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Forensic science is a term which describes the application of broad spectrum of sciences for the examination of crime scenes and gathering of evidence to be used for investigation of crimes such as murder, theft, fraud or terrorism activities. It is multidisciplinary field and its major purpose is to assure law enforcement in society. It is also used to analyze the possibility of the presence of chemical warfare agents or high explosives, to monitor compliance with international agreements regarding weapons of mass destruction, or to test for propellant stabilizers. Forensic science encompasses mainly following areas of science; biology, chemistry, and medicine, it also includes the use of physics, computer science or psychology. At crime scene, the objects, substances (including blood or drug samples), chemicals (paints, explosives, fire accelerants, toxins), traces (hair, skin), or impressions (fingerprints or tidemarks) are collected as evidence.
A growing area of forensic science is the analysis and early detection of possible terrorist attacks, or breaches of security. There is a wide range of samples taken from the scene of suspected chemical or biological weapons to be analyzed, but the method of analysis slightly different from a criminal investigation. These samples often contain very minute amount of chemicals and require very accurate and sensitive analytical instruments. In addition to the already-described samples, evidences of weapons of mass destruction are obtained by collecting swabs from objects, water, and plant material. After that they are tested for the detection of radioactive isotopes, toxins, or poisons, as well as chemicals that can be used in production of chemical weapons. Forensic chemistry performs qualitative and quantitative analysis of chemicals found on people, various objects, or in solutions. The chemical analysis is the most varied from all the forensic disciplines. Chemists analyze drugs as well as paints, remnants of explosives, fire debris, gunshot residues, fibers, and soil samples. They can also test for a presence of radioactive substances (nuclear weapons), toxic chemicals (chemical weapons), and biological toxins (biological weapons) [1, 2].
 Nanotechnology and Nanoscience, ISSN: 0976-7630 & E-ISSN: 0976-7649, Vol. 1, Issue 1, 2010, PP-19-21
2. R. Saferstein, J. M. Butler , T. A. Brettell Anal. Chem. 2005, 77, 3839-3860
Nanotechnology is the understanding and control of matter generally in the 1-100â€‰nm dimension range. It is a multidisciplinary field, which covers a vast and diverse array of devices derived from engineering, biology, physics and chemistry and even forensic science. The application of nanotechnology to forensic science, known as nano-forensics, concerns the use of precisely engineered materials at this length scale to develop novel methods of collection and analysis of forensic evidence. Nanomaterials have unique physicochemical properties, such as ultra small size, large surface area to mass ratio, and high reactivity, which make them different from bulk materials of the same composition. These properties can be used to overcome some of the limitations found in traditional methods of analysis of forensic evidence. Nanotechnology in forensics promises new approaches for earlier detection, collection and analysis of forensic evidences.
Many techniques have been developed and applied for the synthesis of nanoparticles but majorly, there are two approaches toward the synthesis of nanosized materials; top-down and bottom-up approaches.
Top-down approach includes milling or attrition, repeated quenching, and lithography. In this approach bulk materials are modified to give small features and such prepared nanoparticles are commonly used in the fabrication of nanocomposites and nanograined bulk materials.
Bottom-up approach includes plasma, laser, liquid phase, flame spray synthesis. In this approach, these "self-assembly" preparation methods generally result in well controlled nanoparticles when small building blocks are assembled into larger structure, allowing the synthesis of more complex materials or the fabrication of nanoparticles with a very narrow size distribution.
Bottom-up approach is far more popular because nanoparticles can be synthesized by confining chemical reactions, nucleation and growth processes in a small space such as micelles. But for any practical application, the processing controlled conditions are needed so that the resulting nanoparticles have the following properties: (1) particles should be monosized or with uniform size distribution, (2) identical shape or morphology, (3) identical chemical composition and crystal structure, so that core and surface composition must be the same, and (4) individually dispersed nanoparticles. For the synthesis of nanoparticles, various methods or techniques can be grouped into two categories: kinetic approach and thermodynamic equilibrium approach.
