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Revealing the elemental distribution within latent fingermarks using synchrotron sourced x-ray fluorescence microscopy Rhiannon E. Boseley, Buddhika N. Dorakumbura, Daryl L Howard, Martin D de Jonge, Mark J Tobin, Jitraporn Vongsvivut, Tracey T.M. Ho, Wilhelm Van Bronswijk, Mark J. Hackett, and Simon W Lewis Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.9b01843 • Publication Date (Web): 19 Jul 2019 Downloaded from pubs.acs.org on July 19, 2019

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Analytical Chemistry

Revealing the elemental distribution within latent fingermarks using synchrotron sourced x-ray fluorescence microscopy Rhiannon E. Boseley,ab Buddhika N. Dorakumbura,ab Daryl L. Howard,c Martin de Jonge,c Mark J. Tobin,c Jitraporn Vongsvivut,c Tracey T. M. Ho, c Wilhelm van Bronswijk,a Mark J. Hackett*ab and Simon W. Lewis*ab a School of Molecular and Life Sciences, Curtin University, GPO Box U1987, Perth, Australia 6845 b Curtin Institute of Functional Molecules and Interfaces, GPO Box U1987, Perth, Australia 6845 c ANSTO, Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria, Australia 3168

*Corresponding authors: [email protected], [email protected]

ABSTRACT 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.

INTRODUCTION In a criminal investigation, fingermarks can be an important form of trace evidence that may provide a link between the crime scene, objects, and persons. Most commonly, they are present as latent fingermarks and their detection relies upon their successful recovery from a scene or object. A range of physical and chemical methods have been developed to visualise latent fingermarks. The detection methods typically target physical or chemical differences between the latent fingermark and the surface upon which it is laid. Unfortunately, limitations in the sensitivity and selectivity of current detection methods means that a large number of fingermarks remain undetected.1-3 An increased understanding of chemical and elemental composition of, and distribution within fingermarks may provide opportunities to optimise current fingermark detection methods or identify new detection strategies. The chemistry of latent fingermark residue heavily impacts the ability to detect and examine latent fingermarks.4-6 Fingermarks are a mixture of the natural secretions from the glands present in the skin and any surface contaminant present. The natural secretion is made up of a combination of components originating from the

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eccrine and sebaceous glands, and while one type of secretion may predominate, there can be no purely eccrine or purely sebaceous deposit.7 Sebaceous secretions are primarily comprised of lipophilic material, such as glycerides, fatty acids, wax esters and squalene.8, 9 Eccrine secretions (sweat) contains a variety of hydrophilic organic and inorganic material such as amino acids, proteins, ions (Cl-, K+, Na+, Mg2+) and trace metals (Fe, Cu, Zn), these components have the potential to be transferred when depositing latent fingermarks.1, 8, 9 A better knowledge of elemental distribution within latent fingermarks is important to increase the understanding of the effects ions and transition metals may have on the underlying chemistry of current methods of detection. For example, the amino acid regent 1,2-indanedione uses the addition of zinc chloride as a Lewis acid catalyst to improve the detection response in conditions of low humidity, the zinc content in fingermark residue could influence this development.10, 11 Researchers have previously exploited the presence of metals in fingermark residue for detection, using heightened temperatures to accelerate metal corrosion potentially developing a mark on metallic surfaces.12, 13 Meanwhile sodium chloride deposited within eccrine sweat has been suggested as a possible target for metal deposition methods and in cyanoacrylate polymerisation.14, 15 The reactivity of these species suggests that they may affect fingermark development, this reinforces the need to better understand the presence and distribution of these ions within fingermark residue. Previous research has demonstrated the highly variable and complex chemical composition and distribution within fingermark residues.7, 16, 17 The organic constituents within fingermark residues have been explored in great detail, using methods such as gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry.16-20 Several studies have used direct chemical imaging methods, such as matrix-assisted laser desorption ionization mass spectrometry,21, 22 Raman microscopy7, 23 and Fourier-transform infrared microspectroscopy (IRM)24, 25 to investigate spatial distribution of organic constituents, but few studies have investigated the distribution of inorganic constituents in fingermarks.26 Recent research has presented elemental imaging using time of flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy, to enhance fingermark development and identify exogenous contaminants, however the relative scarcity of literature aiming to understand the elemental distribution likely reflects the previous unavailability of direct elemental mapping techniques.27-29 Advances in brightness of third generation synchrotron light sources, and upgrades in detector technology and electronics now make possible rapid, direct elemental mapping, at micron spatial resolution, and sub-µM detection limits.30 These advances have thrust X-ray fluorescence microscopy (XFM) at synchrotron light sources into a wide-range of scientific areas to map trace elemental content, including material sciences,31 life sciences32 and cultural heritage studies.33, 34 Previous research has demonstrated the use of XFM imaging of sebaceous fingermarks to provide critical information on elemental distribution; however, the instrumentation available in that study did not have the sensitivity required to detect trace metals at micron spatial resolution.26 In this work, we have used IRM in combination with XFM to characterise the location of organic and inorganic constituents in fingermark residue, to better understand the chemical complexity of natural fingermarks and how it may impact methods of fingermark detection. Our experimental design consists of 3 distinct studies. In study 1 the co-localisation between organic and inorganic components of fingermark residue, revealed by multi-modal imaging provides important information on the environment within the fingermark where these trace metals and ions are located and suggests how the fingermark inorganic and organic matrix may interact and potentially change in response to factors such as substrate and the external environment. Study 2 reveals the variation of inorganic components in fingermark residue across a set of donors (study 2a), with additional experiments undertaken to investigate how sources of exogenous metals (coins, cosmetics) may be transferred to, and distributed within latent fingermarks (study 2b). Lastly, study 3 involves a preliminary assessment of how environmental factors such as exposure to aqueous environments may effect elemental distribution within fingermarks.

