Powder method for detecting latent fingerprints: a review

High-contrast multi-surface imaging of latent fingerprints using color-tunable YOF:Tb3+,Eu3+ ultrafine nanophosphors with high quantum yield

Visualization of latent fingerprints (LFPs) using conventional powders has faced challenges on multicolor surfaces. However, these challenges are addressed by the advent of fluorescent powders in LFP detection, and they have redefined the effectiveness of the powder dusting method. In this study, color-tunable YOF:Tb3+,Eu3+ nanophosphors were examined for LFP recognition and were evaluated for their practicality on different types of surfaces. Under 254 nm UV irradiation, the LFPs developed using these nanophosphors showed clear and distinct ridge patterns with level 1, 2, and 3 details. The ultrafine particles of these nanophosphors adhered to the ridge patterns and replicated the minutiae of the LFPs. Meanwhile, the variation of the Tb3+/Eu3+ ratio demonstrated multicolor fluorescence emission from the nanophosphors, which provided better contrast between the ridge patterns on complex surfaces. Furthermore, the high luminescence quantum yield of the nanophosphors ensured high-resolution fluorescence images of the LFPs with a well-defined pattern that was recognizable even without any microscope or sophisticated instrumentation.

Fabrication of Self-Wrinkling Polymer Films with Tunable Patterns through an Interfacial-Fuming-Induced Surface Instability Process

Inspired by the superglue fuming method for fingerprint collection, this study developed a novel interfacial-fuming-induced surface instability process to generate wrinkled patterns on polymeric substrates. High-electronegativity groups are introduced on the substrate surface to initiate the polymerization of monomer vapors, such as ethyl cyanoacrylate, which results in the formation of a stiff poly(ethyl cyanoacrylate) capping layer. Moreover, interfacial polymerization resulted in the covalent bonding of the substrate, which led to the volumetric shrinkage of the composite and the accumulation of compressive strain. This process ultimately resulted in the development and stabilization of wrinkled surface morphologies. The authors systematically examined parameters such as the modulus of the epoxy substrate, prestrain, the flow rate of fuming, and operating temperature. The aforementioned technique can be easily applied to architectures with complex outer morphologies and inner surfaces, thereby enabling the construction of surface patterns under ambient conditions without vacuum limitations or precise process control. This study is the first to combine fuming-induced interfacial polymerization with surface instability to create robust wrinkles. The proposed method enables the fabrication of intricate microwrinkled patterns and has considerable potential for use in various practical applications, including microfluidics, optical components, bioinspired adhesive devices, and interfacial engineering.

Development of dual-channel fluorescent mesoporous SiO2 nanosphere-coated yttrium aluminum garnet composites for sensitive detection of latent fingerprints

In this study, we investigated the detection of latent fingerprints (LFPs) using green light- and near-infrared (NIR) light-induced up/down-conversion dual-channel composites. Upconverted yttrium aluminium garnet (YAG) was prepared using a citric acid-assisted sol-gel method. After loading rhodamine 6G (RhD-6) into mesoporous silica nanospheres (MSNs), the MSNs-RhD-6 composites were coated with the as-synthesised YAG via electrostatic adsorption using the layer-by-layer method, demonstrating reversible switching between yellow and green light waves under 525 nm green light or 980 nm laser excitation. To evaluate the effectiveness of YAG-MSNs-RhD-6 powder in criminal investigations, we conducted simulations for different fingerprint scenarios. The results indicated that even after prolonged aging (up to 20 days), exposure to water, or high-temperature baking, the fingerprints remained clearly visible in the images. The detection of LFPs on various substrate surfaces exhibited high contrast, with the details of the fingerprints easily observable even after appropriate magnification. This study opens a new path for green light- and near-infrared light-induced up/down-conversion dual-channel composites for optical applications.

