Analysis of Hair as Trace Evidence. In this article, we'll discuss some methodologies used to analyze hair as Trace Evidence.
BIOLOGY OF HAIR
Hair is a product of differentiated organs in the skin of mammals composed of protein (65-95%, essentially keratin), and water. (15-35%), lipids (1-9%) and minerals (<1%). The hair shaft consists of an outer cuticle that surrounds the cortex. The hair shaft develops in a follicle closely associated with sebaceous and apocrine glands. Hair growth occurs in cycles, alternating between periods of growth (anagen phase) and periods of rest (catagen and telogen phases). About 1 million hair follicles on the scalp of adults, about 85% of the hair is in a growing phase and the remaining 15% is in the resting phase. Hair is produced over 4-8 years for head hair (< 6 months for non-head hair) at a rate of approximately 0.22-0.52 mm/day or 0.6-1.42 cm/month for head hair. Growth rate depends on hair type, physiological factors, and anatomical location (Saitoh, Uzaka, Sakamoto, & Kobori, 1969). Ethyl glucuronide (EtG) analysis in hair is a powerful tool for monitoring chronic alcohol abuse due to the typical wide detection window of the hair matrix and the segmentation capability that allows the assessment of alcohol consumption at different periods. Furthermore, hair EtG is often the only diagnostic parameter of choice for alcohol abuse when other clinical parameters such as ALT, AST, γGT, and CDT are in the normal range and urine ETG is negative.
Hair structure consists of two parts i.e. Root and, shaft. Root; DNA is present in the root which is directly attached to the scalp. The hair root is very rare evidence at Crime scenes. Shaft; Hair shaft consists of three layers; Cuticle, Cortex, and medulla. Ref? Cuticle; The outermost layer that covers hair is called the cuticle. Cortex; Hair pigments are present in the cortex and are present around the medulla.
TYPES OF HAIR
There are three types of hair. Pubic Hair, Head Hair (Tonsorial hair), and Body Hair (Axillary hair). Hair as trace evidence is the most challenging evidence in court. Hair is also known as “associate evidence” because it links a crime scene to a suspect or victim. Hair attaches itself to the surface easily due to “ electrostatic forces”.Hair is the only evidence to identify Drug facilitated crime. The hair at the back of the head Vertex posterior is the best sample because they have less variable growth and fewer effects of sex and age on hair.
ANALYSIS OF HAIR
Hair Analysis; The scientific study of hair is called Trichology which demonstrates the use of trichology in criminal justice.Types of Analysis; Chemical Analysis, Microscopic Analysis, Macroscopic Analysis. Chemical Analysis: The exposure of chemicals on hairs is examined.Microscopic Analysis; The comparison of different parts of hair by microscope.Macroscopic Analysis; Examination of hair by the human eye. E. g, color, type length, etc. Hair analysis takes place as; Purification of hair, Shattering r cutting of hair into small parts, Reproduction; Which is done in methanol, acid, sodium hydroxide, and buffer, Removal; liquid-liquid, Solid phase, Solid phase micro-extraction., Analysis; Immunoassay, screening, chromatography ( gas, liquid) coupled with mass spectrometry. Pulverization is paramount since particle size distribution plays a decisive role in drug recovery. This means that it affects the method of recovery and its reproducibility.
Hair Toxicology; Nicotine is a good biomarker for measuring long-term ETS exposure. Nicotine is preserved in the hair shaft throughout the life of the hair and each centimeter of hair reflects approximately 1 month of ETS exposure. In general, hair nicotine assay involves sample collection, digestion, extraction, and instrumental measurement. The extraction procedure plays a critical role in any chromatographic analysis involving biological specimens. It determines the sensitivity, simplicity, time, and cost implication of an assay. Extraction of nicotine from hair is normally done by either liquid-liquid.
The analysis of ethyl glucuronide (EtG) In hair is a powerful tool for chronic alcohol abuse control because of the typical wide detection window of the hair matrix and due to the possibility of segmentation, allowing evaluation of alcohol consumption in different periods. Additionally, EtG in hair is often the only diagnostic parameter of choice for alcohol abuse when other clinical parameters such as ALT, AST, γGT, and CDT are in the normal range and EtG in urine is negative.
