Fingerprints as physical evidence have long supported criminal investigation and adjudication. In practice, however, fingerprint identification relies mainly on examiners' experience. Furthermore, expert opinions tend to be categorical, even though the opinions with the same conclusion could differ substantially in evidential strength. To quantitatively assess fingerprint evidential value, this study proposes a machine learning-based framework as an interpretable decision-support tool. A lightweight residual one-dimensional convolutional neural network was constructed, incorporating channel recalibration and a similarity-driven attention mechanism to learn adaptive contribution weights for different matched minutiae (minutiae for short). Controlled experiments revealed that the predicted evidential value increased with the number of minutiae and was significantly influenced by the quality of minutiae. With 10 minutiae, the mean predicted scores were 4.49, 7.00, and 9.09 for blurred, moderately blurred, and clear minutiae, respectively. Multiple regression analysis indicated that replacing a pair of blurred minutiae with a pair of clear minutiae increased the score by 0.492, whereas replacing it with a pair of moderately blurred minutiae increased the score by only 0.216. By mapping predicted scores to graded levels of evidential strength, the framework contributes to a paradigm shift from categorical expert opinions to graded ones, helping courts evaluate fingerprint evidence more scientifically.

By using naturally abundant diatomite with unique particle and porosity structures as the silica precursor, a novel green-emitting diatomite-derived Zn2SiO4:Mn phosphor has been obtained as a dual functional sensor for developing latent fingerprints, serving as a fingerprint powder and a reagent for small particle reagents (SPRs). Parameters including calcination duration, calcination temperature, molar ratio of manganese salt to zinc and manganese salts, and molar ratio of zinc and manganese salts to diatomite have been adjusted to optimize luminescent property of this phosphor. Formation mechanism has been proposed based on the change of particle morphology and mesopore structure. With respect to material synthesis, high porosity of diatomite plays a critical part in ensuring uniform doping of Mn2+, lowering reaction temperature, sparing inert or reducing atmosphere. Furthermore, surplus diatomite in the precursors results in basic retention of particle morphology which is favorable for latent fingerprint development. Efficient green emission centered at 525 nm of the diatomite-derived Zn2SiO4:Mn under 254 nm excitation originates from the 4T1 → 6A1 transition, making it a very capable fluorescent fingerprint powder that can suppress interferences from various surfaces, especially with the aid of 530 nm band-pass filter as an optical filter and green channel of RGB images as a digital filter. Given that the luminescence of diatomite-derived Zn2SiO4:Mn phosphor is not subject to external environment factors such as water or dissolved components, a fluorescent SPR prepared by adding a certain amount of this powder (10 mg mL-1) to an aqueous solution of sodium dodecyl sulfate (0.050 wt%) shows better performance compared with some commercially available SPRs. Latent fingerprints on glass sheets can be clearly visualized even if they have been immersed in water as long as 5 days. Therefore, the successful acquisition of green luminescent diatomite-derived Zn2SiO4:Mn contributes to both the synthesis of this popular green-emitting phosphor and the application of fingerprint development.

NaYF4:Yb, Er up - conversion fluorescent micron - materials (UC MMs) were synthesized via a typical chemical approach by using rare earth stearate as the precursor and ethanol-water-oleic acid mixture as the solvent. Then, using NaY(F)4:Yb, Er as the matrix material, 1,4-phthalic acid (PTA), Eu3+, and 1,10-phenanthroline (Phen) were sequentially bonded onto its surface to prepare NaYF4:Yb,Er-(PTA)Eu(Phen) micron - composites (NCs) with dual fluorescence properties. The morphology of the NCs was characterized as micro - rods with nano - spheres attached onto the surface. The NCs exhibited strong ultraviolet (UV) and near. infrared (NIR) absorptions in the rang. es of 200-310 nm and 976 nm, respectively. Excited by 254 nm UV and 980 nm NIR light, they could emit 616 nm red down. conversion (DC) and 540 nm green UC fluorescence, respectively. Finally, the micro. suspensions, which were prepared by mixing NCs with sodium dodecyl sulfate (SDS) in water, were used for latent fingerprint development and dual - mode fluorescent enhancement. After optimization, the mass fraction of NCs was 1.67%, the mass fraction of SDS was 0.50%, and the development time was 30 s. Experimental results showed that the fingerprint development combined with fluorescent enhancement possessed high contrast, sensitivity, and selectivity. In addition, the type of fluorescent enhancement mode had a significant impact on comparison but little effect on sensitivity or selectivity.

