Researchers from China’s Soochow University have developed a fluorescent polymer that illuminates latent fingerprints made in blood at crime scenes.

According to researchers, the fluorescent polymer binds to the blood in fingerprints that have been wiped away at crime scenes by perpetrators in an effort to conceal their identity.

Although dyes exist to reveal concealed fingerprints, they are oftentimes limited to surfaces without textures and do not produce high contrast images. As such, the team devised the new polymer that produces high contrast images of the fingerprints as fluorescent compounds reportedly enhance the contrast between fingerprints and the surfaces on which they are held.

Fingerprint patterns made in blood are clearly visible on aluminum foil (left) and painted wood (right) when developed with a fluorescent polymer. Source: Adapted from ACS Applied Materials & Interfaces 2021, DOI: 10.1021/acsami.1c00710

To obtain visible and stable images of bloody fingerprints, researchers had to ensure that the fluorescent polymer wound bond to the blood proteins to reveal clear fingerprints on a variety of surfaces.

To accomplish this, the researchers added a second amino group to a previously developed yellow-green fluorescent polymer, thereby encouraging stable bonds to form between the polymer and blood serum albumin proteins.

The team dissolved the polymer and soaked it into a cotton pad that was placed on prints made using chicken blood on aluminum foil, multicolored plastic and painted wood surfaces. Following an interval of a few minutes, the cotton pad was removed and air-dried, revealing that each of the surfaces demonstrated high contrast between the blood and background under blue-violet light.

According to the team, fingerprint characteristics — ridge endings, short ridges, whorls and sweat pores, for example — were highly visible. These characteristics were also reportedly visible even after researchers contaminated the prints with mold and dust, and after they were held for 600 days in storage.

Additionally, a piece of human DNA was intact after it was combined with the polymer.

The research appears in the journal ACS Applied Materials & Interfaces.