Aggregation induced emission based active conjugated imidazole luminogens for visualization of latent fingerprints and multiple anticounterfeiting applications

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.

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.

Luminescent nanomaterials for developing high-contrast latent fingerprints

Fingerprint patterns (or epidermal ridges) are by far one of the most reliable techniques for individual identification. Fingerprint patterns get deposited on all kinds of solid surfaces due to human transudation or exudation process. Bodily fluids through sweat glands contain moisture, natural oils and proteins. Since latent fingerprint patterns are not readily recognizable they are collected from a crime scene and are further processed physically or chemically. Fingerprints obtained using conventional black and white powders face severe drawbacks including low sensitivity, high background interference from the substrates, involvement of toxic materials, and poor stability. To overcome the above-listed issues, especially for coloured and transparent substrates, luminescent materials have emerged as potential agents for rapid visualization of high-contrast latent fingerprints. This review covers the recent advancements in luminescent nanomaterials of both kinds (up and down conversion) and persistent nanophosphors for developing latent fingerprints. Special emphasis has been given to an unusual class of luminescent materials known as persistent nanophosphors, which do not require a constant excitation, thereby completely eradicating background noise. The review also covers different approaches to gathering fingerprints such as powder dusting, cyanoacrylate fuming, ninhydrin fuming and vacuum metal deposition.

Influence of annealing temperature on persistent luminescence in BaAl2O4:Eu2+/Eu3+ nanocrystals and its application for latent fingerprint detection

The luminescent properties of europium (Eu) doped BaAl2O4 phosphors were strongly influenced by post-annealing temperatures for blue-green persistent luminescence and latent fingerprints (LFPs). The X-ray powder diffraction patterns of the BaAl2O4: 1 mol% Eu nanophosphor, annealed between 1000 and 1300 °C, indicated a hexagonal ferroelectric phase. The X-ray photoelectron spectroscopy (XPS) revealed that the Ba atoms occupied two different sites in the BaAl2O4. The XPS and photoluminescence (PL) results revealed the presence of Eu3+ and Eu2+ states. The Eu-doped BaAl2O4 showed the characteristic red emission of Eu3+ at 251 and 464 nm excitations, while excitations at 340 and 380 nm showed yellowish-green emission. Strong evidence of energy transfer between a charge transfer band and the different energy levels of Eu2+ and Eu3+ ions was obtained. The existence of the Cr ion impurity in the aluminates was confirmed with UV-VIS diffuse reflectance and PL spectroscopy. The present results suggested that and O''i defects have introduced electron and hole traps in the host that acted as luminescent centers for persistent luminescence. LFPs detection using BaAl2O3:Eu2+/Eu3+ phosphor showed an excellent marking agent for applications in forensic science.

Aggregation-induced emission luminogens for latent fingerprint detection

For over a century, fingerprints have served as a pivotal tool for identification of individuals owing to their enduring characteristics and easily apparent features, particularly in the realm of criminal investigations. Latent fingerprints (LFPs) are "invisible fingerprints" that are most commonly available at crime scenes and require a rapid, selective, sensitive, and convenient method for detection. However, existing fingerprint development techniques harbour limitations, prompting the exploration of novel approaches that prioritize investigator safety and environmental sustainability. Leveraging the unique photophysical properties of aggregation-induced emission luminogens (AIEgens) has emerged as a promising strategy for on-site analysis of LFP visualization. In this highlight, we have presented a comparative analysis of various AIEgens (organic compounds, metal complexes, nanoparticles, and polymers) for the development and detection of LFPs. Through this examination, insights into the efficiency and potential applications of AIE-based fingerprint development techniques are provided. In addition, several strategies have been proposed for circumventing the limitations of existing AIEgens. We hope that this highlight article will encourage more researchers to investigate AIEgens in LFP detection, contributing to forensic science.