FORENSIC TECHNIQUES FOR HAIR ANALYSIS
Chromatographic Techniques: Different types of Chromatography methods are used to confirm the presence of certain drugs in hair.Immunoassays: The presence of drugs in a hair sample is checked by many immunological techniques which are used as screening tests.Gas Chromatography-Mass Spectrometry: For hair analysis, to obtain the best results, the mass spectrometer is used with Gas Chromatography because Flame Ionization Detector (FID) is not very useful for hair analysis.Liquid Chromatography-Mass Spectrometry: It is a very widely used technique for hair analysis in forensic science. Because it is very useful and highly sensitive even for a negligible amount of drug present in the hair.Capillary Zone Electrophoresis: The presence of drugs like morphine and cocaine and their quantity is determined by Capillary Zone Electrophoresis (CZE).Fourier Transformation Infrared Spectroscopy: It is the best and most useful and effective method used for hair analysis in forensic science. A sensitive method for the simulta”eous’analysis of cocaine, benzoylecgonine (BE), and ecgonine methyl ester (EME) in human hair by gas chromatography/chemical ionization mass spectroscopy (GC/CIMS) are described. Hair samples are cut into 1 cm sections, washed with 1% sodium dodecyl sulfate, rinsed with deionized water and methanol, and then digested overnight in a solution containing Tris buffer, sodium dodecyl sulfate, Proteinase K, and dithiothreitol. Digested hair samples are extracted with Bond Elut Certify™ solid-phase extraction columns, derivatized with N-methyl-N-(tertbutyldimethylsilyl)-trifluoroacetamide (MTBSTFA), and analyzed by GC/CIMS using isobutane as reagent gas. This method is quantitative, does not cause degradation of cocaine, and requires as little as 5 mg of hair.
Energy-dispersive X-ray fluorescence analysis was applied for the analysis of hair. The hair samples were digested in a mixture of nitric and perchloric acid and the heavy metals were precipitated with ammonium pyrrolidine dithiocarbamate. The accuracy, precision, and recovery of the method for the elements Fe, Ni, Cu, Zn, and Pb were evaluated through the analysis of a standard hair sample.
Laser-induced breakdown spectroscopy:-
The laser-based approach known as “laser-induced breakdown spectroscopy” (LIBS) allows for non-intrusive, qualitative, and quantitative measurements of metals under a variety of testing conditions. LIBS is an emission-type technology that has been used on gas, liquid, and solid sample types with good results. The main benefit of LIBS over other analytical techniques is the absence of the need for laborious sample preparation. LIBS (Laser-Induced Breakdown Spectroscopy) (Laser-Induced Breakdown Spectroscopy). The algorithm for self-absorption correction is applied to three various certified steel NIST samples as well as to three ternary alloys (Au, Ag, and Cu) with known compositions to test the model. The experimental results demonstrate that the self-absorption corrected Calibration-Free approach provides accurate results, enhancing by about one order of magnitude the precision and accuracy of the CF-LIBS procedure. It is capable of carrying out real-time multi-element analysis. Its primary drawback is that the excitation condition is susceptible to changes in both the surroundings and the laser energy, which can lead to imprecise measurement results. Comparing LIBS analysis to atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry (ICP-AES), the tiny amount of sample material employed in LIBS analysis results in lower sensitivity for some metals.
Mitochondrial DNA Analysis:-
In forensic scenarios where nuclear DNA typing is not an option, analysis of the mitochondrial DNA (mtDNA) sequence from human hairs has proven to be a useful supplement to conventional hair comparison microscopy. There has been the minimal linkage of individual information, even though the fields of hair biology and mtDNA sequence analysis are well understood. Forensic DNA scientists may not always be familiar with topics like hair microscopy and hair embryogenesis. Human hair is continuously renewed and grown, involving intricate cellular regeneration processes. In turn, complicated interpretational issues can arise during the study of mtDNA sequencing data (eg, heteroplasmy and the sequence variation it may cause within an individual, or between related individuals). Now we go over the specifics of the histology of hair development, including the movement of mitochondria during hair growth and the corresponding challenges with mtDNA data interpretation. Forensic investigators may find it useful to use the macroscopic and microscopic categories of hair specimens as a guide to more accurately connect mtDNA sequence heteroplasmy data with a hair’s physical attributes. The relative success of sequencing various types and/or forms of human hairs may be assessed using the same classifications for hair specimens. As the usage of mtDNA sequence analysis grows, the ultimate purpose of this review is to bridge the gap between forensic DNA scientists and hair microscopists.
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