That’s the path that Kerala-born Indian-American scientist Dr. Thomas Thundat has chosen for his career at the Department Of Energy’s Oak Ridge National laboratory in Tennessee. And that’s exactly why he was honored this month by Scientific American magazine for being one among the top 50 outstanding leaders in science and technology.

Thundat now joins a distinguished group of scientists who are celebrated for their contributions to a wide variety of areas, from agriculture to computing. “Scientific American believes strongly that the best hope for a safer, healthier, more prosperous world rests in the enlightened use of technology,” says John Rennie, editor-in-chief of the magazine. “The Scientific American 50 is our annual opportunity to salute the people and organizations making that possible through their outstanding efforts as leaders of research, industry, and policymaking.”

Thundat’s forte is America’s defense.

It began in 1991 when Thundat observed an anomalous effect while conducting an experiment with an atomic force microscope (AFM) in his ORNL lab. He had performed the same experiment a few months earlier when he was a postdoctoral researcher at Arizona State University. Strangely, the AFM cantilever at Arizona State had been stable, whereas the one at ORNL kept drifting, ruining the experiment.

"Eventually, I realized that because it rains a lot in Tennessee, my lab´s humidity level often went up, so the cantilever drifted," Thundat says. "There was no variation in the cantilever in Arizona, where it is always dry. Then it occurred to me that the silicon nitride cantilever could be a sensor for humidity, because water vapor adsorbs on silicon nitride."

Thundat went on to discover that microcantilevers, which resembles a tiny diving board, when coated with a material that attracts molecules of a target substance will bend more when near that substance, changing the angle at which incoming laser light will be deflected. Today, the microcantilever sensor invented by him is the heart of numerous emerging physical, chemical, and biological sensors, including a compact airport explosives detector and a more sensitive detector of early-stage prostate cancer.

In the 1990s Thundat´s group fabricated many different cantilever chemical and biological sensors by coating them with special chemicals that attracted and captured molecules of a target material. They made sensors that can detect not only trace amounts of environmental pollutants but also weapons of mass destruction.

Thundat first developed a mercury sensor using the microcantilever. He deposited a layer of gold on a cantilever and exposed it to mercury vapors. Because mercury has an affinity for gold, mercury in the air binds with the gold layer, causing the cantilever to bend. Thundat says the cantilever is a sensitive detector because of mechanical forces induced by chemical binding between probe and target molecules. In 1996 Thundat and his colleagues extended the sensor concept to physical sensing and demonstrated an infrared detector and an infrared camera based on a bimetallic cantilever.

Collaborating teams led by Thundat at ORNL and Jesse Adams at the University of Nevada recently devised a much more compact cantilever-based airport explosive sensor that could detect trace amounts of TNT. The innovation was reported in a paper in the October 2, 2003, issue of Nature; the paper´s lead author, Sri Lanka born Lal Pinnaduwage, is a member of Thundat´s team. The paper proposed distributing microsensors in airport ventilation systems to detect nitrogen-containing explosive molecules wafting through the air.

In each microsensor, a tiny voltage would be applied to an embedded piezoresistive heating element, which would heat the cantilever to 1000 degrees for 0.1 sec. The adsorbed TNT molecules undergo nanoexplosions when the cantilever is heated very rapidly. Consequently, the cantilever would bend down, squeezing a zinc oxide crystal embedded below in a piezoelectric sensor-actuator. An electric charge would be produced, alerting airport officials to the location of an explosive. "This new device overcomes a number of limitations associated with conventional microcantilever sensors," Thundat says. "The process uses integrated elements on each cantilever, consumes 10,000 times less electricity, and allows for an array structure that simplifies the simultaneous use of many cantilevers."

Pinnaduwage and Thundat also developed a coating that, when applied on a cantilever, can very sensitively detect explosives, such as the PETN explosive used by the would-be "shoe bomber." "This sensor can detect PETN within 10 seconds at 1 part per trillion sensitivity," Thundat says.

Thundat found that a cantilever coated with double-stranded "probe" DNA will deflect when it hybridizes with a complementary DNA target, say, from a disease bacterium. He also showed that cantilevers can detect glucose levels in blood.

Thundat believes that cantilevers can be used to detect defective genes that cause breast cancer, colorectal cancer, and cystic fibrosis. These mutant genes have one incorrect DNA base. ORNL experiments have shown that a DNA sequence in a liquid sample will hybridize with a complementary DNA sequence bound to a cantilever, even if the sample sequence has one wrong base, or a mismatch. "We found that a mismatch causes the cantilever to bend up instead of down," Thundat says. "This change in bending direction could be used to detect defective genes that cause disease."

