Dynamics and mechanism of the physical developer process for visualization of latent fingerprints on paper.

We present a detailed mechanistic study of the PD process, focused on the nucleation and growth dynamics of silver particles on fingermarks deposited on a paper surface, from macroscopic (whole fingermark) and microscopic (particle level) perspectives. Conceptually, we separate the outcomes into aspects that precede exposure of the exhibit (relating to the reagent formulation), that relate to the development of the fingermark during immersion in the PD formulation, and that characterise the fully developed mark subsequent to immersion. Initially, dynamic light scattering shows the silver particles in solution to be relatively monodisperse, with a peak particle size of 880 nm. In the second instance, the issue is whether the particles grow to final size in solution then deposit on the surface or deposit as relatively small particles then grow on the surface. To the naked eye, silver deposition is evident after 2 min; corresponding optical profilometry images show evidence of surface-bound particles (mean diameter 2.13 µm) after 30 s. Across the development time (15 min) the particle population density (2.36 ( ± 0.52) x 105 cm-2), is independent of time. During this time, the mean particle diameter increases with the square root of development time to 16.09 µm. The dynamics suggest essentially instantaneous (shorter than observation time) nucleation and diffusionally controlled growth. Surface analysis (EDS) shows the expected high (low) levels of silver on ridge detail (in furrows) but no evidence of iron (from the redox component of the formulation) entrapment at any point on the surface.

Replacing Synperonic® N in the physical developer fingermark visualisation process: Pseudo-operational trial and parameter studies.

A reformulated physical developer (PD) solution has been devised to replace the use of Synperonic® N for environmental reasons. The performance of the replacement solution has proved promising in laboratory trials using planted fingermarks [1] however; this may not always represent how a reagent works on real world samples. This paper therefore explores the effectiveness of the decaethylene glycol monododecyl ether (DGME)-based PD formulation through a pseudo-operational trial. A range of naturally handled, porous substrates were processed, which totalled over 600 samples that had been previously treated with amino acid reagents (1,2-indandione (IND) or 1,8-diazafluoren-9-one (DFO) and ninhydrin). The trial was representative of the operational use of PD at the end of a processing sequence for porous exhibits. The results from the trial establish that DGME is an effective replacement detergent for Synperonic® N in PD solutions and demonstrated the added benefit of using PD as a sequential treatment. Planted mark studies to assess the parameters of the DGME-based PD formulation are also included in this paper. These studies explored the preparation, processing and storage temperature required for the solution as well as the shelf life. The effectiveness of DGME-based PD on items that have been previously wetted was also investigated. These studies show the formulation is suitable for use in an operational laboratory and is therefore an effective replacement formulation for the Synperonic® N-based PD.

Replacing Synperonic® N in the Physical Developer fingermark visualisation process: Reformulation.

The Physical Developer solution currently recommended for use in the United Kingdom for fingermark visualisation uses two surfactants: n-dodecylamine acetate (nDDAA) and Synperonic® N. Synperonic® N is covered by the EU directive 82/242/EEC, which sought to phase out chemicals with degradation products more harmful than their precursor. This study explores the replacement of Synperonic® N with alternative detergents and examines their ability to produce clear, stable solutions that are effective at developing fingermarks. The critical properties of the detergents were investigated, such as the critical micelle concentration and the hydrophilic-lipophilic balance, and planted mark comparisons were performed on promising formulations. Tween® 20 was deemed unsuitable due to the production of cloudy solutions and the requirement to age the formulation to improve effectiveness. Brij® C10 produced clear formulations; however, these were too stable causing unacceptably long exhibit processing times, and an additional preparation stage was necessary. Brij® L23, Brij® S10, Igepal® CO-630, Polyoxyethylene (10) tridecyl ether and Tergitol™ 15-S-9 also proved to be unsuccessful alternatives. Decaethylene glycol monododecyl ether (DGME) was found to be a suitable alternative to Synperonic® N and depletion series experiments suggested that a range of DGME and nDDAA detergent quantities were effective at developing marks. The processing time using DGME was similar to Synperonic® N and the most favourable ratio of reagents is proposed in this paper as a reformulated Physical Developer solution.

Pre-validation of a MALDI MS proteomics-based method for the reliable detection of blood and blood provenance.

