Despite various methods and progress in related bloodstain techniques, determining the age of a bloodstain at a crime scene is one of the greatest and oldest challenges in forensic science.

Mikhail Berezin and co-workers, Washington University School of Medicine, USA, have developed a novel method to evaluate the age of a bloodstain in a crime scene within the first week.

The method is fast (ca. 20 min), reproducible, concentration independent, and requires a miniscule amount of the bloodstain with minimal sample preparation. The approach is based on the fact that the fluorescence lifetime of tryptophan — the major endogenous fluorophore in blood proteins — is highly sensitive to the protein conformation. In the process of blood aging, the major tryptophan-containing proteins, such as albumin and γ-globulins, undergo structural changes. Therefore, the time-related degradation of proteins in blood reflects the blood age. This approach minimizes problems with sampling and provides more accurate results.

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• Dating Bloodstains with Fluorescence Lifetime Measurements,
  K. Guo, S. Achilefu, M. Y. Berezin,
  Chem. Eur. J. 2012.
  DOI: 10.1002/chem.201102935