Powdering latent fingerprints with photoluminescent materials is the most frequently used way to reveal the evidential value. Still, traditional and most emerging fingerprint powders possessing a single luminescence mode are insufficient to deal with the ones on surfaces with multicolor or intricate patterns. Inspired by violet-pump light emitting diode and wavelength division multiplexing technique, we present an intuitive notion and detailed implementation of multiplexing imaging and multichannel enhancement of latent fingerprints by near-white light-emitting copper nanoclusters (CuNCs)/starch composites. Through optimally combining blue-with orange-emitting CuNCs/starch composites, as well as cyan-with orange-emitting CuNCs/starch composites, two near-white light-emitting CuNCs/starch composites with fluorescence emissions across the visible wavelength region and color coordinates of (0.33, 0.28) and (0.33, 0.32) under excitation of 365 nm UV light have been acquired. All three levels of latent fingerprint morphological features can be developed precisely using them. In addition to the visual evaluation of developed fingerprint images, a quantitative and comprehensive analysis of the quality of fingerprint imaging and enhancement has been performed using Python, along with a qualitative commentary concerning fingerprint imaging and enhancement on problematic surfaces based on spectral analysis, proving that our strategy can widen the gap between fingerprint area and furrow-background areas, improve the signal-to-noise ratio, and thus enhance the fingerprint image quality.

The influence of material properties on fingerprint development effects were systematically studied. morphologies, sizes, and surface properties were chemically synthesized and further used for latent fingerprint development. Then, the developing effects were comprehensively evaluated by visual analysis combining with fingerprint development were quantitatively evaluated from three dimensions including contrast, sensitivity, and selectivity. The fluorescence properties of developing materials and substrates could significantly affect the noise, the higher the contrast. The sizes and morphologies of the developing materials could respectively influence the quantity and quality of developed minutiae, and significantly affect the developing sensitivity, namely, the smaller the particle size of developing materials, the more the quantity of developed minutiae and the higher the sensitivity; the smaller the surface area of developing materials, the higher the quality of developed minutiae and the higher the sensitivity. The surface properties together with the sizes and morphologies of developing materials stronger the specific adsorption of developing materials with fingerprint substance, and the weaker the non-specific adsorption of developing materials with substrate, the higher the selectivity. Moreover, the fingerprint development using the materials with suitable surface area and appropriate mass would have a high selectivity.

Latent fingerprints (LFs) are commonly encountered at crime scenes. Developing the LFs clearly is the precondition for further analysis and identification. In this work, titanium dioxide-coated carbon dots (CDs@TiO2) fluorescent nanosuspensions were prepared and used for high-quality LF development. Firstly, carbon dots (CDs) were synthesized via a solvothermal approach using citric acid and urea as raw materials and N,N-dimethylformamide as solvent. Then, CDs@TiO2 nanomaterials (NMs) were formed by coating CDs with a layer of TiO2 shell based on the ammonia-catalyzed hydrolysis of titanium butoxide, and the synthesis conditions were optimized. The optimized synthesis conditions were as follows: the amount of CDs, tetrabutyl orthotitanate, water, and ammonium hydroxide was 3.0, 1.5, 1.5, and 0.1 mL, respectively, the reaction temperature was 50 degrees C, and the dropping period was 30 min. After that, the morphology, composition, structure, and optics properties of CDs and CDs@TiO2 NMs were characterized. Characterization results showed that, CDs were near spherical with an average diameter of 7.54 nm, they could give characteristic Raman scattering peaks as well as infrared absorption peaks of CDs, and possessed the crystal structure of hexagonal graphite, their UV absorption peak was at 343 nm, and their maximum fluorescence excitation and emission wavelength was at 450 and 567 nm respectively; CDs@TiO2 were irregularly spherical with an average diameter of 114.85 nm, they could give characteristic Raman scattering peaks as well as infrared absorption peaks of both CDs and TiO2, and possessed the crystal structure of both hexagonal graphite and tetragonal rutile TiO2, their UV absorption peak was at 321 nm, and their maximum fluorescence excitation and emission wavelength was at 387 and 529 nm respectively. Finally, CDs@TiO2 NMs were made into nanosuspension for developing LFs via hydrophobic interaction. The development conditions were optimized, and the results of LF development were investigated in detail. The optimized development conditions were as follows: the concentration of sodium dodecyl sulfate and choline chloride was 1.0 parts per thousand similar to 2.0 parts per thousand and 4.0 parts per thousand similar to 6.0 parts per thousand respectively, and the developing time period was 10 similar to 20 s. Experimental results showed that, the LFs could emit bright blue fluorescence under 490 nm excitation, which exhibited coherent and clear papillate ridges and distinct minutiae. Our proposed method based on CDs@TiO2 fluorescent nanosuspensions could develop the LFs on common smooth and non-porous substrates with high quality, possessing enough contrast, high sensitivity, good selectivity, and wide applicability.

