Along with forensic evidence in criminal cases, this process can be applied to many situations, said study lead investigator Pieter Dorrestein, a professor in UCSD's School of Medicine and Skaggs School of Pharmacy and Pharmaceutical Sciences.
"I can see it being used to assess toxicological exposures, I can see it as a potential way to monitor -- without needing to use a needle -- medication dosage and disease status," Dorrestein wrote in an email. "I can see it being used to understand the impact of personal care and hygiene products and how to make them even better for skin health."
The new technique might even be used to test how different types of materials affect our skin when used in clothing, he added.
"It's a great first step," said Kevin S. Sweder, director of the Forensic and National Security Sciences Institute at Syracuse University. The authors have shown that it is feasible to do this type of study, he added, but for now it is not cost-effective for use in criminal cases or the other real world applications the authors imagine.
"As the authors point out, a number of things need to be developed," said Sweder, who was not involved in the study. He noted that these requirements include a verifiable database for comparing profiles and additional computing powers.
The study made use of mass spectrometry, a highly sensitive and powerful tool well-known in the forensic community. It essentially converts molecules into particles that have an electric charge and then uses magnetic fields to sort, measure and identify the molecules as basic elements. Usually, this technique is used to identify traces of illicit drugs or explosives.
Wondering if the technique could identify everyday chemical traces, Dorrestein and his colleagues enlisted the help of 39 volunteers -- and their cell phones, perhaps the most touched personal item most of us carry.
The researchers swabbed four spots on each cell phone and eight spots on each person's hand. A total of 588 metabolomic samples were collected, with a significantly higher number of chemicals detected on the back of phones than on the front.
Then, using mass spectrometry, the research team identified as many molecular profiles as possible. This was accomplished by comparing the samples to references in the Global Natural Product Social Molecular Networking database, a crowdsourced mass spectrometry repository developed by Dorrestein and co-author Nuno Bandeira, an associate professor at UCSD.
Medications detected on phones included anti-inflammatory and antifungal skin creams, hair loss treatments, antidepressants and eye drops. Foods included caffeine, citrus, herbs and spices. Even months after their application on skin, sunscreen ingredients and DEET mosquito repellant could be detected on phones.
Based on the molecular evidence found on cell phones, the researchers learned certain habits of each participant: their medications, their preferred cuisines and their use of either high-end or low-end cosmetics.
"All these little clues lead to a composite lifestyle sketch of the individual," Dorrestein said.
Since crime scene fingerprints do not always turn up a match in a police database, investigators face difficulties in narrowing down a subject pool, he explained. The new methodology explored in this study can produce "thousands of little clues," which undoubtedly would help investigators profile likely suspects.
Phone and hand samples were unique to each participant. However, the researchers were not able to match each cell phone owner to their phone with perfect accuracy. In addition, phone chemicals collected from some of the same phones four months later were different from the original samples collected, in part, because the chemical signatures found on our phones change over time depending on our activities.
Future studies will have to look at how sensitive the approach is at discriminating between people, since more than a few will have touched any given cell phone, Sweder said. "Those types of questions will probably be dealt with by these investigators in the long run." Overall, more scientific rigor will be needed for this process to gain acceptance and pass as viable evidence in a court of law, he said.
"There's a misconception that all forensic evidence is present all the time," said Mike Marciano, a research assistant professor at Syracuse's Forensic and National Security Sciences Institute whose background is in DNA analysis.
But sometimes, DNA is missing and fingerprints can't be found, he said.
"There's always a need to fill the gaps," said Marciano, who was not involved in the research."The more information we have, the better we can try to fill the gaps and ensure that the right investigative approach is taken."