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reportForensics
9.9.3 Short description

Forensic investigation deal with scientific analysis of evidence left at a crime scene in order to determine establish means used, time of crime and the person involved in the crime. A fingerprint is considered as extremely vital evidence that establishes an association between a suspect and a criminal act. There are three types of fingerprints are found at a crime scene - visible, indented and latent. The first ones are those that are visible formed in blood, grease, oil or paint. Such marks are generally easy to detect. Indented or plastic marks are produced when fingers are in
contact with malleable materials such as candle wax, putty or wet paint. Latent fingerprints are
the most common and challenging to detect as they are invisible. Optical, physical and chemical
techniques are used to detect latent fingerprints. Fingerprint detection can be done by means of a number of techniques. Each technique offers an efficiency advantage relevant to the application. The advantage of a technique depends on the type of surface where the fingermark is left, whether it is porous, semi-porous or non-porous. It depends on the composition of the secretions,
whether they are eccrine or sebaceous. It also depends on the time for which the fingermark has been left on the surface and whether or not the surface has been wet [200].

The visible fingerprints can be easily detected, photographed and documented. The latent
fingerprints are difficult to detect. Fingerprints are formed primarily from perspiration. A typical fingerprint contains water, organic and inorganic chemicals such as amino-acids, salts, glucose, peptides, salts, lactic acid, ammonia, riboflavin, and lipids, due to a mix between eccrine and sebaceous secretions. The chemical residue hardens when the water evaporates, making it possible to detect fingermarks years after their deposition [201]. Nanoparticles based detection were recently developed to detect the residues of latent fingerprints and provide a good contrast between the residue and the underlying substrate.

A number of methods have been used in detecting fingermarks. The method based on
photoluminscent detection of latent fingerprints has been mentioned. In this method quantum dots are bound to fingerprint residues, following which they are illuminated with the appropriate spectrum of light and the fingerprint is detected by fluorescence. Cadmium sulphide, cadmium selenide or indium phosphide quantum dots with diameter less than 10 nm have been attached to
latent fingerprint using encapsulating agents such as fatty acids or amino acid components. The excitation of the quantum dot is carried out using a laser of near ultra-violet wavelength [202].

Fluorescent nanoparticles for detecting latent fingerprints have been developed by the University of Sunderland. They are processed as sol-gel particles in the presence of derivates of fluorescent dye. Nanoparticles of cadmium sulphide and cadmium selenide showing intrinsic fluorescence can also be used. The processed nanoparticles are spherical in shape with diameters ranging between 30 - 500 nm. Fluorescent dyes of Texas red-labeled gelatin have been used in the process of developing the nanoparticles. Hydrophobic molecules such as phosphatidylcholine and phosphatidylethanolamine are coated on to the nanoparticles. Texas Redporcine
thyroglobulin conjugate embedded in sol-gel derived nanoparticles have been shown to bind
latent fingerprints [203]. Latent fingerprints have been visualized using hydrophobic silica based particles in forensic analysis. Both nano scaled and micro scaled particles have been
synthesized, the nanoparticles being applied in an aqueous solution to fingerprints while
microparticles (aggregates of nanoparticles with an average diameter of 27 microns) are used as dusting agents. The synthesis route described in the literature, mentions the production of colored and fluorescent agents, also colored and magnetisable particles embedded in the agents. Carbon
black and titanium dioxide has been used as embedded particles [204].

The small size of nanoparticles enables the detection of fingerprint sub-structure with greater detail and accuracy, in comparison with larger particles used in the traditional powdering on crime scene. The technique is advantageous due to a better definition of fingerprints recorded from crime scenes. The technique improves the sensitivity and consequently increases the chance to
detect very faint fingermarks, and by the same way increase the possibilities to find a link with
criminals or suspects. Lipid sensitive dyes have been used for imaging and documenting fingerprints in a method and apparatus developed by Ciencia Inc. Exposure to light brings about fluorescence when lipids are bound to the residue of a latent fingerprint [201].

The use of silicon dioxide based nanocomposites has been mentioned in the literature for the latent fingerprint detection. The experimental study has demonstrated the fabrication of sensitising ligands and silicon dioxide based xerogels. The highly fluorescent photo-stable europium metal ions/sensitizer complex into the nanopores of the xerogels. The novel doped xerogels were reported to detect unfumed fingerprints on surfaces such as metal foils, glass, plastic, coloured paper, and organic materials. The advantages offered by the doped nanomaterials are distinct fluorescent characteristics, quick prototyping, cost effective fabrication, and nanoparticle surface customisation for tagging of fingerprints [205].