A deep learning-based method for recognizing the minutiae in fingerprint, as well as a Python programming-based evaluation system for quantifying the evidence value of fingerprint was proposed. Firstly, latent fingerprints, which were developed using a series of fluorescent nanomaterials synthesized by chemical methods, were used as unknown fingerprint (UKFP), while ink impressed fingerprints were used as known fingerprint (KFP). Then, the bifurcations and terminations in minutiae were recognized using the improved YOLOv8 deep learning model. After that, the similarity index (Sim.) of UKFP vs KFP were calculated by analyzing the angle similarity factor (alpha) and the curve similarity factor (beta) between UKFP and KFP, meanwhile, the sensitivity index (Sen.) were calculated by analyzing the fineness factor (gamma) between UKFP and KFP. The evidence value (EV) of fingerprint was thus obtained by the combination of Sim. and Sen.. The calculation formulas for above evaluation factors (i.e. alpha, beta and gamma), evaluation indexes (i.e. Sim. and Sen.), and EV were also put forward. Finally, the evaluation system for quantifying the evidence value of fingerprint was established, the feasibility and reliability of this system were verified, and the external factors that impacted on Sim., Sen., and EV were investigated in detail. The Python-based evaluation system for quantifying the evidence value of fingerprint could achieve the goals objectively, comprehensively, accurately and efficiently, exhibiting easy operability, high efficiency, responsiveness and reliability. This research was expected to provide beneficial references for quantitatively evaluating and thoroughly the evidence value.

The anti-counterfeiting application of three-color fluorescent carbon dots(CDs)in high-quality inkjet printing was studied.Blue,green and red fluorescent CDs were synthesized by solvothermal method using three kinds of isomers of phenylenediamine as precursor,and ethanol-glycerol mixture as solvent.The morphology,composition,structure,and optical properties were characterized.Blue,green and red fluorescent inks were then prepared by diluting CDs with water.The dilution ratio,excitation light source and filtering method were also optimized.The optimal dilution ratio of blue,green and red fluorescent ink was 5,5 and 20,respectively.Under 365,415 and 450 nm light excitation,bright blue,green and red fluorescence from above inks could be observed by using a blue,green and red filter,respectively.These fluorescent inks were finally used for high-quality inkjet printing through monochrome printing mode and polychrome printing mode.In addition,the sensitivity and contrast of printing were quantitatively investigated.The series of three-color fluorescent inks possessed great prospects in ordinary and invisible fluorescent anti-counterfeiting application.

A serious of rare earth luminescent micro/nano-materials- materials with various properties were synthesized via chemical method for fluorescent development of latent fingerprints (LFPs). Three evaluation indexes namely contrast, sensitivity and selectivity were introduced to evaluate the effects of LFP development. Quantitative formulas for calculating the contrast, sensitivity and selectivity were further put forward, and a quality evaluation system based on Python was thus established. In addition, the objective evaluation value was finally confirmed to be consistent with the subjective visual judgment. The reproducibility of this evaluation method was finally confirmed. The effects of luminescence intensity and color of developing materials on the contrast, particle size of developing materials on the sensitivity, and micromorphology and surface property of developing materials on the selectivity were discussed in detail. Five effective ways were also proposed to promote the quality of LFP development, such as increasing the luminescence intensity, tuning the luminescence color, decreasing the particle size, adjusting the micromorphology, and modifying the surface property. This quality evaluation system based on Python could evaluate the effects of LFP development objectively, accurately and comprehensively, exhibiting easy operability, high efficiency, sensitive response, accurate and reliable results, and wide applicability, which would provide beneficial references for the reasonable selection of LFP development methods as well as objective evaluation of evidence value.

