A Study on Automatic Latent Fingerprint Identification System

Latent fingerprints are the unintentional impressions found at the crime scenes and are considered crucial evidence in criminal identification.Law enforcement and forensic agencies have been using latent fingerprints as testimony in courts.However,since the latent fingerprints are accidentally leftover on different surfaces,the lifted prints look inferior.Therefore,a tremendous amount of research is being carried out in automatic latent fingerprint identification to improve the overall fingerprint recognition performance.As a result,there is an ever-growing demand to develop reliable and robust systems.In this regard,we present a comprehensive literature review of the existing methods utilized in latent fingerprint acquisition,segmentation,quality assessment,enhancement,feature extraction,and matching steps.Later,we provide insight into different benchmark latent datasets available to perform research in this area.Our study highlights various research challenges and gaps by performing detailed analysis on the existing state-of-the-art segmentation,enhancement,extraction,and matching approaches to strengthen the research.

Recent progress in background-free latent fingerprint imaging

Owing to their unique pattern and abundant chemical composition, latent fingerprints （LFPs） can serve as ＂ID cards＂ and ＂information banks＂ of donors and therefore are valuable for forensic investigation, access control, and even medical diagnosis. LFP imaging has attracted considerable attention, and a great variety of contrast agents has been developed. In LFP imaging, background signals such as background fluorescence from the underlying surface can seriously blur the LFP images and decrease imaging sensitivity; thus, great efforts have been made to eliminate background interference. Here, we stratify the recent progress in background-free LFP imaging by making use of the difference in properties between contrast agents and background compounds. For example, near-infrared （NIR） light-activatable contrast agents can efficiently remove background signals in LFP imaging because the background compounds cannot be excited by NIR light, showing that the difference in excitation properties between contrast agents and background compounds can be employed to eliminate background interference. This review is organized around background-free LFP imaging based on the difference in optical properties between contrast agents and background compounds： （i） different excitation wavelengths, （ii） different emission wavelengths, （iii） different luminescence lifetime values, （iv） different plasmonic properties, （v） different photothermal properties, and （vi） different electrochemiluminescence properties.

Advances in the development and component recognition of latent fingerprints

Fingerprints have been used as an indispensable tool for personal identification in forensic investigations since the late 19 th century. At present, fingerprinting technology has moved away from its forensic roots and is incorporating a broader scientific range, e.g., material science, spectroscopy and spectral analysis, and even in vitro diagnosis. After a brief introduction to latent fingerprints, this mini-review presents the pioneering progresses of fingerprinting technologies including(i) material and electrochemical techniques, and(ii) spectral and spectroscopy imaging techniques and immunological techniques capable of both the visualization of a fingerprint and the detection of chemicals present in it. Finally, perspectives on this rapidly developing field are discussed.

A general powder dusting method for latent fingerprint development based on AIEgens

Powder dusting method is the most practically useful approach for latent fingerprint development in the crime scene. Herein, a general powder dusting method has been explored for latent fingerprint development based on aggregation-induced emission luminogens(AIEgens). A series of tetraphenylethene(TPE) derivatives with multiple diphenylamine(DPA), namely, TPE-DPA,TPE-2 DPA and TPE-4 DPA, were selected as candidates to dope with magnetic powders and applied for latent fingerprint development. After screening, the magnetic powder 3 doped with TPE-4 DPA proves to be the best, in terms of fluorescent intensity, resolution and adhesiveness. Afterwards, the magnetic powder 3 was applied for visualization of latent fingerprint on various smooth and porous substrates, including glass, stainless steel, leaf, ceram, plastic bag, lime wall, wood and paper money.Specific details, such as island, core, termination and bifurcation, can be clearly observed for the fluorescent fingerprint images.

Latent fingerprint enhancement on conductive substrates using electrodeposition of copper

We presented a novel method for the development of a latent fingerprint by selective electrodeposition of a copper thin film from sulfate solution onto the conductive substrate between fingerprint ridges to generate a negative image of the fingerprint deposit. After optimizing the parameters(deposition time, deposition potential, and copper concentration), the preferential electrodeposition of copper films allowed latent fingerprints on six kinds of conductive surfaces(indium/tin oxide-coated glass, silver sheet, platinum sheet, gold sheet, copper sheet, and a stainless steel coin) to be successfully developed with high resolution. In addition, this technique could also be exploited to visualize latent fingerprints on rough and dirty surfaces. The quality of the developed fingerprints was estimated visually and the morphology of the copper film was characterized by field emission scanning electron microscopy.

