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In forensic science, knowledge and understanding of material transfer and persistence is inherent to the interpretation of trace evidence and can provide vital information on the activity level surrounding a crime. Detecting metal ions in fingermark residue has long been of interest in the field of forensic science, due to the possibility of linking trace metal ion profiles to prior activity with specific metal objects (e.g. gun or explosive handling). Unfortunately, the imaging capability to visualise trace metal ions at sufficient spatial resolution to determine their distribution within a fingermark (micron level) was not previously available. Here, we demonstrate for the first time transfer and persistence of metals in fingermarks, at micron spatial resolution, using synchrotron sourced x-ray fluorescence microscopy. Fingermarks were taken before and after brief handling of a gun barrel, ammunition cartridge case and party sparkler to demonstrate the transfer of metals. The results reveal increased metal content after contact with these objects, and critically, a differential pattern of metal ion increase was observed after handling different objects. Persistence studies indicate that these metals are removed as easily as they are transferred, with a brief period of hand washing appearing to successfully remove metallic residue from subsequent fingermarks. Preliminary work using x-ray absorption near edge structure spectroscopic mapping highlighted the potential use of this technique to differentiate between different chemical forms of metals and metal ions in latent fingermarks. It is anticipated that these findings can now be used to assist future work for the advancement of trace metal detection tests and fingermark development procedures

Degradation of fingermark residue has a major impact on the successful forensic detection of latent fingermarks. The time course of degradation has been previously explored with bulk chemical analyses, but little is known about chemical alterations within specific regions of the fingermark, which is difficult to study with bulk measurement. Here we report the use of synchrotron-sourced attenuated total reflection-Fourier transform infrared (ATR-FTIR) microspectroscopy to provide spatio-temporal resolution of chemical changes within fingermark droplets, as a function of time since deposition, under ambient temperature conditions. Eccrine and sebaceous material within natural fingermark droplets were imaged on the micron scales at hourly intervals from the time of deposition until the first 7-13 hours after deposition, revealing that substantial dehydration occurred within the first 8 hours. Changes to lipid material were more varied, with samples exhibiting an increase or decrease in lipid concentration due to the degradation and redistribution of this material. Across 12 donors, it was noticeable that the initial chemical composition and morphology of the droplet varied greatly, which appeared to influence the rate of change of the droplet over time. Further, this study attempted to quantify the total water content within fingermark samples. The wide-spread nature and strength of the absorption of Terahertz/Far-infrared (THz/Far-IR) radiation by water vapour molecules were exploited for this purpose, using THz/Far-IR gas-phase spectroscopy. Upon heating, water confined in natural fingermarks was evaporated and expanded in a vacuum chamber equipped with multipass optics. The amount of water vapour was then quantified by high-spectral resolution analysis, and fingermarks were observed to lose approximately 14-20 μg of water. The combination of both ATR-FTIR and Far-IR gas-phase techniques highlight important implications for experimental design in fingermark research, and operational practices used by law enforcement agencies.

Latent fingermarks are an important form of crime-scene trace evidence and their usefulness may be increased by a greater understanding of the effect of chemical distribution within fingermarks on the sensitivity and robustness of fingermark detection methods. Specifically, the relative abundance and micro-distribution of sebaceous (lipophilic) and eccrine (hydrophilic) material in fingermarks have long been debated in the field, yet direct visualisation of relative abundance and micro-distribution was rarely achieved. Such a visualisation is nonetheless essential to provide explanations for the variation in reproducibility or robustness of latent fingermark detection with existing methods, and to identify new strategies to increase detection capabilities. In this investigation, we have used SR-ATR-FTIR and confocal Raman microscopy to probe the spatial micro-distribution of the sebaceous and eccrine chemical components within latent fingermarks, deposited on non-porous surfaces. It was determined that fingermarks exhibit a complex spatial distribution, influenced by the ratio of lipophilic to aqueous components, and to a first approximation resemble a water-in-oil or oil-in-water emulsion. Detection of a substantial lipid component in "eccrine enriched fingermarks" (wherein hands are washed to remove lipids) is noteworthy, as it provides a potential explanation for several scenarios of unexpected fingermark detection using methods previously thought unsuitable for "eccrine deposits". Furthermore, the pronounced distribution of lipids observed in natural fingermark deposits was intriguing and agrees with recent discussion in this research field that natural fingermarks contain a much higher lipid content than previously thought.

