Latent Fingerprint Images Research Articles

Neutral red derived red emitting carbon dots and multifunctional applications: pH sensing, anti-counterfeiting and latent fingerprints imaging

Green and red emission carbon dots (G-CDs and R-CDs) with different luminescence properties were prepared using neutral red and oxalic acid through solvothermal reactions and a simple layering procedure. The obtained R-CDs possess more hydrophilic functional groups than G-CDs, exhibiting better hydrophilicity and more sensitive pH responsiveness. Furthermore, based on their different colors and responsiveness to acidity and alkalinity they can be used for drawing fluorescent anti-counterfeiting patterns. In addition, solid-state fluorescent CDs composite materials (S-G-CDs and S-R-CDs) were obtained by doping starch matrix with G-CDs and R-CDs, respectively. More importantly, S-R-CDs still maintain a significant pH response, which can be further applied in LFPs detection and anti-counterfeiting, expanding the application fields of CDs.

Three multifunctional difluoroboron fluorescent dyes with five member N-heterocyclic ring for mechanofluorochromic behaviors, the ink-free writing and latent fingerprints imaging

To further advance the development of multifunctional fluorescent dyes, three difluoroboron compounds (F-1, F-2, and F-3) containing five-membered N-heterocyclic ring moieties that act as the electron-withdrawing units were synthesized. It was observed that compound F-1, which incorporated a 1,2,4-triazole segment, and compound F-3 with 1,2,3-triazole portion exhibited aggregation-induced emission activities suitable for latent fingerprints imaging. In contrast, compound F-2 featuring a pyrazole unit demonstrated an aggregation-caused quenching phenomenon. Additionally, all three compounds displayed mechanofluorochromic behaviors. Specifically, the emission spectra of compound F-1 in the solid state experienced only a slight shift of approximately 5 nm upon grinding, however, compound F-2 underwent a red shift from 475 to 501 nm while compound F-3 shifted from 482 to 507 nm. Furthermore, both compounds F-2 and F-3 could be utilized in ink-free writing applications. Notably, the safety paper prepared using compound F-2 was designed for single-use due to its irreversible mechanofluorochromic behavior, conversely, the safety paper derived from compound F-3 was rewritable owing to its reversible mechanofluorochromic behavior. It provided a foundation for exploration the application of multifunctional difluoroboron compounds with 1,2,3-triazole moiety.

Dual-mode visual imaging of latent fingerprints based on organic fluorescent probe with enhanced TICT emission

Fluorescence-based imaging has emerged as a promising technique for high-resolution visualization of latent fingerprints (LFPs), but detecting LFPs by fluorescent probes remains challenging at present. Herein, a water-soluble fluorescent dye (DEPN) with red emission and twisted intramolecular charge transfer (TICT) properties was synthesized, which function as a dual-mode in-situ imaging probe for LFPs. The desired solid composite fluorescent fingerprint powder DEPN@MMT can be obtained by milling with montmorillonite (MMT) to realize the imaging of LFPs with 1–3 levels of details, which has the advantages of simple preparation, low doping ratio, good photostability, and is not limited by the substrate. Comparison with the actual fingerprint details extracted by fingerprint reader revealed a good match between the both, indicating that the fingerprint powder has high application value. The permanent preservation of LFPs with different curvatures was also realized by making rubbings. In addition, DEPN was able to image LFPs in aqueous solution with a concentration of 50 μM over a wide pH range, and it took only 20 s to obtain high-quality images that met the NFIQ2 detection standard. This dual-mode imaging probe of LFPs is highly practical, offering adaptable detection patterns for a range of complicated situations. It provides a valuable method for rapid and convenient visualization of LFPs, as well as their subsequent preservation and analysis.

AIE Active Imidazole-Stilbene Conjugated Fluorescent Probes: Illuminating Latent Fingerprints and Advancing Anticounterfeiting Technologies.

