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Trace evidence > Lecture 15 & 16 - Hairs > Flashcards

Lecture 15 & 16 - Hairs Flashcards

1
Q

Hair as trace evidence

History

A
  • Microscopical examination of hairs can be traced back to the dawn of the field and the seminal text Micrographia by Robert Hooke, published in 1665.
  • One of the first recorded applications of hair microscopy to a criminal case was reported in 1838…Hairs on the suspected murder weapon were determined to be of animal origin, leading to the acquittal of the accused
  • It has been understood since 1873 that microscopical hair examinations do not result in individualisation
  • (i.e. it can’t be said that any given questioned hair originates from a specific person based upon microscopy alone)
  • SWGMAT hair subgroup guidelines published in 2005.
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2
Q

Hair as trace evidence

Evidential value

A

Hair is a great form of forensic trace evidence, because:
* It’s found on all humans and other mammals
* It’s easily overlooked by criminals involved in nefarious activities
* It’s readily transferred from one person/object to another person/object
* It’s constantly being produced & shed in their immediate environments
* It’s highly stable, resisting both physical and chemical degradation
* Hairs from different individuals can be distinguished from each other, and with DNA testing
* Forensic labs moving away from anything other than DNA testing!! Mistake!!
* Information from the examination of hairs can provide investigative leads or help with the reconstruction of events in contention.

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3
Q

Chemistry of hairs

A
  • Hairs are composed primarily of protein, specifically keratins
  • Remarkably stable tissues, both chemically and physically. Can persist for thousands of years, nearly unchanged, even at the ultrastructural level
  • Because all true hairs have the same basic chemistry, it is generally not practical to differentiate them using chemical techniques
  • However, elemental analysis and spectroscopic techniques for hair have an emerging number of applications. Particular for tracing the movements of a person from the hair or understanding where the hair has come from.
  • Looking at isotope ratios of elements in the hair can be used to identify locations where an individual may have travelled based on changes in drinking water isotopes in different locations.
  • Similar uses to link substances of abuse.
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4
Q

Types of hairs

A

In humans, hairs are commonly divided into 3 types:
1. Lanugo
2. Vellus
3. Terminal

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5
Q

Lanugo

Type of hair

A
  • Hairs are formed in utero and are typically described as being fine & un-pigmented
  • Typically shed before or shortly after birth
  • Rarely a form of evidence found unless talking about an unborn child or newborn.
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6
Q

Vellus

Type of hair

A
  • Fine, short (∼1 mm), typically un-pigmented or lightly coloured hairs present on almost all skin surfaces including seemingly hairless areas such as the forehead, nose, ears & bald scalp
  • Not found on palms of hands or soles of feet
  • Fine and short
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7
Q

Terminal

Types of hair

A
  • Typical hairs macroscopically visible on children and adults
  • Primary Hairs - Head, eyelash & eyebrow
  • Secondary Hairs - Pubic, underarm & beard.
  • Forensic analysis of hairs are generally restricted to terminal haits. Most commonly head and pubic hair are analysed.
  • In order to analyse hair, we need a reasonable chunk.
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8
Q

Cuticle

Histology of hair

A
  • Outermost layer of hair
  • Largely responsible for the chemical resistance of hair
  • More details revealed in SEM/TEM
  • Cuticle hair persists from a long time, it is the most envirionemtnal resistant.
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9
Q

Cortex

Histology of hair

A
  • Main bulk of hair
  • Largely responsible for the mechanical properties of hair - flexibility, strength, floppability
  • Contains most of the pigment granules giving hair a colour
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10
Q

Medulla

Histology of hair

A
  • Innermost layer of hair shaft
  • Not very well studied or understood
  • Not present in all hairs
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11
Q

Cell membrane complex (CMC)

Histology of hairs

A
  • CMC is found at the interphase between the cuticle and cortex. It has slightly different mechanical properties. It drives some of the chemistry and morphology of hair.
  • Binds all the cells together.
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12
Q

Where is the place most likely to contain DNA?

