Fingerprint Deposits Research Articles

A chemically relevant artificial fingerprint material for the cross-comparison of mass spectrometry techniques

The development of a chemically relevant artificial fingerprint material as well as a preliminary method for artificial fingerprint deposition for mass spectrometric analysis and chemical imaging is presented. The material is an emulsified combination of artificial eccrine and sebaceous components designed to mimic the chemical profile of a latent fingerprint. In order to deposit this material in a manner that resembles a latent fingerprint, an artificial fingerprint stamp, created using 3-D printing, was used. Development of this material was spurred by the inability to cross-compare mass spectrometric techniques using real fingerprint deposits because of their inherent heterogeneity. To determine how well this material mimicked the chemical composition of actual fingerprint deposits, ambient ionization mass spectrometry and secondary ion mass spectrometry techniques were used to compare the signatures of the artificial and real fingerprint deposits. Chemical imaging comparisons of the artificial fingerprints across different imaging platforms are also presented as well as a comparison using fingerprint development agents. The use of a material such as this may provide a way to compare the capabilities of different techniques in analyzing a sample as complex as a fingerprint as well as providing a method to create fingerprints with controlled amounts of exogenous material for research and technique validation purposes.

Response Assessment of Thermal Papers from Four Continents to Fingerprint Development by Heat.

Latent fingerprint deposits on thermal paper sourced from the U.S., China, the U.K., and Australia have been visualized by heating. U.S. and Chinese sourced paper produced two distinct types of fingerprint development. In one type (type 1), the paper dye colors where the deposit is present (as previously reported) and in the other type (type 2) the 'inverse' of this gives paper coloring only in areas not coincident with the deposit. Both development types gave identifiable fingerprints, the majority fading within 24h of heating. Fingerprint development from U.K. and Australian sourced paper was exclusively type 1 and resistant to fading. Temperatures for fingerprint visualization were higher for U.S. paper (64-71°C) and Chinese paper (75-95°C) than for U.K. and Australian sourced paper (43-50°C). Particularly for Chinese sourced paper, these temperatures were within a few degrees of the normal paper color temperature. A mechanism for type 2 fingerprint development is proposed.

A Noninvasive and Speculative Method of Visualizing Latent Fingerprint Deposits on Thermal Paper.

Latent fingerprint deposits on thermal paper have been visualized noninvasively at visible wavelengths when illuminated with a UV-A light source (peak 365nm). A higher intensity UV source (250W/m(2) at 0.38m) gave superior fingerprint visibility when compared with a 60W/m(2) (at 0.4m) source. Removing the visible (blue) component of the light source emission did not adversely affect the visibility of the fingerprint. Sample fingerprints from 100 donors, when examined 24h after deposition, produced identifiable fingerprints from nearly 34% of fingerprint deposits. A mechanism for the observed visibility is proposed based on low emission of visible wavelengths from areas of thermal paper coincident with the fingerprint deposit, when illuminated with UV. This is likely due to a weak color change in the thermal paper dye arising from protonated amino acid components of the sweat. This effect was not observed on nonthermal paper.

Latent fingerprint enhancement on conductive substrates using electrodeposition of copper

We present a novel method for the development of a latent fingerprint by selective electrodeposition of a copper thin film from sulfate solution onto the conductive substrate between fingerprint ridges to generate a negative image of the fingerprint deposit. After optimizing the parameters (deposition time, deposition potential, and copper concentration), the preferential electrodeposition of copper films allowed latent fingerprints on six kinds of conductive surfaces (indium/tin oxide-coated glass, silver sheet, platinum sheet, gold sheet, copper sheet, and a stainless steel coin) to be successfully developed with high resolution. In addition, this technique could also be exploited to visualize latent fingerprints on rough and dirty surfaces. The quality of the developed fingerprints was estimated visually and the morphology of the copper film was characterized by field emission scanning electron microscopy.

Inside Cover: Oxidation Monitoring by Fluorescence Spectroscopy Reveals the Age of Fingermarks (Angew. Chem. Int. Ed. 24/2014)

Forensic fingerprint-age estimation is currently impossible. Knowledge on time passed since fingerprint deposition is desired as it can distinguish between crime-related and unrelated fingerprints and support or refute statements made by fingerprint donors. In their Communication on page 6272 ff., S. A. G. Lambrechts and co-workers describe a successful fluorescence-based method to estimate fingerprint age that relies on the protein–lipid oxidation rate and the subsequent generation of fluorescent oxidation products.

