Thursday, July 28, 2011

Environmental pollutants lurk long after they 'disappear'

The health implications of polluting the environment weigh increasingly on our public consciousness, and pharmaceutical wastes continue to be a main culprit. Now a Tel Aviv University researcher says that current testing for these dangerous contaminants isn't going far enough.

Dr. Dror Avisar, head of the Hydro-Chemistry Laboratory at TAU's Department of Geography and the Human Environment, says that, when our environment doesn't test positive for the presence of a specific drug, we assume it's not there. But through biological or chemical processes such as sun exposure or oxidization, drugs break down, or degrade, into different forms -- and could still be lurking in our water or soil.

In his lab, Dr. Avisar is doing extensive testing to determine how drugs degrade and identify the many forms they take in the environment. He has published his findings in Environmental Chemistry and the Journal of Environmental Science and Health.

Replicating nature

Drug products have been in our environment for years, whether they derive from domestic wastewater, hospitals, industry or agriculture. But those who are searching for these drugs in the environment are typically looking for known compounds -- parent drugs -- such as antibiotics, pain killers, lipid controllers, anti-psychotic medications and many more.

"If we don't find a particular compound, we don't see contamination -- but that's not true," Dr. Avisar explains. "We may have several degradation products with even higher levels of bioactivity." Not only do environmental scientists need to identify the degraded products, but they must also understand the biological-chemical processes that produce them in natural environments. When they degrade, compounds form new chemicals entirely, he cautions.

For the first time, Dr. Avisar and his research group have been working to simulate environmental conditions identical to our natural environment, down to the last molecule, in order to identify the conditions under which compounds degrade, how they degrade, and the resulting chemical products. Among the factors they consider are sun exposure, water composition, temperatures, pH levels and organic content.

Currently using amoxicillin, a common antibiotic prescribed for bacterial infections such as strep throat, as a test case, Dr. Avisar has successfully identified nine degradation products with different levels of stability. Two may even be toxic, he notes.

Classifying compounds with a fine-tooth comb

According to Dr. Avisar, who will soon expand his research to include the degraded products of chemotherapy drugs, his research is breaking new ground, extending past research. And while the attempt to catalogue the degraded products of common compounds in our environment may feel like looking for needles in haystacks, it's research that the world can't afford to ignore.

"It's important to talk about the new chemicals in our environment, derived from parent drugs. They are part of the mixture," Dr. Avisar warns. "Chemicals do not simply disappear -- we must understand what they've turned into. We are dealing with a whole new range of contaminants."

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by American Friends of Tel Aviv University.

Journal Reference:

Igal Gozlan, Adi Rotstein, Dror Avisar. Investigation of an amoxicillin oxidative degradation product formed under controlled environmental conditions. Environmental Chemistry, 2010; 7 (5): 435 DOI: 10.1071/EN10037

Pocket chemistry: DNA helps glucose meters measure more than sugar

 Glucose meters aren't just for diabetics anymore. Thanks to University of Illinois chemists, they can be used as simple, portable, inexpensive meters for a number of target molecules in blood, serum, water or food.

Chemistry professor Yi Lu and postdoctoral researcher Yu Xiang published their findings in the journal Nature Chemistry.

"The advantages of our method are high portability, low cost, wide availability and quantitative detection of a broad range of targets in medical diagnostics and environmental monitoring," Lu said. "Anyone could use it for a wide range of detections at home and in the field for targets they may care about, such as vital metabolites for a healthy living, contaminants in their drinking water or food, or potential disease markers."

A glucose meter is one of the few widely available devices that can quantitatively detect target molecules in a solution, a necessity for diagnosis and detection, but only responds to one chemical: glucose. To use them to detect another target, the researchers coupled them with a class of molecular sensors called functional DNA sensors.

Functional DNA sensors use short segments of DNA that bind to specific targets. A number of functional DNAs and RNAs are available to recognize a wide variety of targets.

They have been used in the laboratory in conjunction with complex and more expensive equipment, but Lu and Xiang saw the potential for partnering them with pocket glucose meters.

The DNA segments, immobilized on magnetic particles, are bound to the enzyme invertase, which can catalyze conversion of sucrose (table sugar) to glucose. The user adds a sample of blood, serum or water to the functional DNA sensor to test for drugs, disease markers, contaminants or other molecules. When the target molecule binds to the DNA, invertase is released into the solution. After removing the magnetic particle by a magnet, the glucose level of the sample rises in proportion to the amount of invertase released, so the user then can employ a glucose meter to quantify the target molecule in the original sample.