Aggregation-induced emission luminogens (AIEgens) are widely used in the realm of latent fingerprint visualization owing to their luminosity and resistance to photobleaching. However, challenges such as significant background interference and limited resolution hinder their rapid advancement. Consequently, there is a pressing need to improve the detailed visualization of latent fingerprint (LFP) imaging, particularly for analyzing level 3 details. To address this, we have designed donor-acceptor (D-A) type AIEgens named MMIMV, DMIMV, and TMIMV. These compounds exhibit robust emissions ranging from 481 to 552 nm and signify positive fluorosolvatochromism. When applied as powder dusting, these derivatives enable the fluorescence imaging of LFPs on various material substrates. The analysis of these imaged LFPs yields intricate details regarding fingerprint ridge patterns. Our results underscore the potential of highly emissive AIEgens MMIMV, DMIMV, and TMIMV as promising candidates for fingerprint visualization, thus offering significant implications for forensic investigations. Furthermore, these derivatives serve as effective fluorescent security inks for writing and drawing, presenting a novel avenue for robust anticounterfeiting applications.

AIEE-Active Green Fluorescence Imaging Technique for Latent Fingerprint Application.

Latent fingerprint imaging is a crucial tool for national security and crime recognition, requiring environmentally sustainable, nontoxic materials. To address this need, we have developed a green fluorescence-emitting material, THCHO, that binds effectively to latent fingerprints, enabling clear, high-resolution visualization. The solution produces strong green fluorescence that highlights fingerprint imprints with exceptional detail and contrast. The material is applicable across various substrates, making it efficient for on-site visualization. The synthesized organic conjugated material THCHO rapidly visualizes precise fingerprint substructures within 5 s using a simple spray method. It maintains high contrast and low interference across different substrates, such as glass, aluminum foil, plastic, and ironware, even in diverse backgrounds. Additionally, the THCHO material demonstrates high stability, retaining its fluorescence imaging capabilities for up to 35 days and after water washing. This is the first report of using a conjugated organic thiophene material for latent fingerprint fluorescence imaging, suggesting potential applications in other fields.

Aggregation-induced emission sensors based on sulfide-containing naphthalimides for imaging latent fingerprints

Aggregation-induced emission luminogens have attracted extensive attention due to their wide applications. In this work, two naphthalimide derivatives (NIS1 and NIS2) were designed and synthesized which could be used as the solid imaging agents for their AIE effects. In both molecules, V-shape structures were introduced to construct de-planar conjugated systems using O and N atoms as the centers. The center atoms tune the emissions of these molecules in deep blue (411∼436 nm, NIS1) and yellow-green (521∼540 nm, NIS2) regions in organic solvents with different polarity. NIS1 and NIS2 exhibit AIE-active fluorescence in their aqueous solutions (545 nm for NIS1 and 600 nm for NIS2). Further studies on their photophysical properties indicate that the introduction of methylmercapto group (-SCH3) can enhance the AIE intensities compared to their mimic. DFT calculation was performed to explore the different transitions occurred in these compounds. At last, NIS1 and NIS2 were successfully fabricated as the solid imaging agents and applied to the latent fingerprints imaging on varied substances. A highlight in this work is these imaging agents can work well on the scene with high background fluorescence by optimizing the excitation wavelength and selecting suitable emission channel.

Rotor proliferation promotes high-brightness AIE of iridium emitter accomplishing high-contrast luminous imaging of latent fingerprints to level 3 details

Luminous imaging of latent fingerprints (LFPs) necessitates the possession of high-brightness aggregation-state luminescence by developers to ensure sufficient imaging contrast and resolution. A novel strategy involving incremental rotor modification is presented for AIE activation of the iridium developer. The rotor proliferation prominently improves the rotational activity of groups and facilitates high-efficiency RIM, thereby prompting the AIE activation of iridium developer with high luminous efficiency. Subsequently, a prompt, high-contrast, and robust LFP imaging protocol is developed utilizing the high-brightness AIE-active iridium developer. This innovative protocol realizes the luminous imaging and quantification of microscopic features in fingerprint ridges and furrows, including ridge widths, edge morphology of ridges, included angles, pores, and pore pitches with exceptional imaging contrast and refined detail resolution. Moreover, it allows for accurate identification of individual traits across diverse substrates without any pre-/post-processing to LFPs. The high-brightness AIE-active iridium developer provides outstanding aging resistance to developed fingerprints, thereby strongly supporting the acquisition, transfer, and preservation of fingerprint evidence. The luminous imaging protocol of LFPs based on high-brightness AIE exhibits robust adaptability to actual scenes and offers a premium scheme for facilitating forensic investigation.