The reliable identification of blood, as well as the determination of its origin (human or animal) is of great importance in a forensic investigation. Whilst presumptive tests are rapid and deployed in situ, their very nature requires confirmatory tests to be performed remotely. However, only serological tests can determine blood provenance. The present study improves on a previously devised Matrix Assisted Laser Desorption Ionisation Mass Spectrometry (MALDI MS)-proteomics based method for the reliable detection of blood by enabling the determination of blood provenance. The overall protocol was developed to be more specific than presumptive tests and faster/easier than the gold standard liquid chromatography (LC) MS/MS analysis. This is considered a pre-validation study that has investigated stains and fingermarks made in blood, other biofluids and substances that can elicit a false-positive response to colorimetric or presumptive tests, in a blind fashion. Stains and marks were either untreated or enhanced with a range of presumptive tests. Human and animal blood were correctly discriminated from other biofluids and non-biofluid related matrices; animal species determination was also possible within the system investigated. The procedure is compatible with the prior application of presumptive tests. The refined strategy resulting from iterative improvements through a trial and error study of 56 samples was applied to a final set of 13 blind samples. This final study yielded 12/13 correct identifications with the 13th sample being correctly identified as animal blood but with no species attribution. This body of work will contribute towards the validation of MALDI MS based methods and deployment in violent crimes involving bloodshed.

An evaluation of the effect of incorporating metal salts into 1,8 diazafluoren-9-one (DFO) formulations for fingermark enhancement.

A study into the modification of 1,8-diazafluoren-9-one (DFO) formulations by the additions of metal salts into the working solution is reported. Similar additions have been found to increase the fluorescence of marks developed using other amino acid reagents including 1,2-indandione and the ninhydrin analogue 5-methylthioninhydrin. It was found that adding zinc chloride to give a 1:1 ratio of zinc ions:DFO molecules gave optimum fluorescence, and improvements in performance over the standard DFO formulation were achieved. Attempts to produce equivalent formulations with iron, nickel and palladium chlorides were unsuccessful. In a comparative trial with a 1,2-indandione-zinc formulation on brown paper and cardboard substrates, 1,2-indandione-zinc gave superior results and it was decided to focus further research on this reagent instead of DFO-zinc.

Fingermark visualisation with iron oxide powder suspension: The variable effectiveness of iron (II/III) oxide powders, and Tween® 20 as an alternative to Triton™ X-100.

The effectiveness of the current UK iron oxide powder suspension formulation, 'C-IOPS-09' (Triton X-100 based), for fingermark or latent fingerprint visualization is shown to be affected by variations between batches of the recommended iron oxide powder from Fisher Scientific (I/1100/53). When incorporated into the C-IOPS-09 formulation, a 2015 powder batch resulted in the detection of ∼19% fewer fingermarks, of broadly reduced contrast, when compared to powder suspension prepared with a 2008 batch of the same product. Furthermore, the 2015 powder batch was found to be unsuitable in experimental reduced-surfactant concentration powder suspension, because it caused surface-wide or background staining. The studies in this paper also investigated the use of Tween 20 surfactant as an alternative to the currently utilised Triton X-100, in preparation for the potential unavailability of Triton X-100 in the future. Powder suspensions prepared with Tween 20 surfactant solutions of 4% and 40% were shown to offer similar effectiveness to the currently recommended C-IOPS-09 formulation, when compared using the same batch of Fisher Scientific iron oxide powder (2008 or 2015). The difference between the 2008 and 2015 iron oxide batches was hence also evident with these alternative surfactant solutions. Particle size distribution analysis of the iron oxide powders in Tween 20 and Triton X-100 based surfactant solutions show that the more effective powder exhibits a higher sub-micrometre particle population than the less effective powder. This work leads to an improved specification for powder suspension formulations. This is demonstrated with an example powder suspension formulation which uses a 10% Tween 20 surfactant solution and iron oxide nanopowder (50-100nm) from Sigma Aldrich, which was shown to visualise 27% more fingermarks than the C-IOPS-09 formulation prepared with the 2015 Fisher Scientific powder batch, in a comparative study.

A validation study of the 1,2-indandione reagent for operational use in the UK: Part 3-Laboratory comparison and pseudo-operational trials on porous items.

Laboratory trials, followed by a comparative pseudo-operational trial of a 1,2-indandione/zinc formulation and 1,8-diazafluoren-9-one (DFO) was carried out on a range of realistically-handled papers, card and cardboard. In laboratory trials over 7500 split marks were assessed and in the pseudo-operational trial in excess of 400 samples were treated with each of these processes before all the samples were then treated with ninhydrin. The results presented from both stages of the trials establish that 1,2-indandione was the most effective single process and that 1,2-indanedione followed by ninhydrin the most effective process sequence, with ninhydrin developing a significant number of new marks after 1,2-indandione.

A validation study of the 1,2-indandione reagent for operational use in the UK: Part 1 - Formulation optimization.

