NIR-induced highly sensitive detection of latent finger-marks by NaYF4:Yb,Er upconversion nanoparticles in a dry powder state

An AIEE-active Triphenylethylene Derivative with Photoresponsive Character for Latent Fingerprints Detection via a Simple Soaking Method

Latent fingerprints (LFPs) is one of the most important physical evidence in the criminal scene, playing an important role in forensic investigations. Therefore, developing highly sensitive and convenient materials for the visualization of LFPs is of great significance. We designed and synthesized an organic fluorescent molecule TP-PH with aggregation-induced enhanced emission (AIEE) activity. By simply soaking, blue fluorescent images with high contrast and resolution are readily developed on various surfaces including tinfoil, steel, glass and plastic. Remarkably, LFPs can be visualized within 5 min including the first-, second- and tertiary-level details. In addition, TP-PH exhibits interesting photoactivated fluorescence enhancement properties. Under irradiation of 365 nm UV light with a power density of 382 mW/cm2, the fluorescence quantum yield displays approximately 21.5-fold enhancement. Mechanism studies reveals that the photoactivated fluorescence is attributed to the irreversible cyclodehydrogenation reactions under UV irradiation. This work provides a guideline for the design of multifunctional AIEE fluorescent materials.

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.

Enhancing the upconversion efficiency of NaYF4:Yb,Er microparticles for infrared vision applications

In this study, (NaYF₄:Yb,Er) microparticles dispersed in water and ethanol, were used to generate 540 nm visible light from 980 nm infrared light by means of a nonlinear stepwise two-photon process. IR-reflecting mirrors placed on four sides of the cuvette that contained the microparticles increased the intensity of the upconverted 540 nm light by a factor of three. We also designed and constructed microparticle-coated lenses that can be used as eyeglasses, making it possible to see rather intense infrared light images that are converted to visible.

Hydrothermal Synthesis and Properties of Yb3+/Tm3+ Doped Sr2LaF7 Upconversion Nanoparticles

We report the procedure for hydrothermal synthesis of ultrasmall Yb³⁺/Tm³⁺ co-doped Sr₂LaF₇ (SLF) upconversion phosphors. These phosphors were synthesized by varying the concentrations of Yb³⁺ (x = 10, 15, 20, and 25 mol%) and Tm³⁺ (y = 0.75, 1, 2, and 3 mol%) with the aim to analyze their emissions in the near IR spectral range. According to the detailed structural analysis, Yb³⁺ and Tm³⁺ occupy the La³⁺ sites in the SLF host. The addition of Yb³⁺/Tm³⁺ ions has a huge impact on the lattice constant, particle size, and PL emission properties of the synthesized SLF nanophosphor. The results show that the optimal dopant concentrations for upconversion luminescence of Yb³⁺/Tm³⁺ co-doped SLF are 20 mol% Yb³⁺ and 1 mol% Tm³⁺ with EDTA as the chelating agent. Under 980 nm light excitation, a strong upconversion emission of Tm³⁺ ions around 800 nm was achieved. In addition, the experimental photoluminescence lifetime of Tm³⁺ emission in the SLF host is reported. This study discovered that efficient near IR emission from ultrasmall Yb³⁺/Tm³⁺ co-doped SLF phosphors may have potential applications in the fields of fluorescent labels in bioimaging and security applications.

In-depth insight into the Yb3+ effect in NaErF4-based host sensitization upconversion: a double-edged sword

NaErF₄ is the most extensively studied host for self-sensitized upconversion (UC), and Yb³⁺ is the most commonly used energy absorber. It has been reported that the red luminescence of Er³⁺ can be enhanced by introducing Yb³⁺ into the NaErF₄ host lattice, where Yb³⁺ ions serve as trapping centers to confine the excitation energy. Also, it has been pointed out that the Yb³⁺ doping in the shell of NaErF₄-hosted core-shell nanocrystals can further improve the red emission intensity. Conversely, it can be argued that the Yb³⁺ doping in the shell always results in the luminescence quenching of the NaErF₄ core. These imply that the impact of Yb³⁺ on NaErF₄-based host-sensitized UC is rather complicated and must be probed deeply. In this study, we thoroughly discussed the effect of Yb³⁺ located in the core/shell on the NaErF₄-based host sensitization UC and afforded the related mechanism interpretations. In the NaErF₄ core nanocrystals, the green-dominated UCL presented an enhancement on increasing the concentration of the Yb³⁺ dopant owing to the promoted energy harvesting for luminescence. Furthermore, the emission properties of NaErF₄:10%Yb shelled with diverse inert layers were also investigated, and the intensity difference of these core-inert shell nanoparticles could be explained by the lattice mismatch and shell thickness. In NaErF₄:10%Yb@NaYF₄:Yb with variable Yb³⁺ doping in the shell, the red-dominated UCL was generally weakened with more Yb³⁺ localized in the shell, which was ascribed to the competition of energy pooling and energy dissipation of Yb³⁺ in the outer layer. Therefore, Yb³⁺ ions wield a two-sided influence (termed a "double-edged sword") on the UC emissions of the Er³⁺ host. Additionally, we demonstrated the application potential of such UCNPs in water sensing and high-level anti-counterfeiting. This work offers an in-depth insight into the UC mechanism of Yb³⁺-doped NaErF₄ nanocrystals and inspires the engineering of novel luminescent materials with distinguished properties.

