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Miniaturized Sensors

By Linda Fresques

Professors examine carbon nanotubes

Left to right: Engineering professors Shuguang Deng, Pedro Cortes, and biology Professor Geoffrey Smith examine grown spores in the presence of carbon nanotubes.

Miniaturized Sensors could be the Answer to Large-scale Biosecurity

If terrorists contaminated our drinking water supply with a deadly pathogen such as Bacillis anthracis, or anthrax, would we be able to detect the toxin before people consumed it and became ill? A team of researchers from New Mexico State University and Los Alamos National Laboratory (LANL) has been working on a technology to improve our detection capabilities.

Using carbon-based nanotubes (CNTs), they are working toward the development of a sensor that would enable the quick detection of minute amounts of potentially harmful waterborne pathogens, which typically are colorless, odorless and tasteless, before they pose a threat to our communities.

The research project began with a Memorandum of Understanding between Los Alamos National Laboratory and NMSU in 2005 and has grown into a collaborative campus effort among the chemical and mechanical engineering departments as well as the biology department.

“The collaborative effort bridges the gap between materials science and microbiology, enabling synthesis and testing on the project,” said Geoffrey Smith, professor of biology.

These researchers are manipulating the fundamental components of matter, atoms and molecules to develop the sensor. At the nanoscale, substances behave differently than they do at larger scales. For example, carbon nanotubes – long, cylindrical carbon structures that are 1/100,000 the diameter of a human hair – are remarkably strong and have excellent adsorption and electrical properties.

Carbon nanotubes.

Commercially available carbon nanotubes.

“Current methods to detect pathogens in water are not sensitive enough to detect small amounts of pathogens in large amounts of water,” said Shuguang Deng, associate professor of chemical engineering. “Current methods involve using a membrane process to concentrate hundreds of gallons of water to less than one liter to detect small amounts of pathogens.”

Deng, Smith, and Pedro Cortes, assistant professor of mechanical engineering, are using the unique properties of carbon nanotubes to develop a sensor that can simultaneously concentrate and detect pathogens, and do it quickly.

Their work builds on research conducted by Venkata K.K. Upadhyayula, a former Ph.D. student of Deng’s. They hope ultimately to develop a pencil-sized device that could be taken into the field and dipped into a water source to give an instantaneous reading.

The researchers have been working with E. coli and S. aureus bacteria and Bacillus subtilis spores, which are a surrogate for the organism that causes anthrax, to determine how fast the substances adhere to the nanotubes, and to what extent. They have been working with non-pathogenic substances for safety reasons. The next step will be to conduct studies using more realistic organisms with the help of LANL, which has laboratories capable of working with pathogens in a safe manner.

“Carbon nanotubes have outstanding electrical conductive properties to chemical and biological substances,” said Cortes. “You can detect substances attached to the surface through an electrical response picked up by a sensor.”

The group removes impurities from commercially produced nanotubes and modifies their surface to enhance the electrical properties so that the active surface is increased and can be adhered to more quickly. The reaction has to be calibrated with a sensor to quantify exact amounts of pathogens detected, eliminating the need for a microscope in a laboratory.

They found that the nanotubes were, in fact, very effective at quickly attracting bacteria and concentrating them: within 30 minutes the nanotubes adsorbed greater than 99 percent of the bacteria.

Petri Dish Examination

Assistant Professor Pedro Cortes examines a petri dish containing grown spores in the presence of carbon nanotubes.

Differentiating between biological substances in the same water sample poses another problem.

“We hope to develop a sensor that has specific areas that will adsorb targeted pathogens,” Deng said. “In the future, we hope to establish a database of pathogens that the sensor could detect. It’s a few years away, but there is very real promise that this can be done.”

They have begun by mixing very basic chemicals, glucose and sucrose, in the same water sample. The nanotubes were able to successfully distinguish between the two and quantify the different concentrations.

“The first time we did this we used a voltmeter from RadioShack,” Smith said. “It worked.”

“Because nanotubes are lightweight and have a huge surface-to-volume area for interacting with other substances, they can be miniaturized,” Cortes said. “We are now starting to develop prototypes for a sensor that could be carried into the field.”

The same technology could also be used to develop a purification process for water or to detect explosives in the air.

Because the potential for nanotechnology is so great, the federal government is supporting research efforts in this area, making the United States a global leader in nanotechnology development, reports the U.S. National Nanotechnology Initiative (NNI). Federal funding for nanotechnology research and development has increased from $464 million in 2001 to an estimated $1,392 million in 2007, with a 2008 budget request of $1,445 million.

“There is huge commercial interest in the use of nanotubes,” said Smith, who describes this research as some of the most rewarding work he’s done in his career. “Aside from the defense applications that we are investigating, there are environmental and medical applications that could be used in our everyday lives.”


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