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EXPERIMENTAL Fingermark Deposition Fingermarks were collected from 8 donors; information on each of the donors can be found in Table 1. The donors gave natural deposits by gently pressing their index finger down for 5-10 s on silicon nitride slides (Melbourne Centre for Nanofabrication, Australia) and Ultralene Thin Film (SPEX Sample Prep, USA). Table 1 Details of the donors for this study

Donor Donor 1 Donor 2 Donor 3 Donor 4 Donor 5 Donor 6 Donor 7 Donor 8

Age (years) 23 23 50 32 40 34 77 32

Gender Female Female Male Male Female Female Male Female

Cosmetic use Moisturiser/Cosmetics Moisturiser/Cosmetics None None Moisturiser/Cosmetics Moisturiser/Cosmetics None None

Benchtop thermal source FTIR Microspectroscopy Analysis of the organic components within fingermark residue was conducted using an offline FTIR microspectroscopic system at the Australian Synchrotron IRM beamline. Fingermark samples were analysed as per the method outlined by Dorakumbura et al.7 in transmission mode using a Bruker Hyperion 3000 FTIR microscope with a liquid nitrogen cooled 64  64 Focal Plane Array (FPA) detector and a matching 15 objective and condenser (NA = 0.40), coupled to a Globar sourced Bruker Vertex 70 FTIR spectrometer (Bruker Optik, Ettlingen, Germany). The sample chamber was purged with dry nitrogen prior to scanning to reduce spectral contribution of atmospheric water vapour and CO2. FPA-FTIR images were acquired within a 4000–800 cm-1 spectral region as a single FTIR image covering a sampling area of 180  180 m2. The FPA consists of a 64 x 64 pixel array, where the physical pixel size is 40 um. At 15x magnification the effective pixel size is 2.67 um. In this study, focal plan array data was collected with 2 x 2 pixel binning of the 64 x 64 pixel array, to yield a final pixel size of 5.3 µm. For each FTIR image, high-quality FTIR spectral images were collected at 8 cm-1 resolution, with 32 co-added scans, Blackman-Harris 3-Term apodization, Power-Spectrum phase correction, and a zero-filling factor of 2 using OPUS 7.2 imaging software (Bruker). Background measurements were taken using the same acquisition parameters prior to sample spectral images, by focusing on a clean surface area of the substrate without the fingermark. All spectra were analysed using OPUS v7.2 software and CytoSpec 2.00.01 software. Images were further processed with ImageJ 1.50i software. Synchrotron sourced XFM Microscopy Elemental analysis of fingermark residue was conducted at the XFM beamline at the Australian Synchrotron. Following the method published by Summers et al.35 Data was collected using a Kirkpatrick–Baez mirror pair and a monochromatic incident beam of energy 15.8 keV was focused to a ~1 μm spot on the sample. The sample was oriented normal to the incident beam and with the detector positioned in backscatter geometry. X-ray emissions were collected using the low-latency, 384-channel Maia detector in event-mode. The sample was raster scanned through the beam with an effective dwell time of 0.1 ms per effective step (image pixel) size of 1 μm. The images collected were 1 μm pixel size and all analysis utilised a 3 point moving average to increase signal to noise ratio and enhance image contrast. Calibration of the data against a standard of known composition, elemental foils (Micromatter, Canada), as well as taking into account the composition and density of the substrate, the air path between the sample and the detector and the approximate composition of the sample provided elemental quantification. For full details of this process please refer to Summers et al.35 Data was analysed by extracting as TIFF files of per-pixel elemental areal density in ng cm-2, and then importing into ImageJ v1.50i.