Fluorescence Enhancement of Dicyanomethylene-4H-Pyran Derivatives in Solid State for Visualization of Latent Fingerprints

The efficient development of latent fingerprint (LFP) is attractively important for criminal investigation. The low-cost and high-contrast developer is still a challenge. In this study, we designed and synthesized dicyanomethylene-4H-pyran (DCM) derivatives PZ-DCM and Boc-PZ-DCM by introducing of large steric hindrance group Boc, the solid-state fluorescence of DCM derivatives was greatly enhanced. The low-cost fluorescent LFP developers were prepared by blending with different proportion of montmorillonite (MMT). As a result, clear and high contrast fingerprint patterns were obtained with dusting method by the developer with 3% content of Boc-PZ-DCM. Furthermore, we employed the developer with 3% content of Boc-PZ-DCM to develop the sweat latent fingerprints on different substrates by powder dusting, and collected clear fingerprint patterns, indicating that the developer is universal. In a word, the Boc-PZ-DCM/MMT powder is a promising candidate for LFP developer.

Time-Gated Imaging of Latent Fingerprints with Level 3 Details Achieved by Persistent Luminescent Fluoride Nanoparticles

The discovery of X-ray-charged persistent luminescence (PersL) in fluoride nanoparticles enables these materials to emit photons without real-time excitation, which provides a great possibility for the development of new luminescent nanotechnologies. In this work, we developed NaLuF₄:Mn nanoparticles with intense green PersL and functionalized surfaces and accordingly achieved time-gated imaging of latent fingerprints (LFPs) with Level 3 details. These surface-modified NaLuF₄:Mn nanoparticles exhibited near-spherical morphology, long-lasting emission for several hours, appropriate trap depth distribution, and tight chemical bonding with amino acids from fingerprints, thus greatly improving the accuracy of LFP imaging in a variety of environments. The developed NaLuF₄:Mn PersL nanoparticles are expected to find broad applications in the fields of LFP imaging and in vivo biological imaging.

Fast and quantitative analysis of level 3 details for latent fingerprints

Level 3 details play essential roles in practical latent fingerprint (LFP) identification. To reliably extract reproducible and identifiable level 3 features, high-resolution images of fingerprints with adequate quality are required. Conventional methods for acquiring level 3 details often involve specific pretreatment, intricate peripheral, leading to time-consuming analysis. Herein, we simply used water to develop the sebaceous LFPs deposited on nitrocellulose (NC) membranes with only one step, and then the high-resolution (2048 pixels per inch) optical micrographs were captured to reflect the live fingertip with high fidelity. From the pictures, level 3 features, including all dimensional attributes of the ridges and pores such as number, size, location, shape, and edge contour can be extracted accurately and reproducibly. Among them, qualitative features (the structures of ridge edges) and several quantitative characteristics (the number and the relative location of sweat pores) exhibit good reproducibility. Remarkably, we proposed a new parameter termed "frequency distribution of the distance between adjacent sweat pores", short form "FDDasp", which was further proved highly identifiable in different individuals, enabling the successful distinguishment between two fragmentary fingerprints with similar level 2 structures. We believe that this methodology provides a fast and quantitative analytical paradigm for latent fingerprint identification at level 3 details.

