Food Safety
Biosensor that detects pathogens in poultry and other foods being tested in in metro Atlanta
Recent incidences of contaminated meat in grocery stores and restaurants have heightened consumer concern. But people who eat meat may rest easier if a new bacterial-sensing device being field tested this winter delivers the accurate and speedy results, plus the low costs its developers predict.
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The device, called a biosensor, was developed at the Georgia Tech Research Institute (GTRI). It can simultaneously identify species and determine concentrations of multiple pathogens — including the deadly E. coli 0157:H7 and Salmonella — in food products in less than two hours while operating on a processing plant floor.
"The most significant advantage of the biosensor is the time reduction in assessing the presence of contamination," says Nile Hartman, a biosensor developer and senior research engineer at GTRI.
Lab tests for E. coli and Salmonella in meat are required by federal regulators, but there are no standards for bacterial concentration. Most companies perform laboratory tests, but they are costly and slow — sometimes not even yielding results for 48 to 72 hours. That delay requires that food products remain stored in warehouses for longer periods.
"The biosensor will help in overall quality control in food processing plants," says collaborator Dr. Paul Edmonds, a professor of biology at Georgia Tech. "It would minimize the chance of the final product being contaminated."
Georgia Tech researchers — in collaboration with Dr. Robert Brackett, a professor at the University of Georgia's Center for Food Safety and Quality Enhancement in Griffin, Ga. — have been developing and testing the biosensor in their laboratories for about four years. Recently, they began a field test at Gold Kist in Carrollton, Ga., just west of Atlanta.
Laboratory tests have proven the biosensor is extremely sensitive, meaning it can detect pathogens at minute levels of 500 cells per milliliter. Researchers believe they can improve that sensitivity to 100 cells per milliliter. Current laboratory methods only achieve sensitivity levels of 5,000 cells per milliliter, and they usually take from eight to 24 hours to yield results. In addition, lab equipment costs $12,000 to $20,000 per instrument compared to an estimated $1,000 to $5,000 for a biosensor.
But before the biosensor gains market acceptance, it must prove its effectiveness in the field test. The first phase will last three to six months, and researchers will compare their biosensor test results with the company's lab findings.
"One of the things we will be looking at is reproducability of results," Hartman says. "We will split a sample for testing with both of the technologies (the biosensor and lab tests). For every 1,000 tests we do, we will look for the variation between results of the two methods."
The biosensor can simultaneously detect 12 different pathogens, but researchers are concentrating on six bacterial species for now. They are Salmonella, E. coli 0157:H7, generic E. coli, Listeria monocytogenes, Campylobacter jejuni and Yersenia enterocolitica (found primarily in red meat). All of these pathogens are associated with stomach illness in humans. When detected, they are usually found in meat, but sometimes they occur in produce.
The biosensor operates with three primary components — integrated optics, immunoassay techniques and surface chemistry tests. It indirectly detects pathogens by combining immunoassays with a chemical-sensing scheme. In the immunoassay, a series of antibodies selectively recognize target bacteria. The "capture" antibody is bound to the biosensor and captures the target bacteria as it passes nearby. A set of "reporter" antibodies, which bind with the same target pathogen, contains the enzyme urease, which breaks down urea that is then added and subsequently produces ammonia. The chemical sensor detects the ammonia, affecting the optical properties of the sensor and signaling changes in transmitted laser light. These changes reveal both the presence and concentration of specific pathogens in a sample at extremely minute levels.
"If pathogens are found with the biosensor, then food processors can make decisions more quickly about applying treatments, such as antiseptics," Edmonds says. "Or they might divert those products to cooking operations, which would kill the pathogens. And companies could modify their sanitation plans."
The integrated optic interferometric sensor technology upon which the biosensor is based has already been patented by Hartman and the Georgia Tech Research Corporation. But commercialization for the biosensor is still some time away, researchers say. After the field test at Gold Kist is completed, researchers plan to return to their laboratories to further refine the technology.
— Jane M. Sanders
The full-text news release version of this article is available at www.gtri.gatech.edu/res-news/SENSOR.html. For more information, contact Nile Hartman, GTRI, Atlanta, GA, 30332-0825. (Telephone: 404-894-3503) (E-mail: nile.hartman@gtri.gatech.edu)
The Cost of Cleaning the Air
Study shows permit application costs lower than expected — with key benefits
A study of some 500 U.S. manufacturers found that the cost of applying for air emissions permits under new national regulations was lower than industry estimates. The Georgia Institute of Technology research is believed to be the first detailed examination of business costs involved in applying for permits under Title V of the 1990 Clean Air Act Amendments.