Fluorescent carbon dots(CDs)were synthesized via a solvothermal method with citric acid and urea as raw materials,and ethylene glycol as reaction solvent.The micromorphology,crystal structure,elemental composition,surface functional group,and optical property of as-synthesized CDs were characterized.The excitation-dependent fluorescence property of CDs was investigated,and the effects of synthesis conditions including reaction temperature,reaction time and raw materials on excitation and emission wavelengths of the CDs were also discussed.Then,a series of CDs-based fluorescent composites were prepared by combining CDs with starch,nano-silica,montmorillonite,kaoline,kieselguhr and magnesium oxide,respectively.Finally,the CDs-starch composites were used for latent fingerprint development on smooth substrates,and the qualitative as well as quantitative evaluation of the contrast,sensitivity and selectivity in fingerprint development were also made.Enhanced development of latent fingerprints was thus achieved by the aid of the excitation-dependent fluorescence property of CDs-starch composite combined with the optical filtering technique,which could decrease the background noise interference to a great extent.Experimental results showed that,the contrast between fingerprint(developing signal)and substrate(background noise)was obvious,exhibiting a strong contrast;the minutiae of papillary ridges were clear,indicating a high sensitivity;the adsorption between CDs-starch composites and fingerprint residues was specific,showing a good selectivity.

It is a fundamental task in forensic science to utilize latent fingerprints to identify individuals who may be involved in a crime. Over the past two decades, owing to multiple benefits of using infrared-related materials and techniques in the development, imaging, and analysis of latent fingerprints, numerous studies have been performed to solve substantial challenges faced by conventional methods in this area. In this review, to appeal the communities in related research fields and to provide the wider scientific community with broad implications, comprehensive review and detailed discussion of the infrared-related materials and techniques are presented according to the imaging modes applied to capture and analyze fingerprints, namely, NIR to VIS mode, UV-VIS to NIR mode, NIR to NIR mode, and IR absorption/reflection mode. Finally, based on the overview of recent progress, three main aspects that require to be explored and improved in the research of this field are proposed.

Latent fingerprints, as one of the most frequently encountered traces in crime scene investigation and also one of the largest sources of forensic evidence, can play a critical role in determining the identity of a person who may be involved in a crime. Due to the invisible characteristic of latent fingerprints, exploring efficient techniques to visualize them (especially the ones resided on metallic surfaces) while retain the biological and chemical information (e.g., touch DNA) has become a multidisciplinary research focus. Herein we reported a new and highly sensitive electrochemical interfacial strategy of simultaneously developing and enhancing latent fingerprints on stainless steel based on synchronous electrodeposition and electrochromism of manganese oxides in a neutral aqueous electrolyte. By utilizing a specially designed device for electrochemical testing and image capture, a series of electrochemical measurements, physical characterization and image analysis have been applied to evaluate the feasibility, development accuracy and enhancement efficacy of the proposed electrochemical system. The qualitative and quantitative analysis on the in situ and ex situ fingerprint images indicates that the three levels of fingerprint features can be precisely developed and effectively enhanced. Forensic DNA typing has also been performed to reveal actual impact of the proposed electrochemical system on subsequent analysis of touch DNA in fingerprint residues. The ratio of detected loci after electrochemical treatment reaches up to 98.5 %, showing non-destructive nature of this fingerprint development and enhancement technique.

The research of new efficient materials as fingerprint powders has been receiving a lot of attention and interest from researchers of chemistry and material science. Up to now, due to multiple advantages of silica and silicate as matrix materials, numerous studies have been performed to design and synthesize silica- and silicate-based materials that can be applied to fingerprint development and analysis. In this review, we highlight the recent progress of this area from a unique perspective that considers the structure and function of matrix materials. Accordingly, the discussion of this review has been divided into four sections. In the end, with respect to the design, synthesis and forensic application of silica- and silicate-based materials as fingerprint powders, a summary based on previous research and perspectives on future research are presented.