In the thermodynamic approach, synthesis process consists of (1) generation of super-saturation, (2) nucleation, and (3) subsequent growth of nanoparticles. In the kinetic approach, nanoparticles are synthesized by either confining the process in a limited space such as aerosol synthesis or micelle synthesis, or limiting the amount of precursors available for the growth such as used in molecular beam epitaxy .
3. Nanoparticles: Building Blocks for Nanotechnology by Vincent M. Rotello, Springer, 2004
Miscellaneous techniques are used for determining size and certain properties of nanoparticles. The methods using TEM, SEM, conductivity measurements, and electron diffraction techniques provide information on particles.
Several other techniques are used for studying particles in the bulk. For example, X-ray diffraction can be used for determining particle sizes and internal structures.
Here, we consider microscopy in sufficient detail, because it is the major technique for determining the nanoparticle size. As a rule, this concerns electron microscopy, which
employs beams of accelerated electrons and also different versions of probe microscopes.
Electron microscopy, in turn, has the following two main directions:
_ TEM, in which the high-resolution electron microscopy is currently a separate
Transmission electron microscopy
A sample shaped as a thin film is transilluminated by a beam of accelerated electrons with
an energy of 50-200keV in vacuum of ca. 10_6mmHg. Those electrons that were deflected at
small angles by atoms in a sample and passed through the sample get into a system of magnetic
lenses to form a bright-field image of the sample internal structure on a screen and a
film. Aresolution of 0.1 nm was achieved, which corresponds to a magnification factor of 106.
The resolution depends on the nature of the sample and the method of its preparation.
Usually, films of 0.01-ƒ¬m thickness are studied; the contrast range can be extended using
carbon replicas. Modern ultramicrotomes allow obtaining sections 10-100-nm thick. Metals
are studied as thin foils. Transmission microscopes make it possible to obtain diffraction
patterns, which provide information on the crystalline structure of a sample.
Scanning electron microscopy
This technique is largely used for studying surface particles. An electron beam is
constricted by magnetic lenses to give a thin (1-10 mm) probe, which travels progressively,
point-by-point over a sample, thus scanning the latter. The interaction of electrons with the
surface generates several types of emission:
_ secondary and reflected electrons;
_ transmitted electrons;
X-ray slowing-down radiation;
_ optic radiation.
Any of the radiation types listed above can be registered and converted into electrical
signals. The signals are amplified and fed to a cathode-ray tube. A similar situation occurs
in TV kinescopes. Images are formed on the screen and photographed. The major advantage
of this technique is the great body of information it provides; its significant drawback
concerns long scanning times. High resolution is only possible for low scanning rates. The
method is usually employed for particles measuring more than 5nm. A restriction on the
sample thickness limits the method of application. For electrons with energies of 100 keV,
the sample thickness should be about 50 nm. To prevent destruction of samples, special
procedures are used for sample preparation. Moreover, the possible effect of electron emission
on the samples should be taken into account, for instance, the electron-beam-induced
aggregation of particles.
Explosives are unstable chemical compounds (chemical or nuclear) that can be initiated to undergo very rapid and self-propagating decomposition which result in the high release of heat or the development of sudden pressure effect and formation of more stable material. Explosives have been classified into many types on the basis of structure and performance (Fig. 1). Explosives are classified as low and high explosives on the basis of their detonation velocities (burn rates) and these types are further classified into different forms.