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The study also produced one surprising result: three-fourths of the responding companies saw important business benefits in the new regulations.
Title V requires companies that emit certain amounts of air pollutants to document their emission sources, air pollution control equipment and regulatory requirements in a single document. By providing a centralized source of information, the legislative goals were to help regulators enforce air quality standards, to help companies understand and comply with them, and to help citizens monitor industry compliance.
"Before Title V was implemented, industry officials were concerned that the law would be costly, with no benefit to them," says Dr. Barry Bozeman, lead author of the study and a researcher in Georgia Tech's State Data and Research Center. "But the study results show that this is not the case. More often than not, the cost was modest, and complying companies found positive aspects to the law."
Corporate environmental managers responding to the survey reported their firms spent an average of $113 per employee to apply for the air emissions permits. For an average 566-person company, that translates to $63,958 per facility. Applying these costs to the estimated 20,000 facilities covered by Title V suggests the total bill for national compliance will be about $1.3 billion.
These numbers are lower than the estimates reported last spring by an industry group, says Leisha DeHart-Davis, a co-author of the study and a research associate in Georgia Tech's Air Quality Laboratory. An April 1999 report released by Washington law firm Morgan, Lewis & Bockius, LLP, estimated that the average company would spend $100,000 per facility, with a total bill of $2 billion for the 20,000 locations.
The Georgia Tech study, sponsored by the U.S. Environmental Protection Agency (EPA), provides a direct measure of permit application costs for manufacturers. DeHart-Davis cautioned that the costs reported are a "moving target" because the permitting work continues in some cases — though some 97 percent of respondents had filed applications at the time the survey was conducted.
The most significant direct costs were for outside consultants, but also included time of company personnel and expenses for new administrative systems.
The researchers used a mail survey to contact environmental managers at 1,614 randomly selected companies in Wisconsin, Oregon, Georgia and South Carolina. These states were chosen to provide a cross-section of industry types and sizes. State response rates for the confidential surveys ranged from 31 percent to 43 percent, and yielded 542 completed questionnaires.
The researchers also contacted state environmental regulatory agencies to gain their assessment of the regulations. They obtained 90 agency responses.
— John Toon
The full-text news release version of this article is available at www.gtri.gatech.edu/res-news/TITLEV.html. For more information, contact Leisha DeHart-Davis, Air Quality Laboratory, Georgia Tech, Atlanta, GA 30332-0340. (Telephone: 404-894-9345) (E-mail: leisha.davis@aql.eas.gatech.edu)
Measuring the Smallest Air Pollutants
Scientists conduct intensive study of fine particulate matter.
Atmospheric scientists led by Georgia Institute of Technology researchers are determining the best ways to measure the fine particulate matter that is polluting the nation's air, particularly in large urban areas.
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Particulate matter, which is federally regulated, has raised concern recently because of numerous studies linking it to serious health problems. Fine particulate matter (called PM 2.5 because it is less than 2.5 microns in diameter or 30 times smaller than the diameter of a human hair) includes soot, dust, aerosols, metals and sulfates primarily emitted by vehicles and industrial sources. It contributes to the smog so common in American cities.
In the first of two "SuperSite" studies initiated by the U.S. Environmental Protection Agency (EPA), about 60 scientists from the Georgia Institute of Technology and other institutions converged last summer at an Atlanta air quality research facility owned by Georgia Power. They measured PM 2.5 around the clock for one whole month. They are now analyzing that data and preparing a preliminary report for delivery to EPA this summer.
"We are trying to determine how to measure the concentration and composition of fine particulate matter in the atmosphere and the types of instruments best suited to do that," says Dr. William Chameides, a professor in the Georgia Tech School of Earth and Atmospheric Sciences and head of the SuperSite study. "We need to do this to understand the health effects and the sources, and to monitor compliance with EPA standards."
Specifically, the research team expects to:
- evaluate emerging and/or state-of-the-science PM measurements.
- compare and contrast similar and dissimilar PM measurements.
- evaluate the precision, accuracy and completeness of information that can be gained
from the planned EPA network of SuperSites.
- evaluate the scientific information gained by combining various independent and complementary PM measurements.
- address various scientific issues and their ozone- and PM-related policy implications with the database they are developing.
"It's possible that controlling one pollutant without controlling the other might make one worse," Chameides says. "The trick is to fully understand how they interact so you can come up with a strategy to deal with both of them."
Chameides is spearheading the SuperSite study under the auspices of the ongoing Southern Oxidants Study (SOS), which involves about 20 universities and agencies. EPA is providing the primary funding for the Atlanta SuperSite study. Other funds are coming from the U.S. Department of Energy, Tennessee Valley Authority, and the National Oceanic and Atmospheric Administration. Georgia Power and its parent, Southern Company, are providing the research facility and some equipment.
