Quantifying fluorescence contrast of latent fingerprints developed with micro/nanoparticles through spectroscopic...

Fluorescent micro/nanoparticles have been used to visualize latent fingerprints in forensic science. However, due to the current lack of a systematic method to quantify the fluorescence contrast of developed fingerprints, the comparison of fingerprint visualization effects of various developing agents is still limited to empirical evaluation. Here, we presented a fingerprint fluorescence contrast quantification strategy that comprehensively considers fluorescence intensity and color indexes, based on photoluminescence spectroscopy analysis. The intensity index represents the relative fluorescence intensity (I) between the fingerprint and the background. The color index is quantified by its three elements, including hue, saturation, and value (L), where hue and saturation are reflected by chroma (C). Fluorescence contrast is defined as the product of relative fluorescence intensity, chroma parameter, and the common logarithm of value index (I·C·lg L). The proposed approach quantified fingerprints deposited on substrates with varying degrees of patterning and fluorescence interference, using full-color-emitting micro/nanoparticles, and was compared with existing methods, demonstrating its high detection limit, accuracy, and sensitivity. Finally, we developed a tunable multi-color fingerprint enhancement technique to enhance low-quality and low-contrast fingerprints. Therefore, the established comprehensive fluorescence contrast quantification and enhancement strategy provides a new avenue for practical forensic analysis and identification.