"Our method significantly expands the range of targets the glucose monitor can detect," said Lu, who also is affiliated with the Beckman Institute for Advanced Science and Technology and with the Frederick Seitz Materials Research Lab at U. of I. "It is simple enough for someone to use at home, without the high costs and long waiting period of going to the clinics or sending samples to professional labs."

The researchers demonstrated using functional DNA with glucose meters to detect cocaine, the disease marker interferon, adenosine and uranium. The two-step method could be used to detect any kind of molecule that a functional DNA or RNA can bind.

Next, the researchers plan to further simplify their method, which now requires users to first apply the sample to the functional DNA sensor and then to the glucose meter.

"We are working on integrating the procedures into one step to make it even simpler," Lu said. "Our technology is new and, given time, it will be developed into an even more user-friendly format."

The U.S. Department of Energy, the National Institutes of Health and the National Science Foundation supported this work.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Illinois at Urbana-Champaign, via EurekAlert!, a service of AAAS.

Journal Reference:

Yu Xiang, Yi Lu. Using personal glucose meters and functional DNA sensors to quantify a variety of analytical targets. Nature Chemistry, 2011; DOI: 10.1038/nchem.1092

Shining a light on the elusive 'blackbody' of energy research: Designer material has potential applications for thermophotovoltaics

 A designer metamaterial has shown it can engineer emitted "blackbody" radiation with an efficiency beyond the natural limits imposed by the material's temperature, a team of researchers led by Boston College physicist Willie Padilla report in the current edition of Physical Review Letters.

A "blackbody" object represents a theorized ideal of performance for a material that perfectly absorbs all radiation to strike it and also emits energy based on the material's temperature. According to this blackbody law, the energy absorbed is equal to the energy emitted in equilibrium.

The breakthrough reported by Padilla and colleagues from Duke University and SensorMetrix, Inc., could lead to innovative technologies used to cull energy from waste heat produced by numerous industrial processes. Furthermore, the human-made metamaterial offers the ability to control emissivity, which could further enhance energy conversion efficiency.

"For the first time, metamaterials are shown to be able to engineer blackbody radiation and that opens the door for a number of energy harvesting applications," said Padilla. "The energy a natural surface emits is based on its temperature and nothing more. You don't have a lot of choice. Metamaterials, on the other hand, allow you to tailor that radiation coming off in any desirable manner, so you have great control over the emitted energy."

Researchers have long sought to find the ideal "blackbody" material for use in solar or thermoelectric energy generation. So far, the hunt for such a class of thermal emitters has proved elusive. Certain rare earth oxides are in limited supply and expensive, in addition to being almost impossible to control. Photonic crystals proved to be inferior emitters that failed to yield significant efficiencies.

Constructed from artificial composites, metamaterials are designed to give them new properties that exceed the performance limits of their actual physical components and allow them to produce "tailored" responses to radiation. Metamaterials have exhibited effects such as a negative index of refraction and researchers have combined metamaterials with artificial optical devices to demonstrate the "invisibility cloak" effect, essentially directing light around a space and masking its existence.

Three years ago, the team developed a "perfect" metamaterial absorber capable of absorbing all of the light that strikes it thanks to its nano-scale geometric surface features. Knowing that, the researches sought to exploit Kirchoffs's law of thermal radiation, which holds that the ability of a material to emit radiation equals its ability to absorb radiation.

Working in the mid-infrared range, the thermal emitter achieved experimental emissivity of 98 percent. A dual-band emitter delivered emission peaks of 85 percent and 89 percent. The results confirmed achieving performance consistent with Kirchoff's law, the researchers report.

"We also show by performing both emissivity and absorptivity measurements that emissivity and absorptivity agree very well," said Padilla. "Even though the agreement is predicted by Kirchoff's law, this is the first time that Kirchoff's law has been demonstrated for metamaterials."

The researchers said altering the composition of the metamaterial can results in single-, dual-band and broadband metamaterials, which could allow greater control of emitted photons in order to improve energy conversion efficiency.

"Potential applications could lie in energy harvesting area such as using this metamaterial as the selective thermal emitter for thermophotovoltaic (TPV) cells," said Padilla. "Since this metamaterial has the ability to engineer the thermal radiation so that the emitted photons match the band gap of the semiconductor -- part of the TPV cell -- the converting efficiency could be greatly enhanced.

In addition to Padilla, the research team included BC graduate student Xianliang Liu, Duke University's Nan Marie Jokerst and Talmage Tyler and SensorMetrix, Inc., researchers Tatiana Starr and Anthony F. Starr.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Boston College, via EurekAlert!, a service of AAAS.