Comparison of Chemical and Heating Methods to Enhance Latent Fingerprint Deposits on Thermal Paper

A comparison is made of proprietary methods to develop latent fingerprint deposits on the inked side of thermal paper using either chemical treatment (Thermanin) or the application of heat to the paper (Hot Print System). Results with a trial of five donors show that the application of heat produces statistically significantly more fingerprint ridge detail than the chemical treatment for both fingerprint deposits aged up to 4 weeks and for a nine sequence depletion series. Subjecting the thermal paper to heat treatment with the Hot Print System did not inhibit subsequent ninhydrin chemical development of fingerprint deposits on the noninked side of the paper. A further benefit of the application of heat is the rapid development of fingerprint deposits (less than a minute) compared with up to 12 h for the Thermanin chemical treatment.

Effect of Temperature on the Visualization by Digital Color Mapping of Latent Fingerprint Deposits on Metal

Visualization of fingerprint deposits by digital color mapping of light reflected from the surface of heated brass, copper, aluminum, and tin has been investigated using Adobe® Photoshop®. Metals were heated to a range of temperatures (T) between 50°C and 500°C in 50°C intervals with enhancement being optimal when the metals are heated to 250°C, 350°C, 50°C, and 300°C, respectively, and the hue values adjusted to 247°, 245°, 5°, and 34°, respectively. Fingerprint visualization after color mapping was not degraded by subsequent washing of the metals and color mapping did not compromise the visibility of the fingerprint for all values of T. The optimum value of T for fingerprint visibility is significantly dependent of the standard reduction potential of the metal with Kendall’s Tau (τ) = 0.953 (p < 0.001). For brass, this correlation is obtained when considering the standard reduction potential of zinc rather than copper.

Application of Electrodepositing Graphene Nanosheets for Latent Fingerprint Enhancement

AbstractFingerprints are still one of the most powerful and important means of biometric identification. This paper presents a green and fast electrochemical method for improved development of latent fingerprints (LFPs) on five kinds of commonly encountered conductive substrates by the use of spatial selective electrodeposition of graphene nanosheets. Since secretions produced in the fingerprint deposit lead the underlying surface to be electrochemically inert or less active, the electrodeposition process only occurs on the areas without fingerprint residue. As a result, a high contrast negative image of the fingerprint was achieved by the electrochemical reduction of graphene oxide (GO) after optimizing the factors (applied potential, deposition time and scan rate).

P.132: Enhancing the Visual Performance of Touch Screen Displays

AbstractProperly designed touch screens are bringing previously unattainable levels of intuitive human‐computer interactions for managing aircraft information. Human‐factor issues, such as the visual appearance of the display in high ambient sunlight conditions, avoidance of accidental activation, and resistance to the deposition of fingerprints, are all influenced by the touch screen construction and integration with the active matrix liquid crystal display (AMLCD). This paper describes a touch screen display designed with Human‐Machine‐Interface (HMI) features required for flight deck applications.

Enhancing the visualization of latent fingerprints by electrochemiluminescence of rubrene

We report how electrochemiluminescence (ECL) of rubrene can be utilized for enhancing the visualization of latent fingerprints in two different modes. The enhancement arises from the spatially selective ECL generation either from the substrate surface uncovered by the fingerprint or the fingerprint itself, designated negative or positive imaging mode, respectively. The negative mode is performed directly in an electrolyte solution containing rubrene and co-reactant. Given that organic residues in the fingerprint deposit make the underlying surface electrochemically inert or less active, ECL reaction occurs only on the surface untouched by the fingertip, generating a negative impression with a dark ridge pattern against the illuminated background. The positive imaging mode is based on the preferential adsorption of rubrene aggregates to the ridge materials via physical attraction; then the fingerprint can glow via ECL reaction in a solution containing co-reactant under an appropriate applied potential.

