Microscopic examination of fingermark residues: Opportunities for fundamental studies.

G Model

FSI-8019; No. of Pages 10 Forensic Science International xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

Forensic Science International journal homepage: www.elsevier.com/locate/forsciint

Microscopic examination of fingermark residues: Opportunities for fundamental studies Se´bastien Moret a,*, Xanthe Spindler a, Chris Lennard b, Claude Roux a a b

Centre for Forensic Science, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia School of Science and Health, University of Western Sydney, Richmond, NSW 2753, Australia

A R T I C L E I N F O

A B S T R A C T

Article history: Received 24 December 2014 Received in revised form 22 April 2015 Accepted 19 May 2015 Available online xxx

Despite significant ongoing research, a substantial proportion of latent fingermarks remain undetected in casework. Therefore, to improve existing detection techniques and to allow the development of new approaches, it is important to gain a better understanding of detection mechanisms rather than solely focusing on method formulations. As a starting point, it is crucial to gain a deeper understanding of the fingermark residue itself. Even if the chemical composition is reasonably well understood, little research has been reported on the physical aspects related to the deposition of fingermarks and their interactions with the environment and underlying substrates. This study aimed at exploring various techniques that can be used for the non-destructive visualisation of fingermarks before applying detection techniques. Both light and electron microscopy were investigated. Phase contrast imaging and environmental scanning electron microscopy, coupled with energy-dispersive X-ray spectrometry, proved to be essential tools for the study of latent fingermark deposits. These methods can be used to gather fundamental information that will add to our body of knowledge in this field. ß 2015 Elsevier Ireland Ltd. All rights reserved.

Keywords: Optical microscopy Electron microscopy Phase contrast Detection Latent fingermark

1. Introduction When bare hands (including fingers) touch an item, substances present on the skin are transferred, reproducing the complex ridge patterns of the palm and the fingers. The resulting marks are often latent and must therefore be detected before being exploited for comparison purposes. The choice of a particular detection technique is related to the substrate, the type of mark, environmental conditions and even the circumstances of the case at stake. Moreover, in order to improve the chances of detecting a mark, several techniques are typically applied in a sequence to successively target the various components present in the secretions. Dozens of detection techniques have been investigated and optimised to date [1,2]. Emerging technologies such as nanotechnology [3] and immunodetection techniques [4,5] have also been applied in the field, leading to the discovery of new, highly promising detection methods. But, despite the numerous available options and current endeavours to find increasingly more effective methods, a general lack of sensitivity and specificity has been noted. According to Jaber et al., 50% of the available marks

* Corresponding author. Tel.: +61 2 9514 2758. E-mail address: [email protected] (S. Moret).

remain undetected on porous substrates [6]. Despite significant ongoing research, it seems that the field has reached its detection threshold; no major realistic advances or ground-breaking discoveries have been made these past few years. This situation can be explained by the fact that researchers are mainly focused on results, rather than on the understanding of principles underlying the techniques. Historically, the vast majority of the detection methods have been adapted from preexisting ones in other fields. Biology offers a glaring example since molecules such as ninhydrin were firstly used to detect amino acids on thin-layer chromatography plates. The formulation was then adapted to detect amino acids found in fingermark secretions on porous substrates (Fig. 1a) [7]. The same can be said for lipid stains such as Oil Red O (Fig. 1b) and Nile Red used in histochemistry and adapted to detect the lipid fraction of fingermark residues originating from sebaceous glands [8–10]. Other fields have also impacted on the range of available fingermark detection techniques. For example, the ‘physical developer’ (PD) technique was originally adapted from a photographic developer used to process photosensitive films. Its formulation was then further optimised to trigger silver reduction onto fingermark ridges (Fig. 1c) [11,12]. This trial-and-error approach has led to the development of highly sensitive techniques currently used worldwide. However, it

http://dx.doi.org/10.1016/j.forsciint.2015.05.027 0379-0738/ß 2015 Elsevier Ireland Ltd. All rights reserved.

Please cite this article in press as: S. Moret, et al., Microscopic examination of fingermark residues: Opportunities for fundamental studies, Forensic Sci. Int. (2015), http://dx.doi.org/10.1016/j.forsciint.2015.05.027

G Model

FSI-8019; No. of Pages 10 2

S. Moret et al. / Forensic Science International xxx (2015) xxx–xxx

Fig. 1. Illustration of fingermarks detected on paper with (a) ninhydrin, (b) Oil Red O, and (c) physical developer.

