Chemical Education Today
Reports from Other Journals
Research Advances by Angela G. King
“Powerhouses” from Living Cells Power a New Explosives Detector
1. Germain, Marguerite N.; Arechederra, Robert L.; Minteer, Shelley D. Nitroaromatic Actuation of Mitochondrial Bioelectrocatalysis for Self-Powered Explosive Sensors. J. Am. Chem. Soc. 2008, 130, 15272–15273. 2. This Journal has previously published an article on the chemistry behind fuel cell design. See J. Chem. Educ. 1983, 60, 320. 3. More information on Minteer’s research can be found online at http://chemistry.slu.edu/Faculty_Staff/Minteer/ (accessed Feb 2009). 4. Fuel Cells 2000 at http://www.fuelcells.org/ced/education.html (accessed Feb 2009) has great resources for science educators interested in incorporating fuel cells into their classes or for students looking for science fair projects or internships. 542
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Reactivation After Addition of Nitroaromatic
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Borrowing the technology that living cells use to produce energy, researchers in Missouri have developed a tiny, selfpowered sensor for rapid detection of hidden explosives. The experimental sensor, about the size of a postage stamp, represents the first of its kind to be powered by mitochondria, the microscopic “powerhouses” that provide energy to living cells. In the new study, Shelley Minteer, Marguerite Germain, and Robert Arechederra point out that today’s explosives detectors are expensive, bulky, and complex. Society needs smaller, cheaper, simpler detection devices, based on technology that might be incorporated into cell phones and portable digital music players. The scientists describe development of an experimental sensor built from a special biofuel cell, essentially a battery-like device consisting of a thin layer of mitochondria sandwiched between a carbon-based electrode and a gas-permeable electrode. Minteer’s team had previously constructed a biofuel cell that produced electricity from mitochondrial oxidation of a fuel such as pyruvate. The resulting cell could be turned off by the addition of a select enzyme inhibitor, such as oligomycin that “turns off ” the mitochondrial power plant. The researchers’ new work was built upon this foundation, exploiting the ability of nitroaromatic compounds to serve as decouplers of mitochondrial inhibition. Thus, they developed sensors whose power supply, the mitochondria-based fuel cell, was initially turned off by the addition of oligomycin. When nitroaromatic compounds are present, they decouple the enzyme inhibition and the biofuel cell will produce power that can be measured or used to signal the presence of the nitroaromatic (Figure 1). This is important because nitroaromatic compounds are common explosives that could be used by terrorists. In laboratory studies that use nitrobenzene as a test compound, the sensor showed a significant boost in electrical power in the presence of the substance, demonstrating the sensor’s potential for detecting TNT and related explosives, the researchers say.
Oligomycin Inhibition of Bioelectrocatalysis
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Figure 1. Scientists have developed a stamp-sized sensor for detecting hidden explosives. The sensor is powered by mitochondria, which provide energy to living cells. Reprinted with permission from J. Am. Chem. Soc. 2008, 130, 15272–15273. Copyright 2008 American Chemical Society.
Microcapsules Act As “Roach Motel” To Kill Harmful Bacteria Researchers in New Mexico and Florida report development of microscopic particles that act as chemical booby traps for bacteria. The traps attract and kill more than 95% of nearby bacteria, including microbes responsible for worrisome hospitalbased infections. The scientists describe their discovery as tiny “roach motels” for harmful bacteria. In a report in the inaugural issue of the American Chemical Society’s new journal, ACS Applied Materials & Interfaces, David G. Whitten of the University of New Mexico and Kirk S. Schanze of the University of Florida, working together with a team of faculty and graduate student collaborators, point out that bacterial contamination of medical devices causes up to 1.4 million deaths per year. In addition, bacteria are becoming more resistant to standard disinfection methods. Scientists are also increasingly concerned about the possibility of intentional release of harmful bacteria by terrorists. As a result, researchers are attempting to develop new and improved methods of disinfection. The research team has made great progress toward this goal with the development of light-activated, hollow microcapsules composed of an organic conducting polymer. Alternating layers of oppositely charged poly(phenylene ethylene)-type conjugated polyelectrolytes (CPEs) were fabricated by deposition onto a spherical MnCO3 template particle, layer upon layer. The template particles were then dissolved with a solution of the chelator
Journal of Chemical Education • Vol. 86 No. 5 May 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
Chemical Education Today
Figure 2. (A) Confocal microscope image of a μRM cluster 10 min after introduction into a solution of P. aeruginosa (107/mL) kept in the dark. (B) Interior image of a μRM cluster, showing bacteria entrapped within the cluster and killed after 1 h of exposure to white light. Reprinted with permission from ACS Appl. Mater. Interfaces 2009, 1, 48–52. Copyright 2009 American Chemical Society.
