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Understanding physical developer (PD): Part I – Is PD targeting lipids?

Mackenzie de la Hunty a,*, Sebastien Moret a, Scott Chadwick a, Chris Lennard b,Xanthe Spindler a, Claude Roux a

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

A R T I C L E I N F O

Article history:

Received 7 April 2015

Received in revised form 31 May 2015

Accepted 30 June 2015

Available online xxx

Keywords:

Latent fingermarks

Physical developer

Porous surfaces

Fingermark development

A B S T R A C T

Physical developer (PD) is a fingermark development technique that involves the selective reduction of

silver onto fingermark residue. PD can develop marks on porous substrates even if they have been wet,

leading to the logical, long held belief that the reagent targets the water insoluble constituents in the

fingermark residue. The present research has tested this hypothesis as part of a broader study that aims

to identify the targets of physical developer. Spot tests of some fatty acids, cholesterol and squalene,

treated with PD, showed that only cholesterol produced significant silver deposition. PD is known to be

particularly effective on aged marks, however cholesterol degrades over time. These observations

indicate that PD reactivity with fingermarks cannot solely be due to the presence of cholesterol.

Fingermarks were deposited on paper and washed with various organic solvents before being treated

with PD. PD effectiveness was intermittent on both solvent washed and unwashed sides of both natural

and groomed marks; however, it was seen to effectively develop groomed samples that had been exposed

to common lipid extraction solvents, shown to have removed the lipids by visualisation using the lipid

stain Nile red. PD effectiveness was most affected by exposure of samples to solvents that could dissolve

water soluble components, showing that the removal of these constituents (by either water, or other

solvents) decreases the amount of silver deposited on the fingermark residue by the working solution.

Close observation of PD developed samples showed variation in silver deposition uniformity when

comparing a developed ridge to a pore site located on that ridge. Some samples showed an absence of

silver, and other showed an increase of silver at pore locations. This indicates that the material excreted by

the pores on the finger has an effect on silver deposition, suggesting that PD may be specifically targeting

eccrine constituents that are present along the ridges but are more concentrated at the pore locations.

These findings indicate that PD is not targeting the lipids in the fingermark residue per se, and may

instead be targeting eccrine constituents or a more complex mixture of both eccrine and lipid

constituents. Further investigation is underway within our group to investigate the components targeted

by PD to gain a better understanding of what is a notoriously sensitive and hard to employ technique in

the hope that it can be improved or simplified, or alternatives identified.

� 2015 Elsevier Ireland Ltd. All rights reserved.

Contents lists available at ScienceDirect

Forensic Science International

jou r nal h o mep age: w ww.els evier . co m/lo c ate / fo r sc i in t

1. Introduction

Physical developer (PD) is a silver-based latent fingermarkreagent that was first patented for use in fingermark develop-ment by Morris and Wells in 1979 [1]. In 1981, Hardwickdetailed a stable physical developer in the first operational user’sguide [2] that was developed by the Atomic Weapons ResearchEstablishment for the Police Scientific Development Branch. Thetechnique was recommended for use if ninhydrin yielded no

* Corresponding author. Tel.: +61 401165356.

E-mail address: Mackenzie.delahunty@uts.edu.au (M. de la Hunty).

Please cite this article in press as: M. de la Hunty, et al., UnderstandinSci. Int. (2015), http://dx.doi.org/10.1016/j.forsciint.2015.06.034

http://dx.doi.org/10.1016/j.forsciint.2015.06.034

0379-0738/� 2015 Elsevier Ireland Ltd. All rights reserved.

useable marks. PD is an effective technique for the detection oflatent fingermarks on porous surfaces and has been shown todevelop marks not targeted by other fingermark developmenttechniques [3–8], marks on substrates that have been wet orexposed to high humidity, extremely aged marks (up to 50 yearsold [9]) and marks on charred paper that has subsequently beenwetted [10,11]. The PD solution works by selectively reducingsilver ions in solution to silver metal on the fingermark residue,whilst Fe2+ is oxidised to Fe3+ in the solution in a workingsolution that has been extensively studied and modified from theearly formulations [12]. The reason that the silver reduces ontothe fingermark residue is largely unknown, despite a moderateunderstanding of the working solution chemistry. PD is not used

g physical developer (PD): Part I – Is PD targeting lipids? Forensic

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on non-porous substrates as the precipitated silver is notretained as effectively on smooth surfaces and the surface areaavailable for silver deposition is greatly reduced when comparedto that of porous surfaces. The surface area of the substrate isimportant as it is thought to allow the working solution to makecontact with the fingermark deposit from all sides of the residuewhen the reagent absorbs into the medium during treatment[13]. Nonetheless, the current major belief is that PD isdepositing silver on the lipids, or other water insolubleconstituents, contained within the residue because it is effectiveafter substrates have been wetted, most likely removing thewater soluble compounds, and only leaving the non-watersoluble compounds available for development.

