Analyzing hair samples at a crime scene isn't always an exact science. When forensic investigators don't have the time or need toanalyze a hair's DNA, they often stick samples under a microscope and visually compare them to hair from a known suspect. But a new technique could allow police to analyze and detect hair dye in extreme detail, giving investigators yet another to look at hair as crime scene evidence.The technique, developed by researchers from Northwestern University and described in a paper published in the journal Analytical Chemistry, uses a well-known but underutilized method of analysis called surface-enhanced Raman spectroscopy (SERS). When applied to hair, the researchers wrote, SERS can give investigators a detailed peek at the chemical residue left behind by hair dye—even if it was applied weeks before analysis."SERS can identify whether hair was artificially dyed or not, and determine whether permanent or semipermanent colorants were used," the authors wrote. "Our results indicate that SERS is capable of distinguishing the commercial brands that were utilized to dye hair, as long as their commercial formulas are different."Although DNA analysis is becoming more affordable, it is still pretty expensive to perform. SERS analysis, which enhances any traces of molecules adsorbed by a surface, is not only highly accurate, but relatively easy to perform quickly and at low cost. And while with DNA analysis Investigators need an intact bulb at the bottom of the hair follicle, SERS analysis can be performed on a hair sample just a millimetre long and with commercially available handheld SERS detectors in a matter of minutes."Raman spectrometers offer a unique opportunity to perform forensic examinations of hair directly at the crime scene," according to the authors.While using SERS for forensic analysis is a first, the technique has been used experimentally for other types of analysis in the past. The authors recently worked with other researchers on an analogue approach known as tip-enhanced Raman spectroscopy (TERS) to detect the presence of dyes and ink on a piece of 19th century manuscript. Other uses for the technique include sniffing out cancer in saliva.Of course, one can imagine other, more practical uses for such an accurate method for determining hair dyes, too. Like, for example, trying to remember which brand of hair dye you used last month to get the perfect shade of teal on your armpit hair, if you're into that sort of thing.
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