Carboxyl functionalized terbium fluorescent nanocomplex was chemically synthesized by a one-step process using terbium ion as the luminescence center, p-phthalic acid as the first ligand, and phenanthroline as the second ligand. The carboxyl groups on the surface of these nanocomplexes were further activated using 1-(3dimethyl-amino-propyl) -3-ethylcarbodiimine hydrochloride as the activator combined with N-hydroxy succinimide as the stabilizer. Due to the rapid and mild amide reaction between the activated carboxyl groups on the surface of the nanocomplexes and the amino groups in bloody fingerprint residuals, the resulting nanocomplexes were finally used as fluorescent probes for the targeted development of latent bloody fingerprints. Excited with 254 nm ultraviolet light, the papillary ridges could emit strong green fluorescence, which could give a sufficient contrast between the developing signal and the background noise; the papillary ridges were coherent, the minutiae were sharp, and the sweat pores were distinct; the contrast between the ridges and the furrows were obvious. The parameters for fingerprint development were optimized, namely, the mass ratio of nanocomplex to water in suspension was recommended to be 1:35, and the period for staining was recommended to be 20 s. In addition, the contrast, sensitivity, selectivity, and applicability in fingerprint development were also investigated in detail. Experimental results show that the activated carboxyl functionalized terbium fluorescent nanocomplexes are suitable for developing the latent bloody fingerprints on smooth non- and semi-porous surfaces with high quality and high efficiency.

Latent fingerprints left at crime scenes are important trace evidence but invisible to the unaided eye. It is essential to use some methods to make latent fingerprints visible before analysis and identification. The introduction of new materials and techniques has promoted the innovation of fingerprint development methods in recent years. Especially many photoluminescent materials such as rare earth luminescent materials, quantum dots and fluorescent metal nano-clusters have shown high potentials in this field. Carbon dots ( CDs) , as a type of relatively new nanomaterial exhibiting good photoluminescent properties, have lately caught the attention of researchers in fingerprint development. In this paper, recent advances in the application of solution-dispersed CDs and solid-state CDs powders in fingerprint development are reviewed. To be specific , solution-dispersed CDs used in fingerprint development rely on either the classical mechanism of small particle reagents or some special effects including coffee-ring effect and interfacial segregation effect; while solid-state CDs powders used in fingerprint development include CDs powders and CDs-based composite powders which are prepared following different strategies. The challenges in this research area concerning morphologies and surface properties of CDs , photoluminescent properties of CDs, and compatibility with chemical and biological analysis are analyzed. Meanwhile , possible solutions are also proposed to provide guidance to researchers.

SrAl2O4: Eu, Dy, La afterglow luminescence materials were prepared via a one-step combustion approach at a relatively low temperature by using aluminum nitrate, strontium nitrate and rare earth nitrate as oxidants, carbamide as reductants and fuels , and boric acid as fluxing agents. The preparation conditions including furnace temperature, amount of carbamide, amount of boric acid, and doping concentrations of LW + ions were optimized. Then, the micromorphology, crystal structure , ultraviolet absorption property, and luminescence performance of as-prepared materials were characterized by scanning electron microscopy, X-ray diffraction pattern, ultraviolet-visible spectrum , and fluorescence emission spectrum, respectively. The prepared materials were polyhedral in shape with micron size, and monoclinal in phase with good crystallinity, which could emit strong luminescence at 514 nm under excitation of 252 or 334 nm ultraviolet light. After excited with 365 nm long-wavelength ultraviolet light for 30 s and then removing the excitation source, these materials could maintain strong green emission in dark field. Finally, the afterglow luminescence powders were applied for background-free development of latent fingerprints on various smooth substrates. The contrast, sensitivity and selectivity in fingerprint development were discussed in detail. After enhancing by afterglow luminescence treatment, the contrast between the developing signal and background noise were strong, all the detailed features of papillary ridges were obvious, and the adsorption between the developing powders and papillary ridges were specific, showing prominent advantages such as strong contrast, high sensitivity and good selectivity. Experimental results showed that, the method proposed here based on afterglow luminescence effect could achieve a high performance in background-free development of latent fingerprints on common substrates with smooth surface, especially on substrates with complex colors as well as strong fluorescence, exhibiting easy operability, high efficiency, and wide applicability.