9.9.3.1 Metal Nanoparticles in Forensics

Multi-metal deposition (MMD) is a technique that can efficiently detect fingerprints on a wide
range of substrates, as well as old and fresh fingermarks, even if they have been wet [206]. It consists in a two-step process in which gold nanoparticles are first deposited onto the secretions, before being covered by silver through a chemical deposition performed in solution. Gold nanoparticles have been reported in the literature as intermediaries, for latent fingerprint detection. The MMD technique has further been modified to improve the operational limitations of multiple immersion baths for gold nanoparticle. Successful demonstration of detection of fingermarks was achieved using gold nanoparticles functionalized with molecular hosts bearing
organic dyes [207]. Another modification consisted in replacing the silver deposition step by a second gold deposition, on the gold nanoparticles, leading to an alternative MMD formulation which constitutes a serious alternative to the classical method [208]. Luminescent techniques are considered beneficial due to high sensitivity and their ability to remove the colour of the background material on which the fingerprint is formed. A modification of the original two step
process has been reported in the literature for fingerprint detection, in the first step colloidal gold particles are deposited onto the fingerprint, and in the second step zinc oxide covers the gold nanoparticles (instead of silver for the classical MMD). A luminescent fingermark is obtained due
to the in situ–formed zinc oxide nanoparticles. Luminescent nanoparticles offer advantages over other deposition material such as silver or functionalised gold nanoparticles. Zinc oxide is used due to its photo-luminescent capabilities, which when excited with UV luminescent (300-400nm) in visible range (~ 580nm) due to defects in the structure [209].

Schematic diagram of the multimetal deposition process for fingerprint detection

Figure F.1 - Schematic diagram of the multimetal deposition process for fingerprint detection [207]

Experimental studies have been performed on detection of latent fingerprints using lipophilic and polycationic chitosan polymer. Gold nanoparticles treated with chitosan have been used to attach it with lipids in the latent fingerprints. The research was mainly aimed at understanding the mechanism of detecting latent fingerprints using gold nanoparticles. Two approaches were used, in the first one, gold colloids were capped with chitosan. In the second approach fingerprints were pre-treated with chitosan, which was followed by immersion in a gold colloidal solution, and
addition of mono sodium glutamate to agglomerate the gold nanoparticles. Reproducible results could lead to its potential use in forensic detection of fingerprints [210].

The application of gold nanoparticles using lipophilic interactions between fatty acids of latent fingerprints has been reported in the literature [211].Gold nanoparticles of size 1-3 nm, stabilized with alkanethiol have been synthesized and characterized [212]. Gold nanoparticles functionalized with anti-body of cotinine, have been demonstrated in detecting fingermarks as well as giving information whether the person was a smoker or a non-smoker. This was done by
pipeting the nanoparticle-anti-cotinine conjugate onto the fingerprint, following which a fluorescent agent was added and the fingerprint imaged. Lack of fluorescence would confirm absence of cotinine and that the individual was non-smoker [213].

Gold and silver nanoparticles have been demonstrated to detect latent fingerprints on non-porous surfaces. Interaction of the oleylamine gold nanoparticles with the fatty acids in the latent fingerprints causes them to deposit on the surface. These were reported to be advantageous over conventional powder as they produce sharper patterns and do not stain the background of the non-porous material [214].

Other techniques such as gas chromatography, mass spectrometry, infrared spectro-microscopy and micro-X-ray fluorescence have been used in analyzing the finger mark composition [215, 216, 217].

9.9.3.2 Metal oxide nanoparticles in fingerprint detection

Metal oxide nanoparticles have found applications as pigments or colorant, fluorescent agent and as fingerprinting powder. Titanium dioxide particles with particle diameter of 21nm have been reported in suspension for the detection of fingerprints on porous and non-porous surfaces [218]. Titanium dioxide nanoparticles in methanol provided good results for fingerprint detection in blood
on non-porous and semi-porous surfaces. The results of the research were reproducible for both old and new fingerprints [219]. For fingerprint detection on dark adhesive surfaces, titanium dioxide nanoparticles suspended in a surfactant solution has been mentioned as the most optimum method [220]. The use of suspended titanium dioxide nanoparticles for developing latent fingerprints on wet surfaces has been reported in the literature. According to the authors, the quality of fingerprint detection mainly depends on the way the surface has been touched and the
time the contact with the surface lasted [221]. Research on a highly fluorescent dye was
conducted that is absorbed onto nanoparticles of titanium dioxide, for detection of latent
fingerprints on non-porous surfaces. The research produced better results than conventional fluorescent powders, due to a better quality of latent fingerprint details and contrast produced by the nanoparticles and the reduced background developed [222].