Hair

A
  • Hair follicle is the place most likely to contain DNA.
  • This is where the hair grows from and changes size and shape throughout the hair cycle.
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13
Q

Hair cycle

A
  • Anagen
  • Catagen
  • Telogen
  • Estimated that 100,000-200,000 hairs on average human scalp
  • Hard to measure but literature suggests 30-100 hairs shed every day depending on a huge range environmental factors
  • Commonly accepted that human head hair grows ~1cm per month
  • There is variation between ancestral groups and age.
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14
Q

Anagen

A
  • Active growing phase of hair extending progressively from the follicle root outwards from skin
  • 85-90% of human head hairs in this phase
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15
Q

Catagen

A
  • Transition phase when growth slows and eventually stops
  • 1-2% are in this stage
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16
Q

Telogen

A
  • Resting phase when minimal force is required to remove hair and natural shedding (exigent) likely to occur
  • ~10-15% of human head hairs in this phase
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17
Q

Grey hairs

A
  • Hair doesn’t ‘turn grey’ - hair pigment is incredibly stable!!
  • Pigment stops being produced giving the appearance of white/grey.
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18
Q

Forceps

Collection and isolation of hairs

A
  • For individual hairs forceps can be used to isolate and collect
  • Careful damaging hairs with too much pressure!
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19
Q

Collection and isolation of hairs

Tape lift

A
  • Solves problems with forceps and most efficient when collecting hairs from large surface
  • Combings also possible.
  • Less precise than forceps
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20
Q

Collection and isolation of hairs

A
  • When collecting known samples, need to collect a representative sample due to the inherent variation.
  • Latest ENFSI (2015) recommendations suggest collecting 20 hairs from 5 head regions and package them separately.
  • Should be collected through a combination of plucking and combing.
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21
Q

Analytical workflow of hairs

A
  • Gross examination, recovery and collection
  • Preliminary evaluation of physical characteristics
  • Microscopic Techniques
  • DNA
  • SEM (Very occasionally TEM)
  • Spectroscopic Techniques - IR & Raman
  • Chromatographic Techniques & Mass Spectrometry
  • SEM can help show more morphological features
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22
Q

Toxicology from hair

Destructive chromographic techniques

A
  • GC-MS
  • ICP-MS
  • LC-MS
  • LA-ICP-MS
  • MALDI-MSI
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23
Q

Toxicology of hair

Minimmaly and non destructice spectroscopic

A
  • FTIR
  • Raman
  • FT-Rama
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24
Q

Elemental/chemical composition of hair

A
  • FTIR
  • Raman
  • FT-Rama
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25
Q

Elemental/chemical composition of hair

Destructive chromatographic

A
  • GC-MS
  • ICP-MS
  • LA-ICP-MS
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26
Q

Microscopic techniques for hair

A
  • Stereoscopic
  • Comparison
  • Polarised
  • Reflected light
  • Fluorescence
  • Brightfield
  • SEM and TEM -These are used if we think there is something more useful to find.
  • Thermal could be used rarely
27
Q

Macroscopic Observations

A

Macroscopical and microscopical examination of hairs reveals that they exhibit a wide variety of different morphological characteristics.
Those first evaluated at the macroscopic level include:
* Macroscopic colour - Colourless, blonde, red, brown or black.
* Length - Measured in absolute units e.g. mm
* General contour & curliness - Straight, wavy, curly, kinked etc.
* Approximate Diameter - Thin, medium or thick
* Macroscopic observations can be augmented with a stereoscopic microscope
* Colour may be evaluated using coloured backgrounds to provide contrast.

28
Q

Compound light microscopy

A
  • Hairs mounted in appropriate medium for examination with a compound light microscope with polarising filters.
  • Questioned and known hairs should be in the same media in order to provide equivalent contrast.
29
Q

What features can a compound light microscope evaluate for hair?

A
  • Colour
  • Cosmetic Treatments - Bleached or dyed
  • Thickness Range (Measured in um)
  • Cross-Sectional Shape e.g. Round, oval, flattening etc.
  • Shaft Irregularities e.g. Buckling or twisting
  • General Damage e.g. Split, frayed, broken, crushed, burned etc.
  • Biological Damage e.g. Insect bites, fungal or bacterial activity
  • Adhering Material e.g. Blood, nits, particles or residues
  • Non-Root Morphologies e.g. Rounded, cut, broken
  • Polarising filters allows us to get more information on what we’re looking at.
  • TEM doesn’t actually show anything useful or new and takes a lot of time and is expensive.
30
Q

Microscopic features of the cuticle

A

Microscopic features of the cuticle include:
* Colour - Colourless, or unnatural colour indicative of dyeing
* Pigment Granules - Presence or absence
* Thickness - Thin, Medium, Thick
* Inner Margin - Distinct/Indistinct, Smooth or Cracked
* Damage - Lifted, cracked or looped
* Scale Protrusion - Indistinct, minimal, prominent etc.