The cantilever technology could also be used to detect prostate cancer. ORNL researchers have immobilized on a cantilever the antibody for prostate-specific antigen (PSA), the chemical signal for the disease. An ORNL collaboration with the University of California´s Professor Arun Majumdar has shown that the cantilever bends when its antibody matches PSA in serum samples supplied by Majumdar. They showed that this technique in which PSA binds with the antibody coating on the cantilever, causing it to bend, detected early signs of prostate cancer in serum samples with 10 times higher sensitivity than conventional techniques.

Using ink-jet printing techniques, Thundat and Majumdar have developed a parallel array of 500 DNA- and antibody-coated cantilevers. Stacked charge-coupled device camera images show which cantilevers deflected after exposure to disease proteins. If this array could rapidly detect in body fluids any one of 100 different cancer markers, such as elevated or depressed levels of antibodies and enzymes, it could be the heart of a hand-held device for fast disease diagnosis.

CONCERN FOR LANDMINES

Thundat believes that the underlying philosophy of all scientists is to make life better and easier for people. Which is why he is concerned about landmines.

"Most people don´t care about landmines, because it is not in our backyards but it is rampant in poor countries and we need to do something about it. I got interested in it because it causes a lot of problems in third world countries. I looked at it from the humanitarian point" observed Thundat.

The figures speak for themselves. Landmines kill every year 26,000 people. In Angola alone, there are 80,00 landmine amputees, most of them children- almost 1 out of 140 people.

Fewer than 10 per cent ever receive prosthetic limbs. Current figures show that more than 110 million active mines are scattered over 64 countries. For every mine removed, 10 more are laid. At the current rate of removal, it will take a few thousand years to remove all the mines that are estimated to be deployed worldwide.

In Afghanistan alone, assuming no additional mines are laid, it will take about 4000 years to remove all the mines. It takes just three dollars to fashion a crude land mine, but conventional landmine detectors cost at least $20 K. Since it is so expensive to detect landmines, in third-world countries, landmines are often removed by hand. It is given to the poorest of the poor, who crawl through suspect terrain poking the ground with sticks.

"There exists a wide-spread need for humanitarian de-mining in many parts of the world. Current devices for locating landmines are expensive and require bulky, complex, and cumbersome equipment and trained personnel," said Thundat. The cantilever, on the contrary will be small, cheap and easy to use when eventually used on the field.

"The beauty of this revolutionary technology is that it is extremely sensitive, selective and regenerates itself after each use for continuous operation. It is a simple technology that can be used in any corner of the world by local people without elaborate training. It consumes such little power that it can be operated with a battery or photovoltaic cell," said Thundat.

But the main problem facing landmine detection research is funding. "Landmines is a third world problem, so there is not much money going into its research," lamented Thundat.

MODIFYING CANTILEVERS

As a platform par excellence, the cantilever can be modified and made into a biosensor or an explosion sensor. Thundat and his team have already modifed it to make a Night vision camera.

"We all emit infrared radiation. When it falls on an array of cantilevers, it will produce pictures. The night vision camera will be much cheaper than than the ones available in the market now. Right now they vary from $25,000- $100,000. If we can make it for $300, then everybody can use it," explained Thundat.

Thundat and his team are also researching the cantilever technology to detect DNA mismatches in certain cancers. " If you go to the doctor´s office, you can get your results right away. That´s our goal. We can have not only one cantilever but also 100s of cantilevers in one square area. So we can detect many diseases at the same time. This technology will save time and money and it will also work faster," said Thundat.

Four years ago, ORNL´s Mike Barnes, Thomas Thundat and Adosh Mehta collaborated with Ramesh Bhargava of Nanocrystals Technology in Briarcliff, N.Y., to cage single europium atoms in nanocrystals not much larger than the atoms themselves. The process enables them to study the properties of a single atom at room temperature using conventional microscopy techniques.

DOE scientists say that a whole new technology awaits exploration with the discovery of that technique for trapping single atoms.

Thundat is a distinguished staff scientist and the leader of the Nanoscale Science and Devices Group at ORNL. He is also a research professor at the University of Tennessee and a visiting professor at the University of Burgundy, France. He is the author of over 135 publications in refereed journals, six book chapters, 11 patents and nine pending patents. Dr Thundat’s research is focused on novel physical, chemical and biological detection using micromechanical sensors. He received his PhD in Physics from the State University of New York in 1987, his M.Sc from the IIT (1980), and his B.Sc (1978) from (Sacred Heart College, Thevara) Kerala University.

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