Nanostructured zinc oxide was demonstrated to produce fluorescent recognition of the latent fingerprint marks on non porous surfaces such as glass, polyethylene and aluminum foil. The latent fingerprints were visualized when ultraviolet light was directed towards the surface [218]. Europium offers a narrow emission band and long excited life's in relation to organic fluorescent that have short excited lifetimes and broad emission bands. This presents an advantage in detecting fluorescence on difficult surfaces. Experimental research has demonstrated the use of europium oxide nanoparticles that are functionalized with amines. The nanoparticles target carboxylic acid constituent of the latent fingerprints, which are subsequently detected using photoluminescence [223].

9.9.3.3 Metal sulfide nanoparticles in fingerprinting detection

Nanocrystals and nanocomposites of cadmium sulfide have been applied in detecting fingerprint marks on soft drink and aluminum foil. The nanocrystals were capped with dioctyl sulfosuccinate in heptane or hexane, which detected the fingermarks by intense luminescence under near ultraviolet light. The disadvantage this presents is that unfumed prints on metal, glass and plastic
cannot be adequately developed [224]. Dendrimers with terminal amine groups have been research as reagents for fluorescent cadmium sulphide–dendrimer nanocomposties. The amine group reacts with carboxylic acids found in deposits of fingermarks. Luminescence showed thepresence of fingermarks on aluminium foil, polyethylene and paper. The disadvantage of the
process was reported to be long immersion time required for development on paper surfaces [225]. CdS with carboxylate terminal functionalisation have been used for fingerprint detection [226]. Zinc Sulfide capped cadmium selnide nanocrystals have been used in fingerprint detection. These bind to the amino acid component of the fingerprint residue. Fluorescent CdSe/ZnS stablised with octadecaneamine, have been used in detecting latent fingerprints on silicon wafers
and paper. The results on silicon wafer had detailed marks detection whilst on paper they were not obtainable due to high background fluorescence [211]. One the main disadvantages of using cadmium if the health risk posed by the material. One of the main risks posed along with the toxicity is the half life in the human body which is reported to be nearly 30 years [227].

9.9.3.4 Microscopy and Spectroscopy

Forensic digital imaging spectrograph developed by MS Macrosystems is used in both large- and micro-scale document examinations. Two-dimensional and three-dimensional imaging is used for
analysis in the digital imaging spectroscopy hardware. Forged documents examined by forensics experts for establishing authenticity use this tool to objectively compare physical parameters. Small differences between inks and papers can be identified by the application of spectral imaging technology and advanced processing. It can also reveal any information that has been removed. The advantages of this technique are the nondestructive evaluation of documents and three dimensional high resolution color imaging [228]

Scanning Probe Microscopy (SPM) is useful for characterizing surfaces based on
topographical features and physical and chemical properties. It has been used for nondestructive evaluation of forged documents and applications in micro-nanometre resolution of latent fingerprints. Forensic Science applications of scanning probe microscopes (including atomic force microscope) has been mentioned in the literature [229]. Fingerprints were detected under air or liquid with no discernable difference using an AFM. Successful development of two overlapping fingerprints was also demonstrated. Analysis of thin layer of pen ink on the surface of a paper document was conducted. The profile of the line was observed to have an average height
of 200nm. Writing history on a sample can be verified using this information obtained from the AFM. The main disadvantages of this technique are the long time taken for data acquisition and small area of the scan. Analysis of single bits in electronic devices has also been performed using Scanning Probe Microscopy. Recovery of raw data from damaged specimen has been demonstrated by Forensic Science Services. Information was recovered from sim cards recovered from the site of London bombings despite the strong vibrations from the shock waves [230].

