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Species in a snap: Raman analysis of blood
SIKIRZHYTSKI VITALI
Raman spectroscopy doesn’t destroy validation methods, such as contiguous Solving crimes just got easier. A recent sample, unlike the tests currently in use by block, confirmed that these components study in AC (2009, DOI 10.1021/ crime investigators for species identificadidn’t arise from artifacts. ac901350a) shows how collecting a Ration. “It is important to preserve as man spectrum from a dry blood much material as possible for fusample can uncover its species of ture DNA analyses,” says Hicks. origin. The method is fast, nonde“At the moment, this method structive, and amenable to use at a holds the most promise for identicrime scene. fying the species of origin of a “For forensic purposes, Raman blood or other body-fluid stain is great,” says Igor Lednev, who is without consuming any of the at the University at Albany, State original material.” University of New York, and coauAnother advantage of Raman thored the paper with his student spectroscopy is that it can be taken Kelly Virkler. The relatively low out of the laboratory. “You can sensitivity of Raman spectroscopy, hold a portable Raman instrument a disadvantage for applications usin your hands,” says Lednev. “The ing dilute samples, is not a probtechnology is there.” lem for forensics samples, explains This will result in faster turnLednev. “Even if you have just a around times, giving investigators a trace of body fluid...it won’t be jump on critical information in a diluted.” case. “Being able to identify the The need to match a stain at a source of a stain at the crime scene crime scene to a species arises from would [ensure] that lab technicians the fact that crimes tend to be Raman spectra of blood samples from a cat, dog, and pertest only the most probative messy. “In processing a violent son. Statistical analysis allowed for differentiation of the stains,” says Hicks. crime scene, the investigators may But the method may not be find lots of substances, like blood,” spectra. quite ready for the field. “They says John Hicks, director of the To determine if the components contrib- need to do a larger study to look at false Northeast Regional Forensic Institute. positives and false negatives,” says Al“It would be helpful then...to be able to uted differing amounts to each species testedOwhich would allow researchers to mirall. “Making a decision in the field and identify whether blood is human or differentiate among speciesOall 24 sample deciding not to collect [a sample] is a big from some other origin.” spectra received three “scores” corresponddeal.” In the study, Lednev and Virkler coling to each of the three most significant With more data sets, it may also be poslected Raman spectra from 24 dry blood principal components (using all six composible to go beyond species information. “If samples: 8 each from humans, cats, and nents was deemed unnecessary). After plotyou have a sensitive enough instrument, you dogs. Each blood sample came from a ting the sample scores in three dimensions, could categorize blood based on composidifferent individual for intraspecies diverthe researchers observed a clear clustering of tion,” says Almirall. “Man or woman: there sity, according to Lednev, and was dried may be a signal in there associated with horto simulate crime scene stains. Because dry samples from the same species and separasamples are heterogeneous, the researchers tion from other species. Ninety-nine-percent mones. Smoker or nonsmoker: nicotine confidence ellipsoids drawn around each signals may be in there.” collected spectra from 16 random points species’ cluster did not overlap. That’s just what Lednev is after. “What within each sample’s area and used the “When you look at the spectra, they all we’ll do as the next step...is create a specaccrued data to calculate an average speclook very similar,” says Jose´ Almirall, an astroscopic library based on donors,” intrum for each of the 24 samples. sociate professor at Florida International cluding donors of different genders, races, The data from each average spectrum University and an expert in analytical forenand ages. If Raman could reveal all that, a was combined into a single matrix for sigsic techniques. “Very subtle differences behandheld spectrometer could someday nificant factor analysis and principal comtween canine, feline, and human blood gave turn every detective into Sherlock ponent analysis. These analyses revealed rise to differences in the Raman that princiHolmes. Criminals, beware. six significant componentsObasis sets that —Erika Gebel pal component analysis and significant factor can be used in combination to build any of the spectra. Performing a series of cross- analysis picked up on.” 7862
ANALYTICAL CHEMISTRY /
OCTOBER 1, 2009
10.1021/AC901827U 2009 AMERICAN CHEMICAL SOCIETY
Published on Web 09/01/2009