Synthesis of High-Fluorescent Diphenyl-anthracene Derivatives and Application in Detection of Nitroaromatic Explosives and Fingerprint Identification

The development of high-intensity fluorescent materials is always the focuses and forefront projects because of their important applications in displays, sensing and detection fields. In recent years, the detection of explosives has attracted increasing attention due to security and counterterrorism issues. Herein, two diphenyl-anthracene (DPA) derivatives were designed and synthesized by introducing strong electron withdrawing fluorine atoms and cyano-groups to DPA, which exhibited strong fluorescence both in the solution and solid phase with the absolute quantum yields up to 70.4 % and 45.9 % respectively. The detection behavior of nitroaromatic explosives such as picric acid (PA), 2,4,6-trinitrotoluene (TNT) and 3-Nitropropionic acid (3-NP) also shows good sensitivity with the quenching constant as high as 6.3×104  L mol-1 . Theoretical calculation demonstrates that the fluorescence quenching behavior of the two DPA derivatives is caused by the behavior of photoinduced electron transfer (PET) and the resonance energy transfer (RET) studies explained the higher sensitivity and selectivity of both compounds towards PA than other nitro-containing explosives. Furthermore, the strong solid-state fluorescence of the DPA derivatives also shows excellent advantages in enhancing latent fingerprint recognition.

Upconversion luminescence based temperature sensing properties and anti-counterfeiting applications of GdNbO4:Tm3+/Yb3+ phosphor

Pure monoclinic phase GdNbO4:Tm3+/Yb3+ phosphor was prepared using solid state reaction method for upconversion emission, optical thermometry, latent fingerprints visualization and anti-counterfeiting applications. The prepared phosphor exhibits colour tunability with temperature variation (from blue to almost white) and good suppression of thermal quenching. The temperature sensing characteristic from thermally and non-thermally coupled levels of Tm3+ ion were investigated using the fluorescence intensity ratio (FIR) approach. The result shows that the sensitivity for non-thermally coupled level is about ∼ 45 times higher than thermally coupled level. Latent fingerprint detection on various surfaces and anti-counterfeiting ink application were also shown upon 980 nm laser diode excitation. Above results indicate that the prepared GdNbO4:Tm3+/Yb3+ phosphor have applicability in the field of frequency upconversion, optical thermometry, color tunable devices, latent fingerprint visualization and anti-counterfeiting applications.

Simple Donor-π-Acceptor Compounds Exhibiting Aggregation-Induced Emission as Hidden Fingerprints Detecting Agents

Latent fingerprints are a significant carrier of information for a court expert. To detect this type of forensic trace, what is necessary is a method that is easy to use, compact, and versatile. The research aimed to investigate the physicochemical properties of luminescent substances of donor-π-acceptor systems in terms of their potential use in detecting hidden fingerprints. During the research, a group of fluorene compounds consisting of the (-CH=C(CN)(COOR)) moiety was designed and successfully synthesized. The optical, electrochemical, and aggregation-induced emission properties were studied. The aggregation-induced emission of compounds has been studied in the mixture of THF (as a good solvent) and water (as a poor solvent) with different water fractions ranging from 0% to 99%. Due to the molecular structure, substances showed different affinities to organic traces. As a result, it was noticed that all compounds showed the AIE phenomenon, while during tests on latent fingerprints, it was observed that two substances had particularly forward-looking features in this field.

Barium Lanthanum Oxide Nanosheets in Photocatalytic and Forensic Applications: One-Pot Synthesis and Characterization

The present work elucidates the fabrication of Barium Lanthanum Oxide nanosheets (BaLa2O4 NSs) via a simple one-pot precipitation method. The acquired results show an orthorhombic crystal system with an average crystallite size of 27 nm. The morphological studies revealed irregular-shaped sheets stacked together in a layered structure, with the confirmation of the precursor elements. The diffused reflectance studies revealed a strong absorption between 200 nm and 350 nm, from which the band-gap energy was evaluated to be 4.03 eV. Furthermore, the fluorescence spectrum was recorded for the prepared samples; the excitation spectrum shows a strong peak at 397 nm, attributed to the 4F7/2→4G11/2 transition, while the emission shows two prominent peaks at 420 nm (4G7/2→4F7/2) and 440 nm (4G5/2→4F7/2). The acquired emission results were utilized to confirm the color emission using a chromaticity plot, which found the coordinates to be at (0.1529 0.1040), and the calculated temperature was 3171 K. The as-prepared nanosheets were utilized in detecting latent fingerprints (LFPs) on various non-porous surfaces. The powder-dusting method was used to develop latent fingerprints on various non-porous surfaces, which resulted in detecting all the three ridge patterns. Furthermore, the as-synthesized nanosheets were used to degrade methyl red (MR) dye, the results of which show more than 60% degradation at the 70th minute. It was also found that there was no further degradation after 70 min. All the acquired results suggest the clear potential of the prepared BaLa2O4 NSs for use in advanced forensic and photocatalytic applications.