Scanning electron microscopes (SEM) play an important role in forensic examinations. Extremely good depth of focus and high to low magnification of SEMs are considered useful for a range of applications and materials. It has been used in gunshot analysis, firearm detection, identification of gemstones and jewellery, examination of paint particles and fibres, handwriting and print examination, counterfeit bank notes, trace comparisons, examination of non-conducting
materials, and high resolution surface imaging. SEM identifies the particles due to their high
contrast with the stub background in the analysis of specimen stubs obtained from gun shot residues. Bullets fired from the same gun have been identified from the marks left from the barrel and the firing pin, in test conducted to compare bullets. SEM provides an advantage over optical microscopy due to their high depth of focus in such forensic examinations. In addition, the backscattered electron detector in SEMs can enhance markings on the bullets and suppress the
detection of dust particles. The literature points towards an Electron microscopy investigation
conducted into metal nanoparticles of gun shot residues. The investigation determined the
method of formation of the nanoparticles and proposed a method for the synthesis. The additional information obtained from synthesis is expected to assist in solving crime through forensic examination [231]. Variable pressure scanning electron microscopy along with energy dispersive X-ray has been successfully demonstrated as analytical tool in diagnosis of electrocution cases. In an accidental death caused by electrocution by means of histological examination of the skin
and identifying titanium metallization [232].

Desorption electrospray ionization is a detection that is used in forensic examination of surfaces. The advantage of the technique is that is can be used at distances up to 3m with no need for sample preparation. The technique is also rapid, highly sensitive and selection. Trace amount of a wide range of chemical can be detected in nanogram quantities such as drug formulations, illicit drugs, organic salts, peptides and chemical warfare agents. In this process the analyte ions generated by the interaction of charged particles and neutral molecules on the surface are analysed by the mass spectrometer. This disadvantage of this technique it is constraints faced
when limited access to sample. It was shown in experimental studies that illicit drugs were

identified with high level of sensitivity and selection. The technique also showed a highthroughput rate for the samples [233].

9.9.3.5 Biosensors

Biosensors are used in forensics to solve crimes and identify perpetrators. Prostrate specific antigen (PSA) has been used to confirm the presence of semen, and absence of sperm in sexual assault cases. The use of PSA is forensic analysis has a different set of requirements than used in clinical samples. The challenge for detection lies in detecting samples contaminated by other bodily fluids, lack of the sample or the need to extract the sample from different fabrics. Nanoparticles and nanostructures are used to enable the analyte detection [234]. Biobarcode arrays have been mentioned, where magnetic particles coating is where the PSA to PSA antibodies binding takes place. Nanoparticles probes coated with anti-body and strands of DNA barcode are applied in bind to the immoblised PSA [235]. Surface enhanced Raman scattering
has been used for the detection of PSA in sandwich immunoassays to a concentration of 1 pg/ml. Gold nanoparticle probes are attached to antibodies that are labeled with Raman dyes [236]. Nanostructure based assays have been regarded robust for PSA detection due to being label free and inexpensive. Cantilever can be used for PSA detection in resonance response variation and bending of the cantilever. An electrical measurement of changes in resonant frequency of cantilever has been mentioned, when binding of PSA with its antibody takes place [237]. Antibodies coated on silicon nanowire field effect sensors have been reported in the literature, for
highly sensitive detection of PSA. The transduction of the signal in the nanowire takes place when the PSA - antibody binding takes place on the surface of the nanowire [238].

9.9.3.6 Role of DNA in forensics

A need for developing cost effective, rapid and precise methodology for detecting DNA has been mentioned in the literature. DNA based identification plays an important role in forensics. Gold nanoparticle conjugates with DNA are fabricated via gel electrophoresis, are used for precise identification of target DNA samples. The mean particle diameter of gold nanoparticles was reported as 10 nm. The quantitative analysis was done to produce a linear correlation between target DNA and conjugate groupings [239]. DNA extraction, quantitation, amplification and separation can be performed on microfabricated devices. The analytical microchip has numerous
advantages such as fast processing times, reduced reagent used, sample handling and use. Reduced sample handling leads to a reduction in contamination of the sample. The increase in efficiency is attributed to reduced sample volumes that are in nanolitre range and high surface area to volume. The low cost of these devices make them an ideal platform for DNA forensic analysis. A review by Horseman et al. has looked at the different methods applied at each of the stages in the analysis. Modular, single and integrated systems for sample analysis have been reported to be in a development stage [240].

An identification method for analyzing molecules based on cantilevers has been developed by Intel. The method is used in the identity verification of criminal investigations and for forensic examination. It is also referred to as DNA testing. The method is based on the identification of target molecules (also known as analyte) by the use of probe molecules that bind to the analyte. A deflection in the cantilever takes place if a binding between probe and analyte takes place. The
cantilever is balanced using a magnetic force, and therefore the detection is based on this
counterbalancing force. Oligonucleotides-nucleic acid and protein/peptide antibodies have been successfully demonstrated probe analyte combinations [241]. A method for detecting target nucleic acid has been patented by Integrated Nanotechnologies. Oligonucleotide probes are
integrated are integrated into an electrical circuit in such a manner that they are not in contact with each other. The complimentary target nucleic acid joining the two probes bridges the gap, resulting in a flow of current through the probes [242].

