Crime-busting chemical imaging

Engineers at Imperial College London have designed a method of collecting fingerprints with their chemical residue, and keeping them intact for future reference.



As well as potentially detecting the diet, race and sex of a suspect from their fingerprint, the technology could identify traces of substances that people have come into contact with, such as gunpowder, drugs and biological or chemical weapons.



All fingerprints contain a few millionths of a gram of chemical fluid that is often distorted or destroyed in traditional fingerprinting techniques. The scientists found that by using commercial gelatine-based tapes to lift prints, they can be transported safely and intact to the laboratory for chemical imaging analysis.



In the laboratory, the prints can be analysed in a spectroscopic microscope, where infrared rays excite the sample to identify individual molecules within the print to give the composition of the chemical. This information is then processed by an infrared array detector, originally developed by the US military in smart missile technology, which maps the residue and returns a chemical photograph of the sample.



‘The combined operational advantages for forensic scientists of tape lifting prints and spectroscopic imaging really maximises the amount of information one can obtain from fingerprints,’ said Prof Sergei Kazarian, leader of the research project.



The sex of the person could be identified from the level of urea, a chemical found in urine, in a sample. A strong trace of urea might indicate a male, for example, or a weak trace of urea could indicate a female. Specific amino acids could also detect whether a suspect is vegetarian or a meat-eater.



According to Kazarian, this method of print collection could be used to analyse how fingerprints change over time and in different environments.



‘By focussing on what is left in a fingerprint after periods of time, scientists could potentially gauge how old a crime scene is. Studying what happens to prints, when they are exposed to high temperatures, could also be particularly significant, especially in arson cases where lifting prints has been notoriously hard,’ he said.



In the future, Kazarian also believed the technology could be used as key evidence in a courtroom.