A near-infrared AIE fluorescent probe for accurate detection of sulfur dioxide derivatives and visualization of fingerprints

In most biophysiological processes, sulfur dioxide (SO2) is an important intracellular signaling molecule that plays an important role. The change of SO2 in cells are closely related to various diseases such as neurological disorders and lung cancer, so it is necessary to develop fluorescent probes with the ability to accurately detect SO2 during physiological processes. In this work, we designed and synthesized a multifunctional fluorescent probe TIS. TIS has excellent properties such as near-infrared emission, large stokes shift, excellent SO2 detection capabilities, low detection limit, high specificity and visualization of color change before and after reaction. Simultaneously, TIS has low cytotoxicity, good biocompatibility, clear cell imaging capability and mitochondrial targeting ability. In addition, the ability of TIS to be applied to different material surfaces for latent fingerprint fluorescence imaging was also explored. TIS provides an excellent method for the accurate detection of SO2 derivatives and shows great potential applications in near-infrared cellular imaging and latent fingerprint fluorescence imaging.

Colloidal Polymer Nanoparticles as Smart Inks for Authentication and Indication of Latent Fingerprints and Scratch

An environmentally friendly smart ink was developed by incorporating fluorescein into functionalized poly(methyl methacrylate) (PMMA) nanoparticles synthesized using an emulsifier-free emulsion copolymerization approach. The functional comonomers of 2-(dimethylamino)ethyl methacrylate (DMAEMA), acrylamide, hydroxyethyl methacrylate, and glycidyl methacrylate in 10 wt % with respect to methyl methacrylate were used to obtain the functionalized colloidal PMMA nanoparticles. Functional groups of the latex nanoparticles were characterized by Fourier-transform infrared spectroscopy. Field emission scanning electron microscopy results showed that all of the latex nanoparticles have nearly spherical morphologies with variations in size and surface smoothness due to the presence of different comonomers. Ultraviolet-visible and fluorescence spectra indicated that the fluorescein-doped latex nanoparticles containing the DMAEMA comonomer had the highest absorbance and fluorescence intensity. In the alkaline media, fluorescein turns to a dianion, showing a red shift and increased absorbance in the UV-vis spectroscopy. In addition, the electron inductive characteristics of the tertiary amine groups result in enhancing the conjugation of fluorescein molecules and increasing the fluorescence intensities. Therefore, the colloidal nanoparticles with amine functional groups were used in the formulation of a smart ink with applications in securing documents and fingerprints, encrypting banknotes and money, detecting latent fingerprints, crafting anticounterfeiting paper, and eventually providing optical detection and indication of surface scratches.

Fluorene-naphthalene Schiff base as a smart pigment in invisible ink with multiple security features for advanced anticounterfeiting and forensic applications

Smart functional materials with captivating optical properties are of immense importance due to their versatile applicability in anticounterfeiting and forensic science. A fluorene-naphthalene Schiff base (FNH) that displays aggregation induced emission, mechanofluorochromism and excitation wavelength dependent fluorescence inherent to the pristine and ground samples is synthesized. Water/solvent-based invisible security inks for flexo/screen printing were formulated using FNH as a smart pigment to check the originality of documents/branded products etc. The prints with good photostability, adherence to substrate and rub resistance are invisible in daylight showcasing multiple non-destructive and destructive techniques to authenticate the document. The inked area on UV dull paper substrate exhibits a weak emission, which is observed by the forger under UVA light. However, the user can validate the authenticity of the document by rubbing the print with hard objects, especially using a metal coin or glass rod to perceive a human eye detectable intensification in the orange fluorescence under the same illumination source. The intensity of the orange fluorescence reverts to the original, which enables the reuse of the security document after originality check. Yet another nondestructive authentication method is to observe a cyan fluorescence from the print and orangish yellow fluorescence from the rubbed printed region when shined with a 270-400 nm light source, whereas a cyanish green fluorescence both from the unrubbed and rubbed regions of the print when illuminated with a visible light source ranging from 420 to 480 nm. An additional verification through a destructive technique is to perceive red and yellow fluorescence of the ink film upon contact with THF and NaOH/KOH, respectively and a penetrating red fluorescence from the rear side of the THF-exposed printed area of the paper. The multi-level security features that cannot be easily replicated by the forger but allows a simple and easy validation process by the user are unique to FNH, used as a single pigment in the inks. Further, the applicability of the ground FNH in forensic science is established to distinctly observe Level I to II details of latent fingerprints.