Green mediated synthesis of lanthanum doped zinc oxide:Study of its structural,optical and latent fingerprint application

The present paper summarises the synthesis of La3+doped zinc oxide nanoparticles using Aloe vera gel by solution combustion method and the characterization using a powder X-ray diffractometer(PXRD),a transmission electron microscope(TEM),an X-ray photometric spectrometer(XPS),a Raman spectrometer and their applications in optical devices and latent fingerprinting.PXRD pattern confirms the crystallite size of La3+doped ZnO varies from 13 to 20 nm.Crystallite size varies inversely with doping concentration.Photoluminescence properties are found to be the maximum for 2 mol% doping concentration.PL spectra extends the use of ZnO:La3+nanoparticles in blue green LED.These nanoparticles also have superior property as a fluorescent labels in fingerprints.

Blue light-induced rare-earth free phosphors for the highly sensitive and selective imaging of latent fingerprints based on enhanced hydrophobic interaction

The demand for in-situ detection of latent fingerprints(LFPs)in ways of high sensitivity,high selectivity,high contrast,low cost and user-friendly is still urgent.To overcome this challenge,a moisture-stable,red-emitting fluoride phosphor K_(3)AlF_(6):Mn^(4+)(KAF:Mn^(4+))with an organic hydrophobic skin was prepared.The phosphor has a uniform and superfine morphology with excellent luminescence properties.More importantly,this non-ultraviolet(UV)or non-near infrared(NIR)induced phosphor was proved to be an ideal fluorescent label for LFP imaging,which is both friendly for touch DNA analysis and compatible to forensic light sources.The well-defined ridge details with little background interference on various surfaces were presented by the oleic acid(OA)modified KAF:Mn^(4+)(KAF:Mn^(4+)-OA)phosphor in few seconds using the powder dusting method.To confirm the high selectivity of KAF:Mn^(4+)-OA for LFP imaging,an efficient quantitative evaluation method is proposed with the aid of ImageJ&Origin software.Due to the superiority of the Mn^(4+)-doped fluoride for the rapid imaging of LFPs in terms of lowcost,high compatibility and good availability,it is expected to be a promising candidate for forensic science as well as fluorescence imaging in other fields instead of rare earth luminescent materials.

Simultaneous extraction of level 2 and level 3 characteristics from latent fingerprints imaged with quantum dots for improved fingerprint analysis

Fingerprints are unique and life-long to everyone, so they occupy very important statuses in forensic science. However, due to the limit of current imaging technologies and instruments, recognition and matching of fingerprints are mostly based on their level 2 structures（bifurcation, crossover, and etc.）.Moreover, in real-world cases, fingerprints collected in the field are often incomplete or damaged, which adds further difficulty in fingerprint analysis. Quantum dots（QDs） are superior fluorescent imaging agents for latent fingerprints, which can provide both level 2 and level 3（sweat pores） details. Here, we used red-emitting N-acetylcysteine-capped Cd Te QDs as imaging agent for staining of eccrine LFPs. The numbers of level 2 and level 3 features that can be mapped are significantly larger than those obtained by cyanoacrylate fuming, a standard technique being adopted at forensic scene. Therefore, the level 2 and level 3 characteristics from QD-staining were simultaneously extracted for improved fingerprint analysis.A preliminary fingerprint matching based modified Pore Matching algorithm was thus developed based on the integration of both level 2 and level 3 characteristics. Satisfactory results of fingerprint matching were obtained, demonstrating the advantage of the QD-staining for advanced fingerprint analysis.