Rational design of fluorescent nanoparticles: From wavelength redshift to increased water solubility for stable and high-resolution imaging of latent fingerprints

Efficient and accurate visual identification of latent fingerprints is crucial in areas such as criminal investigation and information security. Aggregation-induced luminescence (AIE) fluorescent materials are widely used in this field because of their strong fluorescence and easy functionalization. They have attracted significant interest and emerged as a promising area since the introduction of the AIE concept. Here a new water-soluble fluorescent nanoparticle, flu-p-DITPA, through amphiphilic self-assembly with amphiphilic polymers macro-CTA-mPEG2000 (P1) and exhibits typical AIE properties. The core molecule, indo-DITPA, derived from the triphenylamine backbone, was obtained through rational molecular design and theoretical calculations, and the calculated results were confirmed with experimental results. The photophysical properties of indo-DITPA and flu-p-DITPA have been meticulously studied, revealing their remarkable characteristics. Taking advantage of their favorable photophysical properties, good water solubility, and biocompatibility, the researchers have devised a simple yet effective method for visualizing latent fingerprints (LFPs) with high resolution under UV light. This method enables the easy decoding of latent fingerprint information at primary, secondary, and tertiary levels. Importantly, this technique is simple, rapid, and user-friendly, marking a significant step forward in the field of forensic science and fingerprint analysis.

A Comprehensive Review of Small Particle Reagent Efficacy in Developing Latent Fingerprints Immersed in Water: An Empirical Analysis

A latent fingerprint is a shred of inevitable evidence left on a scene of the crime by the offender. Being aware of fingerprints, offenders tend to deteriorate all possible pieces of evidence by different methods that include burning, immersing the evidence in water, and many more. Water-immersed latent fingerprints are still viable for the development process due to the presence of water-insoluble components (Lipids, oils, etc.) in the latent fingerprint. Different methods have been tested for the imaging of water-immersed latent fingerprints among which Small Particle Reagent (SPR) was found to be the most efficient by many researchers. This method involves the application of fine particles suspended in a reagent based liquid medium onto the surface containing latent prints immersed in water, resulting in the development of highly detailed fingerprint impressions. The reagent comprised of hydrophobic head and hydrophilic tails that adhere to latent fingerprint and suspended particle respectively and thus act as a junction among them. The diverse composition of Small Particle Reagent, various surfaces for taking impressions of latent fingerprint (followed by immersing in water), the Shelf life of SPR, immersion time of latent fingerprint, and various immersion medium studied by researchers has been reviewed in this paper. The maximum shelf life of SPR reported by a researcher is 6 months and the maximum immersion time is 45 days. Furthermore, the need for green synthesis of SPR is emphasized due to its toxicity caused by long-term exposure.

Curcumin Analogues as Organic Fluorophores for Latent Fingerprint Imaging

AbstractSynthesis and characterization of two curcumin analogues BAA and Br‐AA via a condensation reaction was reported. Both the synthesized organic luminophores exhibited aggregation‐induced emission (AIE) with bright yellow and green emission respectively. Increase in the water% enhanced the emission by both the compounds confirmed the AIE property. A detailed study of latent fingerprints visualization was also carried out for both the analogues. Both the compounds showed good to normal capability to develop latent fingerprints (LFPs). Compound BAA performed better as a fluorescent material to develop LFPs compared to Br‐AA. The LFPs developed were analyzed to obtain 1–3 level of fingerprint patterns under UV 365 nm illumination. The LFPs developed using BAA exhibited excellent efficiency, sensitivity, high contrast with low background interreference. All three levels of fingerprint patterns were identified by BAA. However, Br‐AA showed inability to develop high clarity images of latent fingerprints. The solid‐state emission nature of the analogues was also evaluated from their emission spectra and CIE coordinates were found to be were (0,187, 0.518) and (0.265, 0.484) for BAA and Br‐AA respectively.