A method for application in forensics has been developed for genomagnetic nanocapture
(GMNC). Magnetic nanoparticles are functionalised with molecular beacons in this method. The method is advantageous as molecular beacons offer high sensitivity and selectivity along with excellent separation capability of magnetic nanoparticles. The GMNC was fabricated using the
magnetic nanoparticle as carrier, which was coated which was then functionalised with a DNA probe for recognition and collection. An illustration and an example is shown in the figure below. The experimental investigation was performed using samples containing cancer cells, random DNA and proteins. It was effectively used in separation, and collection of trace amounts of DNA/mRNA strands with a single base difference. The efficiency was reported to be over 90% DNA collection [243].

Schematic diagram of genomagnetic nanocapture

Figure F.2 - A). Schematic diagram of genomagnetic nanocapture, Representations are 1. Magnetic nanoparticle, 2, silica layer, 3 Biotin-avidin linkage, 4 molecular beacon DNA probe B). TEM image of a silica-coated magnetic nanoparticle with a diameter range of 28 nm [243]

DNA electrochemical sensors have application in forensics. The detection methodology used by electrochemical sensors is fundamentally based on hybridisation. The advantages offered by electrochemical sensors for forensic applications are they are cheap, simple, reliable, sensitive and selective for genetic identification. A number of electrochemical methods have been reported
in the literature based on impedance of voltametry. Gold nanoparticle based electrochemical chip for DNA identification has been reported [244]. Electrochemical assays based on tracer quantum dots of ZnS, CdS, PbS, and CuS have also been reported [245]. The main disadvantage of electrochemical DNA sensors is the need to label the and also in some instances providing lower sensitivity. A metal sulphide (Cadmium or Lead) based detection of DNA provides attomolar
sensitivity of the targeted DNA [246].

Single molecule spectroscopy has been reported to have applications in forensic analysis. The technique offers ultrahigh sensitivity to detect molecules hidden condensed matter. Single molecule spectroscopy has been used for DNA fragment sizing in forensic applications. Fluorescent tags incorporated by a species provide physical information such as size, surface
area, volume and reactivity. Distribution of fluorescent tags on a specie is identified by
measurement of fluorescent burst size of particles. Identification in forensics is done using information that is provided by distribution size of fragments achieved by restriction digest of DNA. This technique offers advantages over gel electrophoresis such as high sensitivity as picogram mass is needed as opposed to nanograms, shorter time scale being in minutes as opposed to hours, and the ability to work with super coiled DNA [247].

Lab-on-a chip is considered to be a very useful for forensics due to its high sensitivity, high
specificity and portability. Lab on a chip devices offer the potential of high performance analysis
of substances rapidly by conducting sample preparation, injection, sampling, mixing, chemical reactions, product separation, detection and collection on the same chip. To ensure its disposability, they are made out of polymer, glass or hybrids of polymer-glass and silicon-glass. A number of factors have to be considered in the design namely miniaturization, integration of the
different functional elements and low cost of the commercial devices. The device is capable of handling numerous biological samples such as DNA. The advantages offered by the technique are the reduction in process steps and the ability to make a number of analytical measurements. Picolitre volumes of oligonucliotides have been experimentally separated and analysed in glass
micro fluidic chip. Capillary electrophoresis on the microfluidic chip was demonstrated to shorten the separation time by one order of magnitude in relation to traditional capillary electrophoresis [248]. Lab on a chip can be used in a number of relevant applications including identifying DNA profiles and explosives at the incident site. The quick results, reliability and sensitivity of capillary electrophoresis based method offers significant advantages for explosives analysis. The pace of information analysis can act as an effective decision making tool in conducting on site forensic
analysis by agencies [249].

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Tags: nanoparticles, Fluorescent particles, Nanocomposites, Gold and silver nanoparticle, Titanium dioxide nanoparticles, Zinc oxide nanoparticles, nanocrystals, dendrimers, SPM for document analysis, SPM for explosive specimen, SPM for fingerprints, Biosensors in forensics, DNA in forensics, lab on a chip

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reportForensics 9.9.3 Short description