Many research groups have improved the original PDworking solution formulation in terms of stability and solutionlongevity [14–16]; however, PD still has limitations: theglassware requires meticulous cleaning as PD is extremelysensitive to contaminants; variability in solution effectivenessfrom batch-to-batch; and the working solution only has aneffective shelf life of two days to two weeks and must be storedin the dark. Best results are obtained with fresh workingsolutions (when using Synperonic N in the surfactant solution).The processing and development is time consuming and theintegrity of the paper substrate is compromised due to its serialimmersion in acidic and aqueous solutions. Due to the issuesencountered when using the technique, the training of person-nel must be comprehensive to ensure that exhibit integrity ismaintained and that the technique is financially viable. PD canalso interfere with the further forensic examination of hand-writing, ink, paper, indented impressions and body fluids forDNA recovery [17], so carefully planned sequential analyses areimportant. As a consequence of these drawbacks, law enforce-ment and forensic science laboratories usually only use PD forthe development of fingermarks in major crime cases and not forvolume crime, so alternatives have been suggested for increasedease of use.

Oil red O (ORO) and Nile red have been investigated as potentialalternatives; however, the results obtained with such techniquessuggest that they are targeting different fingermark components tothose targeted by PD. ORO is a lysochrome dye that has been shownto develop latent fingermarks on porous substrates that have beenwet [6,8,18]. Rawji and Beaudoin showed the lipid stain tooutperform PD on fresh marks that had been soaked in water forvarious times [7]; however, ORO development quality decreasedwith the age of the mark. Nile red is a benzophenoxazine dye that isextremely lipophilic and has also been recently used to developlatent fingermarks [3,4]. New research has shown developmentaldiscrepancies between PD and Nile red [3] as the two techniqueshave been shown to target completely different aged fingermarkswhen used in sequence in a pseudo-operational study on 5 year oldexam booklets (i.e., the application of the second techniquedeveloped marks that were previously undeveloped by the firsttechnique applied).

There has been extensive research into the composition ofskin surface lipids in the fields of dermatology and medicine [19–22], and a few studies on the composition of initial and agedlatent residue [23–26]. However, a recent review highlights thelack of translational data between the disciplines and a majordeficiency of research into the interaction of fingermark residuewith receiving substrates [27]. There are a few studies thatdiscuss the physical interaction between the residue and thesubstrate [28,29], and lipid extraction methods from poroussubstrates [30]; however, there is a lack of information on thechemical interaction and retention of the residue on poroussubstrates. Considering this, the determination of the chemicaltargets of PD is convoluted; all compounds on the skin surface

Please cite this article in press as: M. de la Hunty, et al., UnderstandinSci. Int. (2015), http://dx.doi.org/10.1016/j.forsciint.2015.06.034

and their combinations must be considered as potential targetsof PD.

There are three major glands in the human body that areresponsible for the secretion of bodily fluids through the epidermalmedium; the eccrine glands, the sebaceous glands and theapocrine glands. These glands secrete a variety of inorganic andorganic compounds such as numerous fatty acids, inorganiccompounds, amino acids and over 400 polypeptides [31,32]. Theeccrine glands are found throughout the entire body, but in thehighest density in the palms of the hands and soles of the feet andconsist predominantly of water, with a minor constituent of amixture of organic and inorganic material. Sebaceous glands arefound in regions with hair follicles and on the face and the back;they are mostly made up of fatty acids, glycerides, cholesterol,squalene and a mixture of lipid esters [32,33]. The apocrine glandsare found in auxiliary regions (genital area, armpits, etc.) [32]. Theeccrine and sebaceous secretions are most commonly found inlatent fingermarks which occur as a result of the residues that aredeposited onto a surface when the friction skin of a hand comesinto contact with that surface. Eccrine secretions consist predomi-nantly of water, with a minor constituent of a mixture of organicand inorganic material, and sebaceous secretions are mostly madeup of fatty acids, glycerides, cholesterol, squalene and a mixture oflipid esters [33]. It is interesting to note that there is reportedcontamination of eccrine lipids with epidermal origin in sebaceousladen latent fingermark residue, that is, that lipids do not solelyoriginates in the sebaceous gland, but are also contained in thehydrolipidic film that is present on the surface of the skin thatoriginates in the epidermal layers [32].

This study is part of a broader research project aimed atinvestigating three hypotheses as to the fingermark residuecomponents targeted by PD, namely: (i) the lipids (and othernon-water-soluble constituents); (ii) eccrine constituents (andother water-soluble compounds); or (iii) mixtures of both watersoluble and insoluble constituents.