Coordination effect enhanced visualization of latent fingerprint with Eu (TTA)3phen-SiO2 microspheres

Latent fingerprint (LFP) powders are crucial in the detection of LFPs in forensic science. However, it is often plagued by poor image resolution and low contrast. Herein, enhanced LFP fluorescence (FL) visualizations are achieved by doping Eu(III) coordination compound Eu(TTA)3phen directly into SiO2 microspheres instead of Eu(III) ions. Using the synthesized Eu(TTA)3phen-SiO2 microspheres, the fine characteristic structure of LFP can be seen and recognized under 365 nm irradiation, up to Level 3. However, the Eu3+-SiO2 microspheres were difficult to recognize the Level 2,3 fingerprint structure. The difference between the ridge and furrow gray values of Eu(TTA)3phen-SiO2 microspheres is 2.1 times that of Eu3+-SiO2 microspheres. The coordination effect increased the asymmetry around Eu(III) ions, resulting in the ultrasensitive 5D0→7F2 transition, thus increasing the FL intensity, and the uniform doping of the Eu(III) coordination compound into SiO2 also reduced the surface FL quenching due to shielding from oxygen. Under this dual effect, the LFP performance of Eu(TTA)3phen-SiO2 microspheres has been significantly improved. We believe that this novel and easy LFP visualization method is a promising routine in specific target detection including criminal investigation, customhouse check-in, and drug control.

TOF-SIMS study of latent fingerprints on challenging substrates with the aid of transfer films

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been applied in forensic science for fingerprint detection. However, due to limitations of the instrument, it is not always possible to directly sample fingerprints on certain substrates. In this report, we indirectly sampled fingerprints using transfer films. First, we optimized the experimental conditions and identified transfer films with better results. We then explored the feasibility of revealing fingerprints after transfer and successfully transferred and revealed the detailed features of fingerprints on several common objects that could not be directly sampled. Fingerprints transferred from smooth surfaces yield clearer feature details in ion images. Additionally, we analyzed the substances in the transferred fingerprints and detected components of morphine and MDMA(3,4-methylenedioxy-n-methylamphetamine). By combining feature details with identified chemical components, the identity of a person can be determined, linking suspects to the crime scene. This work provides a new approach for sample introduction in instrumental analysis, enabling TOF-SIMS to be applied in more scenarios.

Annealing-assisted optimization for persistency of afterglow of SrAl2O4:Eu2+/Dy3+ microparticles for forensic detection

In the present work, Eu2+/Dy3+ ions doped/co-doped into persistent SrAl2O4 microparticles have been developed through solid-state synthesis followed by homogenization and particle size reduction in a ball milling device. These particles have shown a broad and long-persistent afterglow around the 528 nm wavelength of electromagnetic radiation through a broad excitation at around 400 nm. The luminescence intensity was optimized through the selection of different annealing temperatures in the range of 1100 °C to 1500 °C, with intervals of 100 °C. Several structural and optical characterization techniques, such as XRD, SEM, FTIR, thermogravimetric analysis, and photoluminescence, were utilized to judge the preparation and ability of these particles in possible applications in latent fingermark detection on various difficult surfaces. The persistency and stability of these particles were calculated using a digital lux meter.

Synthesis and Characterization of MC/TiO2 NPs Nanocomposite for Removal of Pb2+ and Reuse of Spent Adsorbent for Blood Fingerprint Detection