Low explosives that detonate at low rates (cm sâˆ’1) include propellants, pyrotechnics, smokeless powder, black powder, etc. High explosives detonate at very high velocities of km sâˆ’1, the chemical reaction propagates with such rapidity that it exceeds the velocity of sound. High explosives have again been sub-divided into two groups, i.e. primary explosives and secondary explosives. Primary explosives, often referred as 'initiating explosives' are highly shock sensitive and can be used to ignite secondary explosives i.e. lead azide and lead styphnate. Secondary explosives, which include nitroaromatics and nitramines are used as main charge or bolstering explosives much more prevalent at military sites than primary explosives. They can be further categorized into melt-pour explosives and plastic bonded explosives. Melt-pour explosives are based on nitroaromatics, such as trinitrotoluene (TNT), dinitrotoluene (DNT) and plastic bonded explosives are based on a binder and crystalline explosive formulated with one or more high explosives, such as hexahydro-1,3,5 trinitroazine (RDX). The propellants and explosives are mostly organic compounds and can be classified into following based on their chemistry: (1) Nitramines or nitrosamines, such as octogen (HMX) or RDX; (2) Azide explosives (3) Organic peroxides, such as HMTD [hexamethylenetriperoxidediamine], also known as home-made explosives (HMEs) (4) Nitroaromatic compounds, such as TNT, dinitrobenzene (DNB), hexanitrostilbene, picric acid (5) Nitrate esters, such as pentrite (PETN), ethylene glycol dinitrate (EDGN), nitroglycerine, and nitroguanidine (NQ) .
. S. Singh, Journal of Hazardous Materials 144 (2007) 15-28
Fig. 1 Classification of Explosive based on structure and explosion rate.
The energetic material used by the military as propellant and explosive are mostly organic compounds containing nitro (-NO2) groups. Identification, quantification and remediation of explosives have become a highly significant task in forensic science, anti terrorist activities and global demining projects. There are two major threats from these nitroexplosives. One of the threats is their illegal use for terrorism, which will cause chaos in the nation, other one is the health associated risks with the release of these compounds in environment. The nitroaromatics has a special characteristics or ability to penetrate in the skin causing the formation of methemoglobin on acute exposure and severe anaemia on chronical exposure.
The problem of contamination of soil and groundwater by nitroaromatic compounds is a widespread environmental concern with environmental deterioration. These compounds have several applications in agricultural, industrial, and military and assessments of the hazards from these applications quite often do not take into account chemical processes .
Picric acid is synthesized by nitration of phenol with transient sulfonation, using sulfuric acid and nitric acid, or by nitration of chlorobenzene followed by hydrolysis and further nitration (Roth, 1980a). It is relatively soluble in water (13.1 g/l) and has an octanol-water partitioning coefficient Ã°log PowÞ value of 2.03 (Gorontzy et al., 1994).
Picric acid or its stable salts (ammonium picrate, explosive D) found use in naval ordnance and were common in many other types of ordnance in the early part of this century .
. T. A. Lewis, D. A. Newcombe, R. L. Crawford, Journal of Environmental Management 70 (2004) 291-307
The tendency of picric acid to form unstable metal salts and its high melting temperature (122 8C) have led to its replacement by other explosives (Roth, 1980a) Picric acid (pKa ) 0.38)s when in contact with waters dissociates to form the yellow colored picrate anion. Figure 2 shows the absorption spectrum of picrate in pure water (c: ìmax) 356 nm) and of picric acid in CH2Cl2 (a: ìmax ) 336 nm) [6, 7].
 Ve´ronique Pimienta,â€ Roberto Etchenique,â€¡ and Thomas Buhse
 Yoshikawa and Matsubara [J. Am. Chem. Soc. 1984, 106, 4423-4427]
Picric acid is atrinitroaromatic compoundthat is a flammable solid whenpurchased wet with 30%water, by mass.
Picric acid is a high-poweredexplosive when allowed todehydrate. As an explosivepicric acid is not shock sensitive, but when in contact with metals can form shock sensitive metal picrates.
Picric acid can be detonated by extreme heat, a blasting cap, or an electric charge. Dehydrated picric acid appears as a yellow-orange colored, dry crystalline solid with visible air pockets below the surface. When wet with 30% water, picric acid is an orange colored, compact crystalline solid with the consistency of wet sand. When dissolved in water or an organic solvent, picric acid forms a bright yellow solution.