This paper investigates the hypothesis that PD targets the lipidsand other water-insoluble constituents found in fingermarkresidue. This is the most common hypothesis [14,15,34]; PDdevelops marks on articles that have been wet, leading to theassumption that PD only targets the non-water soluble constitu-ents of fingermark residue, predominantly comprising of lipids.Various hypotheses pertaining to the possible mechanisms ofdevelopment have previously been extensively reviewed [13,35]and will not be discussed in this paper.

2. Materials and methods

Citric acid, maleic acid, cholesterol, all solvents (AR grade) andsilver nitrate were obtained from BDH-Prolabo Chemicals (VWRInternational Pty. Ltd., Australia). Ferric nitrate nonahydrate(Chem-Supply Pty. Ltd., Australia), ammonium ferrous sulphate(Chem-Supply Pty. Ltd., Australia), N-dodecylamine acetate(Optimum technologies, Australia), Tween 20 surfactant (Sigma–Aldrich, USA), palmitic acid (Sigma–Aldrich, USA), stearic acid(Hopkin & Williams Ltd., England), oleic acid (Sigma–Aldrich, USA),squalene (Sigma–Aldrich, USA) and Nile red (BioReagent, Sigma–Aldrich, USA) were used as supplied.

2.1. Physical developer formulation and application

PD was prepared and applied as described previously byRamotowski [36] with one deviation; the detergent solution wasprepared by the addition of 1.5 mL Tween 20 and 1.5 g n-dodecylamine acetate into 1 L of deionised water, instead of the3 mL and 3 g of, respectively, Tween 20 and n-dodecylamine

g physical developer (PD): Part I – Is PD targeting lipids? Forensic

Table 1Properties of organic solvents used to wash the fingermark samples including

dipole moment, dielectric constant, solubility of the solvent in water and solubility

of water in the solvent [41].

Solvent Dipole

moment

Dielectric

constant

(20 8C)

Solubility of

solvent in

water

(25 8C %w/w)

Solubility

of water

in solvent

(25 8C %w/w)

Acetone 2.9 20.6 Total Total

Ethyl acetate 1.7 6.02 7.7 3.3

Methanol 1.7 32.6 Total Total

Chloroform 1.1 4.8 0.82 0.072

Dichloromethane 1.8 9.1 1.30 0.20

Hexane 0 1.9 9.5E�4 110E�4

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acetate recommended by Ramotowski. A 50% reduction in theconcentration of surfactants leads to shorter development times.

2.2. Fingermark deposition

Fingermarks were deposited using a downward pressure thatresulted in a reading of 300 g on a laboratory balance, for a durationof 8 s by two donors. The experiment was performed in duplicateon 80 gsm Reflex Virgin Fibre UltraWhite copy paper. Theassessment of development techniques was performed on bothnatural and groomed marks. Careful consideration was given whengrooming fingers for residue deposition, as it is known thatgroomed residue usually contains contaminants such as cosmetics.To avoid this issue, donors were asked to groom their fingers alongthe back of the neck and top of the back, where cosmetic use isusually at a minimum. While it is considered best practice toevaluate the performance of latent fingermark enhancementreagents using natural marks, which are more representative ofthe marks encountered in case work [37] and contain a variablemixture of eccrine and sebaceous content dependent on personalhabits [38–40], fingermarks known to be lipid-rich were alsorequired to test the hypothesis that PD targets the sebaceous andskin surface originating lipids. Therefore, consideration of PDreactivity on both natural and groomed marks was necessary forthis research.

2.3. Spot tests

An assessment of the specificity and reactivity of PD wasundertaken by treating individual compounds found in latentfingermark residue that either originate in the sebaceous glands(and are present in the residue as an exogenous contaminant) orare endogenous epidermal originating lipids. Palmitic acid(50 mM, 10 mM, 1 mM), stearic acid (100 mM, 10 mM, 1 mM),oleic acid (100 mM, 10 mM, 1 mM), cholesterol (50 mM, 10 mM,1 mM) and squalene (100 mM, 10 mM, 1 mM) were dissolved indichloromethane (variation in the largest concentration was dueto the solubility of the compounds in the solvent). Compoundswere chosen based on their reported abundance in fingermarkresidue in a recent review [27]; all compounds were reported tobe present in a fingermark in amounts greater than 700 ng. 15 mLof each solution was applied to Whatman no. 41 ashless filterpaper and left to dry under ambient conditions (21 8C, 50% RH) inthe dark for two days. Samples were then immersed in water for5 min, placed in the maleic acid wash for fifteen minutes andplaced in the PD development solution until adequate develop-ment was achieved or background development became high(times ranged from 10 to 30 min). Samples were then washedthree times in deionised water for 5 min, ensuring clean waterwas placed in the tray each time. Negative controls comprised ofonly dichloromethane were also assessed to ensure that thesolvent (or surface changes caused by its application) did notpromote PD development. The experiment was performed intriplicate.