Study on mechanofluorochromism, ink-free writing, and latent fingerprint imaging of the functionalized difluoroboron compounds with methyl and methoxy

Two difluoroboron compounds including amide linkage moiety, compound F-1 with methoxy group and compound F-2 with methyl group, were designed and successfully synthesized. The results indicated that the solid powders of two compounds both displayed mechanofluorochromism phenomena, which originated from phase transformation between the well-ordered microcrystalline and amorphous states, and the intramolecular charge transfer, as well as the mechanofluorochromism of compound F-1 was better than that of compound F-2 due to larger dipole moment change value between the ground and excited states. Additionally, compound F-1 had more twisted molecular spatial conformation, which exhibited aggregation-induced emission in mixtures of THF/water, yet compound F-2 was observed aggregation-caused quenching phenomenon. It was gratified that two compounds had the potential application in the field of ink-free writing owing to their reversibly mechanofluorochromism behaviors, not only that, compound F-1 could be used to latent fingerprint imaging because of its aggregation-induced emission feature.

Latent fingerprint imaging using irradiated novel mixed metal oxides (MXOY, M=Ba, Zn, Al, Ce) nanophosphor.

Latent fingerprint developed at the site of crime is considered as crucial physical evidence in forensic investigation. The mixed metal oxides (MXOY, M=Ba, Zn, Al, Ce) nanophosphor was synthesised by irradiating the precursor solution with 60Co gamma radiation followed by solution combustion method. The structural, morphological, optical characteristics and fingerprint imaging were studied using X-ray diffraction (XRD), scanning electron microscopy, UV-visible spectroscopy and powder dusting method, respectively. The XRD results revealed that the average crystallite size is found to be 30nm with the estimated bandgap of 3.18eV. The broadband UV exited luminescence of the phosphors was observed at λMax=330nm. The PL spectrum shows three emission bands at 432, 444 and 460nm that corresponds to blue regions, suggesting that the synthesised nanophosphor is a potential luminous material for latent fingerprinting and luminescent devices.

Instant in situ highlighting of latent fingerprints by a green fluorescent probe based on aggregation-induced emission

Fluorescence sensing of latent fingerprints (LFPs) has gained extensive attention due to its high sensitivity, non-destructive testing, low biotoxicity, ease of operation, and the potential for in situ visualization. However, the realization of in situ visualization of LFPs especially with green emission and rapid speed is still a challenge. Herein, we synthesized an amphibious green-emission AIE-gen TPE–NI–AOH (PLQY = 62%) for instant in situ LFP detecting, which integrates the excellent fluorescence properties of naphthalimide (NI) with a hydrophilic head and the AIE character as well as the donating property of tetraphenylethene (TPE). TPE–NI–AOH in ethanol/water binary solvent was used as an environmentally friendly LFP developer and achieved in situ green-fluorescence visualization of LFPs. The fluorescence signal achieves its 60% saturated intensity in 0.37 s and nearly 100% in 2.50 s, which is an instant process for the naked eye. Moreover, level 3 details and super-resolution images of LFPs could be observed clearly. Besides, the TPE–NI–AOH developer could be stored for at least 6 months, suitable for long-term storage. This instant in situ highlighting method does not require post-processing operations, providing a more convenient, rapid, and efficient detection method of LFPs. This work would inspire the further advancement of fluorescent sensors for fingerprint imaging.

Particle Size-Tunable Polydopamine Nanoparticles for Optical and Electrochemical Imaging of Latent Fingerprints on Various Surfaces.

Powder dusting method is the most widely used approach due to its low cost, simplicity, minimal instrument dependence, and extensive applicability for developing latent fingerprints (LFPs). Herein, a novel optical and electrochemical dual-mode method for high-resolution LFP enhancement has been explored based on size-tunable polydopamine (PDA) nanoparticles (NPs) and scanning electrochemical microscopy (SECM). Dark PDAs rich in functional groups and negative charges can combine with the residues of LFPs on various surfaces with high sensitivity and selectivity to realize high-resolution visual fingerprint physical patterns on various porous and nonporous substrates with light color. However, optical visualization is not feasible for LFPs on dark or multicolored surfaces. Fortunately, based on the differences in electrochemical reactivity between ridges and furrows caused by the conductivity and reducibility of PDA powders, SECM can serve as a powerful supplement to optical methods to effectively overcome background color interference and distinctly display fingerprint patterns. Intriguingly, it is noteworthy that the binding amount and particle size of PDA powder significantly affected the optical and electrochemical visualization of LFPs: more powder binding amounts provided darker ridges in optical, and more surface reaction sites (larger powder binding mass at the same particle size or smaller particle size at the same mass) provided higher currents of ridges in electrochemical imaging. It demonstrates that the PDA powder as a dual-mode developer for LFPs offers a promising method for individual identification in forensics.