ethylenediaminetetracetic acid. The resulting hollow capsules showed fluorescence from CPE layers, and microscopy revealed creases in the capsule walls, indicating flexibility. The researchers then tested the ability of the prepared capsules, or micro “Roach Motels” (μRM) to trap and hold bacteria. In controlled laboratory tests with one of the deadliest and most common hospital-based pathogens, Pseudomonas aeruginosa, or Cobetia marina, a type of bacterium that fouls the hulls of ships and other marine equipment, interactions between the μRM and the microorganisms were monitored with confocal fluorescence microscopy. The antibacterial microcapsules attracted and captured bacteria. Bacterial viability was assessed using stains that penetrate cells and produce red emissions for live cells or green emissions for dead cells. The results demonstrated that more than 95% of the exposed bacteria are killed by 15–60 minutes of exposure to visible light (Figure 2). Researchers hypothesize that the μRM kill bacteria through the production of singlet oxygen, since earlier work has shown that CPEs are effective sensitizers of singlet oxygen. The increase in speed and effectiveness of the new μRM stems from a proposed greater efficiency in irreversibly trapping bacteria. The light-activated capsules, essentially deathtraps for bacteria, can be applied to a variety of surfaces, including medical equipment. More Information 1. Corbitt, Thomas S.; Sommer, Jonathan R.; Chemburu, Sireesha; Ogawa, Katsu; Ista, Linnea K.; Lopez, Gabriel P.; Whitten, David G.; Schanze, Kirk S. Conjugated Polyelectrolyte Capsules: LightActivated Antimicrobial Micro “Roach Motels”. ACS Appl. Mater. Interfaces 2009, 1, 48–52. 2. Schanze’s research projects, including more details on the described research, can be found online at http://web.chem.ufl.edu/people/ faculty/research.php?id=4 (accessed Feb 2009). 3. JCE has previously published two papers on the incorporation of polyelectrolytes into physical chemistry. See J. Chem. Educ. 1980, 57, 902 and 1979, 56, 481.
Reducing the Energy Demand of Water Purification Water and energy are two resources on which modern society depends. As demands for these increase, researchers look to alternative technologies that promise both sustainability and reduced environmental impact. Engineered osmosis holds a key to addressing both the global need for affordable clean water and inexpensive sustainable energy, according to Yale researchers. Robert McGinnis and Menachem Elimelech, who chairs the department of Chemical and Environmental Engineering, have designed systems that harness the power of osmosis to harvest freshwater from non-potable sources—including seawater—and generate electricity from low-temperature heat sources, such as waste heat from conventional power plants. “The ideal solution,” says Elimelech, “is a process that effectively utilizes waste heat.” Yale University is commercializing their desalination technology, which requires only one-tenth the electric energy used with conventional desalination systems, through a newlyestablished company, Oasys. According to the authors, desalination and reuse are the only options for increasing water supply beyond what is available through the hydrologic cycle—the continuous movement of water on, above, and below the surface of the Earth. However, conventional desalination and reuse technologies use substantial energy. Using a new twist on an old technology, the engineers are employing “forward osmosis,” which exploits the natural diffusion of water through a semi-permeable membrane. Their process “draws” pure water from its contaminants to a solution of concentrated salts, which can easily be removed with low heat treatment—effectively desalinating or removing contaminants from water with little energy input. The osmotic heat engine, another application of engineered osmosis the Yale researchers are pioneering, may be used to generate electrical energy. Elimelech and McGinnis say that it is possible to produce electricity economically from lowertemperature heat sources, including industrial waste heat, using
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 5 May 2009 • Journal of Chemical Education
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Reports from Other Journals a related method—pressure-retarded osmosis. In this closedloop process, the “draw” solution is held under high hydraulic pressure. As water moves into the pressurized draw solution, the pressure of the expanded volume is released through a turbine to generate electrical energy. The applied hydraulic pressure can be recovered by a pressure exchanger like those used in modern reverse osmosis desalination plants. “The cost of producing electricity by this method could be competitive with existing means of power production” says Elimelech.
that has information on the challenges of maintaining a potable water supply. 3. Elimelech’s research is described online at http://www.yale. edu/env/elimelech/bio.html (accessed Feb 2009). 4. This Journal has previously reported numerous demos and activities related to osmosis and reverse osmosis. For instance, see J. Chem. Educ. 1999, 76, 64; 1993, 70, A258; 1971, 48, 226; and 1971, 48, 190.
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1. McGinnis, Robert L.; Elimelech, Menachem. Global Challenges in Energy and Water Supply: The Promise of Engineered Osmosis. Environ. Sci. Technol. 2008, 42, 8625–8629. 2. The Water Campws is an online resource found at http://www. watercampws.uiuc.edu/index.php?menu_item_id=2 (accessed Feb 2009)
Full text (PDF) with links to cited URLs and JCE articles
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Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2009/May/abs542.html
Angela G. King is Senior Lecturer in Chemistry at Wake Forest University, P.O. Box 7486, Winston-Salem, NC 27109;
[email protected].
Journal of Chemical Education • Vol. 86 No. 5 May 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