Development of Latent Fingerprints on Thermal Paper by the Controlled Application of Heat

Apparatus to produce a spatially and temporally uniform heat source is described and this is used to visualize latent fingerprints deposited onto thermal paper by raising the temperature of the paper. Results show an improvement over previous research when fingerprint deposits are aged or the developed fingerprints faint; visualization being enhanced by the use of a blue LED light source of 465nm peak wavelength. An investigation of the components in fingerprint sweat likely to affect the solubility and hence color change of the dye present in the thermal paper has shown that polar protic solvents able to donate a proton are favored and a polar amino acid found commonly in eccrine fingerprint sweat (lysine) has been shown able to produce the desired color change. Aged fingerprint deposits on thermal paper from a variety of sources up to 4years old have been visualized with this technique.

Nanoscale control of interfacial processes for latent fingerprint enhancement

Latent fingerprints on metal surfaces may be visualized by exploiting the insulating characteristics of the fingerprint deposit as a "mask" to direct electrodeposition of an electroactive polymer to the bare metal between the fingerprint ridges. This approach is complementary to most latent fingerprint enhancement methods, which involve physical or chemical interaction with the fingerprint residue. It has the advantages of sensitivity (a nanoscale residue can block electron transfer) and, using a suitable polymer, optimization of visual contrast. This study extends the concept in two significant respects. First, it explores the feasibility of combining observation based on optical absorption with observation based on fluorescence. Second, it extends the methodology to materials (here, polypyrrole) that may undergo post-deposition substitution chemistry, here binding of a fluorophore whose size and geometry preclude direct polymerization of the functionalised monomer. The scenario involves a lateral spatial image (the whole fingerprint, first level detail) at the centimetre scale, with identification features (minutiae, second level detail) at the 100-200 microm scale and finer features (third level detail) at the 10-50 microm scale. However, the strategy used requires vertical spatial control of the (electro)chemistry at the 10-100 nm scale. We show that this can be accomplished by polymerization of pyrrole functionalised with a good leaving group, ester-bound FMOC, which can be hydrolysed and eluted from the deposited polymer to generate solvent "voids". Overall the "void" volume and the resulting effect on polymer dynamics facilitate entry and amide bonding of Dylight 649 NHS ester, a large fluorophore. FTIR spectra demonstrate the spatially integrated compositional changes. Both the hydrolysis and fluorophore functionalization were followed using neutron reflectivity to determine vertical spatial composition variations, which control image development in the lateral direction.

Non-destructive enhancement of latent fingerprints on stainless steel surfaces by electrochemiluminescence

Visualization and detection of latent fingerprints (LFPs) on metal surfaces are of highly practical importance, e.g., in identifying gun cartridges. We report herein the visualization of LFPs on stainless steel surfaces by electrochemiluminescence (ECL). Since organic residues, such as fatty acids, in the fingerprint deposit make the underlying surface electrochemically inert or less active, an ECL reaction occurs only on the metal portions untouched by the fingertip, hence generating a negative image of the fingerprint. The popular ECL reaction solution, consisting of ruthenium(ii) tris(2,2'-bipyridyl) and tri-n-propylamine, was used for this imaging purpose. Factors, including the applied potential and the concentration of ECL luminophore, as well as the stability of ECL negative images, were investigated to achieve a satisfactory visualization enhancement. This imaging approach is simple, rapid, non-invasive, and no pre-treatment either on the background or on the fingerprint itself is needed. It constitutes a powerful tool for visualizing LFPs on metal surfaces. This method was also demonstrated to be suitable for enhancing LFPs collected from various surfaces.

Determining the order of deposition of natural latent fingerprints and laser printed ink using chemical mapping with secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) chemical mapping was used to investigate the order of deposition of natural latent fingerprints and laser printed ink on paper. This feasibility study shows that sodium, potassium and C(3)H(5) positive ions were particularly abundant endogenous components of the natural fingerprints and also present in the paper examined, but were mostly absent in the laser printed ink. Mapping of these ions enables the observation of friction ridges from latent prints on the ink surface, only when a fingerprint was deposited above the layer of ink. As a demonstration of proof of concept, blind testing of 21 samples from three donors resulted in a 100% success rate. The sensitivity of this technique was investigated within this trial through the examination of up to fifth depletion fingerprints and ageing of up to 28 days. Migration of fingerprint and paper components to the ink surface, although observed with increased ageing time, was not found to compromise determination of the deposition sequence.