Journal Reference:

Xianliang Liu, Talmage Tyler, Tatiana Starr, Anthony Starr, Nan Jokerst, Willie Padilla. Taming the Blackbody with Infrared Metamaterials as Selective Thermal Emitters. Physical Review Letters, 2011; 107 (4) DOI: 10.1103/PhysRevLett.107.045901

Molecules 'light up' Alzheimer's roots: Light-switching complex attaches itself to amyloid proteins

 A breakthrough in sensing at Rice University could make finding signs of Alzheimer's disease nearly as simple as switching on a light.

The technique reported in the should help researchers design better medications to treat the devastating disease.

The lab of Rice Angel Martí is testing metallic molecules that naturally attach themselves to a collection of beta called fibrils, which form plaques in the brains of Alzheimer's sufferers. When the molecules, complexes of dipyridophenazine ruthenium, latch onto amyloid fibrils, their photoluminescence increases 50-fold.

The large increase in fluorescence may be an alternative to molecules currently used to study amyloid fibrils, which researchers believe form when misfolded proteins begin to aggregate. Researchers use changes in fluorescence to characterize the protein transition from disordered monomers to aggregated structures.

Nathan Cook, a former Houston high school teacher and now a Rice graduate student and lead author of the new paper, began studying beta amyloids when he joined Martí's lab after taking a Nanotechnology for Teachers course taught by Rice Dean of Undergraduates and Professor of Chemistry John Hutchinson. Cook's goal was to find a way to dissolve amyloid fibrils in Alzheimer's patients.

But the Colorado native's research led him down a different path when he realized the ruthenium complexes, the subject of much study in Martí's group, had a distinctive ability to luminesce when combined in a solution with amyloid fibrils.

Such fibrils are simple to make in the lab, he said. Molecules of beta amyloid naturally aggregate in a solution, as they appear to do in the brain. Ruthenium-based molecules added to the amyloid monomers do not fluoresce, Cook said. But once the amyloids begin to aggregate into fibrils that resemble "microscopic strands of spaghetti," hydrophobic parts of the metal complex are naturally drawn to them. "The microenvironment around the aggregated peptide changes and flips the switch" that allows the metallic complexes to light up when excited by a spectroscope, he said.

Thioflavin T (ThT) dyes are the standard sensors for detecting amyloid fibrils and work much the same way, Marti said. But ThT has a disadvantage because it fluoresces when excited at 440 nanometers and emits light at 480 nanometers -- a 40-nanometer window.

That gap between excitation and emission wavelengths is known as the Stokes shift. "In the case of our metal complexes, the Stokes is 180 nanometers," said Martí, an assistant professor of chemistry and bioengineering. "We excite at 440 and detect in almost the near-infrared range, at 620 nanometers.

"That's an advantage when we want to screen drugs to retard the growth of amyloid fibrils," he said. "Some of these drugs are also fluorescent and can obscure the fluorescence of ThT, making assays unreliable."

Cook also exploited the metallic's long-lived fluorescence by "time gating" spectroscopic assays. "We specifically took the values only from 300 to 700 nanoseconds after excitation," he said. "At that point, all of the fluorescent media have pretty much disappeared, except for ours. The exciting part of this experiment is that traditional probes primarily measure fluorescence in two dimensions: intensity and wavelength. We have demonstrated that we can add a third dimension -- time -- to enhance the resolution of a fluorescent assay."

The researchers said their complexes could be fitting partners in a new technique called fluorescence lifetime imaging microscopy, which discriminates microenvironments based on the length of a particle's fluorescence rather than its wavelength.

Cook's goal remains the same: to treat Alzheimer's -- and possibly such other diseases as Parkinson's -- through the technique. He sees a path forward that may combine the ruthenium complex's ability to target and other molecules' potential to dissolve them in the brain.

"That's something we are actively trying to target," Martí said.

More information: http://pubs.acs.or … 21/ja204656r

Provided by Rice University (news : web)

New material could offer hope to those with no voice

In 1997, the actress and singer Julie Andrews lost her singing voice following surgery to remove noncancerous lesions from her vocal cords. She came to Steven Zeitels, a professor of laryngeal surgery at Harvard Medical School, for help.

Zeitels was already starting to develop a new type of material that could be implanted into scarred to restore their normal function. In 2002, he enlisted the help of MIT’s Robert Langer, the David H. Koch Institute Professor in the Department of Chemical Engineering, an expert in developing polymers for biomedical applications.