has also several downsides: the optimisation itself is time consuming; it cannot be generalised to every substrate; and it often leads to the development of techniques that are not fully understood (with PD being an excellent example of this). The optimisation of a technique implies mandatory and very tedious lab work since each parameter involved in the procedure has to be adjusted independently. Problematic situations can arise where techniques perform effectively on certain substrates but not on others. Even worse, some formulations are effective in some parts of the world but are unsatisfactory elsewhere, which can be due to environmental factors such as humidity levels or substrate differences from variations in primary materials used in manufactured products [13]. Without a deeper understanding of the mechanisms involved in the process, unwanted background staining or a failure to detect marks cannot be adequately explained and the optimisation of relevant techniques can be problematic. There is a current trend to improve our understanding of certain detection mechanisms, such as amino acids reagents [13] or the interaction occurring between nanoparticles and fingermarks [14]. Until now, however, only a small number of techniques are fully understood. In order to improve our knowledge in the field, it is important to pursue this trend by refocusing on a fundamental understanding of the latent fingermark itself. From a chemical perspective, the fingermark residue has been extensively investigated. The dermatological studies of the components present on the skin and excreted by the glands (eccrine, apocrine and sebaceous) offer a good starting point. Nonetheless, they are not entirely representative of the actual composition of fingermarks, since the residue is affected by numerous parameters after its deposition. Extensive studies of the residue itself have been conducted and reviews are available [15,16]. The chemical decomposition processes within the residue are currently under study by several research groups around the world, mainly for age estimation purposes [17–19]. Even if the chemical composition of fingermarks represents critical information to determine which components to target specifically, it is not sufficient in itself. Physical information such as morphology of the fingermark ridges, distribution and accessibility of the components within the residue, as well as interactions with the substrate and with the environment are important considerations. This knowledge remains restricted to only a handful of studies conducted nearly four decades ago [20–23] and should therefore be investigated more thoroughly. To study the residue itself, the first step is to find techniques that enable the collection of extensive data in situ on a wide range of substrates, without altering the fine details of the pattern and the distribution of components within ridges. To preserve the initial aspect of the residue, these observations have to be

performed before the application of any fingermark detection technique. This paper reports various instruments and imaging techniques that can be applied to study the fingermark residue in situ; preliminary observations were also obtained from fingermarks deposited on several substrates. A deeper understanding of fingermark physics will not only help optimise current fingermark detection techniques and determine optimal parameters, but will also shed light on the lack of results on certain substrates. Better indepth knowledge of the residue, encompassing both chemical and physical properties, will facilitate the development or reformulation of more efficient and more effective detection techniques. This study is a first step in this direction. 2. Materials and methods 2.1. Fingermark samples This study was limited to one male donor since it was focused on the various possibilities for fingermark visualisation and imaging rather than on a comparison of their quality. Three different types of marks were collected: sebaceous, natural and eccrine marks. Sebaceous marks were artificially enriched with sebum not naturally present on the friction ridge skin surface. Before fingermark deposition, the donor was asked to rub his fingers on his forehead to enrich the amount of sebaceous material already present. This type of mark contained a higher quantity of secretions than a natural mark, which in turn was collected without any particular preparation of the fingers and for which no artificial enrichment was applied. For natural mark collection, the donor was asked not to wash his hands for 1 h prior to deposition and to rub his hands together to homogenise the secretions already present on the skin. This type of mark therefore consisted of a natural mix of both eccrine and sebaceous secretions. Finally, to collect eccrine marks, the donor was asked to thoroughly wash his hands twice with soap and warm water to remove any sebaceous secretions. The fingers were then air dried. After 15 min avoiding touching anything, the fingermarks were simply deposited on the substrates. In order to observe the influence of the surface type, marks were collected on a variety of non-porous substrates as listed in Table 1. Table 1 Description of the substrate samples used for this study. Substrate

Composition

Microscope slide (Livingstone Pathology Grade) Thick document protector (Marbig) Thin A4 sheet protector (Cumberland) Cling film (GladWrap) Tape, non-adhesive side (Scotch Police)

Glass Polyvinyl chloride (PVC) Polyvinyl chloride (PVC) Polyethylene (PE) Polypropylene (PP)


G Model

FSI-8019; No. of Pages 10 S. Moret et al. / Forensic Science International xxx (2015) xxx–xxx