SECM imaging of latent fingerprints developed by deposition of Al-doped ZnO thin film

A novel vacuum metal deposition (VMD) based technique has been efficiently employed for the visualization of latent fingerprints on glass and plastic substrates. Al-doped ZnO thin film (ZAO) was deposited on the bare surface and the valleys between the fingerprint ridges by direct current magnetron sputtering with the oblique target, which yielded normal development of latent fingerprints. The enhanced results of latent fingerprints have been photographed with good contrast by a conventional digital camera. Additionally, an electrochemical method, scanning electrochemical microscopy (SECM), has also been successfully applied to the image acquisition of a latent fingerprint developed on the glass surface due to its superb sensitivity toward the small variation of the conductivities at the substrate surface. The SECM image of a latent fingerprint on glass substrate provided good contrast between valleys and ridges and micrometer-scale resolution images of fingerprints under wet conditions by using ferrocene methanol as a redox mediator to detect the topology of the fingerprint deposits in constant-height feedback mode.

Label‐Free Electrochemical Imaging of Latent Fingerprints on Metal Surfaces

AbstractA label‐free electrochemical method based on scanning electrochemical microscopy (SECM) has been developed to image latent fingerprints with high resolution on five kinds of metal surfaces (platinum, gold, silver, copper and stainless steel), as it could measure the minor conductivity differences of the substrate surface and avoid the interference of the background‐color. The images of sebaceous fingerprints on clean metals were revealed by SECM with ferrocene methanol acting as a redox mediator to detect the topology of the fingerprint deposits in constant‐height feedback mode. Inhibition of electrochemical processes on areas of the surface masked by the insulating fingerprint residues generated a negative image of the fingerprint.

Electrochromic enhancement of latent fingerprints by poly(3,4-ethylenedioxythiophene)

Spatially selective electrodeposition of poly-3,4-ethylenedioxythiophene (PEDOT) thin films on metallic surfaces is shown to be an effective means of visualizing latent fingerprints. The technique exploits the fingerprint deposit as an insulating mask, such that electrochemical processes (here, polymer deposition) may only take place on deposit-free areas of the surface between the ridges of the fingerprint deposit; the end result is a negative image of the fingermark. Use of a surfactant (sodium dodecylsulphate, SDS) to solubilise the EDOT monomer allows the use of an aqueous electrolyte. Electrochemical (coulometric) data provide a total assay of deposited material, yielding spatially averaged film thicknesses, which are commensurate with substantive filling of the trenches between fingerprint deposit ridges, but not overfilling to the extent that the ridge detail is covered. This is confirmed by optical microscopy and AFM images, which show continuous polymer deposition within the trenches and good definition at the ridge edges. Stainless steel substrates treated in this manner and transferred to background electrolyte (aqueous sulphuric acid) showed enhanced fingerprints when the contrast between the polymer background and fingerprint deposit was optimised using the electrochromic properties of the PEDOT films. The facility of the method to reveal fingerprints of various ages and subjected to plausible environmental histories was demonstrated. Comparison of this enhancement methodology with commonly used fingerprint enhancement methods (dusting with powder, application of wet powder suspensions and cyanoacrylate fuming) showed promising performance in selected scenarios of practical interest.

Nano fingerprints

Investigating recent research improving forensic fingerprint detection and expanding the information obtainable from fingerprint deposits.

Optical Enhancement of Fingerprint Deposits on Brass Using Digital Color Mapping

The reflection of visible light from α-phase brass subject to surface oxidation in air at elevated temperatures is investigated. X-ray photoelectron and auger electron spectroscopy confirm that covered areas of brass (not exposed to air) display dezincification but an absence of significant surface oxidation, confirming a differential oxidation mechanism. Visualization of differential oxidation is shown to be enhanced by selective digital mapping of colors reflected from the surface of the brass using Adobe(®) Photoshop(®). Enhancement is optimal when the brass is heated to ∼ 250°C with areas of oxidation having a mirror-like appearance. The use of this enhancement method to produce a faithful image of fingerprint ridge characteristics is demonstrated on brass shell casings where fingerprints were deposited prefiring.

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.