31
Q

Microscopic features of the cortex

A

Microscopic features of the cortex include:
* Pigment Granules: density, size, shape, aggregates, distribution , uniform, clumped, granular
* Texture - Fine, medium or coarse
* Cortical Fusi or Ovoid bodies
* Appearance of the medulla are also examined.
* Features of the root are examined if present - Growth stage, follicular Material, abnormalities.

32
Q

Comparison microscopy

Hairs

A
  • Hairs determined to be similar to each other should then be examined using a comparison microscope with transmitted light.
  • All instrumental parameters and preparation conditions should be exactly the same for comparison.
  • Head hairs typically exhibit more variation between people than any other type of hair, thus have the most discriminative value.
  • The results of a microscopical hair comparison cannot be fully peer-reviewed without a second examiner observing the hairs directly using a microscope. This should be carried out ‘blind’ to initial conclusions.
  • Final analysis unless more detail required (SEM/Fluorescence or Elemental Analysis) or root requires evaluation to explore possibility of DNA testing.
33
Q

Scanning electrion microscopy

Hairs

A
  • Employed when additional features of hair examined under the light microscopes warrant further analysis in higher resolution
  • Can directly examine the surface of the hair to highlight scales or physical damage to the hair
  • Combined with Secondary Electron, Backscatter Electron and EDX modes can also start to provide elemental data about the hair or residues etc. identified in the hair
  • No current examples of usage of TEM in forensic cases.
  • SEM only occasionally used.
34
Q

IR and Raman for hair analysis

A
  • IR & Raman micro-spectroscopy can be used to distinguish hair treatments and chemical damage along the length of a hair
  • Possible to distinguish between dye colours and brands.
  • Chemometrics and strong training required
  • Can distinguish between untreated hair and chemically damaged hair.
  • Allow us to compare an unknown to known a sample and trace back a hir sample to a different place.
  • You can look get different spectras for similar coloured hair.
  • You can distinguish between different spectral bands.
35
Q

What is a mass spectrometer

A

A mass spectrometer is a device for producing ions from a compound in order to obtain molecular weight and structural information.

36
Q

What can a mass spectrometer determine?

A
  • Atomic Mass
  • Molecular weight
  • Molecular Formula
  • Elemental Prescene
  • Chemical Structure
37
Q

What is mass spec used for?

A
  • Used for the detection and analysis of minute amounts of materials
  • Useful for detecting minute amounts within a hair.
  • Drugs substance of abuse, isotopes of the water we consume would vary, etc.
  • Providing evidence in tracking the movement of people and/or chemicals.
  • Only charged species are detected by mass spectrometry
    Ionisation is the conversion to a charged species
    Can pick out minute amounts of something within a material.
38
Q

Electron ionisation

A
  • Works on small volatile analytes
  • Uses GC or Probe on sample
  • <1000 mass
  • Hard ionisation
  • Can determine structure
39
Q

Chemical ionisation

A
  • Small, volatile analytes
  • GC or probe sampling
  • <1000 mass
  • Soft ionisation
  • Forms the molecular ion (M+H)
40
Q

Electrospray ionisation

A
  • Non-volatile peptides and proteins (hairs) analytes
  • LC to create ions for sample
  • <200,000 mass
  • Much larger mass can be detected
  • Soft ionisation
  • Can generate multiply charged ions
  • Have a sample onf interest taken from probe or gc column it travel flows through the capillary, a potential is applied across the cone which gives a charge to the droplets. The charged droplets on the surface are drawn into the mass analyser.
41
Q

ESI method

A
  • 3-6 kV is applied between the capillary tip and a ciricule cone electrode.
  • Solution of analyte flows through a capillary into MS.
  • Charged droplets leave the tip as a fine mist with a positive or negative charge.
  • Drawn into the mass analyser by circular electrode.
42
Q

Desoption Electrospray Ionisation (DESI)