Versatile core-shell magnetic fluorescent mesoporous microspheres for multilevel latent fingerprints magneto-optic information recognition

Latent fingerprints are extremely vital for personal identification and criminalinvestigation,and potential information recognition techniques have been widelyused in the fields of information and communication electronics.Although physicalpowder dusting methods have been frequently employed to develop latent fingerprintsand most of them are carried out by using single component powders ofmicron-sized fluorescent particles,magnetic powders,or metal particles,there isstill an enormous challenge in producing high-resolution image of latent fingerprintsat different backgrounds or substrates.Herein,a novel and effectivenanoimpregnation method is developed to synthesize bifunctional magnetic fluorescentmesoporous microspheres for latent fingerprints visualization by growthof mesoporous silica(mesoSiO_(2))on magical Fe_(3)O_(4) core and then deposition offluorescent YVO4:Eu^(3+)nanoparticles in the mesopores.The obtainedFe_(3)O_(4)@mesoSiO_(2)@YVO4:Eu^(3+)microspheres possess spatially isolated magneticcore and fluorescent shell which were insulated by mesoporous silica layer.Dueto their small particle size of submicrometer scale,high magnetization and lowmagnetic remanence as well as the combined magnetic and fluorescent properties,the microspheres show superior performance in visual latent fingerprint recognitionwith high contrast,high anti-interference,and sensitivity as well as goodretention on multifarious substrates regardless of surface permeability,roughness,refraction,colorfulness,and background fluorescence interference,and it makesthem ideal candidates for practical application in fingerprint visualization andeven magneto-optic information storage.

A dual-stimuli-responsive intelligent layered lanthanide hydroxide for application in information security and latent fingerprint identification

With the rapid changes in the field of information,the research and development of optical storage materials with high security and large storage capacity are particularly important in the development of contemporary society.However,conventional memo ry materials with static fluorescent outputs have the disadvantages of easy simulation and forgery,which limits their practical application in the protection of confidential information.In this research,a dual-stimuli-responsive intelligent fluorescent material based on Tb^(3+)and Eu^(3+)ions doped layered lanthanide hydroxide(LYH:Eu_(x)Tb_(1-x)DPA)was fabricated,which can realize reversible multi-color luminescence conversion(from green to red)by varying the pH and temperature.Combined with the Morse code and security pattern,the multiple encryption and decryption of confidential information and anti-counterfeiting can also be realized.Therefore,the obtained intelligent fluorescent material has a great application prospect for information security.In addition,due to the excellent color tunability,the material can provide the possibility to obtain potential fingerprints with high contrast and no background interference on different color substrates.The unique dual-stimuli-responsive behavior of this material provides more ingenious design inspiration for the design of multi-color intelligent fluorescent devices.

Detection of latent fingerprints using luminescent Gd_(0.95)Eu_(0.05)PO_(4) nanorods

Lanthanide ions doped luminescent materials are widely studied for latent fingerprint detection.However,most of these materials are synthesized at very high temperatures and use UV C light for visualization,which is harmful to eye,skin,etc.Herein,the Gd_(0.95)Eu_(0.05)PO_(4) nanorods synthesized by a simple co-precipitation method at 185℃ were reported for latent fingerprint visualization under 395 nm light.The Gd_(0.95)Eu_(0.05)PO_(4) nanomaterial has monoclinic crystal structure and shows rod-shaped morphology.Further,these Gd_(0.95)Eu_(0.05)PO_(4) nanorods exhibit excellent photoluminescence properties and strong fuchsia emission under UV light.These nanorods have been employed for developing latent fingerprints on various porous and non-porous substrates by the powder dusting technique,which exhibits clear and well defined details with high contrast,selectivity and sensitivity under 395 nm UV light.Latent fingerprints developed after 72 h of their deposition also show clear contrast with these nanorods.Therefore,the Gd_(0.95)Eu_(0.05)PO_(4) nanorods can be used for latent fingerprint visualization applications.

