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NMSU geologist uses high-powered laser to pinpoint elements, answer questions

Imagine a machine that can assure quality control for highways, identify foodborne bacteria and determine with 98 percent accuracy where a gemstone originated. Although this technology is going to Mars, it is not science fiction. For New Mexico State University researcher Nancy McMillan, laser-induced breakdown spectroscopy (LIBS) is providing answers to a number of important scientific questions.



Left to right: Geology majors Austin Hanson and Carlos Montoya demonstrate a geochemistry technique known as laser-induced breakdown spectroscopy. (NMSU photo by Darren Phillips)

One of the many ways McMillan, a geology professor and department head, is using LIBS is to speed up the chemical analysis of rocks and minerals for use in highway aggregates, where quality control is essential to ensure safety.

"You might have the aggregate come down a conveyor belt, and the laser would be shooting away, and it could shoot maybe not all of the particles, but easily half of them," McMillan said. "So you would know really what's going into the highways and into the concrete."

The LIBS high-powered laser pulses directly into a rock or mineral sample at temperatures of 15,000 kelvins, more the two times hotter than the surface of the sun, causing atoms to release and become plasma, a burning gas.

As the gas cools, excited electrons decay and release a rainbow of light of different wavelengths. A fiber optics captures the light. Using a spectrometer, McMillan examines individual peaks in the spectrum of light. The peaks belong to certain elements, and the higher the peak, the higher the amount of the element.

"One of the incredible things about LIBS, and why it's taking off, is that there is no sample prep," McMillan said. "Most techniques we use for chemical analysis or isotopical analysis require hours and hours, maybe even weeks of sample prep."

Originating in the Los Alamos laboratories during the 1980's, this research has been used mostly in commercial and industrial applications. McMillan said it's only been in the last five years that it was introduced into the field of geology.

After LIBS analysis on a scoop of rocks used in highway aggregate, McMillan can determine exactly how much and what types of rock are in a full dump truck load. The analysis also identifies individual limestone beds, which is helpful not only in highway construction but to geologists as well.

"A lot of ore minerals are deposited as water moves through veins or cracks in the rock, and they leave behind small traces, or small hints, of where the real deposit is going to be," McMillan said. "This is a technique where you can actually make a map." McMillan said.

McMillan is currently working with a team to develop a 30-pound backpack LIBS, with the laser and a camera strategically placed on a wand.

"Anywhere you can get your body, you can do chemical analysis, which is quite revolutionary," McMillan said. "For the Star Trek fans, it's a real tricorder. It's not science fiction anymore."

Kristen Yetter, a former student of McMillan's and NMSU alumna, recently used the technology on rubies and sapphires to discover their origin. She compared LIBS spectrums with other spectrums in a database that contained information known to specific locations, according to McMillan.

"The LIBS spectrum is so rich. It has information about every single element," McMillan said.

McMillan said the originating country determines the value of the gem, and it's currently illegal to purchase gems from Myanmar. The database provides that information.

"Right now, the only people on the planet who can tell you where a gemstone comes from is my research group, and a big part of that is a former student, Catherine McManus, who started a company called Materialytics," McMillan said. "We have a 95 to 98 percent success rate."

LIBS could potentially be used to check for different strains of E. coli, which is a type of bacteria that can cause serious illness. John Gustafson, professor and department head of biology at NMSU, was instrumental in the E. coli research.

"This is really fast. You don't have to culture it, you don't have to look at it, all you have to do is shoot it with a laser," McMillan said. "The goal there would be to draw blood, shoot it with a laser, and see what bacteria you have. Then you would know which drug to treat it with."

She hopes future LIBS technology could be used to combat today's foodborne bacterium like Listeria monocytogenes, which has claimed 28 lives since the August 2011 outbreak.

"This technology is going to Mars on the next Rover that's going to be launched later this year," McMillan said. "And so, you know, it's so simple even a robot can do it, which means it could be automated for a lot of applications."