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.

Chiroptical Nanocellulose Bio-Labels for Independent Multi-Channel Optical Encryption

Advanced multiplexing optical labels with multiple information channels provide a powerful strategy for large-capacity and high-security information encryption. However, current optical labels face challenges of difficulty to realize independent multi-channel encryption, cumbersome design, and environmental pollution. Herein, multiplexing chiroptical bio-labels integrating with multiple optical elements, including structural color, photoluminescence (PL), circular polarized light activity, humidity-responsible color, and micro/nano physical patterns, are constructed in complex design based on host-guest self-assembly of cellulose nanocrystals and bio-gold nanoclusters. The thin nanocellulose labels exhibit tunable circular polarized structural color crossover the entire visible wavelength and circularly polarized PL with the highest-recorded dissymmetry factor up to 1.05 due to the well-ordered chiral organization of templated gold nanoclusters. Most importantly, these elements can independently encode customized anti-counterfeiting information to achieve five independent channels of high-level anti-counterfeiting, which are rarely achieved in traditional materials and design counterparts. Considering the exceptional seamless integration of five independent encryption channels and the recyclable features of labels, the bio-labels have great potential for the next generation anti-counterfeiting materials technology.

High-definition and robust visualization of latent fingerprints utilizing ultrabright aggregation-induced emission of iridium developer

Creation of AIEgens with high brightness is compactly related to acquiring optimum AIE capabilities and still faces challenges. This study proposes an ingenious structurally regulative approach for preparing ultrabright AIEgens, taking iridium complexes as the model. The incremental rotational activity of substituents obtained by fine adjustment of the stereoscopic configuration efficaciously activates the AIE of iridium complexes and synchronously imparts high-brightness luminescence. Subsequently, benefitting from the ultrabright AIE, high-resolution visualization of latent fingerprints (LFPs) is achieved on diverse substrates by transient immersion in a solution of the AIE-active iridium complex (Ir3) for 60 s. The LFPs stained by Ir3 are integral and distinct enough to possess level 1-3 detail features, which allow precisely realizing personal identification. The LFP photograph emerges inconspicuous attenuation of contrast when aged under ambient light for 10 days and then being continuously irradiated with high-power ultraviolet light for 1 h, reflecting extraordinary aging resistance. Notably, the ultrabright AIE of Ir3 with room-temperature phosphorescence feature successfully achieves enhanced visualization of local fingerprint details with ultrahigh contrast. This LFP visualization protocol based on the ultrabright AIEgens is practical and provides a reliable solution for forensic investigations in actual scenarios.

Strongly Fluorescent Conjugated Polymer Nanoparticles in Aqueous Colloidal Solution for Universal, Efficient and Effective Development of Sebaceous and Blood Fingerprints

Taking the same developing strategy for different types of latent fingerprints is helpful in improving the efficiency of criminal investigation. Here we advanced a new strategy based on amino-functionalized poly(p-phenylenevinylene) nanoparticles (PPV-brPEI NPs) in aqueous colloidal solution as the developing reagent. The desirable amino functionality and strong emission of NPs were simultaneously realized by adding branched polyethyleneimine (brPEI) during the process of thermal elimination of the PPV polymer precursor. The NPs were demonstrated to have negligible effects on the extraction of biological information from DNA. Using the PPV-brPEI NPs-soaked cotton pad, both latent sebaceous fingerprints (LSFPs) and latent blood fingerprints (LBFPs) can be effectively developed on different nonporous substrates. This strategy was highly sensitive and effective for aged, contaminated and moldy fingerprints. Additionally, the developed fingerprints could tolerate humidity environment and the alcohol atmosphere. The mechanism investigation suggests that interaction between PPV-brPEI NPs and sebum ingredients contributes to the development of LSFPs and interaction between PPV-brPEI NPs and proteins in blood contributes to the development of LBFPs, but the former is not as stable as the latter. This work provides a simple, environment/operator-friendly strategy for efficient fingerprint development, which is very promising for practical criminal investigations.

