Fluorescent spray detects fingerprints at crime scenes

Scientists have developed a water-soluble, non-toxic fluorescent spray that makes fingerprints visible in just a few seconds, which should make forensic investigations safer, easier and quicker.

Latent fingerprints (LFPs) are invisible prints formed by sweat or oil left on an object after it’s been touched. Traditional forensic methods for detecting these fingerprints either use toxic powders that can harm DNA evidence or environmentally damaging petrochemical solvents.

The new dye spray, developed by scientists at Shanghai Normal University (SHNU) and the University of Bath, exhibits low toxicity and enables rapid visualisation of fingerprints at the crime scene. The researchers created two different coloured dyes — called LFP-Yellow and LFP-Red — which bind selectively with the negatively charged molecules found in fingerprints, locking the dye molecules in place and emitting a fluorescent glow that can be seen under blue light.

The dyes are based on a fluorescent protein found in jellyfish, called Green Fluorescent Protein (GFP), which is used extensively by research scientists to visualise biological processes. This means the dyes are biologically compatible and don’t interfere with subsequent DNA analysis of the fingerprints. Furthermore, the spray prevents splashes that could damage prints; is less messy than a powder; and works quickly even on rough surfaces where it is harder to capture fingerprints, such as brick.

“This system is safer, more sustainable and works faster than existing technologies, and can even be used on fingerprints that are a week old,” said Professor Tony James, from the University of Bath.

“Having two different colours available means the spray can be used on different coloured surfaces. We’re hoping to produce more colours in the future.”

Dr Luling Wu, also from the University of Bath, added, “The probes are only weakly fluorescent in aqueous solution, but emit strong fluorescence once they bind to the fingerprints through the interaction between the probes and fatty acids or amino acids.”

With the results of their research now published in the Journal of the American Chemical Society, SHNU’s Professor Chusen Huang said the scientists are now collaborating with companies to make the dyes available for sale.

“Further work is still ongoing,” the principal investigator said.

Image caption: The researchers have made two different coloured sprays which detect fingerprints on a range of different surfaces. Image has been cropped from the original and is courtesy of the study authors under CC-BY 4.0