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Forensic Identification Using Individual Chemical Signatures

By touching a cell phone, car keys, or even a pen, you are leaving behind a chemical signature that can reveal much about how you live your daily life.
Date Published
July 10, 2017

Imagine that an investigator at a crime scene finds a smashed cell phone near the body of a homicide victim. The phone, apparently dropped by the person who committed the crime, is rushed to a forensics laboratory where it undergoes what researchers describe as a “lifestyle chemistry analysis.”

Using a mass spectrometer to analyze the molecules on the surface of the phone, laboratory scientists quickly discern that the person who committed the crime was likely a person who wears high-end cosmetics, suffers from a fungal infection, uses eye drops, and takes an antidepressant. Further analysis of the phone’s surface reveals the person smokes, uses sunscreen and anti-mosquito sprays, and recently took an antihistamine. The person also drinks coffee, likes citrus fruit, and has a diet that involves a lot of chili peppers.

That scenario is moving from the imaginary to the real based on research recently done with National Institute of Justice support by chemical biologist Pieter Dorrestein at the University of California, San Diego. In the paper “Forensic Identification Using Individual Chemical Signatures ”published in the Proceedings of the National Academy of Sciences (PNAS) online in November 2016, Dorrestein said his research team developed an approach to translate chemistries recovered from personal objects such as phones into a lifestyle sketch of the owner, using mass spectrometry and informatics approaches. The molecules found on personal belongings, such as pens, keys, phones, or handbags reflect a personalized lifestyle profile that highlights the type of hygiene/beauty products the person uses, diet, medical status, and even the location where a person may have been.

In the PNAS paper, Dorrenstein’s team explained that, “the external environment influences the chemical composition of the outermost layer of the skin. Our daily routines leave chemicals on [the] skin surface originating from our surroundings and the human habitats to which we are exposed.” In addition, skin-associated chemicals arise “from personal habits including diet, exercise, clothes, medications, and personal care products. Together, these sources represent the vast majority of identifiable chemical entities on the human skin surface.”

As part of their pilot study of lifestyle chemistry, the researchers swabbed the phones of 39 people, and then monitored the chemistries found on phones and hands of 10 individuals four months after the first sample collection to determine how stable the chemical signatures were. The signatures, they found, were very stable over the four-month period.

In total, mass spectrometry data collection was completed for 1,200 samples collected from hands and personal objects of 80 volunteers. The statistical analysis showed that samples collected from hands and phones of 39 individuals were “significantly more similar to hands of the owners than to other individuals, highlighting the transfer of our skin molecules on objects that we touch.” The research also found that of the mass spectrometry data gathered, 52 percent of the spectra were shared between hands and phones of all volunteers, “highlighting that many skin associated molecules are found on personal objects.” The work also showed that for both hands and phones, “many chemicals are unique and are found only in one or a few of the volunteers. Only a few ion signatures from molecules were shared among all of the volunteers, suggesting that, “unique chemistries distinguish and link the phone and hand of each person.”

The researchers were able to match a phone to a person with 88 percent accuracy, and matching hands to samples from the back of the phone appears to be much more accurate (69 percent) than matching samples from the front of phones (33 percent), suggesting that molecules from hands transfer and adhere better to the back of phones.

In the PNAS, the researchers noted that, “the chemical interpretation of [chemical] traces recovered from objects found on a crime scene can help a criminal investigator to construct a ‘profile’ of individual lifestyle and learn about the lifestyle of the individual who used/touched these objects, even when DNA evidence is also available. The molecular analysis would help a criminal investigator in narrowing down the owners of the object (for example a suspect of a crime scene or understanding the habits of a terrorist) by identifying specific lifestyle characteristics from objects they touch.”

In their PNAS paper, the researchers call for the construction of a database of lifestyle/personal habits that is tied to reference spectra from mass spectrometry. “We believe that an extensive database with appropriate metadata of where these molecules are found and their associated lifestyles can become available. Such a database would not only benefit forensic science, but also would be useful for toxicological analysis as it would be a noninvasive way to measure environmental exposures.”

About This Article
The research described in this article was funded by NIJ cooperative agreement number 2015-DN-BX-K047, awarded to the University of California, San Diego. 

Date Published: July 10, 2017