Hairs Flashcards
Why is hair a great form of trace evidence?
- its found on all humans and animals
- it is constantly being produced and shed
- it is easily overlooked by criminals
- it is readily transferred from one person/object to another person/object
- highly stable - resisting both physical and chemical degradation
- can be distinguished from each other and with DNA testing
Why is it not general practice to differentiate hair using chemical techniques?
All true hairs have the same basic chemistry
What does looking at isotope ratio of elements in hair show?
- 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
What are the three types of human hair?
- lanugo
- vellus
- terminal
What are lanugo hairs?
- hairs that are formed in utero
- fine and unpigmented
- typically shed before or shortly after birth
What are vellus hairs?
- fine, short, unpigmented/lightly coloured
- on almost all skin surfaces (forhead, nose, ears, bald scalp)
- not found on palms of hands or soles of feet
What are terminal hairs and what are the two types of terminal hairs?
Macroscopically visible on children and adults
1. primary - head, eyelash, eyebrow
2. secondary - pubic, underarms, beard
What are the three main histological layers of hair?
- cuticle - outermost layer
- cortext - main bulk of hair
- medulla - innermost layer of hair shaft
What is the cuticle most responsible for?
chemical resistance
What is the cortext most responsible for?
mechanical properties
* contains most of the pigment granules giving hair its colour
What is the medulla for?
not well understood
* not present in all hairs
What is the cycle that every hair goes through?
- anagen - active growing phase of hair extending progressively from the follicle root outwards
- catagen - transition phase when growth slows and eventually stops
- telogen - resting phase when minimal force is required to remove hair and natural shedding occurs
How does hair go grey?
Pigment stops being produced
How is hair collected and isolated?
- for individual hairs forceps can be used
- tape lift can be used to remove the pressure when using forceps - most efficient when collecting hairs from large surfaces
- combing
- 20 hairs from 5 head regions should be collected and packaged separately - plucking and combing (gives variation)
What is the analytical workflow for hair?
- gross examination, recovery and collection
- preliminary evaluation of physical characteristics
- microscopic techniques
- DNA
- SEM (sometimes TEM) - morphological features
- spectroscopic techniques - IR and Raman
- chromatographic techniques and MS
What microscopic techniques should be used for hairs?
- optical: stereoscopic, reflected light, comparsion, fluorescence, brightfield, polarised
- SEM and TEM
What macroscopic observations should be looked for?
- macroscopic colour
- length
- general contour and curliness
- approximate diameter
What features should be looked at when using a compound light microscope?
- colour
- cosmetic treatments
- cross-sectional shape
- biological damage
- adhering material
- thickness range
- general damage
- non-root morphological
What microscopic features of the cuticle are looked at when using a compound light microscope?
- colour
- pigment granules
- inner margin
- thickness
- damage
- scale protrusion
What microscopic features of the cortex are looked at when using a compound light microscope?
- pigment granules - density, size, shape
- texture
- appearance of medulla
- root features if present - growth stage, follicular material, abnormalities
Comparision microscope analysis of hairs
- head hairs have the most discriminative value
- results of a microscopical hair comparision must be completed with a second examiner and should be blind to initial conclusions
- final analysis unless more detail is required or root requires evaluation to explore DNA testing
Scanning electron microscopy of hairs
- employed when further analysis is required
- can examine the surface of hair to highlight scales or physical damage to the hair
- combined with SE, BSE and EDX modes - provide elemental data about hairs or residues
IR and Raman analysis of hair
- used to distinguish hair treatments and chemical damage along the length of hair
- possible to distinguish between dye colour and brands
- chemometrics and strong training required
What are the steps involved in tandem mass spec?
- employ a first mass analysis stage to select a precursor ion
- then excite this selected ion species (usually by collosion with a neutral target gas)
- this causes it to fragment further to give one or more product ions plus neutral fragments
- then employ a second mass analysis stage to determine the mass spectrum of the product ions
What is the second generation ions mass spectrum called?
MS/MS or MS^2
What is the next step of tandem mass spec when it is extended to perform additional tandem experiments?
- mass selecting a product ion formed in the first fragmentation stage and exciting by further collision
- determining the mass spectrum of the third generation ion formed
What is the mass spec of the third generation ion called?
MS/MS/MS or MS^3
What are the two configurations of tandem MS?
- tandem-in-space
- tandem-in-time
What is tandem-in-space?
- mass analysis stages are physically separated from each other spatially so that they occur in different regions of the overall instrument
- employ ion beam-type mass analysers
- require a lot more space for extra instrumentation
- greater mass spectral specificity
- can see when someone has consumed drugs knowing that hair grows around 1cm/month
What is isotope ratio mass spec?
- can identify certain elements more clearly due to isotopes
- can be used to identify locations where an individual may have travelled based on changes in drinking water isotopes in different locations
How does isotope ratio mass spec work?
- converts samples of the hair into oxygen gas and then perform isotopic analysis by MS
- determine the levels of isotopic enrichment of the possible oxygen isotopes
What does it suggest if the isotope ratio was the same as reference samples of hair from different areas?
individual has died in the same region that they consumed water in
What would it mean if the isotope ratio was different for two samples?
the investigators could rule out some potential locations
What are the three main conclusions that can be drawn from the interpretation of microscopical hair analysis alone?
- association
- inconclusive
- exclusion
What does an association conclusion mean?
- questioned hair cannot be distinguished from known sample
What are some factors that stengthen an association conclusion?
- distinctive cosmetic treatments
- abnormalities
What are some weakeness with an association conclusion?
- short hairs
- incomplete hairs
- colourless/pigmented
What does a inconclusive conclusion mean with hair?
Questioned hair exhibits some similarities and some differences with known sample, but limiting factors are complicating the comparision
What are some factors which limit the inconclusive conclusion?
environmental conditions - buried vs direct sunlight
What does a exclusion conclusion of hair mean?
Questioned hair exhibits a meaningful difference compared to a known sample
How can you improve an exclusion conclusion?
collect many hairs from multiple sub-areas from known sample
What can effect the tranfer and persistence of hairs?
- object texture
- wearing a hat
- animal hair transfer
- hairloss
- washing
- artificial drying
- secondary tranfer
- fingernail scrapings
- migration
What type of reference samples are collected?
- different ancestral groups
- different cosmetic treatments
- exhibiting different diseases
- different locations on the body
- different damage types
- degraded in different ways