Transition metals and metal oxides have unique properties of high adsorption and catalytic ability, which have resulted in their applications as natural adsorbents and catalysts in the development of clean-up technologies.
A Fourier transform infrared spectrophotometer (FTIR) is an instrument used to examine specimens, both to detect the presence of target compounds and to measure the quantities of the compounds (quantification). FTIR can be an important analytical instrument in a forensic investigation.
A FTIR can be useful in detecting both organic chemicals (i.e., those that contain carbon) and inorganic chemicals. As with other forms of spectrophotometry, FTIR utilizes light. In this case, the wavelength of the light (the distance between a point of one light wave and the corresponding point of an adjacent wave) is in the infrared range. Infrared light lies in between the visible light and microwave portions of the electromagnetic spectrum. The infrared light that is nearest to visible light ("near infrared") has a wavelength of approximately 770 nanometers (nm; 10 meter). At the other end of the range, infrared light that is nearest to microwave radiation ("far infrared") has a wavelength of approximately 1,000,000 nm (1.0 millimeter).
The basis of FTIR is the absorption of the infrared light by various molecules in a sample. Depending on their chemical structure and three-dimensional orientation, the different sample molecules will absorb different portions of the infrared spectrum.
Depending on the nature of the chemical bond that absorbs the infrared light, a chemical bond will vibrate in varying ways. Reflecting the different types of bonds, a number of events can occur. For example, the input of vibrational energy can stretch the bonds between the carbon atom and the surrounding hydrogen atoms in CH3. Also, the carbon-hydrogen linkages of CH3 can remain the same length while the linked atoms are moved back and forth laterally to one another (rocking). Other chemical linkages, such as that between a silicon atom and CH3 group, can be altered asymmetrically along their lengths, with some regions of the bond stretching and other regions contracting (asymmetric deformation).
The absorption of light by the sample will decrease the energy of the infrared light that exits the sample chamber or produce a wave that is "out of synch" with light that has not passed through the sample. A computational comparison of the frequency patterns of the incoming and exiting infrared light can be made as described subsequently and displayed as a series of peaks rising above the background baseline. The height of the peaks corresponds to the degree of absorption and/or to the nature of the chemical bond change (i.e., stretching, rocking, deformation).
Within the spectrophotometer, the incoming infrared light beam is split in two by a mirror. Half of the beam is directed through the sample. The aforementioned chemical interactions within the samples will produce an emerging light beam that is different in optical character from the portion of the light that has been directed away from the sample.
The two light beams will be out of phase will one another. Since light consists of waves, the out of phase waves can cancel one another or lessen the overall wave intensity through interference. The pattern that results from the interaction of the two beams is known as an interferogram.
The end result of the Fourier transform is the spectrum of peaks and valleys that is displayed to the analyst. The resulting absorption pattern can be compared to the millions of patterns that are stored in computer databases, both on-site and remotely via the Internet. If a matching spectrum is obtained, then the identity of the sample compound can be determined.
FTIR is a valuable forensic technique because of its detection sensitivity and versatility. Chemicals from a variety of sample types including blood, paints, polymer coatings, drugs and both organic and inorganic contaminants can be identified.
Liquid samples such as blood can be prepared for FTIR examination by placing a drop between two plates made of sodium chloride (salt). The salt molecules are transparent to the infrared light and so form convenient sandwiching layers to produce a thin layer of sample. Solid samples can be converted to a fine powder in combination with a carrier material like potassium bromide (KBr, which is also infrared transparent). Alternatively, solids such as polymers can be dissolved in a solvent such as methylene chloride and added to a salt plate. When the solvent evaporates, the sample forms a thin layer on the salt plate.
Solids as complex as soil have been successfully analyzed using FTIR in forensic studies.
FTIR is not a technique that can be done at the scene of a crime or accident. The spectrophotometer and ancillary computer equipment are too bulky and heavy for transport. Rather, samples need to be carefully collected and transported to a specialized laboratory that has the necessary FTIR equipment.