ABSTRACT
Chemical composition in fingermarks could provide useful information for forensic studies and applications. Here, we evaluate the feasibility of analysis and imaging of fingermarks via elements by synchrotron radiation X-ray fluorescence (SRXRF) and commercial X-ray fluorescence (XRF). As a proof of concept, we chose four brands of sunscreens to make fingermarks on different substrates, including plastic film, glass, paper, and silicon wafer. We obtained an evident image of fingermarks via zinc and titanium by XRF methods. In addition, the ratios of element concentrations in sunscreen fingermarks were obtained, which were in accordance with the results obtained by acid digestion and ICP-OES analysis. In comparison, commercial XRF offers the most advantages in terms of non-destructive detection, easy accessibility, fast element images, and broad applicability. The possibility to acquire fingermark images simultaneously with element information opens up new avenues for forensic science. Graphical abstract.
Subject(s)
Sunscreening Agents/chemistry , Proof of Concept Study , Spectrometry, X-Ray Emission , Titanium/analysis , Zinc/analysisABSTRACT
Selecting appropriate developing methods/reagents or their combination to enhance the effect for fingerprint development is of great significance for practical forensic investigation. Ethyl-2-cyanoacrylate ester (superglue) fuming is a popular method for "in-situ" developing fingerprints in forensic science, followed by fluorescence staining to enhance the contrast of the fingerprint image in some occasion. In this study, a series of fluorescent poly(p-phenylene vinylene) (PPV) nanoparticles (NPs) in colloidal solution were successfully prepared and the emission color was tuned via a simple way. The fuming process was carried out using a home-made device. The staining was accomplished by immersing a piece of absorbent cotton into the solution of NPs, and then gently applied on the fumed fingerprints for several times. The PPV NPs were found to have a better developing effect than Rhodamine 6G when excited by 365â¯nm UV lamp. Different emission colors of NPs are advantageous in developing fingerprints on various substrates. Mechanism study suggested that the NPs were embedded in the porous structure of the superglue resin. In all, the combination of fuming method with the staining by conjugated polymer NPs has been demonstrated to be successful for fluorescent fingerprint development and be promising for more practical forensic applications.
ABSTRACT
Poly(p-phenylenevinylene) (PPV) nanoparticles in aqueous colloidal solution have been prepared via a modified Wessling method, with the addition of surfactant. The fluorescent colloidal solution was used as the developing solution to develop the fingerprints on different substrates. The developing process was accomplished simply by immersing the substrates into developing solution and then taking out, followed by rinsing with deionized water. The initial study about the fingerprints on the adhesive tapes showed that the developing solution is very effective in fluorescence development on both fresh and aged visible fingerprints; and such an effect was negligibly affected by treating the fingerprints with water or other organic solvents, whether before developing or after. Further study on latent fingerprints (LFPs) demonstrated that PPV nanoparticles in colloidal solution have high sensitivity in developing fingerprints to give very clearly fluorescent patterns. At least 6 months of storage of the colloidal solution did not reduce the developing effect; and each developing solution (3.6 mg/mL, 5.0 mL) can be used to develop at least 30 fingerprints without sacrificing the legibility of the pattern. The preliminary mechanism investigation suggested that selectivity achieved toward the ridge of the fingerprint is very likely due to the affinity between PPV molecules and oily secretions of the fingerprints. Digital magnification of the developed fingerprints provided more details about the fingerprint.