The team led by Langer and Zeitels has now developed a polymer gel that they hope to start testing in a small clinical trial next year. The gel, which mimics key traits of human vocal cords, could help millions of people with voice disorders — not just singers such as Andrews and Steven Tyler, another patient of Zeitels’.

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Video: Watch how the gel mimics human vocal cords

About 6 percent of the U.S. population has some kind of voice disorder, and the majority of those cases involve scarring of the vocal cords, says Sandeep Karajanagi, a former MIT researcher who developed the gel while working as a postdoc in the Langer lab. Many of those are children whose cords are scarred from intubation during surgery, while others are victims of laryngeal cancer.

Other people who could benefit are those with voices strained from overuse, such as teachers. “This would be so valuable to society, because every time a person loses their voice, say, a teacher or a politician, all of their contributions get lost to society, because they can’t communicate their ideas,” Zeitels says.

‘A mechanical problem’

When Langer and his lab joined the effort in 2002, they considered two different approaches: creating a synthetic material that would mimic the properties of vocal cords, or engineering artificial vocal-cord tissue. Both approaches have potential, Langer says, but the team decided to pursue a synthetic material because it would likely take less time to reach patients. “Making a totally natural vocal cord is a more long-term project,” he says.

Some doctors treat vocal-fold scars with materials normally used in dermatology or plastic surgery, in hopes of softening the vocal cords, but those don’t work for everyone, and the effects don’t last long, says Nathan Welham, assistant professor of otolaryngology at the University of Wisconsin School of Medicine.

“Scarred vocal cords are really hard to fix,” says Welham, who is not involved in this project. “People have tried this and that, but there’s really no commonly used, available approach that treats the inherent problem of scarring in the vocal folds.”

Other researchers have tried developing drugs that would dissolve the scar tissue, but the MIT/Harvard team decided on a different approach.

“What we did differently is we looked at this as a mechanical problem that we need to solve. We said, ‘Let’s not look at the scar itself as a problem, let’s think of how we can improve the voice despite the presence of the scar tissue,’” says Karajanagi, who is now an instructor of surgery at Harvard Medical School and a researcher at the Center for Laryngeal Surgery and Voice Rehabilitation at Massachusetts General Hospital.

The team chose polyethylene glycol (PEG) as its starting material, in part because it is already used in many FDA-approved drugs and medical devices.

By altering the structure and linkage of PEG molecules, the researchers can control the material’s viscoelasticity. In this case, they wanted to make a substance with the same viscoelasticity as human vocal cords. Viscoelasticity is critical to voice production because it allows the vocal cords to vibrate when air is expelled through the lungs.

For use in vocal cords, the researchers created and screened many variations of PEG and selected one with the right viscoelasticity, which they called PEG30. In laboratory tests, they showed that the vibration that results from blowing air on a vocal-fold model of PEG30 is very similar to that seen in human vocal folds. Also, tests showed that PEG30 can restore vibration to stiff, non-vibrating vocal folds such as those seen in human patients suffering from vocal-fold scarring.

Under FDA guidelines, the gel would be classified as an injectable medical device, rather than a drug. The researchers, who have published more than a dozen papers on their voice-restoration efforts, have applied for a patent on the material and are working toward FDA approval. If approved for human use, the gel would likely have to be injected at least once every six months, because it eventually breaks down.

The project is funded by the Institute of Laryngology and Voice Restoration, which consists of patients whose mission is to support and fund research and education in treating and restoring voice. Julie Andrews is the foundation’s honorary chairwoman.

Safety tests

In a study recently published in the Annals of Otology, Rhinology & Laryngology, the researchers tested the biocompatibility of the gel by injecting it into the healthy vocal folds of dogs. After four months, the treated dogs showed no damage to their vocal cords.

“That gives us exciting data that this has a real good chance of working in people without creating damage,” Karajanagi says, adding that clinical trials will be needed to confirm this.

The researchers are now working on developing a manufacturing process that will generate enough of the material, in high quality, for human trials. They hope to run a trial of about 10 patients next year. They are also working on developing methods for injecting the material at the right location to treat human vocal cords.

Such gels could find other medical applications, by varying the chemical properties of the PEG, Langer says. “We think of what we do as ‘designer polymers,’” he says. “We can modify them depending on the problem we’re trying to solve.”
This story is republished courtesy of MIT News (, a popular site that covers news about MIT research, innovation and teaching.

Provided by Massachusetts Institute of Technology (news : web)