Surface functionalized inorganic phosphor by grafting organic antenna for long term preservation of latent fingerprints and data-security applications

Creative advancements are enormously sought for the advanced forensic and data security in modern era. Herein, fabrication of Bovine Serum Albumin (BSA) functionalized Gd₂O₃:Eu³⁺ (5 mol %) nanopowders dispersed in a poly(vinyl alcohol) (PVA) matrix for long term preservation and visualization of latent fingerprints, as well as printing. Efficient intramolecular energy transfers from coordinated ligand to the doped Eu³⁺ ions, called the antenna effect was precisely organized by grafting organic molecule, resultant to an enhanced photoluminescence emission. On this basis, the masking of PVA/Gd₂O₃:Eu³⁺ (5 mol %)@BSA solution on a latent fingerprints results a flexible transparent film; a highly stable fingerprint images with well-defined ridge characteristics was developed on the film, which enabling personal individualization. Interestingly, the followed latent fingerprints development technique was non-destructive and stored long duration up to 1 year on filtrating and non-filtrating surfaces. The same mechanism was also validated by utilized for application of PVA/Gd₂O₃:Eu³⁺ (5 mol %)@BSA nanocomposites in dip pen and intaglio printing. Hence, the prepared nanocomposites signify an competent method towards long preservative fingerprints as well as great performance for data security operations. This work endorses a prospective paradigm for luminescence enhancement and its applications in advanced forensic science.

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.

Fingermark detection using upconverting nanoparticles and comparison with cyanoacrylate fuming

This paper reports the synthesis of high-quality upconverting nanoparticles (UCNPs) - sodium yttrium tetrafluoride doped with ytterbium and erbium (NaYF4:Yb,Er) with a silica shell and capped with phenyl functional groups. The main goal of this research was to design tailor-made UCNPs for fingermark detection, to test and validate a nanoparticle-based detection technique and to compare their performance against a benchmark method to assess potential implementation in routine practice by law enforcement agencies. The water-based UCNPs solution was applied to natural fingermarks on a number of substrates. This is the first ever systematic comparative study between UCNPs and a benchmark fingermark detection technique - cyanoacrylate fuming (CAF) followed by luminescent dye staining. Fingermark detection effectiveness was studied by treating 300 latent fingermark specimens on aluminium foil, polyethylene, polypropylene and glass slides. It was concluded that, on average, CAF performed better across the substrates tested. Nevertheless, UCNPs can be advantageous for fingermark detection on multicoloured, patterned or luminescent substrates due to their unique optical properties. There are, however, shortfalls associated with their synthesis and use that need to be addressed before they can be considered for operational purposes.

Carbohydrate biopolymers, lignin based adsorbents for removal of heavy metals (Cd2+, Pb2+, Zn2+) from wastewater, regeneration and reuse for spent adsorbents including latent fingerprint detection: A review

Living organisms are created by carbohydrate biopolymers such as chitosan, carboxymethyl cellulose, alginate and lignin. These carbohydrate biopolymers have been extensively used for environmental applications because they are bio-degradable, bio-compatible, non-toxic and inexpensive. Recently, carbohydrate biopolymers have been used to prepare different nanocomposite adsorbents for treatment of wastewater. These adsorbents explored the removal effectiveness of inorganic pollutants from aqueous solution. This review article discusses the synthesis and application of chitosan, carboxymethyl cellulose, alginate and lignin nanocomposites as adsorbents for heavy metals. Toxic metals can be efficiently absorbed by cross-linkers, distributed in aqueous solutions of divalent heavy metal ions to examine their polymer absorption capacity. These nanocomposites were used for the adsorption of highly toxic metals such as Cd2+, Pb2+ and Zn2+ in water. To make heavy metal ion uptake more effective, more functionalization has been implemented such as blending, grafting, or mixing with different nanomaterials with an extra functional group. The integration of the second part into the main polymer chain not only adds functionality but also increases mechanical efficiency, one of the core criteria for adsorbent recyclability. The remediation method of metal ions from wastewater is cheaper as long as the adsorbent is reused. Furthermore, they exhibited good performance for the reuse of spent adsorbents after adsorption-desorption processes including latent fingerprint detection with nanomaterials by using the powder dusting method. Chitosan, carboxymethyl cellulose, alginate and lignin based nanocomposites have demonstrated better adsorption activities due to great physical and chemical properties for the chelation of heavy metals such as Cd2+, Pb2+ and Zn2+ from water and also higher regeneration with various eluents after several desorption-adsorption cycles. In addition, reuse of the spent adsorbents in latent fingerprint detection with different nanomaterials is discussed. Finally, this review article makes recommendations for future studies in light of environmentally favourable and economical applications.