The removal of toxic heavy metals from wastewater through the use of novel adsorbents is expensive. The challenge arises after the heavy metal is removed by the adsorbent, and the fate of the adsorbent is not taken care of. This may create secondary pollution. The study aimed to prepare mesoporous carbon (MC) from macadamia nutshells coated with titanium dioxide nanoparticles (TiO2 NPs) using a hydrothermal method to remove Pb2+ and to test the effectiveness of reusing the lead-loaded spent adsorbent (Pb2+-MC/TiO2 NP nanocomposite) in blood fingerprint detection. The samples were characterized using SEM, which confirmed spherical and flower-like structures of the nanomaterials, whereas TEM confirmed a particle size of 5 nm. The presence of functional groups such as C and Ti and a crystalline size of 4 nm were confirmed by FTIR and XRD, respectively. The surface area of 1283.822 m2/g for the MC/TiO2 NP nanocomposite was examined by BET. The removal of Pb2+ at pH 4 and the dosage of 1.6 g/L with the highest percentage removal of 98% were analyzed by ICP-OES. The Langmuir isotherm model best fit the experimental data, and the maximum adsorption capacity of the MC/TiO2 NP nanocomposite was 168.919 mg/g. The adsorption followed the pseudo-second-order kinetic model. The ΔH° (-54.783) represented the exothermic nature, and ΔG° (-0.133 to -4.743) indicated that the adsorption process is spontaneous. In the blood fingerprint detection, the fingerprint details were more visible after applying the Pb2+-MC/TiO2 NP nanocomposite than before the application. The reuse application experiments showed that the Pb2+-MC/TiO2 NP nanocomposite might be a useful alternative material for blood fingerprint enhancement when applied on nonporous surfaces, eliminating secondary pollution.

Preparation of a low-cost fingerprint powder that harnesses white light to emit long-lived phosphorescence

An inexpensive, commercially available doped strontium aluminate phosphor with long-lived afterglow has been prepared and assessed in the role of a luminescent fingerprint dusting powder. Blue, green, and aqua phosphorescence persisting for ca. 30 s was obtainable from treated fingermarks after charging the powders with the white light (400-700 nm) setting of a forensic light source. Imaging the phosphorescent afterglow enabled the elimination of background emissions encountered during latent fingermark examination. This was demonstrated by visualising fingermarks on substrates that possess inbuilt fluorescent security features and highly patterned substrate backgrounds, without any need for bespoke scientific equipment.

Nanosheets of two-dimensional photoluminescent lanthanide phosphonocarboxylate frameworks decorated with free carboxylic groups for latent fingerprint imaging

The synthesis, structural characterization, exfoliation, and photophysical studies of two-dimensional (2-D) lanthanide phosphonates, named Ln(m-pbc); [Ln(m-Hpbc)(m-H₂pbc)(H₂O)] (Ln = Eu, Tb; m-pbc = 3-phosphonobenzoic acid) based on the phosphonocarboxylate ligand, are reported. These compounds are neutral polymeric 2D layered structures with pendent uncoordinated carboxylic groups between layers. The nanosheets were obtained by a top-down strategy involving sonication-assisted solution exfoliation and characterized by atomic force microscopy and transmission electron microscropy, showing lateral dimensions from nano- to micro-meter scales, and thicknesses down to several layers. The photoluminescence studies demonstrate that the m-pbc ligand acts as an efficient antenna toward Eu and Tb(III) ions. The emission intensities of dimetallic compounds are clearly enhanced after incorporation of Y(III) ions due to the dilution effect. Ln(m-pbc)s were then applied for labelling latent fingerprints. It is worth noting that the reaction between active carboxylic groups and fingerprint residues benefits the labelling, showing efficient imaging for fingerprints on all kinds of material surfaces.

Eu-Doped Pyrochlore Crystal Nano-Powders as Fluorescent Solid for Fingerprint Visualization and for Anti-Counterfeiting Applications

Undoped Y₂Sn₂O₇ and Eu³⁺ doped Y₂Sn₂O₇ samples with doping concentrations 7%, 8%, 9%, and 10% are successfully synthesized by the co-precipitation method. A complete structural, morphological, and spectroscopic characterization is carried out. XRD measurements reveal that samples crystallize in the pure single pyrochlore phase and Eu³⁺ ions occupy sites with D_3d symmetry. After mechanical grinding, the average crystallite size is less than 100 nm for all compositions. Optical characterization shows emission from the ⁵D₀ level towards the lower lying ⁷F_0,1,2,3,4 levels. The CIE color coordinates of all the pyrochlore phosphors are very close to those of the ideal red light. For the visualization of latent fingerprints, different surfaces are tested, including difficult ones (wood and ceramic), with excellent results. All three levels of fingerprint ridge patterns are visualized: core (Level 1), bifurcation and termination (Level 2), and sweat pores (Level 3). Moreover, our nano-powders are used to prepare a stable fluorescent ink.

