Forensic science: CSI Raman

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  • Published: Nov 1, 2011
  • Author: David Bradley
  • Channels: Raman
thumbnail image: Forensic science: CSI Raman

Raman on the crime scene

Near-infrared Raman microspectroscopy and an adnvanced statistical analysis have now been added to the arsenal of techniques available to law enforcement scientists allowing them to quickly and accurately identify traces of vaginal fluid at a crime scene.

Chemists Aliaksandra Sikirzhytskaya, Vitali Sikirzhytski and Igor Lednev of the University at Albany, SUNY, State University of New York, explain how traces of human bodily ?uids - blood, sweat, saliva, semen and vaginal ?uid - are critical in many crime scene investigations. Unfortunately, extracting such fluids as viable evidence requires non-destructive forensic techniques that are both simple to carry out and rapid, and there are currently no techniques that fit all the requirements perfectly.

"Investigations of rape and sexual assault against females often require an identification of vaginal fluid, among other body fluids," the team explains, "However, in-field analysis of vaginal fluid has only been presented by presumptive tests." They add that more comprehensive studies can be performed under laboratory conditions using specialist equipment, trained personnel and expensive chemicals, but a simpler technology is needed to improve forensic analysis at the scene or without the need to resort to sending samples to specialist laboratories. Earlier techniques for identification of vaginal fluid rely on detecting specific biomolecules as markers, such as female sex hormones, but the requisite tests involves time-consuming sample preparation that are also destructive and so offer a single opportunity to obtain definitive evidence.

Raman signatures

Lednev and colleagues have spent the last few years focusing on Raman spectroscopy as one possible approach to forensics that could meet all the needs of investigators and legal teams. Now, they have demonstrated how Raman can be used to create a spectroscopic signature for vaginal fluid that, added to a database of other bodily fluids, might allow the more rapid identification of stains on clothing, bedding and other surfaces as well as the identification of traces on a suspect's fingers or pubic region.

Vaginal fluid is a mixture of various proteins from the upper genital tract, cervical mucus, transudate from the vaginal mucosa, desquamated cellular debris, and leukocytes, the team says. It thus represents a heterogeneous mixture of substances that will generate a complex spectroscopic signature. The team explains that advanced statistical analysis is coupled to the Raman and ?uorescent spectral components so that a multidimensional spectroscopic signature of ?uid from various donors could be generated for addition to the team's forensic database. The spectroscopic signature offers good speci?city and can be used to identify heterogeneous samples from different donors.

Extended research

This preliminary study has several shortcomings, the researchers explain, all of which they will attempt to address in future studies. First, they used only a relatively small number of donors, which limits the statistical significance of the spectroscopic signature for vaginal fluid obtained at this point. They also point out that pure vaginal fluid stains on non-luminescent substrate were used and this does not therefore address the possibility of variations in composition, and so signature, that might arise in pregnancy, diseases or when other factors are at play. "Real crime scene investigations deal with mixed and/or contaminated traces of body fluids on various substrates," the researchers emphasise, "The investigation of all three factors, including mixtures, contamination and various substrates, is in progress in our laboratory."

Lednev told SpectroscopyNOW that he has now renewed his grant from the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. "We will further develop our method to determine the age of a body fluid trace from its Raman signature," he says. "This should allow CSI to determine the time of the crime."

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

Credti: Lednev/Elsevier Near-infrared Raman microspectroscopy and an advanced statistical analysis have now been added to the arsenal of techniques available to law enforcement scientists allowing them to quickly and accurately identify traces of vaginal fluid at a crime scene. 

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