In a new study, scientists have come up with a method that could be used to nab terrorists, by detecting how proportions of isotopes in a chemical like sulphur vary throughout the length of a single hair.
The mid-term objective is to be able to use these methods to track the geographical movements of people, including international crime suspects and victims.
In order to carry out this study, the scientists focused on the most abundant sulphur isotopes in hair keratin - sulphur-32 (32S), which accounts for about 95 percent, and sulphur-34 (34S), which makes up around 4 percent.
This proportion can change slightly in response to people's diets and if they travel from one country to another, and the technique is able to detect these small variations.
The scientists use a laser that makes contact with the selected fraction of the hair, generating an aerosol, which later ionizes within plasma, with the spectrometer providing the exact proportions of the sulphur isotopes.
"The advantage of this method compared with others is the high resolution resulting from use of the laser," said Rebeca Santamaria-Fernandez of LGC, lead author of the study.
This advance has enabled the scientists to confirm that the sulphur variations in hair can be linked to peoples' geographical movements.
The researchers collected hair samples of more than 4cm in length donated by three volunteers.
Two were permanent residents in the United Kingdom, while the third - dubbed "the traveler" - had spent the past six months in Croatia, Austria, the United Kingdom and Australia.
"We are what we eat, and the small variations in the 34S/32S relationship reflect changes to our diet, which can in turn be related to movements from one country to another," said Justo Giner, another of the study's authors.
The results of the experiment revealed that the traveller's hair showed significant variations in the sulphur isotopes, while changes in the hairs of the two people living in the United Kingdom were minimal, and similar in both samples.
The scientists are confident they will be able to create databases that will one day make it possible to link the relationship between a specific isotope in hair keratin and a country or region, which would be of great help to the police in tracking down international criminals.
"Although we still cannot say that a certain isotopic variation in a person's hair shows that he or she has been in a particular country, the method can help to break down the alibis of some terrorists who claim not to have moved over recent months," said Santamaria-Fernandez.