Preparation of Novel Magnetic Nanomaterials Based on "Facile Coprecipitation" for Developing Latent Fingerprints (LFP) in Crime Scenes

Recently, the application of novel nanomaterials, especially magnetic nanomaterials in the development of latent fingerprints (LFP), has become the hot focus for forensic scientists and criminal investigators. As a type of recyclable, environment-friendly material, Fe₃O₄ nanoparticles achieve a wonderful effect in visualization of LFP. We first report the synthesis and encapsulation of nano-Fe₃O₄ through "facile coprecipitation", (3-mercaptopropyl)triethoxysilane was covalently embedded into Fe₃O₄ nanoparticles, and the Fe₃O₄ core was encapsulated by the nanosilver to prepare novel magnetic nanomaterials (P-MNP@Ag) with the core-shell configuration. For comparison, the magnetic nanomaterials (S-MNP@Ag) were prepared by surface modification. Their composition, structure, and properties were characterized by SEM, TEM, XRD, IR, XPS, and VSM. Compared with commercially available gold powder, silver powder, bare magnetic powder, and prepared S-MNP@Ag, the development effect of LFP on different objects by using P-MNP@Ag had better performance, which presented the advantages of low background interference, high sensitivity, and clear secondary details in LFP. In the crime scenes of some influential cases, P-MNP@Ag had been applied to the visualization of LFP. The biometric identification of criminal suspects was confirmed through fingerprint comparison, which was highly affirmed by the public security department.

A Facile Microwave-Assisted Green Synthetic Approach of Solid-State Fluorescent Carbon-Dot Nanopowders Derived from Biowaste for Potential Latent-Fingerprint Enhancement

Latent fingerprint detection and visualization remains a challenge especially where problems of poor contrast, auto-fluorescent surfaces and patterned backgrounds are encountered. As a result there is an increasing interest in the development of simple, cost effective, rapid and yet accurate methods for latent fingerprint detection and recovery. Herein, this paper reports the synthesis of bright blue photoluminescent carbon dots (C-dots) via an eco-friendly and simple one-step microwave-assisted carbonization of potato peels’ biomass. The C-dots were prepared in only 3 min and ground into powder and used without any further treatment. The as-prepared C-dots were characterized using atomic force microscope, Fourier transform infra-red spectroscopy and X-ray diffraction with an average size of 1.0[Formula: see text]nm. The optical properties of the as-prepared C-dots were studied by UV-Vis spectroscopy and spectrofluorometer which established an excitation and emission wavelengths of 390[Formula: see text]nm and 480[Formula: see text]nm, respectively. Owing to their strong solid state fluorescence, the as-prepared C-dots’ powder was successfully used in latent fingerprint detection and imaging on porous and nonporous surfaces. Latent fingerprints were recovered with high resolution and excellent quality providing sufficient details for individual identification. These findings demonstrate that C-dots derived from biomass have a great potential in latent fingerprint analysis for forensic applications.

Monitoring the chemical changes in fingermark residue over time using synchrotron infrared spectroscopy

Using synchrotron sourced ATR-FTIR microspectroscopy and THz/Far-IR gas phase spectroscopy to monitor the chemical changes in fingermark residues in the immediate hours following deposition.

An investigation of latent fingerprinting techniques

Background

Latent fingerprints are the unintentional impressions that are left at crime scenes, which are considered to be highly significant in forensic analysis and authenticity verification. It is an extremely crucial tool used by law enforcement and forensic agencies for the conviction of criminals. However, due to the accidental nature of these impressions, the quality of prints uplifted is generally inferior.

Main body

In order to improve the overall fingerprint recognition performance, there is an insistent need to design novel methods to improve the reliability and robustness of the existing techniques. Therefore, a systematic review is presented to study the existing methods for latent fingerprint acquisition, enhancement, reconstruction, and matching, along with various benchmark datasets available for research purposes.

Conclusion

The paper highlights multiple challenges and research gaps using comparative analysis of existing enhancement, reconstruction and matching approaches in order to augment the research in this direction that has become imperative in this digital era.

