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Laser Ablation Spectrometry Cracks Another ’CSI’ Case

Photonics.com
May 2006
FREMONT, Calif., May 10, 2006 -- Brass notes the roll of duct tape on his tool belt. The investigation is followed ... back to the CSI Lab where Nick compares the maintenance man's roll of duct tape with the strips taken off the victim's bed. DNA swabs and prints are also taken. Hodges ... will compare adhesives looking for a match, mentioning ... that it will take a laser ablation test. The laser actually burns into the tape, boiling off the same, transporting the gas residue into a sensor for comparison. The results: no match. The maintenance man is in the clear. -- from a CBS summary of "I Like To Watch," a recent episode of "CSI: Crime Scene Investigation"

Millions of TV viewers now have a better understanding of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and its crime-solving capabilities. For the second season in a row, "CSI: Crime Scene Investigation," the CBS TV series about forensic investigators who use cutting-edge scientific methods to solve crimes, has relied on the technology to nab a suspect.

Last season, LA-ICP-MS was used to identify the makeup of a near-microscopic shard discovered at a crime scene (the shard was far too small for the capabilities of conventional forensic techniques). What LA-ICP-MS revealed -- a fingernail chip smudged with blue paint and motor oil -- was the key to cracking the case. (See: Laser Ablation Goes Primetime)

This season, in the episode "I Like To Watch," LA-ICP-MS is used to analyze two duct-tape samples -- one that was used to bind the victim, the other taken from the maintenance man's tool belt -- to determine if they were from the same roll of tape. The scene in which the results are revealed to be negative includes footage of sample preparation, a laser beam ablating the sample, and laser-induced aerosol entering the ablation chamber.

The episode also features cameos by a gas chromatograph mass spectrometer, which confirmed that a red drop near the victim's bed was nail polish, and a Fourier transform infrared microscope to reveal "the three-layered flake profile as a fabric pattern used as fire-retardant trim in firemen's turnouts for the yellow flakes taken from the plastic scrap found on the wall," as described in the summary. (Sara gets to the point: Hodges is saying that a fireman was in Christina Hollis' bedroom, correct? Correct.) The CSI site also features a handbook of terms for tools, evidence and procedures used by crime scene investigators, at http://www.cbs.com/primetime/csi.

Laima Baltusis, product manager at New Wave Research, a Fremont, Calif., maker of laser ablation systems, said the technology is ideally suited for crime-scene evidence analysis because it is largely nondestructive: Only a near-microscopic amount of material needs to be ablated to create a workable sample for analysis. In contrast, conventional forensic techniques typically require extensive sample preparation and hazardous substances; this can introduce contamination and destroy large amounts of the sample, Baltusis said.

With LA-ICP-MS, and as depicted on CSI, a pulsed laser vaporizes a minute amount of a solid sample. A gas stream carries the sample vapor into a high-temperature plasma where it is ionized before extraction into the mass spectrometer for analysis.

The LA-ICP-MS system featured on CSI is installed in numerous working crime labs and employs the New Wave Research UP-213, a high-performance Nd:YAG deep ultraviolet (213 nm) laser ablation system. The UP-213 improves ablation of all materials for ICP-OES and ICP-MS, including fragile and easily cleaved minerals. It can be used with any ICP, noble-gas or stable-isotope mass spectrometer for solid sampling of semiconductor, geological, biological and environmental specimens.

In addition to LA-ICP-MS systems, New Wave makes a variety of laser-based systems and modules for the microelectronics and analytical instrumentation industries, including wafer scribing, flat panel display repair, semiconductor failure analysis, micromachining, particle image velocimetry, laser ablation/solid sampling, and other scientific applications. The company will exhibit its products (Booth 1248) at CLEO/QELS 2006, to be held May 23-25 at the Long Beach Convention Center.

For more information, visit: www.new-wave.com



GLOSSARY
laser ablation
The removal of material from a surface by high intensity pulsed or CW laser radiation emission.
spectrometry
The study and measurement of spectra and their components.
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