This paper contains details of work carried out to examine the composition of 1,2-indandione formulations and to develop the most effective 1,2-indandione/zinc formulation for use under UK conditions. Previous research into the reactions of 1,2-indandione without zinc ions have concluded that formulations containing methanol produce stable hemiketals, which are less reactive to amino acids, resulting in reduced fluorescence intensity of developed fingermarks. In this study, fingermarks were treated using varying formulations of 1,2-indandione, with and without the presence of methanol and zinc ions. It was found that both were beneficial in producing marks of the highest fluorescence intensity, although too much methanol could have a detrimental effect on the quality the mark due to diffusion of ridge detail. Therefore the 1,2-indandione formulation recommended for further trials has been modified to contain both zinc ions and methanol.

Sequential processing strategies for fingermark visualisation on uncirculated £10 (Bank of England) polymer banknotes.

An investigation was undertaken to assess the relative effectiveness of five fingermark visualisation process sequences on new, uncirculated £10 polymer banknotes from the Bank of England (BoE). Each sequence was challenged with the visualisation of 64 natural fingermarks on eight banknotes, of which half were aged for 2-3days and half were aged for 12-13days (32 donors contributed in each set). The sequences investigated were; After each process was applied, fingermark development was assessed under primary viewing conditions appropriate to the technique (white light or fluorescence). All samples were also assessed under secondary viewing conditions; provided by the optical processes infrared reflection and long-wave ultraviolet reflection, and by gelatin lifting (with scanning). These additional techniques reduced the interfering effect of the complex banknote backgrounds and improved the contrast of enhanced fingermarks. Overall, with all assessment conditions considered, sequence 4 and sequence 3 visualised the most identifiable quality fingermarks (92.2% and 89.1% respectively). The most effective overall process used singularly was found to be black magnetic powder, provided that reflected infrared was used to image the results (82.8%). Further data analysis revealed that sequence 1 was the most effective sequence for fresh marks (aged 2-3days) when only primary viewing conditions within the visible part of the spectrum are considered. The need for further work which considers the sensitivity of the processes, and how they perform on BoE polymer banknotes that have become worn in circulation, is emphasised.

A validation study of the 1,2-indandione reagent for operational use in the UK: Part 2 - Optimization of processing conditions.

This paper contains details of work carried out to identify the most effective processing conditions for the optimized 1,2-indandione/zn formulation developed for use under UK conditions. Using direct measurements of fluorescence taken from test spots of amino acids and eccrine sweat during oven processing, complemented with experiments on real fingermarks, it was established that processing temperatures above 120°C in the oven were detrimental to the fluorescence of the developed mark. Alternative methods of development to oven processing were found to be effective, but less controllable. High levels of humidification were also found to be detrimental to the fluorescence of 1,2-indandione developed marks, and oven processing at 100°C and 0% relative humidity is therefore recommended for further studies. It has also been shown that 1,2-indandione can develop fingermarks at temperatures as low as 20°C, making it a candidate for use at crime scenes.

Fingermark visualisation on uncirculated £5 (Bank of England) polymer notes: Initial process comparison studies.

Experiments were conducted to investigate the effectiveness of a range of fingermark visualisation processes on brand new, uncirculated, £5 polymer banknotes (and their test note predecessors), as produced by the Bank of England (BoE). In the main study of this paper, a total of 14 individual processes were investigated on BoE £5 polymer banknotes, which included both 'Category A' processes (as recommended in the Home Office Fingermark Visualisation Manual) as well as recently developed processes, including fpNatural® 2 powder (cuprorivaite) from Foster+Freeman and a vacuum metal deposition sequence that evaporates silver followed by zinc. Results from this preliminary investigation indicate that fpNatural® 2, multimetal deposition, Wet Powder™ Black, iron oxide powder suspension and black magnetic powder are the most effective processes on these uncirculated £5 BoE polymer banknotes, when viewed under "primary viewing" conditions (white light or fluorescence). Additional fingermarks were visualised on the polymer banknotes following the subsequent use of reflected infrared imaging and lifting techniques, and with the benefit of these techniques taken into consideration, the aforementioned processes remained amongst the most effective overall. This work provides initial insight into fingermark visualisation strategies for BoE £5 polymer banknotes, and the need for further studies in order to generate mature operational guidance is emphasised.

Proteomics goes forensic: Detection and mapping of blood signatures in fingermarks.