Visualisation of Amphetamine Contamination in Fingerprints Using TOF-SIMS Technique

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was applied to detect traces of amphetamine on fingerprints. In the present study, three different lift tapes and latent powder fingerprints were tested. The obtained results show that it is possible to identify traces of a drug as well as its distribution over the tested fingerprint after its transfer from the primary base onto an adhesive lifter (secondary base). Moreover, images obtained by the TOF-SIMS technique enable the observation of very small areas of the analysed fingerprint as well as the identification of micro-objects (residues of a contaminant) that were left on the fingerprint. The use of the black latent fingerprint powder did not interfere with the TOF-SIMS analysis, which makes it possible to effectively use this technique to study the traces of substances on the revealed fingerprints.

Highly stable cesium lead bromide perovskite nanocrystals for ultra-sensitive and selective latent fingerprint detection

Latent fingerprints (LFPs) are one of the most important forms of evidence in crime scenes due to the uniqueness and permanence of the friction ridges in fingerprints. Therefore, an efficient method to detect LFPs is crucial in forensic science. However, there remain several challenges with traditional detection strategies including low sensitivity, low contrast, high background, and complicated processing steps. In order to overcome these drawbacks, we present an approach for developing latent fingerprints using stabilized CsPbBr₃ perovskite nanocrystals (NCs) as solid-state nanopowders. We demonstrate the superior optical stability of CsPbBr₃ NCs with respect to absorption, photoluminescence (PL), and fluorescence lifetime. We then used these highly stable, fluorescent CsPbBr₃ NCs as a powder dusting material to develop LFPs on diverse surfaces. The stable optical properties and hydrophobic surface of the CsPbBr₃ NC nanopowder permitted high resolution images from which unique features of friction ridge arrangements with first, second, and third-level LFP details can be obtained within minutes.

Comparison of NIR powders to conventional fingerprint powders

Fingerprint powders remain one of the most common detection techniques used at the crime scene. However, powder efficiency and contrast can be hindered when applied to highly patterned backgrounds. This problem can be overcome using powders that are luminescent in the near-infrared (NIR) region of the electromagnetic spectrum. Despite being commercially available, those powders have been the focus of only a small number of studies, limited to a few substrates or donors. Their performance and advantages over common techniques are still to be thoroughly investigated. This study aims at assessing the performances of two NIR powder (fpNATURAL 1® and Universal Powder an in-house developed powder) against two conventional powders, a black and a luminescent powder (Sirchie Black, GREENcharge™) under various optical conditions (white light, visible luminescence and NIR luminescence). The powders were compared on four substrates using fingermarks of four different ages from five donors. A total 900 fingermarks were collected for each pairwise comparison. NIR imaging provided good background suppression and a high contrast, however it was shown that conventional powders remained the most effective powdering methods on the substrates tested as sufficient contrast could be achieved under white light or in luminescent mode in the visible region. The results showed that Universal Powder performed similarly to conventional powders, but poor performances were obtained on most substrates with fpNATURAL 1®. Based on the results obtained, it is recommended to use NIR powders only on substrates or conditions where traditional powders are known to perform poorly.

Quantitative evaluation of latent fingermarks with novel enhancement and illumination

A variety of suspended silica and metal nanoparticles have been used over the last 20 years to enhance latent fingermarks. This study quantitatively evaluates enhancement of natural and sebum-enriched fingermarks from three adult subjects acquired with a consistent applied force on glass with a fingermark press using suspended commercially available polystyrene (PS) particles. Images of the enhanced fingermarks acquired with total internal reflection (TIR), or standard overhead white light (WL), illumination are compared with fingermarks enhanced with conventional methods including cyanoacrylate fuming. The different enhancement and illumination methods are quantified based on the brightness and contrast of the fingermark images, as well as the number of minutiae that can be identified and matched to those on an inked manually acquired "template" fingermark using automatic fingerprint identification system (AFIS) software. Enhanced fingermarks acquired with the press are shown to be more consistent than manually acquired fingermarks based on these metrics. The results demonstrate that TIR illumination from a large-area illuminator built in house gives enhanced fingermark images with more matched minutiae and contrast superior to that for WL illumination for all types of enhancement. "Wet-powdering" with PS particles gives fingermark images that are for the most part comparable in terms of the number of matched minutiae to fingermarks enhanced with more conventional methods, suggesting that this novel enhancement method has a performance comparable to conventional enhancement methods. Interestingly, the age of the fingermark appears to have almost no effect on this new type of enhancement; sebum-enriched fingermarks ranging in age from 12 h to 435 days appear to have statistically identical numbers of matched minutiae.

