Raman spectroscopy breakthroughs make CSI real

CSI, Forensic Files and Bones are all must see TV crime shows based on forensics. But as they say, the truth is sometimes stranger than fiction.

Thanks to highly sophisticated spectroscopy methods, forensic scientists can now do things considered science fiction in the past. That includes profiling a person based on body fluids, and identifying a gun’s caliber based on gunshot residue.

Those methods utilize vibrational spectroscopic techniques, Raman and ATR FTIR (Attenuated total reflectance Fourier-transform infrared spectroscopy). But Raman spectroscopy is the star.

Igor K. Lednev, Ph.D. is a professor in the Department of Chemistry at the University at Albany, State University of New York. He has been developing the use of Raman spectroscopy for a variety of forensic applications.

For the past 12 years, the U.S. Department of Justice has provided Lednev and his associates with funding to develop technology that identifies and analyzes body fluid traces at crime scenes.

Biological stains include blood, saliva, semen, vaginal fluid, sweat and urine. Body fluid traces are important because they are the main source of DNA evidence. Currently, police use various biochemical tests to detect and identify body fluids.

The majority of the tests used at the crime scene are presumptive, meaning that false positives are possible and additional confirmatory tests need to be conducted in the lab. In addition, all current tests affect the sample.

“All of those tests are destructive to the sample and most importantly, all those tests are specific to an individual body fluid. There is no a universal test for all bodily fluids,” Lednev said. “We are using Raman spectroscopy to develop a universal, confirmatory test, which can be used for all main body fluids in a nondestructive manner.”

Lednev uses Raman spectroscopy, which can create a non-destructive “fingerprint” of the chemical makeup of the substance tested. Lednev is working with Raman spectroscopy on universal, non-destructive techniques.

He and his associates have developed automated software to identify all the main body fluid traces for samples on a noninterfering aluminum foil substrate.

“We still need to develop software for dry body fluids on common substrates like carpets, floors, tiles, whatever you find at the crime scene,” he said. “That would be the most useful for law enforcement, to make the identification without touching the biological sample.”

Lednev can also analyze biological stains to identify the time since deposition, or the age of a bloodstain. This is important for determining the time of a crime. And if the crime scene includes several blood stains, older stains can be eliminated so police can focus on the relevant evidence.

The next challenge is to transfer this technology from a desktop instrument to a handheld instrument that travels to the crime scene. A portable, handheld Raman instrument, for example.

Lednev is testing some of these instruments in his lab now. He must develop methodology and make it affordable to law enforcement agencies. But it’s a two-edged sword that can save money in the long run. A device like this would not require any consumables and could be used for many other forensic items, including confirmatory identification of illicit drugs.

“The idea is that if they get this instrument, everything else would be very inexpensive,” Lednev said. “Instruments you can use for years without any additional sources.”

This type of instrument would quickly identify which samples to collect at a crime scene. Right now, it’s expensive for police to collect all the miscellaneous samples just to get the ones they want.

When a crime scene is discovered, it’s important for police to immediately build a profile for a suspect. Race, gender, and approximate age help narrow down the suspects.

Most recently, Lednev began working on phenotype profiling. He can determine the sex, race and age of the donor based on a biological stain.

This technique is not ready for use at the crime scene yet. Lednev and his group have published a proof of concept. A large donor population needs to be tested to evaluate the developed methodology, very much like pilot clinical trials validate new methods developed for disease diagnostics.

GSR includes three elements: lead, barium and antimony. This is a unique combination of elements. If police detect all three elements, they assume it’s gunshot residue. There are very few environmental sources that have all three elements.

Lednev and his associates have taken it a step further.

They collected gunshot residue from guns using different caliber ammunition. Next, they analyzed the chemical composition of the gunshot reside with Raman. Then they built a statistical model to differentiate different particles from different firearms.

The model was tested and resulted in 100 percent accuracy. Raman spectroscopy was able to distinguish the various caliber guns from the residue.

“What this means is if there is a shooting incident, and the shooting was from a short distance resulting in gunshot residue on a victim, police can collect this gunshot residue and the suspect’s pistol. We can use this pistol in a range, collect and characterize its GSR and tell if the GSR found on the victim could come from this pistol. We can also exclude firearms this way.”

Lednev thinks this technology is ready for use in the real world. Since the analysis is done in a laboratory, there’s no need to conduct it in the field.

Lead has recently been eliminated from some ammunition to make it more environmentally friendly. If you leave barium and antimony, the accuracy of gunshot residue testing is low because these two elements are common in the environment. That can produce many false positives. The current method only works with the three elements present in inorganic gunshot residue.

That leads to another area of study: Organic versus inorganic gunshot residue. Inorganic residues contain elemental chemicals such as lead, barium, and antimony. Organic gunshot residue primarily consists of partially burned and unburned gunpowder and does not contain lead, barium and antimony. Raman spectroscopy can detect and characterize organic and inorganic particles, helping to overcome the identification of lead-free ammunition.

“Raman spectroscopy is looking for molecular composition,” Lednev said. “Like fingerprints of chemicals, Raman spectroscopy picks up molecules’ chemical structures. Raman is much more specific than elemental analysis.”

This technology is still under development. Lednev and his group have received patents for it, but haven’t made it available for practitioners yet.

“This is where we need to work with HORIBA, to develop user-friendly software and make black-box type instruments, which police can use by just pushing the button and getting the result. I would estimate that a first commercial prototype will be ready for police validation within three to five years,” he said.

Lednev’s lab uses an XploRA™ PLUS confocal Raman microscope and a LabRAM HR Evolution confocal Raman microscope.

“The XploRA PLUS is easy to use and very robust. Students love it,” Lednev said. “We have the LabRAM HR Evolution for high level performance fundamental research.

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