Recent progress on fingerprint visualization and analysis by imaging ridge residue components

Applications of MALDI mass spectrometry in forensic science

Forensic chemistry literature has grown exponentially, with many analytical techniques being used to provide valuable information to help solve criminal cases. Among them, matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS), particularly MALDI MS imaging (MALDI MSI), has shown much potential in forensic applications. Due to its high specificity, MALDI MSI can analyze a wide variety of compounds in complex samples without extensive sample preparation, providing chemical profiles and spatial distributions of given analyte(s). This review introduces MALDI MS(I) to forensic scientists with a focus on its basic principles and the applications of MALDI MS(I) to the analysis of fingerprints, drugs of abuse, and their metabolites in hair, medicine samples, animal tissues, and inks in documents.

Flexible Disk Ultramicroelectrode for High-Resolution and Substrate-Tolerable Scanning Electrochemical Microscopy Imaging

A simple and universal strategy for fabricating flexible 25 μm platinum (Pt) disk ultramicroelectrodes (UMEs) was proposed, where a pulled borosilicate glass micropipette acted as a mold for shaping the flexible tip with flexible epoxy resin. The whole preparation procedure was highly efficient, enabling 10 or more probes to be manually fabricated within 10 h. Intriguingly, this technique permits an adjustable RG ratio, tip length, and stiffness, which could be tuned according to varying experimental demands. Besides, the electroactive area of the probe could be exposed and made renewable with a thin blade, allowing its reuse in multiple experiments. The flexibility characterization was then employed to optimize the resin/hardener mass ratio of epoxy resin and the tip position during HF etching in the fabrication process, suggesting that more hardener, a larger RG value, or a longer tip length obtained stronger deformation resistance. Subsequently, the as-prepared probe was examined by optical microscopy, cyclic voltammetry, and SECM approach curves. The results demonstrated the probe possessed good geometry with a small RG ratio of less than 3 and exceptional electrochemical properties, and its insulating sheath remained undeformed after blade cutting. Owing to the tip's flexibility, it could be operated in contactless mode with an extremely low working distance and even in contact mode scanning to achieve high spatial resolution and high sensitivity while guaranteeing that the tip and samples would suffer minimal damage if the tip crashed. Finally, the flexible probe was successfully employed in three scanning scenarios where tilted and 3D structured PDMS microchips, a latent fingerprint deposited on the stiff copper sheet, and soft egg white were included. In all, the flexible probe encompasses the advantages of traditional disk UMEs and circumvents their principal drawbacks of tip crash and causing sample scratches, which is thus more compatible with large specimens of 3D structured, stiff, or even soft topography.

Recent Progress in Visualization and Analysis of Fingerprint Level 3 Features

Fingerprints provide sufficient and reliable discriminative characteristics which have been considered one of the most robust evidence for individualization. The limitation of current minutiae-based fingerprint technology seems to be solved with the development of level 3 features since they can offer additional information for problematic fingerprint recognition and even donor profiling. So far, tremendous efforts have been devoted to detecting and analysing the third-level details. This review summarizes the advances in level 3 details with an emphasis on their reliability assessment, visualization methods based on physical interaction, residue-response, mass spectrometry and electrochemical techniques, as well as the potentiality for individualization, donor profiling and even other application scenarios. In the end, we also give a personal perspective on the future direction and the remaining challenges in the third-level-detail-related field. We believe that the new exciting progress is expected in the development of level 3 detail detection and analysis with continued interest and attention to this field.

Study of highly stable electrochemiluminescence from [Ru(bpy)3]2+/dicyclohexylamine and its application in visualizing sebaceous fingerprint

For the first time, we report a novel and highly stable visual electrochemiluminescence emission from the [Ru(bpy)₃]²⁺/dicyclohexylamine system at physiological pH conditions, with a quantum efficiency (Φ_ECL) of 95.5%. Furthermore, we have successfully demonstrated the simple and rapid smartphone-based ECL mapping of sebaceous fingerprints via a non-destructive mode.

A review on the advancements in chemical examination of composition of latent fingerprint residues

Background

There are notable developments in the field of DNA analysis and recognition, still fingerprint analysis remains the most preferred approach for obtaining substantial forensic evidences. The identification of individuals through pattern comparison has been used through ages, but it becomes less effective when the pattern is blurred, partial in nature or not found in database. Thus, recent advances in analytical techniques over the last decade will provide additional information to the evidence. In the view of forensic investigations, the compilation of individual chemical profiles with the pattern would enhance the evidentiary value of the latent fingerprints.