Synthesis of D-A typed AIE luminogens in isomeric architecture and their application in latent fingerprints imaging

Among the emitters in powder dusting to visualize the latent fingerprints(LFPs),aggregation-induced emission luminogens(AIEgens)are well employed for their high brightness and resistance to photobleaching.However,the serious background interference and low resolution still limit their fast development.Therefore,to further enhance the signal-to-noise ratio in LFPs imaging,especially to improve the analysis for level 3 details,donor-acceptor(D-A)typed AIEgens of DTPA-2,3-P,DTPA-2,5-P and DTPA-2,6-P are designed here.It is observed that strong emission covering from 450nm to 650nm can be obtained for all these molecules,especially that a high PLQY value of 10.06%in solids is achieved in DTPA-2,3-P.This is much higher than that of the other two cases(0.80%and 0.51%).By utilizing the DTPA-2,3-P in powder dusting,fluorescence imaging of LFPs can be clearly captured on both smooth and rough substrates.Moreover,confocal laser scanning microscope(CLSM)enables us to achieve high-resolution LFPs imaging in both 2D and 3D views,providing more detailed information of fingerprints pores in width,distance,distribution,and shapes.The results here demonstrate that highly emissive AIEgen of DTPA-2,3-P could be an excellent candidate for the visualization of fingerprints,thus providing the potential application in criminal investigation in the future.

Effects of storage time on DNA profiling success from archived latent fingerprint samples using an optimised workflow

Due to recent improvements in forensic DNA testing kit sensitivity,there has been an increased demand in the criminal justice community to revisit past convictions or cold cases.Some of these cases have little biological evidence other than touch DNA in the form of archived latent fingerprint lift cards.In this study,a previously developed optimised workflow for this sample type was tested on aged fingerprints to determine if improved short tandem repeat(STR)profiles could be obtained.Two-year-old samples processed with the optimised workflow produced an average of approximately five more STR alleles per profile over the traditional method.The optimised workflow also produced detectable alleles in samples aged out to 28 years.Of the methods tested,the optimised workflow resulted in the most informative profiles from evidence samples more representative of the forensic need.This workflow is recommended for use with archived latent fingerprint samples,regardless of the archival time.

High-Resolution Imaging of Latent Fingerprints through Near-Infrared Organoboron AIEgens

A new class of near-infrared(NIR)fluorescent organoboron AIEgens was successfully developed for latent fingerprints(LFPs)imaging.They exhibit real-time and in situ high-resolution imaging performance at 1-3 levels of LFPs by spraying method.In addition,we systematically elucidate the fingerprint imaging mechanism of these AIEgens.Significantly,the excellent level 3 structural imaging capabilities enable the application of them for analyzing incomplete LFPs and identifying individuals in different scenarios.

One pot synthesis of TiO_2:Eu^(3+) hierarchical structures as a highly specific luminescent sensing probe for the visualization of latent fingerprints

In the present work, TiO2:Eu^(3+) (1 mol%e11 mol%) nano powders(NPs) were prepared via a facile one-pot hydrothermal method by using Epigallocatechin Gallate(EGCG) as bio-surfactant. The optimized TiO2:Eu^(3+) (5 mol%) NPs can be used as fluorescent labeling agent for visualizing of latent fingerprints(LFPs) on various porous and non-porous surfaces. The obtained results exhibit well defined ridge details with high sensitivity, selectivity, and low background hindrance which show greater advantages as compared to conventional powders. We demonstrated the viability of high-performance security labels thorough excellent luminescence for practical anti-mimetic applications. Morphology of the prepared samples is highly dependent on pH, concentration of the bio-surfactant, temperature and time durations.Photoluminescence(PL) emission spectra exhibit intense red emission at ~ 615 nm due to electric dipole transition(~5 D_0/~7 F_2). Photometric(CIE and CCT) results clearly show the intense warm red emission of the optimized samples. Therefore, this work offers a superior and universal luminescent label, which can be applied to visualize miniature LFPs particulars for individualization and consequently display great prospective in forensic investigation.

Rational design of monovalent ions （Li,Na,K） co-doped ZnAl2O4:Eu3+ nanocrystals enabling versatile robust latent fingerprint visualization

Alkali metal ions(M+ = Na+,Li+,K+) co-doped ZnAl2O4:Eu3+(5 mol%)(ZAE) nanopowders(NPs) were prepared via solution combustion route using Mimosa pudica(MP) leaves extract as a fuel. PXRD results of co-doped samples enhance the crystallinity and grain growth. Photoluminescence(PL) of the prepared ZAE and ZAE:M+(M+ = Na+, Li+, K+) NPs shows intense emission peaks in the range of 550-750 nm and ascribed to 5D0→7FJ(J=0-4) transitions of Eu3+ ions, respectively. A 2-fold enhancement in PL intensity was observed in Li+ co-doped samples. The optimized ZnAl2O4:Eu3+(5 mol%), Li+(1 wt%)(ZAEL)NPs were used to visualize LFPs on various porous, semi-porous and non-porous surfaces through robust powder dusting technique. The visualized latent fingerprints(LFPs) reveal well defined level 1-3 ridge characteristics under several tests such as fingerprint aging and fresh water treatment for various time durations. The obtained results clearly evidence that the prepared NPs are quite useful for multifunctional applications such as advanced forensic and solid state lightning.

