A new laser-powered chemical analysis technique is so sensitive that it can take dozens of samples from a single strand of hair, distinguishing between the chemical signatures of each.

Existing methods destroy small samples, and don’t give exact time-based measurements. But using the new technique, forensic scientists could turn that strand of hair into hour-by-hour measurements of what someone ate or where they went.

“With a single hair, we’ve shown you can take carbon isotope measurements over time instead of just chopping up the sample and averaging everything,” geochemist Jim Moran of Pacific Northwest National Laboratory, whose team describe the technique April 12 in Rapid Communications in Mass Spectrometry.

Standard chemical analysis involves the use of mass spectrometers, machines that weigh and categorize particles from samples after they’re pulverized. Lasers are are typically too powerful to extract samples, as they burn organic material before it can be properly analyzed.

‘Carbon tells you what you’re eating, but nitrogen could tell you whether it’s meat or plants. Oxygen isotopes vary with the water cycle, and sulfur with bedrock, so they’re location proxies. Put them together, and you’ve got some really powerful data in space and time.’

To get around the problem, Moran’s team used an ultraviolet laser that breaks up material rather than scorching it. Once blasted from the sample, the tiny particles are burned and the gas fed into the mass spectrometer.

Moran’s team developed their technique with a focus on subtly different forms of carbon, called isotopes. Because plant species absorb carbon isotopes in different ratios, and animals maintain those ratios, they’re useful in a wide range of testing, from analyzing archaeological relics to reverse-engineering ancient diets.

“Getting [time-based] isotope readings from small samples is a problem people have been working on for about 15 years,” said geochemist Alex Sessions of Caltech, who wasn’t involved in the research. “It’s great someone finally figured out how to do it. You can ask so many more questions about a sample.”

Forensic scientists should find the technique useful, Moran said. “The carbon you eat goes into your hair, so hair is a record of carbon ratios. If you’ve been traveling, I could guess which countries you’ve been to or what you ate.”

It could also be useful to biologists exploring food pathways in microbes and paleontologists using carbon-based data to explore ancient environments. But the uses need not be restricted to carbon: The team is developing its laser-ablation system to work with other chemical isotopes, including nitrogen, oxygen and sulfur.

“Carbon tells you what you’re eating, but nitrogen could tell you whether it’s meat or plants. Oxygen isotopes vary with the water cycle, and sulfur with bedrock, so they’re location proxies,” Sessions said. “Put them together, and you’ve got some really powerful data in space and time.”

Video: An ultraviolet laser blasts a 50-micron-wide hole in a strand of hair without burning it. The hair particles are fine enough to ionize for mass spectrometry analysis, making the technology a valuable new tool for forensic investigations. (Matt Newburn/PNNL)

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