Quantifying contrast of latent fingerprints developed by fluorescent nanomaterials based on spectral analysis.

Fluorescent nanoparticles (NPs) have been used to develop latent fingerprints with enhanced contrast. However, a method for quantifying the contrast is still lacking, making it impossible to achieve quantitative comparison in the contrast enhancement between different fingerprint developing agents. Here we proposed a new method to quantify the developed contrast using two indexes when fluorescent NPs were used to develop the latent fingerprint. One is the intensity index (I) defined as the ratio between the integrated fluorescence intensities of the signal and background in the fluorescence spectra of the developed fingerprint. Another is the chroma index (C) determined from the color difference between developed fingerprints and their substrates in the chromaticity graph. We defined the developed contrast as the product of the chroma index and the common logarithm of the intensity index (C·lg I), and validated this method using both down- and up-conversion fluorescent NPs and on a variety of different substrates (glass, marble, red paper and money). We showed that the developed contrast quantified by our method effectively reflected the true contrast but the intensity or chroma index alone was not always effective. This work opens up a new avenue to quantifying and enhancing the developed contrast.

Rapid visual detection of nitroaromatic explosives using a luminescent europium-organic framework material.

Rapid field screening is enormously important in forensic analysis of explosives. In this article, we used a methodology based on a strong red-fluorescent europium-organic framework (Eu-MOF) material for sensitive and selective detection of picric acid, TNT, and tetryl using the fluorescence quenching effect. Results indicate that Eu-MOF can be used for the visual detection of these three explosives with low detection limits (20-140 µg/mL) and high quenching efficiency (Ksv > 104 M-1). Furthermore, this material can be recycled just by washing it with ethanol. The fluorescence quenching mechanism is also discussed. Importantly, we prepared a portable test strip that can be used for sensing TNT, and using this, we achieved a rapid field test for explosives. Consequently, Eu-MOF is a promising candidate material for use as an explosive optical sensor.