Manipulation of up-conversion emission in NaYF4 core@shell nanoparticles doped by Er3+, Tm3+, or Yb3+ ions by excitation wavelength-three ions-plenty of possibilities

Nanoparticles (NPs) based on host compound NaYF₄ with core@shell structures were synthesised by the precipitation reaction in high-boiling point octadecene/oleic acid solvent. Four laser wavelengths were used (808, 975, 1208, or 1532 nm) for excitation of the obtained NPs. The resulting emission and mechanisms responsible for spectroscopic properties were studied in detail. Depending on NP compositions, i.e. type of doping ion (Er³⁺, Tm³⁺, or Yb³⁺) or presence of dopants in the same or different phases, adjustable up-conversion (UC) could be obtained with emission peaks covering the visible to near-infrared range (475 to 1625 nm). The presented results demonstrated multifunctionality of the prepared NPs. NaYF₄:2%Tm³⁺@NaYF₄ NPs exhibited emission at 700 and 1450 nm under 808 nm laser excitation or 800 and 1625 nm emission under 1208 nm laser radiation, as a result of ground- and excited-state absorption processes (GSA and ESA, respectively). However, NaYF₄:5%Er³⁺,2%Tm³⁺@NaYF₄ NPs showed the most interesting properties, as they can convert all studied laser wavelengths due to the absorption of Tm³⁺ (808, 1208 nm) or Er³⁺ ions (808, 975, 1532 nm), revealing a photon avalanche process under 1208 nm laser excitation, as well as GSA and ESA at other excitation wavelengths. The NaYF₄:2%Tm³⁺@NaYF₄:5%Er³⁺ NPs revealed the resultant emission properties, as the dopant ions were separated within core and shell phases. The NaYF₄:18%Yb³⁺,2%Tm³⁺@NaYF₄ and NaYF₄:18%Yb³⁺,2%Tm³⁺@NaYF₄:5%Er³⁺ samples showed the brightest emission, around 800 nm, under 975 nm excitation, though other laser wavelengths allowed for observation of luminescence, as well, especially in NPs with Er³⁺ in the outer shell, capable of UC under 1532 nm. The presented results highlight the unique and universal properties of lanthanide ions for designing luminescent NPs for a variety of potential applications, such as confocal microscopy.

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.

Barium tungstate doped with terbium ion green nanophosphor: Low temperature preparation, characterization and potential applications

Production of Nano-Terbium doped barium tungstate and its potential applications as a phosphor in forensic science and anti-counterfeiting ink applications have not been reported in the literature to now. Herein, simple, sensitive and bi-functional green Nanophosphor based on BaWO₄: xTb³⁺ was prepared and characterized for latent prints and anti-counterfeiting ink applications. High crystalline tetragonal BaWO₄ phase was obtained with nano-spherical morphology. BWO: xTb³⁺ Nanophosphors emits a strong and dual green and bluish green colors which appear to the human eye upon UVC and UVA excitation resources, respectively. The lifetime values were increased with rising Tb³⁺ ion concentrations from 0.01 to 0.07 mol. BWO: xTb³⁺ Nanophosphor has successfully visualized latent print from various forensic non-porous and porous surfaces. Moreover, BWO: xTb³⁺ Nanophosphor was used to develop luminescent ink for anti-counterfeiting application.

Novel organic-inorganic hybrid powder SrGa12O19:Mn2+-ethyl cellulose for efficient latent fingerprint recognition via time-gated fluorescence

Latent fingerprints (LFPs) are important evidence in crime scenes and forensic investigations, but they are invisible to the naked eye. In this work, a novel fluorescent probe was developed by integrating a narrow-band-emitting green afterglow phosphor, SrGa₁₂O₁₉:Mn²⁺ (SGO:Mn), and ethyl cellulose (EC) for the efficient visualization of LFPs. The hydrophobic interactions between the powder and lipid-rich LFPs made the ridge structures more defined and easily identifiable. The background fluorescence of the substrates was completely avoided because of the time-gated fluorescence of the afterglow phosphor. All the three levels of LFP degrees were clearly imaged due to the high sensitivity. Moreover, the SGO:Mn-EC powder was highly stable in neutral, acidic, and alkaline environments. In addition, 60 day-aged LFPs were successfully visualized by the powder. All performances showed that this strategy for LFP recognition has merits such as low cost, non-destructive nature, reliability, superior universality, and legible details. Together, these results show the great application prospects of this powder in forensic identification and criminal investigation.