A
  • Much softer interaction
  • Charged droplets are released an fired at a surface and when we do this we get the sample of the interest on the surface.
  • We ionise our sample using the highly charged droplets.
  • We can move the sample and scan across different areas of interest on surface.
  • This releases ions as it interacts with the surface and those ions are going to be released into the mass analyser.
  • Using it as a secondary interaction for a sample is a much soft interaction that allow sus to get much more information and not destroy anything.
  • We can detect contaminants on the surface
43
Q

Laser Desoption Electrospray Ionisation (LDESI)

A
  • Use: Plant & animal tissue imaging, live-cell imaging
  • No need for a matrix to assist desorption
  • Put more energy in
  • Take a mid-IR laser that hits the surface and creates a cloud of neutral molecules that chips of from the surface due to irradiating the surface.
  • Anything on the surface is chipped of from the laser but it isn’t useful at this point as the molecules are neutral.
  • Cloud is hit with the electrospray from above to cause ionisation.
  • The capillary creates the charged droplets that flow across with the neutral molecules created from the laser and they interact with one another.
  • This causes the neutral molecules to get ionsied so they get a charge and get detected in the mass analyser.
  • Sample itself is charged.
44
Q

Matrix assisted laser desorption/ionisation (MALDI)

A
  • Our sample is mixed in with the matrix mixture.
  • Ionise the matrix ions with laser, and the matrix is passes the charges to the sample.
  • This is useful because then you’re not destroying the sample so you’re maintaining the sample structure. This allows us to identify the sample in its original scale.
  • Can do large masses
  • When you ionise something you’re breaking it down into its smallest possible component, the way to stop that is by ionising the sample without chipping it off like in LDESI.
45
Q

Mass analysers

A
  • Choosing the right analysis type is vital to define what fragments can be identified and at what resolution to give a degree of discrimination often offset against cost, ease of use and size of instrumentation
  • This allows us the measure the fragments and determine what’s there.
  • Quadruple, time of flight and magnetic sector are the main types.
46
Q

Quadrupole

A
  • 500-2000 resolution
  • 2-2000 mass range
  • 0.1 amu mass accuracy
  • Low cost and reproducible results
  • Low resolution and mass discrimination
  • Quadrupole is when the charge is switched between the 4 poles and they get a path.
  • The control of the path allows us to discriminate different ions of different masses by the peed they moved down.
  • This mass analyser is more portable compared to other methods.
47
Q

Time of flight

A
  • 500-2000 resolution
  • 50 x 106 mass range
  • 0.0001 amu mass accuracy
  • Highest mass range and good limit of detection
  • Its large which is a disadvantage.
  • Time of flight is where you use the speed of differn ions of different sizes and how they change as they move down the tube. The smallest fragments arrive first and the largest fragment arrive later.
  • As a result, we get much higher resolution. Huge mass range as you can extend the tube and mass range. Best LOD.
48
Q

Magentic sector

A
  • Best resolution
  • 800 - 50,000 resolution
  • 2 - 15,000 mass range
  • 0.0001 amu mass accuracy
  • Expensive and large
49
Q

Tandem Mass Spectrometry

A
  • We have a standard analysis stage that we’re going through and separating ions only allowing a particular one through. We’ve ionised our material, separated it only allowing one through using the mass analsyer. That one ion is taken through and made to interact with a second fragmentation and after that we have another mass analysis stage detecting whats happened after the secondary fragmentation.
  • This is useful because we can get much more specify of what the element is with much more detail and a better resolution.
50
Q

Tandem Mass spectrometry underlyig principle

A
  • The underlying principle is to employ a first mass analysis stage to select a precursor (or ‘parent’) ion
  • Next excite this selected ion species (usually via a collision with a neutral ‘target gas’)
  • This causes it to fragment further to give one or more product
  • (or ‘daughter’) ions (plus neutral fragments)
  • Then employ a second mass analysis stage to determine the mass spectrum of the product ions.
51
Q

Tandem mass spectrometry

Alternative names

A
  • Often referred to by the alternative name ‘mass spectrometry/mass spectrometry’ (or ‘MS/MS’ or ‘MS2’)
  • Frequently extended so as to perform additional ‘tandem’ experiments in sequence, e.g. by mass selecting a product ion formed in the first fragmentation stage and exciting by further collision
  • Determining the mass spectrum of the third generation (‘granddaughter’) ions thus formed
  • This is called ‘MS/MS/MS’ or ‘MS3’
52
Q