— Jane M. Sanders
The full-text news release version of this article is available at www.gtri.gatech.edu/res-news/SUPER.html. For more information, contact Dr. William Chameides, School of Earth and Atmospheric Sciences, Georgia Tech, Atlanta, GA 30332-0340. (Telephone: 404-894-1749) (E-mail: william.chameides@eas.gatech.edu). Also, you may visit the Atlanta SuperSite Study Web site at: www-wlc.eas.gatech.edu/supersite.
Charging Through DNA Like a "Slinky"
Researchers suggest new mechanism to explain DNA charge transfer process.
The compression and expansion of a "Slinky" — a child's toy made from a large spring — is how a Georgia Institute of Technology scientist describes his research team's new theory of the charge transport mechanism in DNA.
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The new charge transport model, dubbed "phonon-assisted polaron-like hopping," could help scientists better understand the mechanisms by which DNA — the building blocks of life — is damaged and repaired. It could also lead to development of new diagnostic techniques based on recognition of charge transfer characteristics, and could one day open up applications for one-dimensional DNA "wires" able to assemble themselves into tiny circuits for micromachines.
The Georgia Tech research team proposed in a report published inn the Proceedings of the National Academy of Sciences that electrical charge moves through DNA bases by creating temporary distortions in base structure as the strands naturally flex. The work suggests that the charge transport process is much more complicated than previously believed.
"It's not at all like a conductor or a wire," says Dr. Gary B. Schuster, lead author of the paper and dean of Georgia Tech's College of Sciences. "We think this answers the question of how charge transfers through DNA, at least in a broad-brush way."
Schuster explains the Slinky comparison: "When you inject a charge into DNA, the DNA responds by changing its structure to accommodate that charge. That change in structure distributes the charge over several of the base pairs in the DNA. That creates a local distortion in the DNA. That local distortion, just like the compression in the Slinky toy, can move in the DNA as the structure moves normally in stretching, bending and rotating."
The distortion, known as a polaron, can carry the charge a distance of up to a few hundred Angstroms. The charge transfer stops when it encounters a specific pairing of the DNA structure known as a GG step — the location where two guanine bases exist side by side. The charge trapped at this location then oxidizes the guanine, causing damage that can lead to genetic mutations.
An experiment conducted in Schuster's lab by Dr. Paul T. Henderson — now a post-doctoral student at the Massachusetts Institute of Technology — showed the charge moves rapidly through a duplex strand of DNA with an efficiency that is independent of the base sequence.
Using a tether just four atoms long, Henderson first created a linkage between an anthraquinone and a specific location on a 60-base DNA segment. He then irradiated the anthraquinone with ultraviolet light, causing it to inject a radical cation (a positively charged ion) into the duplex chain of DNA base pairs. He measured the progress of the cation through the DNA by observing where it damaged the strand at GG steps.
The structural independence and efficiency of the transport process were unexpected and could not be explained by existing theories of electron transport. Schuster believes two "averaging" mechanisms inherent in the polaron process tend to even out the speed of the charge transport. This new mechanism is possible only because of the dynamic nature of the DNA structure.
The research team included Denise Jones, Gregory Hampikian and Youngzhi Kan, all of Georgia Tech. The National Institutes of Health and the National Science Foundation sponsored the research.
— John Toon
The full-text news release version of this article is available at www.gtri.gatech.edu/res-news/CHARGE.html. For more information, contact Dr. Gary Schuster, College of Sciences, Georgia Tech, Atlanta, GA 30332-0365. (Telephone: 404-894-0202) (E-mail: gary.schuster@cos.gatech.edu)
Where Oil and Water Mix
Researchers explore use of "near-critical" water for replacing conventional solvents.
Under normal conditions, oil and water don't mix. But "near-critical" water — very hot, but still liquid water at temperatures of 250 to 300 degrees C and pressures of 1,000 psi — can be a good solvent for both salts and non-polar organic compounds, including oils. This makes ordinary water an ideal reaction solvent for certain chemical processes.
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"Our goal is to do the technical work to see where we can use this as a replacement process, and to couple that with an economic analysis to see where this can be used profitably," says Dr. Charles Eckert, director of Georgia Tech's Specialty Separations Center and a professor in the School of Chemical Engineering.
Certain types of chemical reactions operate well in near-critical water and would be top candidates for the new process, he says. Use of water as a solvent could also be attractive for processes in which all traces of hazardous solvents must be removed — such as in pharmaceutical manufacturing.
