Tell-Tale Sign of Age

A person's age may be determined from a bloodstain, right at the crime scene, through an imaging technique called Raman spectroscopy.

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Unlike DNA and fingerprints, human blood changes over the course of a lifetime. An infant’s blood is different from that same person’s blood later as an adolescent, and it is still different when the adolescent becomes a mature adult. Scientists have now developed a new technique that, when perfected, could allow quick determination of the age of a person from a bloodstain, right at the scene of a crime.

Analytic chemists Igor Lednev and Kyle Doty of the State University of New York at Albany applied a technique called Raman spectroscopy to donated blood from infants under one year, adolescents of eleven to thirteen, and adults of forty-three to sixty-eight years of age. They found noticeable differences in how blood from the three different age groups scatter light. For example, infants, compared to adolescents and adults, exhibited higher peaks at a portion of the spectrum that marks the presence of methemoglobin, a form of hemoglobin that cannot bind oxygen.

After they established that Raman spectroscopy could identify differences in bloodstain spectra based on the age of the donors, the researchers next tried to identify the donors’ ages, based on their blood. They built a model of expected spectral variations for each age group, using data from 80 percent of the donated blood samples. When that model was applied to the other twenty percent of the samples, it was 95 percent accurate or better at predicting donor age.

Lednev and Doty emphasize that their research is a “proof of concept” project that they hope to refine in the future. They want to improve their chemical models to determine more precisely a blood donor’s age and control for possible anomalies due to illnesses. They also plan to expand the diversity of the donor pool, to determine any differences in blood components due to ethnicity.

Because Raman spectroscopy is portable and can be used to identify small samples without destroying them, it is increasingly used in forensic analysis. Lednev plans to take the experiments from the lab to the field. As he notes, further refinements to Raman spectroscopy-based models “would substantially contribute to the investigation and help ensure correct resolution of a crime.” (ACS Central Science)