2.4. Solvent wash

Fingermark residue is a complex mixture of constituents, and sointer-constituent interactions need to be considered during waterexposure, that is, to determine if potential retention and protectionof compounds by others. Fingermarks that had been exposed todichloromethane, ethyl acetate, chloroform, acetone, methanoland hexane were developed using PD. This allowed observations asto whether PD was still reactive towards the residual fingermarkmaterial once the lipids, and possibly other constituents, had beenremoved by the different solvents. The solvents were chosen based

Please cite this article in press as: M. de la Hunty, et al., UnderstandinSci. Int. (2015), http://dx.doi.org/10.1016/j.forsciint.2015.06.034

on their availability and their range of dielectric constants andwater miscibilities which are shown in Table 1.

Fingermarks were deposited onto paper using the methoddescribed in Section 2.2. Fingermarks were left to dry underambient conditions (21 8C, 50% RH) in the dark for two days.Observations of PD reactivity on lipid extracted fingermarks wereundertaken by vertically bisecting fingermark depositions andwashing the left half with an organic solvent for 10 s with completeimmersion and gentle agitation. The solvents assessed were ethylacetate, hexane, acetone, methanol, chloroform and dichloro-methane. The left half was allowed to dry for half an hour, and thenboth left and right halves were developed using the standard PDmethod in the same PD solution for the same duration, and thenrecombined for imaging. Samples were imaged using the VideoSpectral Comparator 6000 (VSC 6000) under white light.

2.5. Lipid staining with Nile red

To ensure correct assumptions were made as to the specificityof PD to lipids in fingermark residue, all PD-developed fingermarkswere further treated in a Nile red working solution to visualise anyremaining lipids on both the solvent washed and non-solventwashed sides of the deposits. The Nile red working solution wasprepared and applied as previously described by de la Hunty et al.[4]. Samples were placed in the working solution for 5 min, washedbriefly (1–2 s) in deionised water, and allowed to air dry. Sampleswere viewed using the Rofin Poliview system, with a Polilight PL-500 light source operating at 490 nm and with a 555 nm band-passbarrier filter on the camera.

3. Results and discussion

3.1. Spot test reactivity with PD

The spot test results were consistent in all three repetitions ofthe experiment. The spot tests showed PD to be non-reactivetowards the negative control (DCM). Cholesterol (50 mM, 10 mM,1 mM) was the only compound where PD gave a strong positivereaction, with a dark deposition of silver in the spotted area thatdecreased as the concentration of cholesterol decreased. A weaklypositive reaction was seen for varied concentrations of palmiticacid, stearic acid, squalene and oleic acid (Table 2); however, thesilver deposition was not completely covering the sample loadedarea, or a consistent decrease in reactivity was not observed as thesamples became less concentrated, indicating inconsistent reac-tivity.

Despite the common theory that PD targets lipids in thefingermark residue, it has been shown to not be greatly orconsistently reactive towards the tested fatty acids, also found in aprevious study by Morris [42]. There is a slight reactivity of PD witholeic acid (100 mM, 10 mM), palmitic acid (100 mM), squalene

g physical developer (PD): Part I – Is PD targeting lipids? Forensic

Table 2Images of spot tests of palmitic acid, cholesterol, stearic acid, squalene and oleic acid in varied concentrations developed by PD.

Palmitic acida Cholesterola Stearic acid Squalene Oleic acid

100 mM

10 mM

1 mM

a The maximum concentration of the compound was 50 mM due to low solubility in the solvent. Images obtained using the VSC 6000 with white light at 2.43 magnification.

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(10 mM) and stearic acid (10 mM) however reactivity is notconsistent with all concentrations of each sample (Table 3). Thefatty acids used in this study were selected due to their presence infingermark residue [25,27] and their low solubility in water, asthey would remain on a substrate after water exposure. Thereactivity of PD to the sterol cholesterol does not necessarilyexplain its reactivity to fingermark residue, as PD has been shownto develop aged marks, in which cholesterol degradation would beexpected to have occurred [27,30]. However, cholesterol may bepart of a cumulative group of PD targets that promote silverdeposition on the residue.

3.2. Solvent wash effect on subsequent Nile red treatment

The treatment of all solvent washed marks both prior to, andafter PD treatment using Nile red, showed no development of thefingermark halves that had been exposed to any solvents, andintermittent development of low PD developed areas on bothnatural and groomed unwashed samples, in all three repetitions ofthe experiment. This indicated that the solvents used wereremoving the lipids contained in the residue that are targetedby Nile red, and that lipid concentrated areas in marks developedby PD have available lipids for staining with Nile red post PDtreatment.