Main body

The review has been divided into different parts, describing the various influencing factors which affect the chemical composition of a fingerprint, i.e., lifestyle and occupation, age of an individual, types of substrate on which fingerprint is deposited, environmental conditions, contaminants, and the various advanced instrumental techniques utilized till now in the detection of chemical constituents of fingerprint have been discussed.

Conclusion

The present work aims to enlighten the missing gaps of knowledge in elucidating the detailed chemical composition of fingerprints and highlight the various analytical techniques used till date. Though, there are several analytical techniques employed till date to explicate the constituents of fingerprints, detailed information is still lacking. Therefore, advanced future research is need of the hour for identification of the fingerprints and determining their aging kinetics.

Wearable soft electrochemical microfluidic device integrated with iontophoresis for sweat biosensing

A soft and flexible wearable sweat epidermal microfluidic device capable of simultaneously stimulating, collecting, and electrochemically analyzing sweat is demonstrated. The device represents the first system integrating an iontophoretic pilocarpine delivery system around the inlet channels of epidermal polydimethylsiloxane (PDMS) microfluidic device for sweat collection and analysis. The freshly generated sweat is naturally pumped into the fluidic inlet without the need of exercising. Soft skin-mounted systems, incorporating non-invasive, on-demand sweat sampling/analysis interfaces for tracking target biomarkers, are in urgent need. Existing skin conformal microfluidic-based sensors for continuous monitoring of target sweat biomarkers rely on assays during intense physical exercising. This work demonstrates the first example of combining sweat stimulation, through transdermal pilocarpine delivery, with sample collection through a microfluidic channel for real-time electrochemical monitoring of sweat glucose, in a fully integrated soft and flexible multiplexed device which eliminates the need of exercising. The on-body operational performance and layout of the device were optimized considering the fluid dynamics and evaluated for detecting sweat glucose in several volunteers. Furthermore, the microfluidic monitoring device was integrated with a real-time wireless data transmission system using a flexible electronic board PCB conformal with the body. The new microfluidic platform paves the way to real-time non-invasive monitoring of biomarkers in stimulated sweat samples for diverse healthcare and wellness applications.

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.

Quality Assessment of Licorice Based on Quantitative Analysis of Multicomponents by Single Marker Combined with HPLC Fingerprint

Licorice is a commonly used traditional Chinese medicine and natural sweetening agent, rich in numerous bioactive compounds. Moreover, it is one of the oldest and most frequently employed folk medicines in both eastern and western countries. It is prescribed for the treatment of asthma, fever, and cough. However, with the increasing demand of licorice, its quality and safety become the important issue. The content in licorice varies significantly in materials from different geographical origins. In this study, a reasonable and feasible evaluation method for the quality assessment of licorice was developed based on the analysis of high-performance liquid chromatography (HPLC) fingerprint, combined with the quantitative analysis of multicomponents by single marker (QAMS) method. Glycyrrhizic acid was selected as the internal reference substance, and ten components were simultaneously determined based on relative correction factors. The contents of eleven components in 21 batches of licorice were determined by the QAMS and the ESM (external standard method); there was no significant difference by comparison of the quantitative results between the QAMS and the ESM method; the cosine value (Cir > 0.9999) confirmed the consistency of the two methods. According to the outcomes of 21 batches of licorice samples, the contents of the eleven components were used for further chemometric analysis. All of the samples of licorice from various geographical origins were divided into five categories based on hierarchical cluster analysis, which indicated the crucial influence of geographical origins on licorice. This study showed that QAMS combined with HPLC fingerprint and chemometrics methods could effectively control the quality of licorice. Hence, QAMS is a feasible and promising method for promoting the quality control standardization process of herbal medicines.

Fluorescence imaging of surface-versatile latent fingerprints at the second and third level using double ESIPT-based AIE fluorophore

The nano-aggregates of HPBI on both porous and non-porous surfaces provide fluorescent latent fingerprints with resolution up to the third level, which could be relocated on the tape.

