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When fluorescent powders lead the investigation

Police investigators have various types of powder at their disposal, which they spray on crime scenes in order to reveal fingerprints, because these powders stick to the oily residue left by fingers. Fluorescent powders are part of the kit. The lighting of a UV lamp reveals fingerprints with a very high sensitivity.

A particularly difficult case is the detection of fingerprints on paper, especially when they are old. The trick is to wash the paper in a solution containing a fluorescent dye, and then dry it in an oven. Observation under a UV lamp reveals the fingerprints thanks to the emission of fluorescence. To avoid any disruption from the blue fluorescence caused by the possible presence of an optical brightener, an orange filter is placed between the paper and the camera lens.

Laboratoire de photophysique et photochimie supramoléculaires et macromoléculaires, CNRS-ENS Cachan

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When fluorescent powders lead the investigation