3

2.2. Instrumentation 2.2.1. Light microscopy Optical microscopy examination was conducted with two different microscopes. Bright field, dark field and phase contrast observation were conducted on a Leica DMLS microscope equipped with a 10 (0.25na) dry Leica C PLAN PH objective. Crosspolarisation was performed with a Leica DMLSP microscope fitted with a 10 (0.22na) dry Leica C PLAN POL objective. Each microscope was equipped with a Leica DFC295 camera, controlled with Leica Application Suite software, version 4.1.0. All images were recorded at the highest available resolution (2048 1538 pixels–full frame), in RGB mode and in .tiff format. 2.2.2. Scanning electron microscopy Scanning electron microscopy examination was carried out using a Zeiss EVO LS 15 SEM, equipped with both secondary and backscattered electron detectors, and a Bruker Quantax 400 EDS for elemental analysis and mapping. The samples were mounted on aluminium stubs using double-sided carbon tape and examined in a variable pressure chamber at 80 Pa, with a beam acceleration voltage of 10 kV. 2.3. Comparison of light microscopy techniques In order to compare the efficiency of the above presented techniques, sebaceous, natural and eccrine marks from one donor were collected on the substrates detailed in Table 1. For each mark, the same area was imaged using bright field, dark field and phase contrast microscopy. Each image was then evaluated by taking into account parameters such as contrast, clarity of ridges and amount of detail that could be observed within ridges. Dark field and phase contrast were evaluated comparatively to bright field, using a qualitative grading system as described by McLaren et al. [24] and Chadwick et al. [25]. Positive scores (+1 or +2) were attributed if the technique under evaluation showed an improvement compared to bright field. Negative scores ( 1 or 2) stood for a decrease of the overall quality. A score of 0 meant there was no visible enhancement compared to bright field imaging. 3. Results and discussion 3.1. Light microscopy Optical microscopy is one of the simplest and most basic examination tools, but it still remains one of the most effective. To be visualised, the samples do not require any particular preparation and minimal detrimental effect on the specimen would be expected. However, the substrate must be transparent for observations in the transmission mode. Magnification of 100 was determined to be optimal, since it permitted the visualisation of three to four ridges in the field of view, with a sufficient resolution to conduct detailed observations of the residue distribution within a single ridge. 3.1.1. Bright field microscopy Bright field imaging is commonly applied on stained and coloured samples, but it is problematic with clear and transparent samples. Hence, fingermarks observed in the bright field mode presented very low contrast. Only heavily loaded marks gave images with sufficient contrast to conduct meaningful observations (Fig. 2). The ridge outlines can be distinguished and some darker spots, as well as droplets of secretions, were visible within ridges. The lack of contrast prevented detailed observations of fine ridge characteristics. The contrast was even lower for natural and eccrine secretions, where the outline of the marks was almost

Fig. 2. Fresh sebaceous fingermarks (2 h) deposited on glass and observed with bright field microscopy.

invisible. These marks appeared to be constituted of droplets smaller than for the sebaceous mark, but no clear details were visible and no further observations could be conducted. To improve contrast, biological samples are generally stained with coloured or luminescent compounds. In the case of fingermarks, any sample processing will have an adverse and uncontrolled effect on the residue itself, which deviated from the main aim of this study. Other non-destructive visualisation techniques were therefore implemented. 3.1.2. Dark field microscopy This technique is generally used to enhance the contrast of unstained samples. An oblique illumination is used and only light diffused by the sample will be collected, thus leaving a dark background. Applied to fingermark samples, it improved the contrast and better ridge details could be observed; sebaceous marks showed an obvious improvement compared to bright field microscopy (Fig. 3a). The outline offered a clearer definition and the inner fine structures of the ridges were revealed. Droplet shapes could be more precisely observed and very small amounts of secretions could be detected in the furrows; pores were also well defined. Better contrast was also obtained with natural marks (Fig. 3b). Smaller droplets were observed because less material was present in the natural marks. Eccrine marks remained quite faint and difficult to visualise (Fig. 3c). Droplets of secretions were visible but the outline was not clearly defined. The overall image still lacked contrast. Even with improvements brought by dark field microscopy, fine ridge detail remained hard to distinguish in certain cases. 3.1.3. Phase contrast microscopy Phase contrast microscopy is a powerful and simple technique, significantly enhancing the contrast of transparent specimens without the requirement for staining procedures. It converts phase shifts of light induced by refractive index and thickness variations into brightness intensity variations. Variations in refractive indices and thicknesses will contribute to contrast formation. The method was appropriate for this study since fingermark residue is normally transparent, with a multicomponent nature. The images obtained in this study offered good contrast and provided significantly more information than the bright or dark field techniques. Sebaceous marks on glass presented a high level of detail, with clearly defined ridge outlines (Fig. 4a). Material distribution within ridges could be further analysed; different droplet sizes and shapes were observed, along with solid material. Both natural and eccrine fingermarks on glass produced good detail (Fig. 4b and c). Even with a lower amount of secretions, especially for the eccrine marks; the contrast


G Model


4

Fig. 3. Fresh fingermarks (2 h) deposited on glass and observed with dark field microscopy: (a) sebaceous, (b) natural, and (c) eccrine secretions.