Harnessing long-lived visible phosphorescence to eliminate background interference from fingermark images

Minimising background fluorescence can enhance the visible details of treated fingerprints. Here, a 4-tpt fingerprint powder exhibiting long-lived phosphorescence is applied to this end. The powder was found to suppress background fluorescence, including on challenging surfaces, when using standard forensic equipment and eschewing specialized or bespoke imaging techniques.

Detection of Acetaminophen and Its Glucuronide in Fingerprint by SALDI Mass Spectrometry Using Zeolite and Study of Time-Dependent Changes in Detected Ion Amount

The ingredients of an antipyretic (acetaminophen, AAP) and their metabolites excreted into fingerprint were detected by surface-assisted laser desorption ionization (SALDI) mass spectrometry using zeolite. In the fingerprint taken 4 h after AAP ingestion, not only AAP but also the glucuronic acid conjugate of AAP (GAAP), caffeine (Caf), ethenzamide (Eth), salicylamide (Sala; a metabolite of Eth), and urea were detected. Fingerprints were collected over time to determine how the amounts of AAP and its metabolite changed with time, and the time dependence of the peak intensities of protonated AAP and GAAP was measured. It was found that the increase of [GAAP+H]+ peak started later than that of [AAP+H]+ peak, reflecting the metabolism of AAP. Both AAP and GAAP reached maximum concentrations approximately 3 h after ingestion, and were excreted from the body with a half-life of approximately 3.3 h. In addition, fingerprint preservation was confirmed by optical microscopy, and fingerprint shape was retained even after laser irradiation of the fingerprint. Our method may be used in fingerprint analysis.

A facile construction of bifunctional core-shell magnetic fluorescent Fe3O4@YVO4:Eu3+ microspheres for latent fingerprint detection

Latent fingerprint recognition technique has received increasing attention because it helps to precisely identify human information for many applications. In this study, bifunctional core-shell magnetic fluorescent microspheres have been synthesized via a facile interface Pechini-type sol-gel method using citric acid and polyethylene glycol as chelating agent and cross-linking agent, respectively. The obtained Fe₃O₄@YVO₄:Eu³⁺ microspheres possess a typical core-shell structure, large magnetization, and strong fluorescence emission. The surface morphology and roughness of the microspheres can be flexibly tuned by controlling the multistep interface deposition process and subsequent calcination temperatures. Due to their well-integrated bifunctionalities, these magnetic fluorescent microspheres show outstanding performance in the visualization of latent fingerprints on various substrates with high definition and excellent anti-interference, and therefore they have great potential for application in identity recognition.

Magnetic perovskite nanoparticles for latent fingerprint detection

Fingerprints form when fingers touch a solid surfaceand are considered the best way for individual identification. However, the current latent fingerprint (LFP) developing methods cannot meet the demand for high sensitivity and being convenient and healthy. Herein, bifunctional Fe3O4@SiO2-CsPbBr3 powders have been designed and fabricated and exhibit good magnetic and strong fluorescent properties. The magnetism of Fe3O4 can avoid dust flying, while the fluorescence of CsPbBr3 ensures the high definition of LFPs. Clear fingerprints have been detected on various solid substrates using the Fe3O4@SiO2-CsPbBr3 powders instead of eikonogen. Detailed characterization studies suggest that the ammonium cationic groups on the surface of nanoparticles (NPs) have strong adhesive interactions with the residues of fingerprints because of the electrostatic attraction between them. Therefore, the convenient operation and excellent resolution offer great opportunity in the practical application of fingerprint detection and other areas.

Ultrahigh stable lead halide perovskite nanocrystals as bright fluorescent label for the visualization of latent fingerprints