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Investigation of transfer of exogenous material from Australian currency Prior to deposition Donor 4 was instructed to wash his hands to remove existing exogenous material, one hand was brought into contact with Australian silver-coloured coins, with gentle rubbing, whilst the other was not. Fingermark impressions were taken from both hands on silicon nitride slides and imaged using XFM. Investigation of elemental displacement or redistribution follow immersion of latent fingermarks in water. Fingermarks were collected from 8 donors on silicon nitride slides and imaged using XFM. The samples were then covered with deionised water for 30 min. The samples were dried and reimaged using XFM.

RESULTS This study has used XFM to characterise the elemental distribution within latent fingermarks, at 1µm spatial resolution, to address three specific research questions: 1) What is the spatial association between inorganic and organic components of fingermarks; 2) Are exogenous sources of metals and ions readily transferred to fingermarks (e.g., inorganic components of cosmetics or metal currency); 3) How might the elemental content and distribution change within fingermarks exposed to environmental factors (e.g., exposure to an aqueous environment). Study 1. Multi-Modal XFM and IRM Reveals the Association between Organic and Inorganic Distribution in Natural Fingermarks XFM elemental mapping was used to determine the distribution of inorganic ions and metals in a series of natural fingermarks deposited by 8 donors. Numerous ions and metals were detected in the fingermarks, and these are characterised in Table 2. Many of the ions and metals that were detected are likely to be endogenous (for example, Cl-, K+,Ca2+),9 while some metals detected are not and originate from exogenous sources such as contact with metal alloys or cosmetics (Bi, Ni, Ti).27 Other metals may originate from endogenous or exogenous sources (Fe, Cu, Zn).9 A representative example of XFM elemental maps from a natural fingermark from Donor 1 are presented in Figure 1. In general, the elemental distribution across the sample was found to follow the ridge pattern detail of a latent fingermark, as can be seen in Figure 1.

Figure 1 Large area XFM scan of natural fingermark from Donor 1, deposited on Ultralene Thin Film. Concentration Scale Bar (ng cm–2). See Figure S12 - S19 for large scale images

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Table 2 Components detected in latent fingermarks using XFM and their likely endogenous/exogenous source

Inorganic Component ClK+ Ca2+ Ti Bi Fe Ni Cu Zn

Source Endogenous Endogenous Endogenous Exogenous Exogenous Endogenous/Exogenous Exogenous Endogenous/ exogenous Endogenous/ exogenous

Potential Origin Sweat Sweat Sweat Cosmetics Cosmetics Cosmetics/Sweat Currency Currency/Sweat Cosmetics/Sweat

Dorakumbura et al.7 explored the distribution of organic components at the microscale using synchrotron sourced ATR-FTIR spectroscopy and Raman spectroscopy, demonstrating that eccrine and sebaceous material exists in an emulsion like residue (similar findings were also replicated for the donors used in our current study, supporting information Figure 1). Here, for the first time, synchrotron sourced XFM, used in combination with IRM has been able to demonstrate the distribution of the elemental components within fingermark residue relative to eccrine and sebaceous organic components (Figure 2). Figure 2a displays a FTIR false-colour distribution of eccrine material overlaid on the bright field image. The false-colour FTIR image was generated using a spectroscopic marker band (1520 – 1720 cm-1) presented in Figure 2b, which corresponds to the O-H bending vibration, characteristic of eccrine components, water, lactic acid or urea.7 Figure 2c reveals the elemental distribution in the same natural fingermark that was analysed with IRM, and demonstrates the presence of calcium, zinc, copper, chlorine and potassium. The similarity in location and morphology allows co-localisation of elemental distribution with eccrine components within the fingermark residue. Based on the observed co-localisation it is apparent that the eccrine material of natural fingermarks are enriched in inorganic components. For example, FTIR imaging reveals two distinct eccrine rich droplets in Figure 2a, and XFM revealed that both droplets are strongly enriched n Ca, Cl, Cu, K, and Zn.