Tandem in space

A
  • Mass analysis stages are physically separated from each other spatially so that they occur in different regions of the overall instrument. Can be any mass analysers and even use two different ones into order to give the most precise information.
  • As a results these require a lot more space for the extra instrumentation!!
  • These MS/MS techniques have greater mass spectral specificity that can be obtained with respect to target analytes
53
Q

Drug concentrations in hair are considerably lower than those found in other matrices (e.g., blood), so MS/MS is often used:

Tandem in space

A
  • Combined with Multi-sectional (or segmental) analysis
  • Combined with chemometrics
  • Multiple stages with the same sample allows us to look at the concentration of a drug at different stages of a ahir.
  • This builds on the idea that hair grows 1cm a month which gives a goood timeline.
  • If a hair is found you could detect substances of abuse within particular timelines to give real information.
54
Q

Isotop Ratio mass spectrometry

A
  • Mass Spectrometry can identify certain elements more clearly due to isotopes.
  • e.g. Cl exists in two stable isotopes so both can always be identified in a more complex molecule e.g chloroethane.
55
Q

Ratio of isotopes

Oxygen

A
  • This is useful as it allows us to identify it, a lot of molecules have this.
  • Oxygen has a different amount of naturally occurring isotopes, so we can look at the ratio of oxygen isotopes is used in the oxygen used to produce our hairs. This is useful because we have oxygen in H2O or anything we consume.
  • This ratio is reflected exactly within our hair. We can identify where someone has been based on the oxygen they’ve consumed from water, based on geographic location which allows us to trace the trace evidence to where the person has been.
  • Looking at isotope ratios of elements in the hair can be used to identify locations where an individual may have travelled based on changes in drinking water isotopes in different locations
  • Our hair reflects what we consume.
  • A lot of common elements have more than one natural abundance.
56
Q

Interpretation of hair evidence

A
  • Hair is different than many forms of trace evidence in that it is of biological origin. As a result, hair exhibits significant amounts of morphological variation both within a given individual & between individuals
  • Variation between individuals provides the discriminating potential for forensic hair comparisons. i.e. Hair from different individuals may appear different & therefore it is possible to distinguish hairs from different individuals on the basis of their macroscopic and microscopic morphology
  • However, hair cannot be individualised on the basis of these physical characteristics alone - using microscopy alone can’t determine if an unknown originates from a specific individual.
57
Q

There are three main conclusions that can be drawn from the interpretation of microscopical hair analysis alone:

A

There are three main conclusions that can be drawn from the interpretation of microscopical hair analysis alone:
- Association
- Inconclusive
- Exclusion

58
Q

Associtation conclusion of hair evidence

A

Questioned hair can’t be distinguished from known sample

59
Q

Factors strengthening association conclusion for hair evidence include:

A
  • Distinctive cosmetic treatments (e.g. dye)
  • Abnormalities
60
Q

Factors weakening association conclusion for hair evidence include:

A
  • Short hairs
  • Incomplete hairs
  • Colourless/Pigmented
61
Q

Inconclusive conclusion for hair evidence

A
  • Questioned hair exhibits some similarities & some differences with a known sample, but limiting factors are complicating the comparison
  • Hairs have been exposed to different environmental conditions - buried vs. direct sunlight
  • If reference sample is in different conditions coparerd to the sample been found it can change the hair and cause differences.
62
Q

Exclusioln conclusion for hair evidence

A
  • Questioned hair exhibits a meaningful difference compared to a known source
  • To improve this confidence, important to collect many hairs from multiple sub-areas for known sample
  • Hard to be certain unless from different ancestral characteristics eg asian vs european hair.
63
Q

Factors affecting transfer and persistance of hair evidence

A
  • Wearing a hat
  • Animal hair transfer
  • Washing hair / clothes
  • Artificial dying
  • Secondary transfer
  • In almost all studies found that transfer and persistance of hairs are complex issues with far too many variables to be able to predict the absolute number of hairs expected to be transferred or remain on an object in a real-world scenario.
64
Q

Reference collections

A
  • As with other forms of trace evidence, reference collections for hair are of vital importance.
  • Basic lab human hair reference collection will include:
  • Different ancestral groups
  • Different cosmetic treatments
  • Exhibitng different diseases
  • Different locations on body
  • Different damage types
  • Degraded in different ways
  • Should be updated regularly and stored safely for reference and comparison in any forensic microscope lab for hairs.

Trace evidence (22 decks)

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