Fingerprints formed by the raised papillary ridges are one of the most important markers for individual identification. However, the current visualization methods for latent fingerprints (LFPs) suffer from poor resolution, low contrast, and high toxicity. In this work, the CsPbBr₃/Cs₄PbBr₆nanostructured composite crystal (CsPbBr₃/Cs₄PbBr₆NCC) were synthesized via a simple chemical solvent-assisted method. Compared with conventional perovskites, the as-prepared CsPbBr₃/Cs₄PbBr₆NCC present an outstanding long-term environmental and water stability with 42% and 80% photoluminescence intensity remaining after 28 d under water and air conditions, respectively. Moreover, a special response to biomolecules from fingerprints was observed due to the hydrophobic interactions between the CsPbBr₃/Cs₄PbBr₆NCC surface hydrophobic ligands (oleyl amine and oleic acid) and the hydrophobic groups in the biomolecules from the human fingers. Clear LFPs images were visualized in a bright environment illuminating the prepared CsPbBr₃/Cs₄PbBr₆NCC powder under UV light of wavelength 365 nm. The images were also obtained on porous and non-porous surfaces such as metal, plastic, wood, glass, and paper products. These perovskite nanocrystals are expected a stable and bright luminescent labeling agent for LFPs visualization and have potential application in crime scene and personal identifications.

Fluorescent Cationic Conjugated Polymer-Based Adaptive Developing Strategy for Both Sebaceous and Blood Fingerprints

Both latent sebaceous and blood fingerprints may provide valuable information for forensic investigation. To detect both types of fingerprints with no need to predistinguish them, a new adaptive developing strategy was proposed. A cationic conjugated polymer with poly[p-(phenylene ethylene)-alt-(thienylene ethynylene)] backbone (PPETE-NMe₃⁺) was synthesized, which was dissolved in N,N-dimethylformamide (DMF) to form the developing solution. Fingerprints were developed by a simple dropping and incubating process without any pre-/post-treatments. Fluorescent photographs of the developed fingerprints on various substrates demonstrated that this developing strategy was effective for both types of fingerprints on nonporous substrates. Gray value analysis further confirmed the enhancement of the legibility of the fingerprint images. The preliminary mechanism exploration suggested that certain weak interactions, such as hydrophobic interaction and electrostatic interaction, may synergistically contribute to the interaction between the polymer and fingerprint components. The molecular design of the polymer combined with an appropriate solvent endowed the developing system the adaptiveness toward different types of fingerprints. This adaptive developing strategy made the fingerprint-developing process more efficient and may be further extended to more practical application scenes.

A butterfly-shaped ESIPT molecule with solid-state fluorescence for the detection of latent fingerprints and exogenous and endogenous ONOO- by caging of the phenol donor

The latent fingerprints (LFPs) at the crime scene are unique and stable, which are considered as an important clue in criminal justice and forensic identification. Herein, a butterfly-shaped molecule DPTS with solid fluorescence plus excited-state intramolecular proton transfer (ESIPT) properties was used to develop for enhancing the visualization of the LFPs. Considering the solid fluorescence of DPTS, the color and efficiency of DPTS with a large Stokes shift (216 nm) can be tuned by changing the morphology of its aggregates, and gradually red-shifted (green-yellow-red) with increasing water content. Furthermore, its effectiveness for the detection of LFPs was demonstrated on various different substrates including paper box, tinfoil and weighting paper. The emissive fingerprint of DPTS obtained gave good fluorescence images with high contrast and resolution such as the core, delta, bifurcation, ridge termination, independent ridge and pores. Caging of the phenol donor of DPTS with a sensitive biomarker group provided DPTS-ONOO^-, which had high sensitive with detection limit of 5 nM and the quantification limit of 21 nM toward ONOO^-. Modularly derived DPTS-ONOO^- was synthesized and demonstrated specific fluorescence imaging of exogenous and endogenous peroxynitrite (ONOO^-) in living macrophage cells.

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.

Coronene diimide-based 'bowl' nanostructures as red emitters for the analysis of latent fingerprints and metal ion detection

We report an NIR-based photoluminescent material, namely benzo-coronene diimide (CDI 2), and its use in the visualization of latent fingerprints (LFPs) and in the metal ion detection in an aqueous medium. CDI 2 exhibited nano-sized interlinked fibre structures forming ‘bowl’ shaped nanoarchitectures as red emitters with the Commission Internationale de l'Eclairage (CIE) coordinates (x, y) of (0.67, 0.33) with 100% colour purity in the solid state. CDI 2 was confirmed to be the potential candidate for the analysis of LFPs and the detection of Pd²⁺/Cu²⁺ in an aqueous medium.

We report CDI 2 as a red emitter (CIE 0.67, 0.33) with 100% colour purity in the solid state forming a ‘bowl’ shaped nanoarchitecture and its use in the visualization of latent fingerprints and in the metal ion detection in an aqueous medium.