Figure 2 Natural fingermark from Donor 7, deposited on a silicon nitride slide. Bright field optical image of the area investigated with FTIR-FPA imaging with false colour image generated by integrating over the O–H bending band for the eccrine material (1520–1720 cm−1 ) (a) FTIR spectra of eccrine material obtained using the conventional FTIR spectroscopy (b) and the corresponding elemental distribution maps imaged using XFM (c). XFM Concentration Scale Bar (ng cm–2) An additional example of the colocalisation of metal ions with eccrine material is provided in Figure S2.

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Fingermark regions enriched in sebaceous material were not found to be enriched with inorganic material (e.g., Ca, Cl, Cu, K, and Zn), as highlighted in Supporting Information Figure 2. This pattern of co-localisation was observed across 3 fingermarks, from 3 donors (Figure S3 and S4). Study 2. Sources of Variation in Elemental Content of Latent Fingermarks: Inter-Donor Variability Ourselves and others have previously demonstrated the high level of inter-donor variability that exists with respect to organic composition and distribution within fingermarks.7, 16, 17, 36 Despite the well characterised heterogeneity in organic composition of fingermarks, the variability in inorganic composition has been less studied, due to the previous unavailability of suitable techniques.37 The capability of XFM for rapid, micron level spatial resolution elemental mapping, now provides for the first time, the opportunity to assess inter-donor variability in elemental composition and distribution within natural fingermarks. The variation in inorganic material within fingermark residue across multiple donors (eight separate donors), revealed by XFM is presented in Figure 3. It should be noted that donors 1 and 2 were known cosmetic users and demonstrated higher levels of zinc and titanium in comparison to other donors (see also supporting information Figure 11). As can be seen in Figure 3, using Zn as an example, high inter-donor variability was observed (average Zn areal density across donors was 73.73 ng cm-2 with a standard deviation of 133.59 ng cm-2). Zn is known to be secreted from eccrine pores, and therefore, endogenous Zn is expected to be found in natural fingermarks.9 Figure 3 clearly demonstrates however, that the fingermarks obtained from users of cosmetics contain substantially larger amounts of Zn than non- or light cosmetic users. This suggests exogenous Zn, found in cosmetics may be a large source of the observed inter-donor variation. This is supported by specific metal colocalisations in the fingermarks from Donor 1 a known heavy cosmetic user (Figure 4). Specifically, regions of high Zn content were found to co-localise with high Ti content. Ti is not an endogenous metal in fingermarks, and therefore, can only be sourced from an exogenous source, such as cosmetics (TiO2 is a commonly added to cosmetics to protect against ultraviolet radiation).38 Interestingly, although Ti and Zn were found to co-localise in the fingermarks of cosmetic users, Fe did not show the same level of hot spot co-localisation. Strong co-localisation of ions Ca2+, Cl-, K+ with metals Cu and Zn were also observed in natural fingermarks (Figure 5). Closer examination of the ion distribution revealed that the Cl- and K+ deposits have distinct star shaped morphology, which likely indicates the presence of crystalline material within the fingermark residue.14 Similar findings were reported by Dorakumbura et al.7 where raman spectroscopy showed small salt crystals at the centre of an eccrine droplet .

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Figure 3 Typical results for zinc distribution within natural fingermarks collected from 8 donors on silicon nitride slides. Concentration Scale Bar (ng cm–2). Additional elemental maps are presented in Figure S5 – S11.