Enhancement of Photodynamic Cancer Therapy by Physical and Chemical Factors

The viable use of photodynamic therapy (PDT) in cancer therapy has never been fully realized because of its undesirable effects on healthy tissues. Herein we summarize some physicochemical factors that can make PDT a more viable and effective option to provide future oncological patients with better-quality treatment options. These physicochemical factors include light sources, photosensitizer (PS) carriers, microwaves, electric fields, magnetic fields, and ultrasound. This Review is meant to provide current information pertaining to PDT use, including a discussion of in vitro and in vivo studies. Emphasis is placed on the physicochemical factors and their potential benefits in overcoming the difficulty in transitioning PDT into the medical field. Many advanced techniques, such as employing X-rays as a light source, using nanoparticle-loaded stem cells and bacteriophage bio-nanowires as a photosensitizer carrier, as well as integration with immunotherapy, are among the future directions.

Fluorescence of a Natural Fluorophore as a Key to Improve Fingerprint Contrast Image

The optical and morphological properties of resveratrol were investigated. This nontoxic fluorescent natural material, emitting in the visible blue light, was used as an optical marker, enabling the enhancement of the image contrast coming from relief pictures marked on challenging surfaces. By applying appropriated imaging softwares, this marker was verified to be very useful in the latent fingerprint recognition deposited on different wood surface types, mainly those with high level of roughness, where conventional forensic materials do not allow effective fingerprint image visualization.

In situ reversible color variation of a ready-made upconversion material using the designed component of a three-state fluorescence switching system

In recent years, upconversion materials have attracted considerable attention because of their unique physicochemical features. Numerous studies have focused on the synthesis of upconversion materials with different colors. However, an easier way to vary the upconversion colors without changing the materials' components has not been extensively studied. In this study, we realized the in situ color variation of the designed upconversion material with the help of a three-state fluorescence switching hybrid device. The device was composed of Prussian blue and upconversion materials; the former element functioned as a fluorescence resonance energy transfer acceptor and the latter acted as a donor. Smartly applying the RGB color model guaranteed multicolor of the device. Moreover, the highest fluorescence contrast of the three-state fluorescence switching system was 86% (larger than the result of a previous study), and the three-state reversibility was remarkable; this was probably owing to the unique layer-by-layer dripping/electrodepositing assembly method. To the best of our knowledge, the in situ reversible color variation of the ready-made upconversion material has been demonstrated for the first time.

Nucleation and self-assembly dynamics of hierarchical YAlO3:Ce3+ architectures: Nano probe for in vitro dermatoglyphics and anti-mimetic applications

Highly efficient blue emitting YAlO₃:Ce³⁺ (1-11 mol%) nanopowders have been fabricated via bio-surfactant Epigallocatechin Gallate assisted ultrasound irradiated sonochemical route. The nucleation and self-assembly dynamics of solids in solutions influences many straightforward normal processes, hence it plays a vital role in materials engineering applications. Nevertheless, the comprehensive nucleation and self-assembly mechanisms of hierarchical architectures still poorly acknowledged. In the present work, we have been exploring the nucleation and stepwise self-assembly dynamics of the YAlO₃:Ce³⁺ (5 mol%) nanopowders into hierarchical architectures. We found that under ultrasound irradiation, nucleation in the solution forms via multi step process and self-assembly was stimulated by intermolecular forces between the nanopowders and external forces. The optimized YAlO₃:Ce³⁺ (5 mol%) nanopowders used as a luminescent labeling agent for visualization of latent fingerprints on various porous and non-porous surfaces under ultraviolet 254 nm light. The obtained results exhibit well defined ridge details with high sensitivity, selectivity and low background hindrance which showed greater advantages as compared to the conventional powders. Extensive fingerprint details, namely the number and distribution of sweat pores in a ridge were clearly revealed. Further, demonstrated the viability of high-performance security labels using optimized sample for practical anti-mimetic applications. The present work, enabling understanding of ultrasound assisted nucleation and self-assembly of nanopowders which impart dermatoglyphics and anti- mimetic applications.