Supramolecular Sequential Light-Harvesting Systems for Constructing White LED Device and Latent Fingerprint Imaging.

The fabrication of supramolecular light-harvesting systems (LHS) with sequential energy transfer is of significance in utilizing light energy. In this study, we report the non-covalent self-assembly of a sequential LHS by pillar[5]arene-based host-guest interaction in water and its applications in white light-emitting diode (LED) device and latent fingerprint imaging. The host-guest complex WP5 G self-assembles into nanoparticles in water and shows enhanced aggregation-induced emission (AIE) effect. The nanoparticles can be further used to construct sequential LHS with fluorescent dyes 4,7-di(2-thienyl)-benzo[2,1,3]thiadiazole (DBT) and sulforhodamine 101 (SR101). Impressively, the system shows white-light emission when the molar ratio of WP5 G/DBT/SR101 is 1100/2/16. The material can be coated on a LED bulb to achieve white-light emission. In addition, the sequential LHS exhibit multicolor fluorescence including red emission, which have been successfully applied to high-resolution imaging of latent fingerprints. Therefore, we demonstrated a general strategy for the construction of sequential LHS in water based on macrocyclic host-guest interaction and explored its multi-functional applications in white-light LED device and imaging of latent fingerprints, which will promote future development and application of supramolecular LHSs.

Enhanced fluorescence imaging of level 1–3 latent fingerprints on multi-materials through lipophilicity-tunable probes

Latent fingerprints (LFPs) are crucial for personal information security and forensic medicine. In recent years, there has been a lot of attention on fluorescence probes for LFP imaging, but the effect of lipophilicity on LFP's imaging performance has not been fully explored. Herein, three naphthalimide-based AIE probes (TPA-NA-Pr, TPA-NA-OH, TPA-COOH) with different lipophilicity were designed and analyzed. After optimizations, TPA-NA-Pr and TPA-NA-OH were found to be able to visualize LFPs within 2 seconds under 405 nm LED lamp excitation. By immersing materials with the probe solution or spraying the probe solution on different material surfaces, a series of high-quality LFP images could be quickly developed. Even LFP level 3 details (such as sweat pores) could be directly observed with naked eyes. The probe solution stored for 2 months did not precipitate or deteriorate, but still can be used for accurate LFP imaging on different substrates with high-resolution level 1–3 details. This study provides insights into the role of lipophilicity on LFP probes and furnishes two LFP probes with extended lifespan and reduced costs for their real-life applications in personal identification and criminal investigation scenarios.

Dual-mode excitable Vis/NIR-II luminescence of lanthanide-doped core@multishell nanostructures for anti-counterfeiting and imaging of latent fingerprints

The development of luminescent materials that can simultaneously realize multiple emissions can help improve the reliability of anti-counterfeiting and the security of encrypted information. Lanthanide-doped nanomaterials are very suitable for advanced anti-counterfeiting applications because of their abundant 4 f energy levels and near-infrared (NIR) laser excitability. Herein, we design lanthanide-doped core@multishell nanoparticles NaYF4:Yb,Er/Ho/Tm@NaYF4@NaYF4:Nd@NaYF4, which can realize upconversion luminescence of Er/Ho/Tm under 980 nm excitation, as well as non-overlapping NIR-II luminescence under 980 nm or 808 nm excitation. By precisely controlling the distribution of lanthanide ions in the core-shell layer, the luminescence interference of nanomaterials under different wavelength excitation can be avoided. Experiments show that multi-color security and information encryption under NIR laser excitation can be achieved using aqueous inks containing the designed multilayered core-shell nanostructures, which are covert and difficult to forge. And the multilayer core-shell nanopowder can be used for efficient identification of latent fingerprints on complex surfaces.