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Figure 4 Iron, titanium and zinc distribution within a natural fingermark from Donor 1 deposited on silicon nitride and imaged using XFM. Composite image (right) demonstrates the co-localisation of these metals within the fingermark matrix. Concentration Scale Bar (ng cm–2)

Figure 5 Calcium, Chlorine, Copper, Potassium and Zinc distribution within a natural fingermark from Donor 1 deposited on silicon nitride and imaged using XFM. Composite image (right) demonstrates the co-localisation of these metals within the fingermark matrix, box outlined in the composite image displays crystal like structures seen in particular donors, likely to be salt crystals. Concentration Scale Bar (ng cm–2)

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Study 2. Sources of Variation in Elemental Content of Latent Fingermarks: Metal-contact Contamination Following on from our studies of inter-donor variation in elemental content and distribution within fingermarks, we sought to explore if contact with metal surfaces would transfer material from the surface to fingertips, which would then be deposited in the fingermark. In the eight donors analysed in this study we found that Ni and Cu, major components of metal alloys, were sometimes found in high concentration and co-localised. This was hypothesised to reflect donor contact with metal surfaces, such as coins. The hypothesis was tested using contact between fingertips and Australian currency, specifically silver coins which comprise of 75% Cu and 25% Ni, as a case study. Donor 4 was instructed to wash his hands and then bring one hand into contact with silver-coloured coins, with gentle rubbing, while the other hand remained free of coin-contact. Latent fingermarks were taken from both hands for direct comparison to demonstrate the transfer of metals from the coin to the fingermark. The impression from the finger that had been in contact with the coin displayed higher levels of Cu and Ni, as shown in Figure 6. The most concentrated regions of Cu and Ni in the fingermark were found to be co-localised, and the relative concentration of Cu to Ni were similar to that of Australian currency (Table 3). These results strongly suggest that Cu and Ni originating from contact with Australian currency, or other metal surfaces may be routinely transferred to fingermark residue and be present within a latent fingermark.

Figure 6 Copper and Nickel distribution in fingermark deposited from Donor 4 on silicon nitride and imaged using XFM. Natural deposit (top) and fingermark from hand in contact with Australian currency (bottom). Concentration Scale Bar (ng cm–2) Table 3 Copper and Nickel content of latent fingermarks for Study 2

No Contact

Coin Contact

Study 3. XFM reveals a

Coin

Metal Cu Ni Cu/Ni Cu Ni Cu/Ni Cu/Ni

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Composition 42.5 ng cm-2 36.3 ng cm-2 1.17 284 ng cm-2 106 ng cm-2 2.67 3.00


differential effect of water


immersion on elemental content of natural fingermarks. Elemental content from eccrine regions of natural fingermarks is leached, but elements in the sebaceous matrix appear preserved In a true forensic context fingermarks may be exposed to a variety of factors, such as water immersion (either from exposure to the environment, or criminal efforts to clean contaminated surfaces). It is therefore, important to understand how exposure of fingermarks to water immersion effects the elemental content and distribution within the fingermark. Such knowledge may help explain the success or failure of different detection methods in varying conditions, or be used to develop improved detection methods for certain scenarios. We have demonstrated in Study 1 that the majority of elements co-localise within the hydrophilic eccrine material of natural fingermarks, and therefore, water immersion would be expected to result in substantial redistribution or leaching of elemental components from the fingermark. As shown in Figure 7, Cl, K, Ca, and Cu were almost completely removed from the fingermark following water immersion. Water immersion substantially reduced the concentration, but did not completely remove Zn from the fingermark. Interestingly, although a large proportion of Zn was removed from the fingermark during water immersion, the relative distribution of Zn after water immersion remained similar to that observed before water immersion. The levels of Fe and Ti in the fingermark were not visibly observed to change as a consequence of water immersion.

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Figure 7 Water immersion experiments showing the removal of metals from fingermarks deposited by Donor 1, original fingermarks (left), rinsed fingermarks visualised on the same colour scale as the original images (middle), rinsed fingermark visualised on maximum colour scale (right). Concentration Scale Bar (ng cm–2)