Fig. 4. Fresh fingermarks (2 h) deposited on glass and observed with phase contrast microscopy: (a) sebaceous, (b) natural, and (c) eccrine secretions.

was weak but still sufficient to visualise some ridge outlines. Droplet size and shape, inner ridge structure, and material distribution could be observed with adequate detail. 3.1.4. Cross-polarisation microscopy Cross-polarisation microscopy is a technique generally used to observe birefringent samples such as crystals or polymers. Several tests were performed on fingermarks, without convincing results. Fingermarks are composed of various heterogeneous materials such as greasy components (triglycerides, fatty acids, wax esters, squalene), water soluble components (amino acids, proteins, various ions) and skin cells. On some samples, these components exhibited weak birefringence, providing some additional information. However, the added value of the technique remained questionable, since the same type of information could be obtained with phase contrast imaging.

all substrates and secretion types, the phase contrast method led to a general improvement (Fig. 5). This was not the case for dark field microscopy where the quality of the images decreased in several instances. For thin PVC, and for all textured substrates, phase contrast was less appropriate since it reinforced the polymer texture thus concealing the mark itself. To conclude, among the four microscopy techniques tested to visualise untreated fingermarks, phase contrast was the most effective. Very fine detail could be observed with good contrast. This technique is therefore suitable for the systematic examination of latent fingermarks and can be occasionally complemented by techniques such as cross-polarisation or bright and dark field microscopy. However, the major limitation inherent to light

3.1.5. Comparison of techniques According to the above presented results, cross-polarisation was discarded due to the limited additional information obtained. The comparison results obtained with bright field, dark field and phase contrast microscopy are summarised in Table 2. For almost Table 2 Evaluation of microscopy techniques for imaging each fingermark type and each substrate. In comparison with BF

Glass Thick PVC Thin PVC PE PP

Sebaceous

Natural

Eccrine

DF

PC

DF

PC

DF

PC

+1 1 1 1 1

+2 +1 +2 +1 +2

+1 +1 1 +1 0

+2 +1 +1 +1 +2

+1 0 0 0 1

+2 +1 0 +1 +1

Note: BF = bright field, DF = dark field, PC = phase contrast.

Fig. 5. Comparison of bright field (BF), dark field (DF) and phase contrast (PC) on a fresh natural fingermark (2 h) deposited on PE.


G Model


5

Fig. 6. Sebaceous fingermarks (1 day) deposited on glass and observed with phase contrast microscopy (a) before observation with ESEM, and (b) after having been in the ESEM chamber at 80 Pa for 3 h.

microscopy is the need for transparent, clear and non-textured substrates in order to properly visualise the samples. This issue could be solved by using scanning electron microscopy, with the additional benefit of a higher resolution and depth of field. 3.2. Scanning electron microscopy 3.2.1. Environmental scanning electron microscopy (ESEM) Scanning electron microscopy (SEM) is a valuable technique used on occasions to study fingermarks after detection. Techniques such as cyanoacrylate fuming [26] and multimetal deposition [27] have been studied in this manner. However, a conventional SEM is

not appropriate to study untreated fingermarks. Firstly, samples generally need to be coated with a conductive layer of metal or graphite. Secondly, samples have to be placed in a high-vacuum chamber to produce a good-quality image. Both coating and high vacuum will have detrimental effects on the fingermark residue; inevitable and uncontrollable modifications such as water and lipid evaporation will occur [28]. Coating procedures, which also require vacuum, will obscure the samples and thus prevent any further light microscopy observation. For these reasons, this study investigated the use of an environmental SEM (ESEM). ESEM operates at a lower vacuum without particular sample preparation. Good images can be obtained on non-conductive substrates with

Fig. 7. ESEM images of a sebaceous fingermark (1 day) deposited on glass, detected with secondary electrons (left) and backscattered electrons (right) at various magnifications: 50 [(a) and (d)], 100 [(b) and (e)] and 200 [(c) and (f)].


G Model



much lower beam intensity. This type of instrument is generally suitable for biological samples [29]; its application for the analysis of fingermarks can therefore be envisaged. The chamber pressure and the beam voltage intensity were respectively set at 80 Pa and 10 kV. Observations of fingermarks with phase contrast microscopy before and after ESEM imaging confirmed that the selected parameter values had limited effects on the samples. Very little modification was observed on fingermarks imaged at 80 Pa for about 3 h (Fig. 6). The general morphology was retained as well as the position and size of the various elements present within the ridges. There was no obvious modification except for some very minor shrinking of small droplets of material. The detrimental pressure identified by Bright et al. was around 2 10 5 Torr (2.6 10 3 Pa), whereas 80 Pa is well above this value [28]. Both secondary and backscattered electron imaging provided complementary information; secondary electron imaging allowed visualisation of the morphology of the deposited secretions, whereas backscattered electron imaging provided insights on elemental composition (Fig. 7). Secondary electron images offered topographical information; the ridge outlines could be visualised, along with various other components. Three types of structures were observed: (1) layers of various densities and thickness coating the ridge surface; (2) crystal-like structures at various locations; and (3) larger aggregates of various sizes and shapes (Fig. 7a–c). The secondary electron images were complemented with the backscattered electron images, which were helpful to determine the composition of the various structures appearing within the ridges (Fig. 7d–f). Elements of high atomic number