Current and proposed nanoparticle-based techniques for development of latent fingermarks suffer a number of drawbacks such as complicated, multi-step and time-consuming procedures, batch-to-batch variability, expensive reagents, large background noise and toxicity. Here, we introduce a promising green development technique based on heavy-metal-free quantum dots (QD) for the detection of latent fingermarks on non-porous surfaces. Red-near infrared luminescent Cu-In-S/ZnS core-shell QDs solution was produced in large scales using a water-based, simple and fast method using N-acetyl-cysteine as a biocompatible surfactant to coat the particles. The coated QDs were applied to the successful development of latent fingermarks deposited on a variety of surfaces, including highly patterned polymer banknotes and the sticky side of adhesive tape.

When considering interdisciplinary applications of rare earth (RE: Sc, Y, Ln, with Ln = lanthanides = La-Lu) research, forensic science likely is not the first discipline that springs to mind. Yet despite this, the unique optical properties of RE materials are excellently suited to address several forensic challenges. Forensic science involves the use of scientific methods and techniques to analyze, interpret and understand the remains of past criminal activity; and RE materials hold promise for two areas of forensic science: materials to frustrate counterfeiting, and developers of latent fingerprints. Opening with common luminescent processes, this chapter describes up-conversion (UC), down-conversion (DS), and a selection of less-common processes like mechanoluminescence (ML), thermoluminescence (TL) and long persistence luminescence (LPL). Next, recent developments in the application of RE materials to frustrate the actions of counterfeiters are detailed. Many RE materials are built into security inks, dyes, labels, taggants and physical keys, to exploit difficult-to-replicate luminescent profiles. Newer materials, such as security resins for 3D printing, and strategies for encryption, such as QR codes, physical unclonable function (PUF) keys and Code-93 barcodes, are also discussed. Recent developments applying RE materials as fingerprint developers, are then outlined, focusing on nanoscale powders, suspensions, solutions, and vapors. In addition to surveying the present state of RE fingerprint developers, suggestions for improving the authenticity of validation studies are provided with the aim of more clearly conveying the value of new and established RE materials in forensic applications. With a goal of boosting engagement and developing clearer discourse, this chapter seeks to spur further innovation and accelerate the uptake of RE materials within the forensic community.

Fingermarks are an important form of crime-scene trace evidence; however, their usefulness may be hampered by a variation in response or a lack of robustness in detection methods. Understanding the chemical composition and distribution within fingermarks may help explain variation in latent fingermark detection with existing methods and identify new strategies to increase detection capabilities. The majority of research in the literature describes investigation of organic components of fingermark residue, leaving the elemental distribution less well understood. The relative scarcity of information regarding the elemental distribution within fingermarks is in part due to previous unavailability of direct, micron resolution elemental mapping techniques. This capability is now provided at third generation synchrotron light sources, where X-ray Fluorescence Microscopy (XFM) provides micron or sub-micron spatial resolution and direct detection with sub-μM detection limits. XFM has been applied in this study to reveal the distribution of inorganic components within fingermark residue, including endogenous trace metals (Fe, Cu, Zn), diffusible ions (Cl-, K+, Ca2+), and exogeneous metals (Ni, Ti, Bi). This study incorporated a multi-modal approach using XFM and Infrared Microspectroscopy (IRM) analyses to demonstrate co-localisation of endogenous metals within the hydrophilic organic components of fingermark residue. Additional experiments were then undertaken to investigate how sources of exogenous metals (e.g. coins and cosmetics) may be transferred to, and distributed within latent fingermarks. Lastly, this study reports a preliminary assessment of how environmental factors such as exposure to aqueous environments may effect elemental distribution within fingermarks. Taken together, the results of this study advance our current understanding of fingermark composition and its spatial distribution of chemical components, and may help explain detection variation observed during detection of fingermarks using standard forensic protocols.

This study explores the performance of the gold nanoparticle based single metal deposition II (SMD II) technique in developing fingermarks on selected polyethylene surfaces under different environmental conditions in a Western Australian context. Latent fingermarks collected on calcium carbonate/polyethylene blend paper and polyethylene ‘zip-lock’ bags were stored in dry and wet environments for up to 30 days. Useful marks were consistently developed after storage in dry conditions; however, the proportion of useful marks decreased after submersion in water for 30 days. Additionally, background staining on the zip-lock bags had a large impact on the performance of the technique. SMD II was subsequently compared to dry powdering using Lightning Black powder for the detection of latent fingermarks on polyethylene zip-lock bags left in indoor and outdoor environments for up to 4 weeks. SMD II outperformed dry powdering in both environments, showing its potential as a detection technique for latent fingermarks on polyethylene surfaces exposed to environmental conditions.