Sensors Provide Early Warning of Biological Threats

Originating Technology/NASA Contribution 

A postage stamp-size biosensor holding millions of carbon nanotubes
Containing millions of carbon nanotubes, the NASA biosensor can alert inspectors to minute amounts of potentially dangerous organic contaminants.

The Centers for Disease Control and Prevention (CDC) estimates there are between 4 and 11 million cases of acute gastrointestinal illnesses in the United States each year—caused by pathogens in public drinking water. The bacteria Escherichia coli (E. coli) and Salmonella have within the past few years contaminated spinach and tomato supplies, leading to nationwide health scares. Elsewhere, waterborne diseases are devastating populations in developing countries like Zimbabwe, where a cholera epidemic erupted in 2008 and claimed over 4,000 lives.

Scientists have found an unexpected source of inspiration in the effort to prevent similar disasters: the search for life on Mars. The possibility of life on the Red Planet has been a subject of popular and scientific fascination since the 19th century. While Martian meteorites have turned up controversial hints of organic activity, and NASA’s exploratory efforts have delivered important discoveries related to potential life—the presence of water ice, and plumes of methane in Mars’s atmosphere—direct evidence of organisms on our closest planetary relative has yet to be found.

In order to help detect biological traces on Mars, scientists at Ames Research Center began work on an ultrasensitive biosensor in 2002. The chief components of the sensor are carbon nanotubes, which are the major focus of research at the Center for Nanotechnology at Ames—the U.S. Government’s largest nanotechnology research group and one of the largest in the world. Tubes of graphite about 1/50,000th the diameter of a human hair, carbon nanotubes can be grown up to several millimeters in length and display remarkable properties. They possess extreme tensile strength (the equivalent of a cable 1 millimeter in diameter supporting nearly 14,000 pounds) and are excellent conductors of heat and electricity.

It is the nanotubes’ electrical properties that Ames researchers employed in creating the biosensor. The sensor contains a bioreceptor made of nanotubes tipped with single strands of nucleic acid of waterborne pathogens, such as E. coli and Cryptosporidium. When the probe strand contacts a matching strand from the environment, it binds into a double helix, releasing a faint electrical charge that the nanotube conducts to the sensor’s transducer, signaling the presence of the specific pathogens found in the water. Because the sensor contains millions of nanotubes, it is highly sensitive to even minute amounts of its target substance. Tiny, requiring little energy and no laboratory expertise, the sensor is ideal for use in space and, as it turns out, on Earth as well.


“Carbon nanotubes are the wonder material of nanotechnology,” says Neil Gordon, president of Early Warning Inc., based in Troy, New York. “The opportunity was ripe to put that technology into a product.” Gordon encountered the director of the Center for Nanotechnology, Meyya Meyyappan, at a number of industry conferences, and the two discussed the possible terrestrial applications of NASA’s biosensor. In 2007, Early Warning exclusively licensed the biosensor from Ames and entered into a Space Act Agreement to support further, joint development of the sensor through 2012.

Product Outcome

Early Warning initially developed a working version of the NASA biosensor calibrated to detect the bacteria strain E. coliO157:H7, known to cause acute gastrointestinal illness. It also detects indicator E. coli, commonly used in water testing. In the process, the company worked out a method for placing multiple sensors on a single wafer, allowing for mass production and cost-effective testing. In April, at the 2009 American Water Works Association “Water Security Congress,” Early Warning launched its commercial Biohazard Water Analyzer, which builds upon the licensed NASA biosensor and can be configured to test for a suite of waterborne pathogens including E. coliCryptosporidiumGiardia, and other bacteria, viruses, and parasitic protozoa. The analyzer uses a biomolecule concentrator—an Early Warning invention—to reduce a 10-liter water sample to 1 milliliter in about 45 minutes. The concentrated sample is then processed and fed to the biosensor. The entire process takes about 2 hours, a drastic improvement over typical laboratory-based water sampling, which can take several days to a week. The sensor operates in the field via a wired or wireless network and without the need for a laboratory or technicians, allowing for rapid, on-the-fly detection and treatment of potentially dangerous organic contaminants.

The Early Warning water analyzer
Early Warning’s analyzer feeds a concentrated water sample to its biosensor, providing rapid pathogen detection.

“The sensor is incredibly sensitive and specific to the type of pathogen it is calibrated to detect in the water,” says Gordon. “Instead of just detecting coliforms in the water that may or may not indicate the presence of pathogens, we will know if there are infectious strains of SalmonellaE. coli, or Giardia that could sicken or even kill vulnerable people if consumed.” (Coliform bacteria levels typically indicate water and food sanitation quality.)

The water analyzer has multiple applications, notes Gordon. Early Warning’s system can monitor recreational water quality at beaches and lakes, which can be contaminated by animal feces, farming activities, and infectious pathogens in human waste. Agricultural companies may use the analyzer to test feed water for cattle, and food and beverage companies may employ the sensor to ensure the purity of water used in their products. Health care organizations have expressed interest in using the analyzer to test water from showers and other potential sources of pathogens like Legionella, which causes the flu-like Legionnaires’ disease.

Early Warning and Kansas State University, in Manhattan, Kansas, are collaborating on sensor enhancements such as improving the safety of imported produce. Since the skins of fruits and vegetables are potential sites of dangerous pathogens, inspectors could collect water sprayed on the produce and, using the analyzer, know within a few hours whether a particular shipment is contaminated. Last year, Kansas State was selected as the home for the U.S. Department of Homeland Security’s new National Bio and Agro-Defense Facility, which could also benefit Early Warning.

“We’re eager to show how the private sector, government agencies, and academia can work together to evolve this platform into products that benefit our citizens,” says Gordon. With an aging U.S. water and wastewater infrastructure, increasingly severe weather systems, global travel and food imports affecting the proliferation of disease-causing organisms, and more than 1 billion people worldwide without access to safe water (according to the World Health Organization), the fruits of this partnership may be more necessary than ever.