In addition to Eckert, the research team included Dr. Charles Liotta, Georgia Tech's Vice-Provost for Research and a professor of chemistry; Dr. Roger Glaser, a post-doctoral fellow; and Ph.D. students James Brown and Shane Nolen.
"Water is about as ideal a solvent as you could imagine," Eckert notes. "Not only is it benign, but the public perception is that it is benign."
Both the benign nature of water and its potential as a powerful solvent depend on its unique system of hydrogen bonding. As water is heated, its normally strong hydrogen bonds weaken, allowing dissociation that forms acidic hydronium ions and basic hydroxide ions. At the near-critical stage, the amount of dissociation is three times what it would be at normal temperatures and pressures.
"Simply from the dissociation of water into acidic and basic ions, a much larger amount of acid and base is present in near-critical water," Eckert explains. "We can use these to run acid-catalyzed and base-catalyzed reactions without the addition of mineral acid."
Near-critical water has properties similar to those of polar organic solvents like ethyl alcohol or acetone. Its dielectric constant drops from 80 to 20, and its density drops from one gram per cubic centimeter to 7/10 gram per cubic centimeter.
"What all this means is that molecules that would normally not be soluble in the same solvent become soluble together in near-critical water and can be processed together," he says. "Virtually all organics are soluble or completely miscible in water above about 250 degrees C."
Dissolving organics in near-critical water allows some reactions now done in multiple phases to be completed in a single aqueous phase. This eliminates high cost and energy associated with stirring rapidly and separating unwanted additives from the final product.
— John Toon
The full-text news release version of this article is available at www.gtri.gatech.edu/res-news/CRITICAL.html. For more information, contact Dr. Charles Eckert, School of Chemical Engineering, Georgia Tech, Atlanta, GA 30332-0100. (Telephone: 404-894-7070) (E-mail: charles.eckert@che.gatech.edu).
MRI for Carpets & Fabrics
Researchers apply medical diagnostic tool to a wide range of industrial challenges.
Magnetic resonance imaging (MRI) has significantly enhanced diagnostic medicine by allowing physicians to look deep inside the human body without using a scalpel.
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Now, researchers at the Georgia Institute of Technology are applying the technique to a broad range of industrial processes, using MRI to watch carpet dry from the inside, peer into peanut shells, and study how fabrics wick moisture away from the body. The work could lead to faster and more efficient drying processes, carpet less prone to mildew and fabrics that are more comfortable to wear.
"The advantages for us are the same as for the medical community," explains Dr. Haskell W. Beckham, associate professor in Georgia Tech's School of Textile and Fiber Engineering. "The technique is non-invasive; we don't need special tracers, dyes or contrast agents for image capture; and information can be extracted from arbitrary locations inside opaque objects."
The Georgia Tech researchers are believed to be the only ones in the world using MRI to study textile drying.
Using the instrumentation in Georgia Tech's Nuclear Magnetic Resonance Center, Beckham and his collaborators have examined how moisture flows into carpets, measured where it accumulates and monitored its removal as a function of time during conditions simulating industrial drying processes. They've also seen how surface fluorocarbon finishes affect the way water penetrates the carpet.
While such information on fluid behavior within textiles is important in itself, it also provides a means for describing the internal structure of the material. This is especially useful for soft porous substrates such as textiles; the traditional method requires physically cutting the sample into thin slices and then examining each slice using microscopy. Soft materials are easily deformed during such sample preparations.
The MRI technique has the unique ability to follow fluid distribution in real time. "For carpets and textiles, you can't get this information any other way," Beckham says. "Simply stated, all we do is wet the sample, put it in the instrument and take snapshot images as a function of drying time."
Beckham's collaborators in the work are Dr. Wallace W. Carr and Dr. Johannes Leisen of Georgia Tech, and Dr. Hubert Kinser of Dalton College.
Magnetic resonance imaging uses powerful magnetic fields to align the magnetic moments of the nuclei in molecules. Following an excitation pulse of electromagnetic radiation, the nuclei return to their original state and give off a signal that can be measured and analyzed, showing scientists where the molecules are located.
The Georgia Tech MRI instrument is much smaller than a hospital machine designed for imaging the human body. Beckham and his collaborators study a sample about one inch in diameter, imaging it repeatedly to see how moisture levels change over time as they apply heated air.
— John Toon
The full-text news release version of this article is available at www.gtri.gatech.edu/res-news/MRI.html. For more information, contact Dr. Haskell Beckham, School of Textile and Fiber Engineering, Georgia Tech, Atlanta, GA 30332-0295. (Telephone: 404-894-4198) (E-mail: haskell.beckham@textiles.gatech.edu)
Also see Research Links news stories.
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