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DISCUSSION Metal ions have previously been established to have an impact on the ability of detection reagents to recover and successfully visualise latent fingermarks, with a number of studies specifically focussing on the interactions of metal ions with organic components of fingermarks and the detection reagents.10, 14, 15 Amino acid (eccrine material) detection reagents 1,2-indanedione and ninhydrin, are both known to interact with metal salts.10, 15 Researchers have shown that the addition of zinc chloride to the 1,2-indanedione working solution improves the colour and luminescence of the detected fingermark, and it is also well established that the addition of zinc and nickel salts as a post treatment for ninhydrin alter the colour of the developed fingermark.10, 15 Understanding the distribution of metal ions in relation to organic components, specifically the localisation of metal ions in relation to eccrine or sebaceous material is therefore, of interest. Such information provides insight into the possible chemical and physical interactions that may occur between the inorganic and organic constituents of fingermarks, and how this may affect fingermark detection. In this study the observation of Zn co-localised with eccrine material may explain in part the variation in detection of latent fingermarks using 1,2-indanedione and ninhydrin. Specifically, the enrichment in Zn that is observed in cosmetic users provides a new avenue to investigate, specifically, to identify if the fingermarks of cosmetic users are more readily detected by 1,2-indanedione and ninhydrin methods, on the basis of their Zn enrichment. The presence of sodium chloride deposited in eccrine sweat has also been suggested as a potential reactive species in fingermark residue, as a possible target for metal deposition methods and in cyanoacrylate polymerisation.14, 15 Since chloride appears to be deposited across a fingermark ridge this research reinforces the potential for chloride ions to be interacting with these development techniques. However the removal of chloride ions through water immersion suggests that this ion cannot be targeted with water dispersive techniques. The results of this study demonstrate that under certain circumstances fingermarks may be enriched in metals such as Zn, Fe, Ti, Bi or contain metals such as Cu and Ni as a result of contact between fingertips and metal surfaces. Most currently available fingermark detection methods are centred on an interaction or reaction between detection reagents and organic components of fingermarks. This current study not only reveals the possibility that metal ions in the fingermark may influence the chemical interactions between reagent and organic fingermark components, but highlights the metal ions themselves could be used as targets. To the best of our knowledge, until now fingermark detection methods have not explored the possibility of targeting other metal ions as a way of visualising fingermarks. This study revealed that even after immersion in water, a process that removes much of the eccrine material (which is targeted by current detection methods), metals ions of Fe, Ti, and Zn can remain. In particular, Fe and Ti appeared largely unaltered by water immersion. Although it is likely that presences of these metals at the concentrations observed in this study are from exogenous sources, the results highlight the potential to develop metal sensing reagents as a possible route to detect latent fingermarks in certain settings. Such detection methods could include fluorescent or colour metal binding compounds, as routinely developed in the biological and environmental sciences. In addition to acting as targets for fingermark detection protocols, these findings presented here on metal transfer, indicate the potential to give information on a person’s recent activities. Previous work has demonstrated how exogenous metals can be detected on the hands after handling a firearm, and chemical methods have been developed to detect iron transferred in hand marks.27, 28, 39-41 The findings of this study encourage further development of methods to detect the transfer of specific metals for the purpose of detecting contact with metallic surfaces such as firearms. It also opens the possibility of the use of synchrotron sourced XFM for fundamental research to better understand the mechanism of transfer, which is a priority for national forensic agencies.42 Related to this, although direct elemental mapping techniques themselves, such as XFM are unlikely to ever become a routine fingermark detection technique, this study has highlighted that the ability to reveal elemental content and distribution within a fingermark provides information on donor traits (e.g., contact with cosmetics or metal surfaces). In forensic cases of high importance, under certain circumstances largely governed by the surface fingermarks are thought to be deposited on), XFM analyses of latent fingermarks may provide valuable information on donor traits.

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CONCLUSIONS This study has demonstrated the capabilities for direct elemental mapping techniques, such as XFM, to study the trace elements present within latent fingermarks. Using this capability, this research begins to explore the elemental distribution within fingermark residue so that we may begin to better understand the effects these ions have on the underlying chemistry of current methods of detection. Specifically, we have demonstrated that the majority of inorganic components within latent fingermarks are localised to eccrine organic material. Such an observation suggests that variation in metal ion content within eccrine material may account for variation in the ability to detect latent fingermarks, especially reagents targeting eccrine material and in which metal ion chemistry is known to effect the detection chemistry. Further, the presence of exogenous material in particular donors reinforces the influence of daily activities, such as cosmetic use and contact with metallic material, on fingermark chemistry. Future work is now underway to determine if these factors correlate with variation in detection with reagents used in 1,2-indanedione and metal deposition methods. Likewise, the effects of these contaminants must be considered when exploring fingermark residue and their impact on fingermark detection methods. This work also demonstrates the potential to use synchrotron sourced XFM to study the fundamentals of transfer processes for forensic science, and the possibility of providing addition information for forensic intelligence purposes. Due to the necessity of a synchrotron facility to undertake the measurements described in this study, routine application for forensic testing is unlikely. However, direct application of the techniques presented in this study, to select forensic cases is achievable. Possibly of greater value, is the knowledge gain relating to greater understanding of the chemical complexity and chemical transfer processes associated with latent fingermarks, which this and future studies will provide. Such insight may provide the necessary founding for the development of new, routinely applicable methods to detect latent fingermarks or identify chemical traits within the fingermark (e.g. presence of cosmetics). Lastly, based on the results of this study, we have begun to explore possibilities to use metal ion sensing compounds as a new, niche opportunity to detect latent fingermarks exposed to environmental factors such as water exposure, in circumstances where traditional approaches fail. These findings highlight only a fraction of the potential studies for which XFM and direct elemental mapping can be applied to study the chemistry of fingermarks. Classical analytical techniques such as HPLC and mass spectrometry, and more recently mapping techniques such as FTIR and Raman microscopy have been invaluable to increasing understanding of the organic chemical composition of latent fingermarks and how it effects detection methods. On the basis of our study, we hope direct elemental mapping can play a similar role to reveal the complexities through which metal ions influence fingermark chemistry, and subsequently improve detection capability.

