Solid powder fluorescence shows great potential for application in medicine, biology, and engineering, especially in the identification of latent fingermarks in forensic science. However, conventional developing methods suffer from some drawbacks, such as low contrast, low sensitivity, low selectivity, and high toxicity. To conquer these challenges, novel SiO2@C-dot microspheres were prepared via a facile one-pot hydrothermal method by using citric acid as a carbon source and aminosilane as a nitrogen source. Interestingly, the results showed that the resultant powders possess good monodispersity, high fluorescence emission, and resistance to self-quenching. Additionally, the mechanism for the solid-state fluorescence of SiO2@C-dot compounds was also investigated. More importantly, the fingermarks on various surfaces, including transparent glasses, ceramic tiles, transparent plastics, aluminum alloys, plastic cards, painted woods, artificial leathers, and Chinese paper money, developed by the powders have indicated well-defined papillary ridges under a 365 nm UV lamp. The novel strategy of using monodisperse SiO2@C-dot microspheres as a fluorescent label for developing latent fingermarks showed greater advantages compared to conventional methods, which was also demonstrated using the automatic fingerprint identification system. It is simple, rapid, low-cost, nontoxic, and effective, and is expected to be a promising alternative for the development of latent fingerprints in forensic science.

Fluorescence color of rare earth-based nanopowder can be modulated by regulating the molar ratio of components, which offers a promising strategy in many fields of applications. Herein, a series of binuclear Eu Tb(AA)Phen ( x = 1, 0.75, 0.5, 0.25, 0.1, 0) complexes were fabricated using acrylic acid (AA) as the first ligand and using 1,10-phenanthroline (Phen) as the second ligand. The characterization results showed that this novel binuclear (Eu, Tb) complex can emit strong red or green light via simply varying the molar ratio of europium and terbium. Moreover, the results of spectroscopic and zeta potential analyses suggested that there was an electrostatic adherence mode in the interaction between the Eu Tb(AA)Phen complex and fingerprint residues. Importantly, our Eu Tb(AA)Phen nanopowder was successfully applied to the enhanced development of latent fingerprints on various surfaces by the powder dusting method, exhibiting a high contrast, sensitivity, and selectivity, as well as a low detection limit in forensic science, which was further confirmed by analysis with an automatic fingerprint identification system. In summary, our synthetic rare earth-based nanopowder exhibits promise as an ideal fluorescent probe for the enhanced development of latent fingerprints, based not only on physical absorption at the macrolevel but also on electrostatic interactions between our rare earth complex and fingerprint residues at the molecular level, which could provide an enhanced affinity compared with traditional fingerprint powders.

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A series of dinuclear complexes with molar ratios of cerium to lanthanum of 1:0, 1:1, 1:2, 1:4, 1:7, 1:9 and 0:1 was synthesized using 5-sulfosalicylic acid (SSA) as the first ligand and 1,10-phenanthroline (Phen) as the second ligand, recorded as Ce1−x La x (SSA)3Phen (x = 0, 0·5, 0·67, 0·8, 0·875, 0·9, 1), and the complexes were blended with tricellulose acetate (TCA) to obtain luminescent polymer materials. The compositions and structures of the rare earth complexes were determined through elemental analysis, energy-dispersive X-ray analysis, infrared spectroscopy and thermogravimetric analysis. Under the optimum excitation wavelengths, all dinuclear complexes emitting blue light displayed the characteristic emission of the cerium (Ce3+) ion. The fluorescence spectra showed that the 85:15 TCA/Ce0·2La0·8(SSA)3Phen composite showed the strongest fluorescence among all composites and the quantum efficiency was calculated as 30·6%. The introduction of the lanthanum (La3+) ion into the cerium ion complex can effectively reinforce the luminescence intensity of the complex and be favorable for retaining the excellent fluorescence in the TCA matrix. The 85:15 TCA/Ce0·2La0·8(SSA)3Phen composite possesses fine luminescence properties and thermal stability for potential usage as a blue fluorescent material.

The requirement of nonfluorescent developers for aged latent fingerprint development is still of great urgency in forensic science. To enhance the specific interaction between fingerprint residue and nano-developers, a γ-methacryloxy propyl trimethoxyl silane (MPTS) modified zinc oxide nanoparticle (ZnO NP) was synthesized. The crystal structure, morphology, surface functional group, thermostability, UV/Vis spectra, photoluminescence and stability of sedimentation were characterized to prove the hydrophobicity, UV blocking nature and nonfluorescence of as-prepared MPTS-modified ZnO NPs. Additionally, after the specific surface area (SSA) of samples with different MPTS amount was analyzed by BET, a competitive adsorption mechanism between silane-ZnO bonding and silane oligomer-ZnO deposition was suggested. In the demonstration of latent fingerprint development, the powder dusting method was utilized on various surfaces both in positive and reversed imaging modes, exhibiting the high contrast, high sensitivity, high selectivity and wide applicability, even for aged fingerprints. Therefore, it provides a new strategy for fast, efficient and inexpensive development of older latent fingerprints in forensic analysis.

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