appear brighter than those of lower atomic number. The darker layer covering the ridges may be composed of carbon and, according to the shape, it may be comprised of components such as fatty acids. The larger aggregates detected with secondary electrons appeared dark as well. Their sizes, shapes and structures suggested that they could be cells from the continuous desquamation of the skin. The crystal-like structures appeared brighter, which indicated a higher atomic number. These structures may consist of ions found in human sweat, such as sodium and potassium. This information can be further complemented with energy-dispersive X-ray spectroscopy, detailed in the next Section 3.2.2. However, even if good quality images were obtained with rich marks (sebaceous) (Fig. 7), it was much more difficult to process poorer marks, containing only eccrine secretions (Fig. 8). Indeed, very few residues were detected. Skin cells were visible, as well as small salt crystals, but it is difficult to conduct a detailed study on this type of mark using only this technique. 3.2.2. Energy-dispersive X-ray spectroscopy (EDS) Energy-dispersive X-ray spectroscopy (EDS) coupled with ESEM provides valuable information on the elemental composition of a sample. An entire image can be scanned and mapping of the elemental composition achieved, even with lighter elements. Qualitative mapping of the elements found in a fingermark can lead to their identification and assist in determining the origins of the various heterogeneous structures observed previously. The samples already imaged with ESEM were processed with EDS (Fig. 10). Attention was focused on four elements commonly

Fig. 8. ESEM images of an eccrine fingermark (1 day) deposited on glass, detected with secondary electrons (left) and backscattered electrons (right) at various magnifications: 50 [(a) and (d)], 100 [(b) and (e)] and 200 [(c) and (f)].


G Model


7

Fig. 9. Energy-dispersive X-ray spectroscopy of a fingermark on glass and illustration of the mapping of various elements: carbon (red), chloride (light blue), potassium (pink) and sodium (yellow). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.).

Fig. 10. Comparison of the same natural mark (1 day old) deposited on glass and visualised using (a) ESEM, secondary electron, (b) phase contrast and (c) ESEM, backscattered electron.

found in fingermark secretions: carbon, chloride, potassium and sodium [15,16]. Successful mapping was obtained for the first three elements. The results for carbon (Fig. 9, in red) were consistent with the above hypotheses. The location of this element can be correlated with the backscattered electron images. There was a higher concentration of carbon in the larger aggregates, confirming their skin cell origin. As observed, the droplets also contained a sufficient amount of carbon to be detected, confirming their organic composition. The lighter areas detected with backscattered electrons contained both chloride and potassium, as indicated by the respective elemental maps (Fig. 9, in light blue for chloride and in pink for potassium). The salt crystal origin can thus be confirmed. However, sodium could not be mapped and localised within crystals or ridges. Since sodium is present in sweat in a greater amount than potassium it should have been detected. This negative result was due to the presence of several interfering elements in the glass substrate, including sodium. Therefore, if precise elemental mapping is to be done, a substrate made of pure material (or containing a low amount of trace elements) must be used; silicon wafers might be an appropriate substrate. This was not done in these experiments since only substrates enabling subsequent examinations by both light and electron imaging were considered. Silicon wafers are not suitable for optical microscopy. 3.2.3. Light versus electron microscopy Light microscopy (phase contrast) has obvious advantages over ESEM (secondary and backscattered electrons) (Fig. 10). Phase contrast is inexpensive, quick, easy to implement and less damaging to fingermark samples. It can thus be applied on a

systematic basis over a large set of samples consisting of several substrates, donors and fingermark types. The technique remains nevertheless limited to flat, transparent and non-textured substrates. Realistic samples such as plastic bottles or bags cannot be imaged without cutting or otherwise damaging the exhibit. Even if ESEM is relatively quick, an extensive observation of a large set of samples may not be practical. In these experiments, locating a precise area of interest (minutiae) proved to be difficult. Weak marks resulted in poor image quality containing very limited information. However, ESEM has several advantages over an optical microscope. It has a better depth of field and a much higher resolution. Non-transparent or patterned substrates can be examined. In addition, the dual detection mode (secondary and backscattered electrons) provided information on both the morphology and the composition of the sample. The backscattered electron mode coupled with EDS proved to be a very effective way to identify, localise and map the various components found in a latent fingermark. Overall, it can be concluded that light microscopy is the most appropriate technique to gather information on an extensive set of samples, and that punctual observations with ESEM and EDS can provide additional valuable information on detailed morphology and elemental composition. However, both microscopy types are mainly applicable to non-porous substrates. Fingermarks detected by amino acid reagents have been observed on paper with optical microscopy (cross-section) [30], but they remain extremely difficult to visualise prior to detection; effective techniques are yet to be identified for fundamental studies of fingermark residue on such substrates.