Tiny Structure Gives Big Boost To Solar Power

Princeton researchers have found a simple and economical way to nearly triple the efficiency of organic solar cells, the cheap and flexible plastic devices that many scientists believe could be the future of solar power.

The researchers, led by electrical engineer Stephen Chou, were able to increase the efficiency of the solar cells 175 percent by using a nanostructured “sandwich” of metal and plastic that collects and traps light. Chou said the technology also should increase the efficiency of conventional inorganic solar collectors, such as standard silicon solar panels, although he cautioned that his team has not yet completed research with inorganic devices.

Chou, the Joseph C. Elgin Professor of Engineering, said the research team used nanotechnology to overcome two primary challenges that cause solar cells to lose energy: light reflecting from the cell, and the inability to fully capture light that enters the cell.

With their new metallic sandwich, the researchers were able to address both problems. The sandwich — called a subwavelength plasmonic cavity — has an extraordinary ability to dampen reflection and trap light. The new technique allowed Chou’s team to create a solar cell that only reflects about 4 percent of light and absorbs as much as 96 percent. It demonstrates 52 percent higher efficiency in converting light to electrical energy than a conventional solar cell.

That is for direct sunlight. The structure achieves even more efficiency for light that strikes the solar cell at large angles, which occurs on cloudy days or when the cell is not directly facing the sun. By capturing these angled rays, the new structure boosts efficiency by an additional 81 percent, leading to the 175 percent total increase.

Chou said the system is ready for commercial use although, as with any new product, there will be a transition period in moving from the lab to mass production.

The physics behind the innovation is formidably complex. But the device structure, in concept, is fairly simple.

The top layer, known as the window layer, of the new solar cell uses an incredibly fine metal mesh: the metal is 30 nanometers thick, and each hole is 175 nanometers in diameter and 25 nanometers apart. (A nanometer is a billionth of a meter and about one hundred-thousandth the width of human hair). This mesh replaces the conventional window layer typically made of a material called indium-tin-oxide (ITO).

The mesh window layer is placed very close to the bottom layer of the sandwich, the same metal film used in conventional solar cells. In between the two metal sheets is a thin strip of semiconducting material used in solar panels. It can be any type — silicon, plastic or gallium arsenide — although Chou’s team used an 85-nanometer-thick plastic.

The solar cell’s features — the spacing of the mesh, the thickness of the sandwich, the diameter of the holes — are all smaller than the wavelength of the light being collected. This is critical because light behaves in very unusual ways in subwavelength structures. Chou’s team discovered that using these subwavelength structures allowed them to create a trap in which light enters, with almost no reflection, and does not leave.

“It is like a black hole for light,” Chou said. “It traps it.”

The team calls the system a “plasmonic cavity with subwavelength hole array” or PlaCSH. Photos  of the surface of the PlaCSH solar cells demonstrate this light-absorbing effect: under sunlight, a standard solar power cell looks tinted in color due to light reflecting from its surface, but the PlaCSH looks deep black because of the extremely low light reflection.

The researchers expected an increase in efficiency from the technique, “but clearly the increase we found was beyond our expectations,” Chou said.

Chou and electrical engineering graduate student Wei Ding reported their findings in the journal Optics Express, published online Nov. 2, 2012. Their work was supported in part by the Defense Advanced Research Projects Agency, the Office of Naval Research and the National Science Foundation.

The researchers said the PlaCSH solar cells can be manufactured cost-effectively in wallpaper-size sheets. Chou’s lab used “nanoimprint,” a low-cost nanofabrication technique Chou invented 16 years ago, which embosses nanostructures over a large area, like printing a newspaper.

Besides the innovative design, the work involved optimizing the system. Getting the structure exactly right “is critical to achieving high efficiency,” Ding said.

Chou said that the development could have a number of applications depending on the type of solar collector. In this series of experiments, Chou and Ding worked with solar cells made from plastic, called organic solar cells. Plastic is cheap and malleable and the technology has great promise, but it has been limited in commercial use because of organic solar cells’ low efficiency.

In addition to a direct boost to the cells’ efficiency, the new nanostructured metal film also replaces the current ITO electrode that is the most expensive part of most current organic solar cells.

“PlaCSH also is extremely bendable,” Chou said. “The mechanical property of ITO is like glass; it is very brittle.”

The nanostructured metal film is also promising for silicon solar panels that now dominate the market. Because the PlaCSH sandwich captures light independent of what electricity-generating material is used as the middle layer, it should boost efficiency of silicon panels as well. It also can reduce the thickness of the silicon used in traditional silicon solar panels by a thousand-fold, which could substantially decrease manufacturing costs and allow the panels to become more flexible.

Chou said the team plans further experiments and expects to increase the efficiency of the PlaCSH system as they refine the technology.


[Princeton Engineering News]

The First Entirely All-Carbon Solar Cell

Stanford University engineers have developed the first solar cell made entirely of carbon – a promising alternative to the expensive materials used in photovoltaic devices today. The thin-film prototype is made of carbon materials that can be coated from solution – a technique that has the potential to reduce manufacturing costs.

“Every component in our solar cell, from top to bottom, is made of carbon materials,” says Stanford graduate student Michael Vosgueritchian. “Other groups have reported making all-carbon solar cells, but they were referring to just the active layer in the middle, not the electrodes.”

The experimental solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes. In a typical thin film solar cell, the electrodes are made of conductive metals and indium tin oxide. One drawback of the all-carbon prototype is that it primarily absorbs near-infrared wavelengths of light, contributing to a laboratory efficiency of less than 1 percent – much lower than commercially available solar cells.