ACKNOWLEDGEMENTS This research was undertaken on the XFM and IR beamlines at the Australian Synchrotron, part of ANSTO. This work was performed in part at the Melbourne Centre for Nanofabrication in the Victorian Node of the Australian National Fabrication Facility. The authors would like to acknowledge the contribution of Australian Government Research Training Program Scholarships in supporting this research. The authors would like to thank all the fingermark donors for their cooperation. This project has been approved by the Curtin University Human Research Ethics Committee (Approval Number SMEC-46-13).

Supporting Information Available: Images showing co-localisation of metal ions with eccrine material, additional elemental maps for latent fingermarks, large scale elemental maps for latent fingermark shown in Figure 1 REFERENCES 1. 2.

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Table of contents entry

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Large area XFM scan of natural fingermark from Donor 1, deposited on Ultralene Thin Film. Concentration Scale Bar (ng cm-2). See Supporting Information Figures 12-19 for large scale images 177x85mm (300 x 300 DPI)


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Natural fingermark from Donor 7, deposited on a silicon nitride slide. Bright field optical image of the area investigated with FTIR-FPA imaging with false colour image generated by integrating over the O–H bending band for the eccrine material (1520–1720 cm-1) (a) FTIR spectra of eccrine material obtained using the conventional FTIR spectroscopy (b) and the corresponding elemental distribution maps imaged using XFM (c). XFM Concentration Scale Bar (ng cm-2). An additional example of the colocalisation of metal ions with eccrine material is provided in Supporting Information Figure 2. 177x98mm (300 x 300 DPI)



Typical results for zinc distribution within natural fingermarks collected from 8 donors on silicon nitride slides. Concentration Scale Bar (ng cm-2). Additional elemental maps are presented in Supporting Information Figure 5 – 11. 177x195mm (300 x 300 DPI)


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Iron, titanium and zinc distribution within a natural fingermark from Donor 1 deposited on silicon nitride and imaged using XFM. Composite image (right) demonstrates the co-localisation of these metals within the fingermark matrix. Concentration Scale Bar (ng cm-2) 177x100mm (300 x 300 DPI)



Calcium, Chlorine, Copper, Potassium and Zinc distribution within a natural fingermark from Donor 1 deposited on silicon nitride and imaged using XFM. Composite image (right) demonstrates the co-localisation of these metals within the fingermark matrix, box outlined in the composite image displays crystal like structures seen in particular donors, likely to be salt crystals. Concentration Scale Bar (ng cm-2) 176x80mm (300 x 300 DPI)


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Copper and Nickel distribution in fingermark deposited from Donor 4 on silicon nitride and imaged using XFM. Natural deposit (top) and fingermark from hand in contact with Australian currency (bottom). Concentration Scale Bar (ng cm–2) 177x188mm (300 x 300 DPI)



Water immersion experiments showing the removal of metals from fingermarks deposited by Donor 1, original fingermarks (left), rinsed fingermarks visualised on the same colour scale as the original images (middle), rinsed fingermark visualised on maximum colour scale (right). Concentration Scale Bar (ng cm–2) 143x228mm (300 x 300 DPI)


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Revealing the Elemental Distribution within Latent ... - ACS Publications

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