G Model



3.3. Fundamental studies – preliminary results This section reports preliminary results based on phase contrast microscopy of fingermarks deposited on non-porous substrates. It was assumed that both water-soluble and non-water-soluble components would remain on the substrate under the environmental conditions of the study. 3.3.1. Fingermark morphology and substrate Observation of fingermarks deposited on various transparent, non-porous substrates showed that the substrate type has a nonnegligible influence on the morphology of the marks and the distribution of components within ridges (Fig. 11). On glass, the ridge outlines were clearly defined and the highest concentration of secretions was located between the centre and the borders of the ridges. The droplet size was heterogeneous and some heavier droplets, appearing brighter, could be seen. The comparison with the same type of marks (sebaceous) deposited on polypropylene showed significant differences (Fig. 11a). Droplets were no longer present; secretions were more spread across the ridge surface forming pools with a higher concentration located on the border of the ridges. A very fine and well defined outline could be systematically observed. Interestingly, the skin cells (dry aspect on glass) appeared embedded within the fingermark matrix on PP. Such differences might be due to substrate properties such as surface tension. Similar results were observed on thick PVC (Fig. 11b), while on thin PVC the ridges presented a significantly different morphology (Fig. 11d); the major part of the secretions was concentrated towards the middle of the ridges. The outline was still well defined, but both droplets and large pools of secretions were visible. The skin cells appeared dry when located on the border of the ridges where less secretions were visible; whereas, when located towards the middle, they appeared embedded in the matrix, as for PP. Conversely, on PE, the larger pools were located on the ridge border, with the centre containing a smaller amount of material. The ridges appeared thinner on PE than on PP.

These limited observations indicate that the substrate has an influence on the distribution of the secreted material and therefore plays an important role in the morphology of the deposit. Of course, the variation in the amount of secretion between each mark must be taken into account, but significant differences observed between the two PVC types clearly supports the fact that more information must be gathered from the substrate itself. Such studies have to be conducted by considering both secretion and substrate characteristics. 3.3.2. Behaviour of secretions on various substrates To further investigate the substrate effect, fingermarks collected on glass, thin PVC and PP were left to age for nearly two months. Images of the same areas were taken over time to monitor how the deposits behaved. For this preliminary study, storage conditions were not the subject of any particular attention. The samples were simply stored in an office drawer (in the dark) without humidity or temperature monitoring. Very interesting results were obtained (Fig. 12). For marks on glass, the observed modifications were relatively slow. There was no drastic change after 4 days; the large pools of secretions retained their shape and size. The smaller droplets showed some signs of shrinkage but only to a limited extend. The most interesting and surprising change did not occur within the ridges, but in the furrows. These areas were visible as a clean substrate immediately after deposition, but droplets started to appear within the furrows after 24 h (not illustrated) and remained visible after 4 days and even 58 days. This phenomenon can be attributed to a redeposition of the more volatile sebaceous compounds; however, this droplet apparition in the furrows remains to be further understood. The changes in the marks over time on PP were completely different. The marks were perfectly visible after deposition, but disappeared almost completely after just 4 days (Fig. 12b). Pools were no longer visible, but a faint ridge outline could still be observed. Between 4 and 58 days, ridge outlines were no longer visible, but tiny droplets of substances retained their original

Fig. 11. Fresh sebaceous marks visualised using phase contrast deposited on glass (left side of each image) and compared with marks deposited on (a) PP, (b) thick PVC, (c) PE, and (d) thin PVC (right side of each image).


G Model


9

Fig. 12. Sebaceous marks, visualised using phase contrast microscopy, deposited on: (a and d) glass, (b and e) PP, and (c and f) thin PVC.

locations (Fig. 12e). This quick degradation cannot solely be attributed to environmental factors since all samples were collected and stored together. The fingermark secretions seem to dissolve into the substrate or into contaminants or coatings present on the surface (e.g. plasticisers). The observed phenomenon needs to be further investigated but the substrate is thought to be the main contributor. The situation on PVC was similar to what was observed on PP, except that degradation of the deposit was even quicker. There are no noticeable differences between 4 and 58 days (Fig. 12c and f). The skin cells, embedded in the secretions just after deposition, appeared to dry. Their edges appear and remain sharper after 4 days. 4. Conclusions In order to further improve knowledge on fingermark detection and to facilitate further optimisation and development of more efficient visualisation techniques, latent fingermarks have to be studied in more detail, including both of their physical and chemical properties. This study investigated a number of non-destructive techniques that can be used to visualise untreated fingermarks. Among these techniques, light microscopy comprising bright and dark field, cross-polarisation and phase contrast was tested. Phase contrast imaging proved to be very efficient and sensitive, not only on heavily loaded marks, but also on weaker marks composed of eccrine secretions only. Scanning electron microscopy was also investigated. Results showed that environmental SEM, operating at