Simultaneous imaging of latent fingerprint and quantification of nicotine residue by NaYF4:Yb/Tm upconversion nanoparticles

Numerous investigations have been devoted to visualizing latent fingerprints (LFPs) for personal identification in forensic investigation and age estimation. While simultaneous detection of chemicals in fingerprint residues has yet to be explored. Herein, fluorescent NaYF₄:Yb/Tm up-conversion nanoparticles (UCNPs), which can emit blue fluorescence upon 980 nm near-infrared irradiation, have been employed in the imaging of LFPs with high contrast and high sensitivity. The furrows and ridges which provide detailed information of LFP have been displayed clearly by Tm-doped UCNPs. Meanwhile, the quantitation of nicotine residue in LFPs has been achieved based on the blue fluorescence absorbed by I₂-nicotine complex, and the data was analyzed by MATLAB with modified OPTA algorithm. It was proved that the established strategy was specific, sensitive, reliable and practical toward nicotine residue in LFPs with a detection limit of 0.05 μg.

Visualization of Latent Fingermarks by Enhanced Chemiluminescence Immunoassay and Pattern Recognition

Herein we report the combination of enzyme-linked immunoassay and pattern recognition analysis for extracting both chemical and spatial information from latent fingermarks (LFMs). The development approach basically involves two steps, namely, specific recognition of protein and polypeptide secretions present in the ridge residues of LFMs by horseradish peroxidase (HRP)-labeled antibodies and the HRP-catalyzed chemiluminescent (CL) reaction between luminol and H₂O₂. The emitted light can spatially resolve the ridges, generating a bright image against the dark object surface for visualization of an LFM. Meanwhile, thanks to the molecular specificity of the immunoassay step, the emission also provides us additional information on the existence of specific substances in LFMs. The developed LFMs are further processed by a set of digital image processing procedures. Quantitative analysis based on minutia features shows that even poorly developed fingermarks can be matched successfully. This work offers the promise of facilitating cross-disciplinary studies between data-processing approaches and fingermark development techniques, such as the extraction of more information from LFM evidence, as well as the establishment of evaluation criteria for an enhancement technique.

Elemental analysis and imaging of sunscreen fingermarks by X-ray fluorescence

Chemical composition in fingermarks could provide useful information for forensic studies and applications. Here, we evaluate the feasibility of analysis and imaging of fingermarks via elements by synchrotron radiation X-ray fluorescence (SRXRF) and commercial X-ray fluorescence (XRF). As a proof of concept, we chose four brands of sunscreens to make fingermarks on different substrates, including plastic film, glass, paper, and silicon wafer. We obtained an evident image of fingermarks via zinc and titanium by XRF methods. In addition, the ratios of element concentrations in sunscreen fingermarks were obtained, which were in accordance with the results obtained by acid digestion and ICP-OES analysis. In comparison, commercial XRF offers the most advantages in terms of non-destructive detection, easy accessibility, fast element images, and broad applicability. The possibility to acquire fingermark images simultaneously with element information opens up new avenues for forensic science. Graphical abstract.

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.

Mass spectrometry imaging of illicit drugs in latent fingerprints by matrix-free and matrix-assisted desorption/ionization techniques

Compared with classical matrix-assisted laser-desorption ionization mass spectrometry (MALDI), the matrix free-based strategies generate a cleaner background, without significant noise or interference coming from an applied matrix, which is beneficial for the analysis of small molecules, such as drugs of abuse. In this work, we probed the detection efficiency of methamphetamine, heroin and cocaine in nanostructure-assisted laser desorption-ionization (NALDI) and desorption electrospray ionization and compared the sensitivity of these two matrix-free tools with a standard MALDI mass spectrometry experiment. In a typical mass spectrometry imaging (MSI) setup, papillary line latent fingerprints were recorded as a mixture a common skin fatty acid or interfering cosmetics with a drug. In a separate experiment, all drugs (1 µL of 1 μM standard solution) were detected by all three ionization techniques on a target. In the case of cocaine and heroin, NALDI mass spectrometry was the most sensitive and revealed signals even from 0.1 μM solution. The drug/drug contaminant (fatty acid or cosmetics) MSI approach could be used by law enforcement personnel to confirm drug abusers of having come into contact with the suspected drug by use of fingerprint scans at time of apprehension which can aid in reducing the work of lab officials.