Recent Trends Concerning Upconversion Nanoparticles and Near-IR Emissive Lanthanide Materials in the Context of Forensic Applications

Upconversion nanoparticles (UCNPs) are materials that, upon absorbing multiple photons of low energy (e.g. infrared radiation), subsequently emit a single photon of higher energy, typically within the visible spectrum. The physics of these materials have been the subject of detailed investigations driven by the potential application of these materials as medical imaging devices. One largely overlooked application of UCNPs is forensic science, wherein the ability to produce visible light from infrared light sources would result in a new generation of fingerprint powders that circumvent background interference which can be encountered with visible and ultraviolet light sources. Using lower energy, infrared radiation would simultaneously improve the safety of forensic practitioners who often employ light sources in less than ideal locations. This review article covers the development of UCNPs, the use of infrared radiation to visualise fingerprints by the forensic sciences, and the potential benefits of applying UCNP materials over current approaches.

Highly-selective recognition of latent fingermarks by La-sensitized Ce nanocomposites via electrostatic binding

A series of binuclear (Ce,La) nanocomposite fluorescent powders was elaborately designed for highly-selective recognition of latent fingermarks, which were proved to combine with fingermark residues electrostatically without any damage to touch-DNA.

Color-Tunable Binuclear (Eu, Tb) Nanocomposite Powder for the Enhanced Development of Latent Fingerprints Based on Electrostatic Interactions

Fluorescence color of rare earth-based nanopowder can be modulated by regulating the molar ratio of components, which offers a promising strategy in many fields of applications. Herein, a series of binuclear Eu _xTb_{1- x}(AA)₃Phen ( x = 1, 0.75, 0.5, 0.25, 0.1, 0) complexes were fabricated using acrylic acid (AA) as the first ligand and using 1,10-phenanthroline (Phen) as the second ligand. The characterization results showed that this novel binuclear (Eu, Tb) complex can emit strong red or green light via simply varying the molar ratio of europium and terbium. Moreover, the results of spectroscopic and zeta potential analyses suggested that there was an electrostatic adherence mode in the interaction between the Eu _xTb_{1- x}(AA)₃Phen complex and fingerprint residues. Importantly, our Eu _xTb_{1- x}(AA)₃Phen nanopowder was successfully applied to the enhanced development of latent fingerprints on various surfaces by the powder dusting method, exhibiting a high contrast, sensitivity, and selectivity, as well as a low detection limit in forensic science, which was further confirmed by analysis with an automatic fingerprint identification system. In summary, our synthetic rare earth-based nanopowder exhibits promise as an ideal fluorescent probe for the enhanced development of latent fingerprints, based not only on physical absorption at the macrolevel but also on electrostatic interactions between our rare earth complex and fingerprint residues at the molecular level, which could provide an enhanced affinity compared with traditional fingerprint powders.

Lanthanide Doped Near Infrared Active Upconversion Nanophosphors: Fundamental Concepts, Synthesis Strategies, and Technological Applications

Near infrared (NIR) light utilization in a range of current technologies has gained huge significance due to its abundance in nature and nondestructive properties. NIR active lanthanide (Ln) doped upconversion nanomaterials synthesized in controlled shape, size, and surface functionality can be combined with various pertinent materials for extensive applications in diverse fields. Upconversion nanophosphors (UCNP) possess unique abilities, such as deep tissue penetration, enhanced photostability, low toxicity, sharp emission peaks, long anti-Stokes shift, etc., which have bestowed them with prodigious advantages over other conventional luminescent materials. As new generation fluorophores, UCNP have found a wide range of applications in various fields. In this Review, a comprehensive overview of lanthanide doped NIR active UCNP is provided by discussing the fundamental concepts including the different mechanisms proposed for explaining the upconversion processes, followed by the different strategies employed for the synthesis of these materials, and finally the technological applications of UCNP, mainly in the fields of bioimaging, drug delivery, sensing, and photocatalysis by highlighting the recent works in these areas. In addition, a brief note on the applications of UCNP in other fields is also provided along with the summary and future perspectives of these materials.

Anisotropic functionalization of upconversion nanoparticles

Despite significant advances toward accurate tuning of the size and shape of colloidal nanoparticles, the precise control of the surface chemistry thereof remains a grand challenge. It is desirable to conjugate functional bio-molecules onto the selected facets of nanoparticles owing to the versatile capabilities rendered by the molecules. We report here facet-selective conjugation of DNA molecules onto upconversion nanoparticles via ligand competition reaction. Different binding strengths of phosphodiester bonds and phosphate groups on DNA and the surfactant molecules allow one to create heterogeneous bio-chemistry surface for upconversion nanoparticles. The tailored surface properties lead to the formation of distinct self-assembly structures. Our findings provide insight into the interactions between biomolecules and nanoparticles, unveiling the potential of using nanoparticles as fundamental building blocks for creating self-assembled nano-architectures.