How Hair Dye Could Help Cops Catch Perps

If you dye your hair and plan on committing a crime, be warned: A new procedure allows scientists to determine if a single microscopic hair has been dyed, if that dye was permanent or temporary, and even what brand of dye was used. Scientists used surface-enhanced Raman spectroscopy, or SERS, to gauge how light reflects off a hair. Essentially, molecules on the hair's surface begin to vibrate and "change the energy of the reflected photons," Science reports. In other words, the light reads differently depending on the dye on a sample. Not only does the technique register hair dye, scientists say it also finds small amounts of body fluids like blood, drugs, explosives, and gunshot residue, according to a study in Analytical Chemistry.

Why all the fuss if scientists can perform DNA testing? For one thing, an intact bulb or root must be present in the hair sample in order for it to be analyzed for DNA, a press release notes. For another, DNA testing can be a lengthy process and the cases quickly pile up. In many cases, scientists resort to comparing a sample hair with that of a suspect under a microscope, a method that can prove both impractical and inconclusive. The SERS method is quick, easy, doesn't damage the sample, "and can be performed directly at the crime scene" using a portable Raman spectrometer, the study authors write. Another bonus: SERS' gentle approach means a key piece of hair can still be examined for DNA afterward. (Pubic hairs could help identify criminals, too.)