In This Issue...
Take F2: NIST’s Latest, Most Accurate Time Standard Debuts
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No Compromises: JILA’s Short, Flexible, Reusable AFM Probe
JILA researchers have engineered a short, flexible, reusable probe for the atomic force microscope (AFM) that enables state-of-the-art precision and stability in picoscale force measurements. Shorter, softer and more agile than standard and recently enhanced AFM probes, the JILA tips will benefit nanotechnology and studies of folding and stretching in biomolecules such as proteins and DNA.
An AFM probe is a cantilever, shaped like a tiny diving board with a small, atomic-scale point on the free end. To measure forces at the molecular scale in a liquid, the probe attaches its tip to a molecule such as a protein and pulls; the resulting deflection of the cantilever is measured. The forces are in the realm of piconewtons, or trillionths of a newton. One newton is roughly the weight of a small apple.
The new probe design, described in ACS Nano,* is the JILA research group's third recent advance in AFM technology. JILA is jointly operated by the National Institute of Standards and Technology (NIST) and University of Colorado Boulder.
The group previously improved AFM position stability by using laser beams to sense motion** and removing the gold coating from long probe tips, or cantilevers, to enhance long-term force stability.*** However, removing the gold reduces the strength of the signal being measured, and using long cantilevers leads to other measurement problems such as slower response to dynamic events like protein unfolding.
The latest modification overcomes these and other issues, improving precision without loss of stability, speed, or sensitivity. JILA researchers used a focused ion beam to cut a hole in the center of a short commercial cantilever and thinned the remaining support structures, thereby reducing the cantilever's stiffness and friction near surfaces. The result is excellent long-term stability and improved short-term precision, respectively, in AFM force measurements.
JILA researchers also added a protective glass cap over the gold coating at the end of the cantilever to retain beneficial reflectivity, and then removed the remaining gold to gain force stability. The modified cantilever enables rapid, precise and stable force measurements across a broad range of operating frequencies.
"Previously, we had to average the Brownian (random) motion of our favorite cantilever for about 60 milliseconds to get a measurement that had a precision of 1 piconewton," JILA/NIST biophysicist Tom Perkins says. "Now, we can get the same precision in 1 millisecond or so."
JILA researchers demonstrated significant benefits for single molecule studies. For instance, the short, soft cantilevers can quickly measure abrupt changes in force when a protein unfolds. Protein folding is required for proper biological function and misfolding can lead to diseases such as Alzheimer's. The new cantilevers match the response of stiffer, unmodified cantilevers but with greater stability and precision. Force stability is crucial in this application because protein folding and unfolding rates are exponentially sensitive to tiny changes (smaller than 1 piconewton) in applied load. The new device also can track fleeting nanoscale events, including protein folding, over hundreds of seconds—much longer periods than previously possible. The new design should also be applicable to rapid probing of the mechanical properties of materials at the nanoscale.
Significantly, the new cantilevers are robust enough to be reused for multiple days. Moreover, JILA researchers say the new design is simple and inexpensive to make, and thus, suitable for routine use.
"Amazingly, this project was spearheaded by a talented undergraduate. We hope other groups with similarly talented students will adopt these cantilevers. We certainly are," Perkins said.
The research was supported by the National Science Foundation and NIST.
*M.S. Bull, R.M.A. Sullan, H. Li and T.T. Perkins. Improved single-molecule force spectroscopy using micromachined cantilevers. ACS Nano. Published online March 26,2014. DOI:10.1021/nn5010588
**See 2009 NIST Tech Beat article, "Making a Point: Picoscale Stability in a Room-Temperature AFM," at www.nist.gov/public_affairs/tech-beat/tb20090324.cfm#afm.
***See 2012 NIST Tech Beat article "Not-So-Precious: Stripping Gold From AFM Probes Allows Better Measurement of Picoscale Forces,"at www.nist.gov/pml/div689/afm-062712.cfm.
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NIST Issues Final Joplin Tornado Report, Begins Effort to Improve Standards and Codes
The National Institute of Standards and Technology (NIST) has released the final report on its technical investigation into the impacts of the May 22, 2011, tornado that struck Joplin, Mo. The final report is strengthened by clarifications and supplemental text suggested by organizations and individuals from across the nation in response to the request for comments on the draft Joplin report, released Nov. 21, 2013.
The revisions did not alter the investigation team's major findings or its 16 recommendations, highlighted by NIST's call for nationally accepted standards for building design and construction, public shelters and emergency communications that can significantly reduce deaths and the steep economic costs of property damage caused by tornadoes.
NIST will now work with the appropriate code development organizations to use the study's recommendations to improve model building codes and lay the foundation for nationally accepted standards. NIST also will work with organizations representing state and local governments—including building officials—to encourage them to consider implementing its recommendations. These include calls to develop and adopt:
The report also includes a number of recommendations for future research and development of technologies and strategies to advance tornado wind measurements, strengthen emergency communications, increase warning time, create more accurate tornado hazard maps and improve public response during tornado events.
The NIST Joplin tornado study was the first to scientifically study a tornado in terms of four key aspects: storm characteristics, building performance, human behavior and emergency communication—and then assess the impact of each on preventing injury or death. It also is the first to recommend that standards and model codes be developed and adopted for designing buildings to better resist tornadoes.
