January 07, 2024 | UR Gate

Shining Light on Invisible Bloodstains Using Fluorescent Polymer

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Illuminating invisible bloody fingerprints with a fluorescent polymer

"In the context of discussing (Invisible Bloodstains Using Fluorescent Polymer), criminals typically thoroughly clean the crime scene, wiping away visible blood and fingerprints. However, numerous traces of invisible bloodstains remain, imperceptible to the naked eye. Stains can be detected using dyes in crime scene investigations, but some surfaces are challenging for dyes to efficiently reveal. Researchers in the ACS journal reported on fluorescent polymers capable of detecting blood associated with fingerprints (without causing damage to the DNA) on surfaces. High-resolution images were captured.

Fingerprints are compelling evidence in forensic medicine because the arches, loops, and whorls they form are unique to each individual and remain unchanged with age. When violent crimes occur, finding bloodstains on the perpetrator's fingerprints becomes difficult, especially if they attempt to clean the crime scene afterward. Scientists typically use dyes to detect such evidence, but some require complex techniques to extract an image. The presence of various items at the crime scene, along with uneven surfaces with engravings like wood, poses a challenge in identifying the identity of the perpetrator. Fluorescent compounds can enhance the contrast between surfaces and fingerprint impressions, even on surfaces that dyes may not efficiently reveal. However, the particles of these compounds need to form strong bonds with blood particles.

Researchers Li-Juan Fan, Rongliang Ma, and their colleagues aimed to discover a simple method to bind fluorescent polymers to blood proteins, enabling them to find clear fingerprints on various surfaces. They modified a previously developed polymer (yellow and green) by adding a second amino compound group, allowing the polymers to form bonds with albumin proteins in the blood. The researchers dissolved the polymer, absorbed it with a cotton swab, and passed it over pre-made fingerprints of chicken blood on various surfaces like aluminum, plastic, and coated wood. After leaving them for a few minutes, they removed them, allowing them to air-dry. All surfaces showed contrast between blood and the background, including surfaces with sharp edges, twists, and openings.

The researchers tested this technique on several surfaces stained with dirt and left stored for 600 days to detect the presence of blood, which was successful. Results showed contrast between blood and the imprinted surfaces. Additionally, experiments demonstrated that when the polymers were mixed with a piece of human DNA, there was no change. This means that any genetic material found can determine the identity of the suspect.

Academic credit for supporting this research goes to Yao Liu from the Chinese Academy of Engineering. This research is one of the projects conducted within the Natural Science Foundation of Higher Education in Jiangsu, China."