason Matusow, Microsoft Corporation senior director of Intellectual Property and Interoperability; Eric Neumann, co-chair of W3C Healthcare and Life Sciences; and Ken Thibodeau, electronic records archives program director at the National Archives and Records Administration, followed by a panel discussion.

For detailed information, see www.mel.nist.gov/div826/msid/sima/interopweek/.

Conference registration: www.nist.gov/public_affairs/confpage/070423.htm.

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Baldrige Recipients Share Quality Best Practices

Learn about the exceptional practices and results of the 2006 recipients of the Malcolm Baldrige National Quality Award at the Quest for Excellence XIX, April 15-17, 2007, at the Hilton Washington in Washington, D.C. The 2006 Baldrige Award recipients are: Premier Inc., MESA Products, Inc. and North Mississippi Medical Center. Throughout the three-day conference, senior leaders and others from each of the 2006 Baldrige Award recipients will give presentations and answer questions on their processes, tools and results in areas such as leadership, strategic planning, and customer and employee satisfaction. Two pre-conference workshops will help attendees better understand how to use the Baldrige criteria for performance excellence as a tool to assess and improve their organization. For more information, see http://baldrige.nist.gov/Quest_for_Excellence.htm.

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National Technology Medal Call for Nominations

Commerce Secretary Carlos M. Gutierrez is seeking nominations for the 2007 National Medal of Technology, the nation’s highest honor awarded by the President to America’s leading inventors and technological innovators.

“The face of competition today is global, and innovation lies at the heart of this competition,” said Gutierrez. “The National Medal of Technology recognizes American innovators who have made lasting contributions to advancing our global competitiveness, economic prosperity and quality of life. These pioneers in the amazing world of science and technology are American heroes.”

The deadline for submitting 2007 nominations is close of business (5:00 p.m. Eastern) May 31, 2007. Nomination forms and guidelines may be downloaded from the National Medal of Technology Web site at www.technology.gov/Medal/Nomination.htm and should be submitted by e-mail to NMT@technology.gov, by fax or regular mail to the number and address listed on the nomination form.

For additional details and a copy of Secretary Gutierrez’ letter announcing the Call for Nominations, see www.technology.gov/Medal/.

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Editor: Michael Baum

Date created: March 30, 2007
Date updated: March 30, 2007
Contact: inquiries@nist.gov