碳点在潜在指纹显影中的应用进展

碳点(CDs)是一种尺寸在10 nm以下的新型纳米材料,由于其独特的发光性能、低毒和环保等特点,在潜指纹检测中展现出了巨大的应用潜力。在潜指纹检测中,碳点的荧光特性可以帮助提高潜指纹的成像和识别能力。本文综述了碳点的合成方法、发光机理及其在潜指纹检测中的应用。通过合成方法优选、元素掺杂、前驱体调控、表面改性等手段可以调控碳点的荧光发射波长;再将碳点纳米粒子均匀分散在天然或常规材料上,所获得的碳点纳米复合材料可以避免因碳点纳米粒子聚集而引发的荧光淬灭现象,保留碳点的荧光性能,并且更适用于潜在指纹显现的常规操作。本文展望了在潜在指纹显影研究中碳点的未来发展方向,通过不断的改进和创新,期许为刑事科学技术领域的研究工作提供重要参考。

金属沉积技术显现金属客体表面油潜指印的应用研究

[目的]研究金属沉积技术在金属客体表面油潜指印显现中应用的可行性,以解决油潜指印显现技术难题。[方法]通过碱性硫酸盐体系电镀铜和化学镀铜显现金属客体表面的油潜指印。研究了电镀液中硫酸镍的加入、电镀时间和电流密度对指印显现效果的影响。在锈蚀程度不同的金属客体表面考察了化学镀铜显现油潜指印的效果。[结果]采用含有8 g/L六水合硫酸镍的碱性硫酸盐体系在电流密度2 A/dm^(2)下电镀铜1 min时,油潜指印的显现效果良好。通过化学镀铜显现油潜指印时,可根据金属客体的锈蚀程度调整施镀时间。[结论]采用金属沉积技术显现金属客体表面油潜指印具有操作简便、显现效果良好的优势。其中化学镀铜可以成功显现锈蚀金属客体表面的油潜指印,满足公安现场勘查的实际需要。

荧光碳点复合材料显现潜手印综合实验设计

为了提高学生的证据意识和综合科研能力,设计了一个涵盖碳点复合材料合成、结构表征和潜手印显现应用的综合性实验。以柠檬酸、三乙烯四胺和罗丹明6G为原料合成荧光碳点材料,通过自组装策略将碳点纳米颗粒原位嵌入金属有机骨架中,从而获得固态下具有强荧光发射的碳点复合材料。利用扫描电子显微镜、荧光光谱仪、粉末X射线衍射仪等分析仪器对复合材料进行表征。采用粉末刷显法将制备的复合材料用于不同客体表面的潜手印显现中,对显现效果进行了分析和评价。教学内容紧密联系学术前沿和实际应用,有助于提高学生分析问题、解决问题的能力,培养创新的科研精神。

悬浮液显现技术应用于潜手印的研究进展

潜手印显现技术对案件侦破和司法鉴定起着重要的作用。根据客体表面的潜手印特点,需使用不同的显现技术,如悬浮液显现技术主要用于陈旧、潮湿或粘性的客体表面,而基于新兴纳米颗粒的悬浮液显现技术还因具备优异的灵敏度、信噪比、选择性等显现性能,日益受到重视。简要介绍了目前普遍使用的传统小颗粒悬浮液显现技术,较为详细地综述了近十几年来新兴纳米颗粒(如量子点、碳纳米点、稀土发光材料、纳米氧化物等)在手印显现方面的应用进展,并概述了悬浮液显现技术的操作方法,最后分析了该技术目前所面临的挑战和未来发展方向,为其在法庭科学、公安教育等领域的应用提供参考。