lower vacuum and reduced beam intensity, could be applied on nonconductive substrates for fingermark visualisation without any significant detrimental effects on the mark. Information on ridge morphology, as well as on elemental composition, can be obtained by detecting secondary and backscattered electrons, respectively. Various elements such as carbon, chloride and potassium were successfully mapped using energy-dispersive X-ray spectroscopy. Overall, phase contrast microscopy can be implemented on a large set of sample for systematic observations, whereas SEM and EDS can be applied to gather punctual additional information on a selected and more restricted range of samples. A preliminary study of marks deposited on various substrates has shown that the substrate has a major impact not only on the morphology of the marks and the component distribution within ridges, but also influences fingermark degradation over time. Ridges remain visible on glass for long periods, whereas they disappear quickly on certain types of plastics. Surface tension, coatings and/or plasticisers are thought to play a role with respect to the observed effects. This hypothesis is currently under further investigation. Acknowledgments The authors would like to thank the Swiss National Science Foundation (SNSF) for the grant provided to support this research (Early Postdoc.Mobility grant no. P2LAP1_151777), and Katie McBean in the Microstructural Analysis Unit at UTS for assistance with the SEM imaging.


G Model



References [1] A. Bećue, S. Moret, C. Champod, P. Margot, Use of stains to detect fingermarks, Biotech. Histochem. 86 (2011) 140–160. [2] C. Champod, C. Lennard, P. Margot, M. Stoilovic, Fingerprints and Other Ridge Skin Impressions, CRC Press, Boca Raton, FL, 2004. [3] J. Dilag, H.J. Kobus, A.V. Ellis, Nanotechnology as a new tool for fingermark detection: a review, Curr. Nanosci. 7 (2011) 153–159. [4] X. Spindler, O. Hofstetter, A.M. McDonagh, C. Roux, C. Lennard, Enhancement of latent fingermarks on non-porous surfaces using anti-L-amino acid antibodies conjugated to gold nanoparticles, Chem. Commun. 47 (2011) 5602–5604. [5] M. Wood, P. Maynard, X. Spindler, C. Lennard, C. Roux, Visualization of latent fingermarks using an aptamer-based reagent, Angew. Chem. Int. Ed. 51 (2012) 12272–12274. [6] N. Jaber, A. Lesniewski, H. Gabizon, S. Shenawi, D. Mandler, J. Almog, Visualization of latent fingermarks by nanotechnology: reversed development on paper—a remedy to the variation in sweat composition, Angew. Chem. Int. Ed. 51 (2012) 12224–12227. [7] S. Odeń, B. Von Hofsten, Detection of fingerprints by the ninhydrin reaction, Nature 173 (1954) 449–450. [8] A. Beaudoin, New technique for revealing latent fingerprints on wet, porous surfaces: Oil Red O, J. Forensic Identif. 54 (2004) 413–420. [9] J. Salama, S. Aumeer-Donovan, C. Lennard, C. Roux, Evaluation of the fingermark reagent Oil Red O as a possible replacement for physical developer, J. Forensic Identif. 58 (2008) 203–237. [10] K. Braasch, M. de la Hunty, J. Deppe, X. Spindler, A.A. Cantu, P. Maynard, C. Lennard, C. Roux, Nile Red: alternative to physical developer for the detection of latent fingermarks on wet porous surfaces? Forensic Sci. Int. 230 (2013) 74–80. [11] G.C. Goode, J.R. Morris, Latent Fingerprints: A Review of their Origin, Composition and Methods for Detection, Technical AWRE Report No. 022/83, Atomic Weapons Research Establishment, Aldermaston, UK, 1983. [12] S.A. Hardwick, User Guide to Physical Developer — A Reagent for Detecting Latent Fingerprints, Home Office Police Scientific Development Branch, Sandridge, UK, 1981 (Vol. Technical User Guide No. 14/81). [13] X. Spindler, R. Shimmon, C. Roux, C. Lennard, The effect of zinc chloride, humidity and the substrate on the reaction of 1,2-indanedione–zinc with amino acids in latent fingermark secretions, Forensic Sci. Int. 212 (2011) 150–157. [14] S. Moret, A. Bećue, C. Champod, Nanoparticles for fingermark detection: an insight into the reaction mechanism, Nanotechnology 25 (2014) 425502. [15] R.S. Ramotowski, Composition of a latent print residue, in: H.C. Lee, R.E. Gaensslen (Eds.), Advances in Fingerprint Technology, 2nd edition, CRC Press, Boca Raton, FL, 2001, pp. 63–104.