3.3. Solvent wash effect on subsequent PD treatment

Table 4 shows the results of the solvent wash experiments onnatural and groomed marks that have been subsequentlydeveloped by PD, and the results were consistent in all threerepetitions of the experiment. The subsequent treatment of allmarks using Nile red showed no development of the fingermark

Table 3Assessment of the reactivity of PD with spot tests of palmitic acid, cholesterol,

stearic acid, squalene and oleic acid in varied concentrations; assessed images are in

Table 2.

Palmitic acida Cholesterola Stearic acid Squalene Oleic acid

100 mM + +++ 0 0 ++

10 mM 0 +++ + + +

1 mM 0 ++ 0 0 0

aThe maximum concentration of the compound was 50 mM due to low solubility in

the solvent. +++ denotes dark/medium silver deposition across sample loaded area;

++ denotes light silver deposition across sample loaded area; + denotes very light

silver deposition across sample loaded area; 0 denotes minimal/no silver deposition

across sample loaded area.

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halves that had been exposed to any solvents, and intermittentdevelopment of low PD developed areas on both natural andgroomed unwashed samples.

Prior to the ‘‘grooming’’ process, fingermark residue present onthe friction ridges would consist of epidermal originating lipidsand a variety of eccrine constituents. When the finger is applied tothe skin for sebaceous grooming, the mixture of eccrineconstituents and epidermal lipids would become covered in theexogenous sebaceous lipids, so when deposited onto a substrate, aconcentration gradient of the two different types of residue wouldbe expected to result. The residue most exposed to the air would bemore concentrated in the eccrine constituents, graduating toresidue more concentrated in the epidermal lipid mixture as itapproaches the paper surface. It is possible that the differencesseen in PD development between groomed and natural finger-marks that have been washed with the same solvent may arise as aresult of the stronger affinity of the eccrine constituents andepidermal lipids to the paper, than the sebaceous lipids. It couldalso be explained by the migration of the eccrine constituents intothe substrate through the lipid barrier (that would be present ingroomed marks) and they may then be protected from solubilisa-tion.

The removal of residue by the solvents showed discrepancies(Table 4) when comparing the PD development of the natural andgroomed marks; for example, the acetone washed marks show thatall of the groomed residue targeted by PD is removed by thesolvent, while only a proportion of the PD targeted residue in thenatural marks is removed. This may be due to potential variationsin residue composition between depositions; however, all of thefingermarks developed in this study were deposited at the sametime from the same donor, so residue variation was minimised.

Acetone can be seen to have removed all of the PD targetedresidue in the groomed marks, but only a proportion of it in thenatural marks. Contrary to the results obtained with acetone, thechloroform washed marks show the solvent to solubilise some ofthe PD targets in natural residue; however, there is no obviouseffect on the development quality of the solvent washed side of thegroomed mark when developed by PD. This is an interesting resultas chloroform is commonly used as a lipid extraction solvent, so itshould logically remove the lipids from the groomed marks. Thisresult suggests that PD is not solely targeting the lipids in theresidue, and may be targeting other non-lipid constituents, or acombination of lipid and non-lipid constituents that persist afterchloroform exposure. This is supported by the results obtainedwith dichloromethane, another commonly used lipid extractionsolvent, and hexane, neither of which removed any of the residue

g physical developer (PD): Part I – Is PD targeting lipids? Forensic

Table 4Natural and groomed fingermarks developed by PD after the left side was washed with acetone, chloroform, ethyl acetate, dichloromethane, methanol and hexane. Images

were aquired using the VSC 6000 under white light and 7.5� magnification.

Natural Groomed Natural Groomed

Acetone Chloroform

Natural Groomed Natural Groomed

Ethyl acetate Dichloromethane

Natural Groomed Natural Groomed

Methanol Hexane

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targeted by PD in both natural and groomed marks. This couldindicate that the solvents are not efficiently removing the lipids;however, the Nile red results indicate that the lipids had beenefficiently removed, so it can be inferred that PD is not specificallytargeting the lipids in the residue, but perhaps requires the lipids tobe present.

Ethyl acetate removed a proportion of the natural residuetargeted by PD, and a slightly larger proportion of the groomedresidue. It is possible that the solvent removes the sebaceous lipidsmore effectively than the other constituents contained in thenatural residue, as these natural constituents may have a higher

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affinity to the cellulose than those from the sebaceous glands.Methanol is seen to remove all of the constituents in groomedresidue targeted by PD, and none of those in natural residue. Thissuggests that PD developmental effectiveness may rely on thepresence of sebaceous lipids; however, the results of the spot testsshow these lipids to not be the specific targets of PD, so it could bethat the sebaceous lipids are protecting water-soluble compoundsthat are possibly the actual targets.