A bottom up in situ proteomic method has been developed enabling the mapping of multiple blood signatures on the intact ridges of blood fingermarks by Matrix Assisted Laser Desorption Mass Spectrometry Imaging (MALDI-MSI). This method, at a proof of concept stage, builds upon recently published work demonstrating the opportunity to profile and identify multiple blood signatures in bloodstains via a bottom up proteomic approach. The present protocol addresses the limitation of the previously developed profiling method with respect to destructivity; destructivity should be avoided for evidence such as blood fingermarks, where the ridge detail must be preserved in order to provide the associative link between the biometric information and the events of bloodshed. Using a blood mark reference model, trypsin concentration and spraying conditions have been optimised within the technical constraints of the depositor eventually employed; the application of MALDI-MSI and Ion Mobility MS have enabled the detection, confirmation and visualisation of blood signatures directly onto the ridge pattern. These results are to be considered a first insight into a method eventually informing investigations (and judicial debates) of violent crimes in which the reliable and non-destructive detection and mapping of blood in fingermarks is paramount to reconstruct the events of bloodshed.

The effects of polymer pigmentation on fingermark development techniques.

The effectiveness of latent fingerprint development techniques is heavily influenced by the physical and chemical properties of the deposition surface. The use of powder suspensions is increasing for development of prints on a range of surfaces. We demonstrate that carbon powder suspension development on polymers is detrimentally affected by the presence of common white pigment, titanium dioxide. Scanning electron microscopy demonstrates that patches of the compound are clearly associated with increased levels of powder adhesion. Substrates with nonlocalized titanium dioxide content also exhibit increased levels of carbon powder staining on a surface-wide basis. Secondary ion mass spectrometry and complementary techniques demonstrate the importance of levels of the pigment within the top 30 nm. The association is independent of fingermark deposition and may be related to surface energy variation. The detrimental effect of the pigment is not observed with small-particle reagent (MoS2 SPR) or cyanoacrylate (superglue) fuming techniques that exploit different development mechanisms.

Nanoscale analysis of the interaction between cyanoacrylate and vacuum metal deposition in the development of latent fingermarks on low-density polyethylene.

Vacuum metal deposition (VMD) has been previously demonstrated as an effective development technique for latent fingermarks and in some cases has been shown to enhance prints developed with cyanoacrylate (CA) (superglue) fuming. This work utilizes scanning electron microscopy (SEM) to investigate the interactions of the two development techniques when applied to latent fingermarks on low-density polyethylene. CA is shown to act principally on the eccrine deposits around sweat pores, where polymerization results in long polymer fibrils a few 100 nm in width. Subsequent VMD processing results in additional areas of development, for example, between pores. However, the primary mode of deposition of zinc is by interaction with the polymerized CA, the fibrils of which become decorated with zinc nanoparticles. Areas with limited CA deposition and no significant polymerization are also enhanced with the VMD process, resulting in increased print development.

Variation in amino acid and lipid composition of latent fingerprints.

The enhancement of latent fingerprints, both at the crime scene and in the laboratory using an array of chemical, physical and optical techniques, permits their use for identification. Despite the plethora of techniques available, there are occasions when latent fingerprints are not successfully enhanced. An understanding of latent fingerprint chemistry and behaviour will aid the improvement of current techniques and the development of novel ones. In this study the amino acid and fatty acid content of 'real' latent fingerprints collected on a non-porous surface was analysed by gas chromatography-mass spectrometry. Squalene was also quantified in addition. Hexadecanoic acid, octadecanoic acid and cis-9-octadecenoic acid were the most abundant fatty acids in all samples. There was, however, wide variation in the relative amounts of each fatty acid in each sample. It was clearly demonstrated that touching sebum-rich areas of the face immediately prior to fingerprint deposition resulted in a significant increase in the amount of fatty acids and squalene deposited in the resulting 'groomed' fingerprints. Serine was the most abundant amino acid identified followed by glycine, alanine and aspartic acid. The significant quantitative differences between the 'natural' and 'groomed' fingerprint samples seen for fatty acids were not observed in the case of the amino acids. This study demonstrates the variation in latent fingerprint composition between individuals and the impact of the sampling protocol on the quantitative analysis of fingerprints.

Development of a GC-MS method for the simultaneous analysis of latent fingerprint components.

Latent fingerprint residue is a complex mixture of organic and inorganic compounds. A full understanding of the composition of this mixture and how it changes after deposition is lacking. Three solvent systems were compared for the simultaneous extraction and derivatization with ethyl chloroformate of selected amino and fatty acids from a nonporous substrate (Mylar for subsequent analysis by gas chromatography-mass spectrometry. A solvent system comprised of sodium hydroxide, ethanol, and pyridine was found to be the most effective. This method was applied to the analysis of latent fingerprint residue deposited on Mylar and preliminary data are presented. Twelve amino acids (e.g., serine, glycine, and aspartic acid) and 10 fatty acids (e.g., tetradecanoic, hexadecanoic, and octadecanoic acids) were identified. The potential application of this method to further the understanding of latent fingerprint chemistry has been demonstrated.