Latent fingerprints are invisible impressions that need to be developed before being used for individual identification. To advance fingerprint powdering, which is the most common method of developing latent fingerprints on nonporous substrates, two types of green-light-excited carbon dots (CDs) were synthesized hydrothermally using rhodamine 6G (R6G) and rhodamine B (RB) as the precursors. Under the physical effects of capillary attraction and coffee-ring effect, they were dispersed into hierarchical porous micron-sized diatomite (DE) in a facile, cost-effective, and eco-friendly way. The evolution of fluorescence characteristics from water-dispersed CDs to solid CDs/DE composite powders is clarified from the perspectives of physical properties and microstructures of the CDs and diatomite matrix. Optimized green fluorescent R6G-CDs/DE and yellow fluorescent RB-CDs/DE can be excited by visible light (green region) and show very high performance in fingerprint development under the luminescence modes, which has low phototoxicity and helps to preserve chemical information in fingerprint residues. Furthermore, image enhancement protocols, called "digital filters", established based on qualitative and quantitative analyses of red, green, and blue (RGB) channel images of fluorescent fingerprints developed with the CDs/DE composite powders are very efficient in eliminating background interferences of challenging surfaces such as multicolored or patterned substrates. The as-prepared new materials for fingerprint development and the created methods for image enhancement show great promise in practical application scenarios.

采用溶剂热法合成出NaYF4∶Yb,Er@YVO4∶Eu核壳型纳米荧光材料,对纳米材料的微观形貌和光学性能进行了表征,将合成的纳米荧光粉末应用于常见客体表面潜在手印的双模式显现,并考察了手印显现的对比度、灵敏度、选择性、适用性和抗背景干扰能力.研究结果表明,经NaYF4∶Yb,Er@YVO4∶Eu核壳型纳米荧光材料显现的手印在254 nm紫外光的激发下可以产生明亮的红色荧光,在980 nm近红外光的激发下可以产生明亮的绿色荧光,显现出的手印具有较高的对比度、灵敏度和选择性,能在很大程度上提升手印显现的效果.该显现方法具有较广的适用性和较强的抗背景干扰能力,可以针对不同类型的客体选择适合的显现模式.

Latent fingerprints are one of the most important trace evidences at crime scenes that can be used for individual recognition. The invisible nature of latent fingerprints gives rise to various kinds of development and imaging techniques, among which a number of electrochemical methods are receiving increasing attention. We report herein a new interfacial strategy based on spatially selective electrodeposition of Co3O4 films with electrochromic properties to develop and enhance latent fingerprints on stainless steel surfaces. During the development process by potentiostatical deposition of Co3O4 on the background, image contrast and development accuracy as two key factors that measure the effectiveness of fingerprint development are systemically evaluated from millimeter to microscopic scales. Three levels of morphological features in latent fingerprints can be well developed. Optical properties of deposited Co3O4 films can be reversibly adjusted by changing applied potential. This phenomenon is analyzed qualitatively through visual appraisal and determined quantitatively by using color channels. The results indicate that image enhancement of developed fingerprints can be easily accomplished by extracting the blue channel of captured images. Forensic DNA typing is also performed to reveal the impact of this method on DNA evidence in fingerprint residues. The ratio of detected loci reaches 80.9% after electrochemical process. This novel method has advantages including high development accuracy, adjustable image contrast, and relatively non-destructive to DNA analysis.

Latent fingerprints containing morphological and biochemical information are one of the most important evidence existed at crime scenes that can be used for personal identification. Despite some traditional development and imaging methods, various novel methods based on different principles have been explored to visualize latent fingerprints in recent years, among which many interesting methods established by using electrochemical techniques have proved to be very efficient. Up to now, a number of electrochemical systems have been utilized to create or detect the disparity between fingerprint ridge area and background area, resulting in sensitive development and imaging of latent fingerprints. In this review, we highlight the recent progress in electrochemical development and imaging of latent fingerprints. To be specific, the introduction of fundamentals and applications of this research area is separated into four main sections: fingerprint development by electrochemical deposition, fingerprint imaging by electrochemiluminescence (ECL), fingerprint imaging by scanning probe electrochemistry techniques, and fingerprint analysis using other electrochemical methods. Finally, our perspectives on future research directions are also presented and discussed. (c) 2021 Elsevier Ltd. All rights reserved.