The tornado in Joplin was rated by the National Oceanic and Atmospheric Administration's National Weather Service (NWS) as category EF 5, the most powerful on the Enhanced Fujita scale. The massive storm impacted an area 35 kilometers (22 miles) long, destroyed some 8,000 structures in its path and killed 161 people. This makes it the single deadliest tornado in the United States in the 64 years that official records have been kept.
The complete text of the final report, Technical Investigation of the May 22, 2011, Tornado in Joplin, Missouri is available at www.nist.gov/manuscript-publication-search.cfm?pub_id=915628. Additional information about the tornado event and the NIST investigation, may be accessed at www.nist.gov/el/disasterstudies/weather/joplin_tornado_2011.cfm.
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NIST's Simple Microfluidic Devices Now Have Valves
Researchers at the National Institute of Standards and Technology (NIST) have added yet another innovation—miniature valves—to their ever-growing collection of inexpensive, easy-to-manufacture and highly efficient microfluidic devices made from plastic films and double-sided tape.
Traditionally, microfluidic devices—tiny gadgets with fluid-carrying channels used in medical diagnostics, DNA forensics and "lab-on-a-chip" chemical analyzers—have been fabricated like microchips using photolithography. A desired pattern of micrometer-sized channels and ports is created on top of a silicon substrate, which can then be replicated many times by techniques such as molding or embossing. However, the process requires specialized cleanroom equipment and can take several days to complete.
If valves are needed in the system, they traditionally have been made from silicones. Unfortunately, silicones are not the best materials to use with particular laboratory assays or for manufacturing lab-on-a-chip structures.
NIST researchers have spent the past few years developing and refining a method for making microfluidic devices using plastic films and double-sided tape that produces a functional apparatus in hours rather than days and requires only simple tools to create channels and ports. The NIST designs allow for folding the films to make multilayer or three-dimensional structures, can be used to make devices with multiple functions, and cost a fraction of traditional fabrication techniques.
But until now, there has not been a practical way to incorporate valves for dynamic control of fluid flow in these devices. In a new paper in the journal Lab on a Chip,* NIST bioengineer Gregory Cooksey and research engineer Javier Atencia describe the first-ever technique for building pneumatic microvalves into 2-D and 3-D microfluidic devices made with plastic films and tape.
Like previous NIST systems,** the new valved microfluidic device is built in layers. Narrow slits and holes are cut into pieces of double-sided tape that become tiny channels and ports when the tape is folded on itself. The microvalve is made by sandwiching a flexible membrane between two channels that intersect, one on top of the other. Applying air pressure to the top channel pushes the membrane down like a diaphragm valve, closing the lower channel.
Cooksey and Atencia have demonstrated that their novel microvalve also can work with more complex configurations of the NIST microfluidic system. These include devices with different designs for performing different tasks simultaneously, multiple layers with different flow rates, and single units with multiple "microfluidic walls" that can fold together to form a 3-D shape. In one trial with a cubed-shaped device, the researchers filled it with agar and grew nematodes (Caenorhabditis elegans) inside. Using the microchannels, ports and valves built into the cube's walls, they injected chemicals at controlled concentrations that either attracted or repelled the worms. This showed that the cube was a unique setup for studying a living organism's response to chemical stimuli within a closed environment.
*G.A. Cooksey and J. Atencia. Pneumatic valves in folded 2D and 3D fluidic devices made from plastic films and tapes. Lab on a Chip (March 2014). DOI:10.1039/C4LC00173G
**See NIST Tech Beat issue of Feb. 7, 2012, "New NIST 'Cell Assay on a Chip': Solid Results from Simple Means" at www.nist.gov/mml/bbd/fluidics-020712.cfm.
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NIST Advisory Committee 2013 Annual Report Highlights Cybersecurity and Manufacturing
The Visiting Committee on Advanced Technology (VCAT) of the National Institute of Standards and Technology (NIST) has sent its 2013 annual report to Congress. The committee focused its primary attention on NIST's role and programs in two key administration priorities—advanced manufacturing and cybersecurity.
The committee report supports NIST's ongoing and planned work in cybersecurity and recognizes the level of effort and planning NIST puts into its outreach and partnership mechanisms for cybersecurity. The report applauds the success of NIST's execution of Executive Order 13636—Improving Critical Infrastructure Cybersecurity and other collaborative efforts. The committee recommends NIST continue its involvement in the framework's future.
The report addresses NIST's broad portfolio of programs in advanced manufacturing and notes that "NIST's measurement science mission, its unique and longstanding relationship with industry, and its broad portfolio of programs make it a critical element of the Administration's efforts to strengthen manufacturing in America." It also acknowledges NIST's diverse mechanisms for partnering with other organizations, including the NIST user facilities and new Centers of Excellence, and calls them critical to NIST's success.
The VCAT was established by Congress in 1988 to review and make recommendations on NIST's policies, organization, budget and programs to support the agency in its mission to promote and support U.S. technological innovation and industrial competitiveness. For the full text of the VCAT 2013 annual report, see www.nist.gov/director/vcat/upload/FINAL-2013-VCAT-Annual-Report.pdf.
The next NIST VCAT meeting will be held in June 2014 in Gaithersburg, Md. VCAT meetings are open to the public. For more information, see www.nist.gov/director/vcat/.
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