Croxton et al. demonstrated that the composition of natural andgroomed residue is relatively consistent qualitatively, but notquantitatively [33]. Groomed marks generally contained a larger

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amount of fatty acids and squalene when compared to naturalmarks. The squalene found in natural marks was attributed tonormal face touching prior to deposition, as it is not endogenous tofriction ridge skin on the palms. Considering these differencesbetween groomed and natural marks, and the fact that the spottests showed low PD reactivity to squalene, the results show thatthe determination of the specific target(s) of physical developerwill be a complex process, with many different factors to consider.

The solvents that can dissolve water-soluble constituentstended to remove a higher proportion of the groomed residue,which is an interesting result considering that it is assumed thatthe groomed residue would have less water, and less water solubleconstituents (as a percentage of the overall deposit). It is possiblethat the solvents that have a higher tendency to solubilise water-soluble constituents, are removing these constituents that may betargeted by PD, and that the PD may not be targeting the lipids.

3.4. Variation in PD development

During analysis of the results, it was noticed that PD-treatedfingermarks showed two different types of development (Fig. 1). Indeveloped samples, silver was deposited relatively uniformlyalong the ridges; however, silver deposition varied at pore sites.Some fingermarks exhibited no development at pore sites (Fig. 1a),and some fingermarks exhibited increased development at poresites (Fig. 1b) when compared to the development of ridges in thesame sample. The variance in pore site development followed noparticular trend; natural and groomed marks both exhibited anincrease or absence of silver deposition at pore sites along theridges of the fingermark. The increase or absence of developmentat the pore sites suggests that the absence or presence of eccrinesecretions has an effect on PD development, and that PD may betargeting the eccrine constituents secreted by the pores if they arepresent in a certain concentration in conjunction with otherfingermark residue constituents.

3.5. Developmental differences of PD with lipid reagents

ORO has previously been recommended as an alternative to PDfor the development of lipid-rich fingermarks [7]; however, if PD isnot specifically targeting the lipids in the residue then, under-standably, it will be outperformed on lipid-rich marks by a lipidstain. ORO has been seen to be more effective on fresh marks andPD more effective on aged marks; however, the reason for thedifference in development effectiveness is not definitive. It may bethe case that there are two sebaceous fractions; a labile fractiontargeted by ORO and a stable fraction targeted by PD, however this

Fig. 1. PD developed marks showing variations in pore development; left image shows no

silver deposition at pore sites on a groomed fingermark. Images taken with Leica EZ4

Please cite this article in press as: M. de la Hunty, et al., UnderstandinSci. Int. (2015), http://dx.doi.org/10.1016/j.forsciint.2015.06.034

does not adequately explain what has been observed in this studyas PD has been seen to not specifically target compounds in thestable fraction. In the PD and ORO comparison experiments, onlyfresh marks were employed; however, using fresh marks does notallow the fingermark residue to cure and so water exposure mayremove water soluble components that might otherwise beprotected within a dehydrated residue, had the fingermarks beengiven time to age. A pseudo-operational study that sequenced PDand Nile red on 5 year old exam booklets [3] indicated that PD andNile red have discrete targets in the residue that occur in differenttypes of fingermarks, as they developed completely different agedmarks when used in sequence (i.e., the application of the secondtechnique developed marks that were previously undeveloped bythe first technique applied). The research presented here supportsthese hypotheses, as the solvent removal of lipids in the residuedoes not always inhibit PD development, indicating that PD maynot be specifically targeting the lipids in the residue, unlike OROand Nile red.

With current knowledge, finding an alternative to PD is verydifficult as we cannot confirm the component(s) of fingermarkresidue that promote(s) silver deposition. The two techniques thathave been suggested as alternative treatments are possiblytargeting components in the fingermark residue that differ tothose targeted by PD. It is therefore important to furtherinvestigate the targets of PD to be able to conclusively decidewhether either of the two suggested lipid sensitive techniquescould replace PD, or whether they should be used in sequence asthey target different components to those targeted by PD.

These results, in conjunction with recent results whensequencing Nile red and PD, show that PD does not specificallytarget the lipids, but it may target the eccrine material, or a mix ofeccrine and lipid components. Research is ongoing within ourgroup to explore the two other proposed hypotheses as to targetsof PD, in the hope of achieving a better understanding of thetechnique so it can be improved or simplified, or an effectivealternative identified.

4. Conclusions

Physical developer (PD) is a silver based technique that is usedto develop fingermarks on porous surfaces. The reason for thedeposition of silver on the latent residue is largely unknown,despite a moderate understanding of the working solutionchemistry. An investigation of the targets of PD is important sothat the technique can be improved or simplified, or an alternativefound, as solution preparation and operational use are problemat-ic. It is also important to understand the latent residue components

silver deposition at pore sites on a natural fingermark, right image shows increased

stereo microscope at 20� magnification using incident white light.