Recent Progress of Advanced AIE Materials for Visualization of 3‐Level Latent Fingerprints

The 3‐level features of Latent fingerprints (LFPs) are pivotal in linking suspects with problematic or incomplete fingerprint data, constituting one of the most robust forms of evidence. Aggregation‐induced emission (AIE) materials, known for their heightened emissive properties in high aggregation states, provide a robust and powerful approach for developing techniques for 3‐level details of LFPs. So far, tremendous efforts have been devoted to solving high background fluorescence interference during the 3‐level LFPs visualization process. This review commences with an overview of 3‐level features and summarizes the interaction and mechanism of visualizing LFPs involving AIE materials and LFPs secretions. Moreover, it encompasses strategies to enhance the contrast and brightness of 3‐level LFPs images. We highlight the mechanism of AIE's physicochemical properties and their effects on the visualization of 3‐level LFPs. Additionally, we provide insights into potential challenges and opportunities in this emerging field.

Meticulously designed red emission carbon dots as efficient and stable luminescent species for rapid latent fingerprint recognition and light emitting diodes

The preparation of carbon dots (CDs) emitting long wavelength has attracted more attentions due to their unique advantages in biological and optoelectronic fields, including the wide absorption, long PL lifetime and deep-tissue penetration. Herein, we prepare the nitrogen and sulfur co-doped red emission carbon dots (R-CDs) from the 2,4-diaminodiphenylamine (DDA) and thiourea via a solvothermal reaction, which exhibit reliable red emission at 613 nm and possess a high quantum yield (QY) of 34 %. Meanwhile, the structural analysis and theoretical calculation reveal that the sulfur doping from thiourea increases the nitrogen and oxygen content of CDs, leading to the red emission observed in R-CDs. Subsequently, we design an integrated fingerprints recognition system based on the R-CDs phosphors for the imaging of latent fingerprints (LFPs) and fast LFPs recognition, expanding the application of biometric identification and comparison technology based on fluorescence. Finally, we successfully apply the R-CDs into red and white light-emitting diodes, improving plant growth efficiency. As a result, this work provides a new in-depth insight of red emission CDs and expands the application in latent fingerprint recognition and light-emitting diodes.

Eu3+ activated gadolinium oxide quantum dots: Biocompatible red luminescent phosphor for photonic, latent fingerprint imaging, and anticancer therapy

In this study, we employed a straightforward chemical reduction method to synthesize Gd2O3 quantum dots (QDs) doped with Eu3+ ions, yielding a remarkable red emission. X-ray diffraction (XRD) analysis confirmed the cubic structure of both pristine and Eu3+ doped Gd2O3 QDs. Characterization of particle size and elemental composition was accomplished through Transmission Electron Microscope (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. Photoluminescence analysis under UV excitation revealed a blue emission at 436 nm for the undoped Gd2O3 QDs. Furthermore, room temperature photoluminescence analysis was conducted on the undoped Gd2O3 quantum dots (QDs) with a UV excitation source. While Gd2O3 QDs emitted a blue light at 436 nm under 396 nm illumination, the Eu3+ doped Gd2O3 QDs exhibited a striking red luminescence under the same 394 nm wavelength. The red luminescence was notably enhanced in Gd2O3 QDs containing 0.5 mol% Eu3+ ions, although concentration quenching was observed when the concentration exceeded this level. A transfer of energy from pristine Gd2O3 QDs to Eu3+ ions was observed, leading to color purity exceeding 80.8% in the optimized sample. Notably, the 0.5 mol% Eu3+-doped Gd2O3 QD phosphor displayed non-cytotoxicity on C2C12 muscle myoblast cells while demonstrating remarkable cytotoxicity against MDA-MB-231 human breast cancer cells. This versatile material holds great promise for applications in latent fingerprinting, security coding, labeling, anticancer therapies, bio-imaging, and the advancement of lanthanide-doped QD phosphors for a wide range of photonic and biomedical applications.