One material, many possibilities via enrichment of luminescence in La2Zr2O7:Tb3+ nanophosphors for forensic stimuli aided applications

Engineering a single material with multidirectional applications is crucial for improving productivity, low cost, flexibility, least power consumption, etc. To achieve these requirements, novel design structures and high-performance materials are in urgent need. Lanthanide-doped nanophosphors have the greatest strengths and ability in order to tune their applications in various dimensions. However, applications of nanophosphor in latent fingerprints visualization, anti-counterfeiting, and luminescent gels/films are still in their infancy. This study demonstrated a simple strategy to enhance the luminescence of Tb³⁺ (1-11 mol %) doped La₂Zr₂O₇ nanophosphors by conjugating various fluxes via a simple solution combustion route. The photoluminescence emission spectra reveal intense peaks at ~ 491, 546, 587, and 622 nm, which arises from ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions, respectively. The highest emission intensity was achieved in the NH₄Cl flux assisted nanophosphor as compared to NaBr and NH₄F assisted samples. The colorimetric images of fingerprints visualized using the optimized nanophosphor on forensic related surfaces exhibit level -III ridge details, including sweat pores, the width of the ridges, bifurcation angle, and the successive distance between sweat pores, etc. These results are decisive parameters that clearly support the statement "no two persons have ever been found to have the same fingerprints". The anti-counterfeiting security ink was formulated using optimized nanophosphor and various patterns were designed by simple screen printing and dip pen technologies. The encoded information was decrypted only under ultraviolet 254 nm light. All the designed patterns are exhibit not just what it looks/feel like and how better it works. As a synergetic contribution of enhanced luminescence of the prepared nanophosphor, the green-emissive films were fabricated, which display excellent flexibility, uniformity, and transparency in the normal and ultraviolet 254 nm light illumination. The aforementioned results revealed that the prepared NH₄Cl flux-assisted La₂Zr₂O₇: Tb³⁺(7 mol %) NPs are considered to be the best candidate for multi-dimensional applications.

Cross-Linking Induced Emission of Polymer Micelles for High-Contrast Visualization Level 3 Details of Latent Fingerprints

Rationally developing an intelligent tool for high-contrast fluorescence imaging of latent fingerprints (LFPs) is gaining much concern in many applications such as medical diagnostics and forensic investigations. Herein, the off-on fluorescent polymer micelles (PMs) have been rationally designed and synthesized for high-contrast fluorescence imaging of LFPs through the cross-linking reaction of hydrazine (N₂H₄) and aldehyde group of polymer. Excitingly, the cross-linking (N₂H₄) induced emission of PMs has the property of aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT), which could effectively address the notorious aggregation-caused quenching (ACQ) effects of conventional organic dyes. In addition, the cross-linking strategy can not only improve structural stability of PMs but also enhance its fluorescence brightness. The experiment results demonstrated that PMs showed high water dispersibility (100% aqueous solution), high selectivity, large Stokes shift (∼150 nm), good photostability, and excellent long-term stability. Because of the hydrophobic interaction between the PMs and fingerprint components, the PMs preferentially adhered onto the ridges of fingerprint, and then cross-linking (N₂H₄) induced emission properties endowed the PMs for high-contrast imaging of LFPs in different substrates, especially the levels 1-3 details of LFPs. We expect that this strategy will provide vital support for LFPs technology.

A fluorescent molecular rotor for the in situ imaging of latent fingerprints

We developed a fluorescent molecular rotor that responds to hydrophobic and viscous environments and visualizes latent fingerprints with level 3 details.