Infrared spectroscopy and spectroscopic imaging in forensic science

Infrared spectroscopy and spectroscopic imaging, are robust, label free and inherently non-destructive methods with a high chemical specificity and sensitivity that are frequently employed in forensic science research and practices. This review aims to discuss the applications and recent developments of these methodologies in this field. Furthermore, the use of recently emerged Fourier transform infrared (FT-IR) spectroscopic imaging in transmission, external reflection and Attenuated Total Reflection (ATR) modes are summarised with relevance and potential for forensic science applications. This spectroscopic imaging approach provides the opportunity to obtain the chemical composition of fingermarks and information about possible contaminants deposited at a crime scene. Research that demonstrates the great potential of these techniques for analysis of fingerprint residues, explosive materials and counterfeit drugs will be reviewed. The implications of this research for the examination of different materials are considered, along with an outlook of possible future research avenues for the application of vibrational spectroscopic methods to the analysis of forensic samples.

Contactless Visualization of Latent Fingerprints on Nonporous Curved Surfaces of Circular Cross Section-A Statistical Evaluation on the Materials as Plane Mirror

A new contactless technique for latent fingerprint visualization on nonporous curved surfaces of circular cross section was introduced by Low et al. (1). The technique utilizes a plane mirror to convey the light rays toward the inspected surfaces for latent fingerprint visualization. This research activity came up as an extension of the previous study which utilized an aluminum plate as the plane mirror to illuminate the inspected surfaces. Dulling spray was used to increase the diffuse component of the reflective aluminum plate. However, the amount of dulling spray will affect the uniformity of the illumination on the inspected curved surfaces. In this study, a study on the new materials for the plane mirror was carried out. Coated aluminum, opal, and ground glass diffusers were selected as the new materials. The performance of the new materials was compared to the aluminum based on the quality of the captured images on various nonporous cylindrical surfaces. A statistical approach known as randomized complete block design was used to design the experiment. The quality of the captured images was obtained using Spectral Image Validation and Verification. Two-way analysis of variance and Fisher's least significant difference test were used to analyze the quality of the images. From the results of the statistical analysis, coated aluminum has the best performance compared to aluminum, opal, and ground glass diffusers.

One-Piece Triboelectric Nanosensor for Self-Triggered Alarm System and Latent Fingerprint Detection

Tactile sensing is of great importance in developing human-machine interface, remote control, and security systems. Here, a self-triggered alarm system based on the one-piece triboelectric nanosensor (TENS) is reported. By using nitrocellulose (NC) membrane as the triboelectric material, the as-designed TENS can not only sensitively respond to physical contacts in a self-triggered mode but also securely detect the third-level details of latent fingerprint. The self-triggered idea based on the triboelectric nanogenerator is compatible with intelligent interactive interface. Besides, this TENS can be conveniently fabricated and integrated into arrays at a large scale due to its freestanding, simple, and low-cost characteristics. This work presents alternative perspectives for the practical applications of the multifunctionalized TENS.

Visualization of Sweat Fingerprints on Various Surfaces Using a Conjugated Polyelectrolyte

A conformation-variable conjugated polyelectrolyte responding to oppositely charged biomolecules was examined as an imaging agent for the detection of latent fingerprints (LFPs). Sulfonated poly(diphenylacetylene) (SPDPA) produces high-resolution fluorescence (FL) LFP images by simple wetting of the target objects with the polymer solution without any additional treatment. SPDPA readily interacts with LFP sweat components (especially amino acids) via electrostatic interactions, leading to significantly enhanced FL images in a "turn-on" mode. The FL emission enhancement was examined in a model reaction between SPDPA and an amino acid standard. Visualization with SPDPA is effective on various surfaces, including both rough (paper) and smooth (glass and plastic) ones. Moreover, SPDPA readily interacts with extremely thin sweat LFPs, especially on smooth glass surfaces.

Present and foreseeable future of metabolomics in forensic analysis

The revulsive publications during the last years on the precariousness of forensic sciences worldwide have promoted the move of major steps towards improvement of this science. One of the steps (viz. a higher involvement of metabolomics in the new era of forensic analysis) deserves to be discussed under different angles. Thus, the characteristics of metabolomics that make it a useful tool in forensic analysis, the aspects in which this omics is so far implicit, but not mentioned in forensic analyses, and how typical forensic parameters such as the post-mortem interval or fingerprints take benefits from metabolomics are critically discussed in this review. The way in which the metabolomics-forensic binomial succeeds when either conventional or less frequent samples are used is highlighted here. Finally, the pillars that should support future developments involving metabolomics and forensic analysis, and the research required for a fruitful in-depth involvement of metabolomics in forensic analysis are critically discussed.