[16] A. Girod, R. Ramotowski, C. Weyermann, Composition of fingermark residue: a qualitative and quantitative review, Forensic Sci. Int. 223 (2012) 10–24. [17] A. Richmond-Aylor, S. Bell, P. Callery, K. Morris, Thermal degradation analysis of amino acids in fingerprint residue by pyrolysis GC–MS to develop new latent fingerprint developing reagents, J. Forensic Sci. 52 (2007) 380–383. [18] G. De Paoli, S.A. Lewis, E.L. Schuette, L.A. Lewis, R.M. Connatser, T. Farkas, Photoand thermal-degradation studies of select eccrine fingerprint constituents, J. Forensic Sci. 55 (2010) 962–969. [19] P. Fritz, W. van Bronswijk, K. Lepkova, S.W. Lewis, K.F. Lim, D.E. Martin, L. Puskar, Infrared microscopy studies of the chemical composition of latent fingermark residues, Microchem. J. 111 (2013) 40–46. [20] G.L. Thomas, A fingerprint thin film, Thin Solid Films 24 (1974) S52–S54. [21] B. Scruton, B.W. Robins, B.H. Blott, The deposition of fingerprint films, J. Phys. D: Appl. Phys. 8 (1975) 714–723. [22] G.L. Thomas, T.E. Reynoldson, Some observations on fingerprint deposits, J. Phys. D: Appl. Phys. 8 (1975) 724–732. [23] G.L. Thomas, The physics of fingerprints and their detection, J. Phys. E: Sci. Instrum. 11 (1978) 722–731. [24] C. McLaren, C. Lennard, M. Stoilovic, Methylamine pretreatment of dry latent fingermarks on polyethylene for enhanced detection by cyanoacrylate fuming, J. Forensic Identif. 60 (2010) 199–222. [25] S. Chadwick, P. Maynard, P. Kirkbride, C. Lennard, X. Spindler, C. Roux, Use of Styryl 11 and STaR 11 for the luminescence enhancement of cyanoacrylatedeveloped fingermarks in the visible and near-infrared regions, J. Forensic Sci. 56 (2011) 1505–1513. [26] M. Paine, H.L. Bandey, S.M. Bleay, H. Willson, The effect of relative humidity on the effectiveness of the cyanoacrylate fuming process for fingermark development and on the microstructure of the developed marks, Forensic Sci. Int. 212 (2011) 130–142. [27] M.J. Choi, K.E. McBean, R. Wuhrer, A.M. McDonagh, P.J. Maynard, C. Lennard, C. Roux, Investigation into the binding of gold nanoparticles to fingermarks using scanning electron microscopy, J. Forensic Identif. 56 (2006) 24–32. [28] N.J. Bright, T.R. Willson, D.J. Driscoll, S.M. Reddy, R.P. Webb, S. Bleay, N.I. Ward, K.J. Kirkby, M.J. Bailey, Chemical changes exhibited by latent fingerprints after exposure to vacuum conditions, Forensic Sci. Int. 230 (2013) 81–86. [29] G.D. Danilatos, Review and outline of environmental SEM at present, J. Microsc. 162 (1991) 391–402. [30] J. Almog, M. Azoury, Y. Elmaliah, L. Berenstein, A. Zaban, Fingerprints’ third dimension: the depth and shape of fingerprints penetration into paper – cross section examination by fluorescence microscopy, J. Forensic Sci. 49 (2004) 981–985.


Microscopic examination of urine.

Quantum resources for purification and cooling: fundamental limits and opportunities.

Electron microscopic location of protein thiol residues.

A rapid method for electron microscopic examination of blood cells.

Determining the effects of routine fingermark detection techniques on the subsequent recovery and analysis of explosive residues on various substrates.

Misinformation from sputum cultures without microscopic examination.

Candle Soot Coating for Latent Fingermark Enhancement on Various Surfaces.

Soundscapes offer unique opportunities for studies of fish communities.

Ultra-Microscopic Examination of the Blood-Serum in Disease.

A scanning electron microscopic examination of retinoblastoma in tissue culture.

Scanning electron microscopic examination of root canal filling materials.

Microscopic examination of the activity-stress ulcer in the rat.

Macroscopic and microscopic examination of pulmonary Crenosoma striatum in hedgehog.

Opportunities for drug repositioning from phenome-wide association studies.

The Use of Polystyrene Beads to Prepare Arrayed Samples of Bacillus thuringiensis for Microscopic Examination.

A simple method for the microscopic examination of unsquashed, stained organs of insects.

Microscopic examination and smear negative pulmonary tuberculosis in Ethiopia.

Fundamental studies on the Cs dynamics under ion source conditions.

Fingermark recovery from riot debris: Bricks and stones.

Epitaxial LiCoO2 films as a model system for fundamental electrochemical studies of positive electrodes.

Fundamental and situational components in a strategy for attaining a positive patient experience of the pelvic examination: a conceptual approach.

The Anisakis Transcriptome Provides a Resource for Fundamental and Applied Studies on Allergy-Causing Parasites.

Fundamental.

A novel method for the photographic recovery of fingermark impressions from ammunition cases using digital imaging.