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targeted by the technique so that appropriate sequencing withother techniques can be employed to maximise the number ofdeveloped fingermarks in any given instance.

PD develops fingermarks on porous surfaces that have beenwet, which led to the assumption that PD specifically targets thelipids in fingermark residue. This research has shown through aseries of spot tests that PD is not selective towards certain lipidsfound in fingermark residue. The spot tests indicated that PD wasreactive towards cholesterol; however, given the susceptibility ofcholesterol to degradation over time, and considering that PD candevelop aged fingermarks, it can be assumed that cholesterol is notthe sole target of PD.

The removal of lipids in fingermark residue by exposure tovarious organic solvents has also shown that PD development canstill occur, demonstrating that PD may not be specifically targetingthe lipids. Close observation of PD development on latent ridgeshas revealed that silver deposition is usually consistent anduniform along the ridges but can vary at pore sites, showing anabsence or increase of deposited silver. These observations implyan effect of the residue excreted through the pores on the level ofsilver deposition by the PD working solution.

This study is part of a broader research project that aims toinvestigate three hypotheses as to the fingermark residue targetsof PD, namely: (i) lipids (and non-water soluble constituents); (ii)eccrine constituents (and water-soluble constituents); or (iii)mixtures, including emulsions, of lipid and eccrine constituents.The results indicate that PD does not specifically or selectivelytarget lipids, and so our research group is currently investigatingthe hypothesis that PD targets certain eccrine constituents infingermark residue.

References

[1] Morris, J.R., Wells, J.M., Patent: 154014 (1979).[2] S.A. Hardwick, User Guide to Physical Developer – A Reagent for Detecting Latent

Fingerprints. User Guide 14/81, Home Office Scientific Research and Develop-ment Branch, London, 1981.

[3] K. Braasch, M. de la Hunty, J. Deppe, X. Spindler, A. Cantu, P. Maynard, C. Lennard,C. Roux, Nile red: alternative to physical developer for the detection of latentfingermarks on wet porous surfaces? Forensic Sci. Int. 230 (2013) 74–80.

[4] M. de la Hunty, X. Spindler, S. Chadwick, C. Lennard, C. Roux, Synthesis andapplication of an aqueous Nile red microemulsion for the development of finger-marks on porous surfaces, Forensic Sci. Int. 244 (2014) pe48–pe55.

[5] R. Ramotowski, Lipid reagents, in: Lee and Gaensslen’s Advances in FingerprintTechnology, 3rd ed., CRC Press, 2012, pp. 83–96.

[6] A. Beaudoin, New technique for revealing latent fingerprints on wet, poroussurfaces: Oil Red O, J. Forensic Identif. 54 (2004) 413–421.

[7] A. Rawji, A. Beaudoin, Oil red O versus physical developer on wet papers: acomparative study, J. Forensic Identif. 56 (2006) 33–54.

[8] M. Wood, T. James, ORO. The physical developer replacement? Sci. Justice 49(2009) 272–276.

[9] Anon, What is the oldest fingerprint that you have developed? in: FingerprintDevelopment and Imaging Update. Publication No. 26/2003, Home Office PoliceScientific Development Branch, 2003.

[10] A. Dominick, N. NicDaeid, S. Bleay, The recoverability of fingerprints on paperexposed to elevated temperatures – Part 1: comparison of enhancement tech-niques, J. Forensic Identif. 59 (2010) 325–339.

[11] W. Della, Friction ridge detection from challenging crime scenes, in: Lee andGaensslen’s Advances in Fingerprint Technology, 3rd ed., CRC Press, 2012, pp.381–418.

[12] A. Cantu, J. Johnson, Silver physical development of latent prints, in: Advances inFingerprint Technology, 2nd ed., CRC Press, 2001.

Please cite this article in press as: M. de la Hunty, et al., UnderstandinSci. Int. (2015), http://dx.doi.org/10.1016/j.forsciint.2015.06.034

[13] A. Cantu, Silver physical developers for the visualisation of latent prints on paper,Forensic Sci. Rev. 13 (2001) 30–64.

[14] G. Sauzier, A. Frick, S. Lewis, Investigation into the performance of physicaldeveloper formulations for visualizing latent fingerprints on paper, J. ForensicIdentif. 63 (2013) 70–89.

[15] D. Burow, D. Seifert, A. Cantu, Modifications to the silver physical developer,J. Forensic Sci. 48 (2003).

[16] S. Houlgrave, M. Andress, R. Ramotowski, Comparison of different physicaldeveloper working solutions – Part I: longevity studies*, J. Forensic Identif. 61(2011) 621–639.

[17] T. Kent, Manual of Fingerprint Development Techniques: A Guide to the Selectionand Use of Processes for the Development of Latent Fingerprints, 2nd ed., PoliceScientific Development Branch, 2004.

[18] J. Salama, S. Aumeer-Donovan, C. Lennard, C. Roux, Evaluation of the fingermarkreagent Oil Red O as a possible replacement for physical developer, J. ForensicIdentif. 58 (2008) 203–237.

[19] N. Nicolaides, T. Ray, Skin lipids. III. Fatty chains in skin lipids. The use of vernixcaseosa to differentiate between endogenous and exogenous components inhuman skin surface lipid, J. Am. Oil Chem. Soc. 42 (1965) 702–707.

[20] W. Cunliffe, J. Cotterill, B. Williamson, Variations in skin surface lipid compositionwith different sampling techniques. I, Br. J. Dermatol. 85 (1971) 40–45.

[21] S. Passi, O. De Pita, P. Puddu, G. Littarru, Lipophilic antioxidants in human sebumand aging, Free Radic. Res. 36 (2002) 471–477.

[22] R. Michael-Jubeli, J. Bleton, A. Baillet-Guffroy, High-temperature gas chromatog-raphy-mass spectrometry for skin surface lipids profiling, J. Lipid Res. 52 (2011)143–151.

[23] N. Archer, Y. Charles, J. Elliott, S. Jickells, Changes in the lipid composition of latentfingerprint residue with time after deposition on a surface, Forensic Sci. Int. 154(2005) 224–239.

[24] D. Song, D. Sommerville, A. Brown, R. Shimmon, B. Reedy, M. Tahtouh, Thermaldevelopment of latent fingermarks on porous surfaces – further observations andrefinements, Forensic Sci. Int. 204 (2011) 97–110.

[25] A. Koenig, A. Girod, C. Weyermann, Identification of wax esters in latent printresidues by gas chromatography-mass spectrometry and their potential use asaging parameters, J. Forensic Identif. 61 (2011).

[26] A. Girod, C. Weyermann, Lipid composition of fingermark residue and donorclassification using GC/MS, Forensic Sci. Int. 238 (2014) 68–82.

[27] A. Girod, R. Ramotowski, C. Weyermann, Composition of fingermark residue: aqualitative and quantitative review, Forensic Sci. Int. 223 (2012) 10–24.

[28] B. Jones, R. Downham, V. Sears, Effect of substrate surface topography on forensicdevelopment of latent fingerprints with iron oxide powder suspension, Surf.Interface Anal. 42 (2010) 438–442.

[29] S. Bacon, Interaction between latent fingermarks, deposition surfaces anddevelopment agents, in: Experimental Techniques Centre, Brunel University,2012.

[30] C. Weyermann, C. Roux, C. Champod, Initial results on the composition offingerprints and its evolution as a function of time by GC/MS analysis, J. ForensicSci. 56 (2011) 102–108.

[31] A. Knowles, Aspects of physicochemical methods for the detection of latentfingerprints, J. Phys. E: Sci. Instrum. 11 (1978) 713–721.

[32] R. Ramotowski, Composition of latent print residue, in: Advances in FingerprintTechnology, 2nd ed., CRC Press, 2001.

[33] R. Croxton, M. Baron, D. Butler, T. Kent, V. Sears, Variation in amino acid and lipidcomposition of latent fingerprints, Forensic Sci. Int. 199 (2010) 93–102.

[34] R. Ramotowski, A comparison of different physical developer systems and acidpre-treatments and their effects on developing latent prints, J. Forensic Identif. 50(2000) 363–384.

[35] A. Becue, A. Cantu, Fingermark detection using nanoparticles, in: Lee and Gaens-slen’s Advances in Fingerprint Technology, 3rd ed., CRC Press, 2012, pp. 307–380.

[36] R. Ramotowski, Metal deposition methods, in: Lee and Gaensslen’s Advances inFingerprint Technology, 3rd ed., CRC Press, 2012, pp. 55–82.

[37] IFRG., International Fingerprint Research Group (IFRG) guidelines for the assess-ment of fingermark detection techniques, J. Forensic Identif. 2 (2014) 175–201.

[38] S. Dimond, R. Harries, Face touching in monkeys, apes and man: evolutionaryorigins and cerebral asymmetry, Neuropsychologia 22 (1984) 227–233.

[39] T. Hatta, S.J. Dimond, Differences in face touching by Japanese and British people,Neuropsychologia 22 (1984) 531–534.

[40] S.D. Suarez, G.G. Gallup Jr., Face touching in primates: a closer look, Neuropsy-chologia 24 (1986) 597–600.

[41] I.M. Smallwood, Handbook of Organic Solvent Properties, Elsevier, 1996.[42] J.R. Morris, The Detection of Latent Fingerprints on Wet Paper Samples, Atomic

Weapons Research Establishment, Aldermaston, 1975.

g physical developer (PD): Part I – Is PD targeting lipids? Forensic