Lecture 15&16 - Hairs Flashcards
can microscopical hair examination lead to individualisation
no, it can’t be said that an known hair comes from a specific person based on microscopy alone
how can the analysis of hairs lead to individualisation
recovery of DNA from the follicle if present
but DNA is not trace evidence
give 6 reasons why hair is a good form of trace evidence
found on all humans and mammals and in large amounts (estimated at 100,000-200,000 on the scalp)
easily overlooked by criminals clearing up
easily transferred from a person to another/object
constantly being produced and shed
very stable - resistant to chemical and physical degradation
can get DNA from follicles
what two bits of information can hairs give that help with investigations
investigative leads and help with reconstruction of events
what are hairs made of
proteins - specifically keratins
which are very robust so allow persistence
why is it difficult to differentiate between hairs from different sources
therefore what techniques are more useful than chemical methods
because all true hairs have the same basic chemistry so chemical techniques are not the most useful
elemental analysis and spectroscopic techniques
what can looking at the isotope ratios of elements in hair provide and how is this done
can give locations an individual has travelled to based on the the change in drinking water at different locations
diet and use of substances of abuse can also affect the elements hairs are made of
done using mass spectrometry
what are the three types of hairs
Lanugo = formed in uterus, shed before or shortly after birth - rarely found unless a newly or unborn child is involved
Vellus = fine and short (1mm approx), tend to be lightly coloured or unpigmented, present on almost all skin surfaces like nose, ears, forehead.
terminal = hairs macroscopically visible
where are vellus hairs not found
palm of hands and feet
what are the two types of terminal hairs
primary hairs = head, eyelash, eyebrows
secondary hairs = pubic, underarm, beard
where are the most commonly analysed in forensic hairs from on the body
head or pubic hair
describe the phases in the growth of a hair
anagen = active growing phase of hair from root outwards from skin
catagen = transition phase where growth slows and stops
telogen = resting phase where minimal force is required to remove hair and natural shedding occurs
what is the shedding of hair affected by
a range of environmental factors e.g weather
what are the 4 layers of a hair
cuticle = outermost layer
cortex = main bulk of hair
medulla = innermost layer - NOT ALWAYS PRESENT - not well understood/studied
cell membrane complex = interface between cuticle and cortex
what is the cuticle of a hair responsible for
largely for the chemical resistance from the environment allowing hairs to persist
what is the cortex of a hair responsible for
the mechanical properties of a hair
most pigmentation here allows for colour
what is the purpose of a hair follicle
this is where the hair grows from - changes shape and size
the presence or not of this could indicate the nature of how the hair was removed - pulled or cut or naturally shed
what phase of the hair cycles are most and least hairs in
most = anagen phase
least = telogen phase
where does the variation in hair growth between individuals lie
age
dependent on the individual
ancestral groups
what lead to the appearance of grey hairs
pigment in hairs stops being produced
what could give characteristic features in the analysis of hairs
use of bleach or hair dye
heat damage
other hair products
what are the two main methods seen in the collected of hair evidence
forceps = good for individual hairs but can damage hair if too much pressure used (seen by bulging of the hair under microscope)
tape lifts = good for collecting hairs from large SA and prevents damage from forceps
what is beneficial when analysing hair evidence from suspects and how is this done
what is the recommended amount from ENFSI guidelines
a representative number of hairs being taken by combing or plucking due to variation even within an individual
combing = better as less pressure and less damage likely
recommended 20 hairs from 5 different head regions
what is the updated analytical workflow when analysing hair evidence
- gross examination, recovery and collection
- prelim evaluation of physical characteristics
- microscopic techniques
- DNA analysis
- SEM (maybe TEM)
- IR and Raman - spectroscopic techniques (non destructive)
- chromatographic techniques and mass spec (destructive)
what is the benefit of using SEM in hair analysis
gives morphological features and surface analysis
at what stage in the analytical workflow of hairs do we normally stop at
microscopic techniques
what microscopic techniques are useful in the analysis of hair evidence
stereoscopic
comparison
polarised
reflected light
bright field
these two only used when more info is needed:
fluorescence
SEM - electron microscopy not light (rest are light)
what 4 characteristics of hairs can be revealed at macroscopic level (initial examination)
macroscopic colour - blonde, red, black, brown
length - in mm
general shape and curliness - straight, wavy, curly, kinked
approx diameter - thin, medium or thick
what can be used to help suggesting the colour of a hair
different background giving more contrast
what can macroscopic observation be improved using
microscopic techniques
what are the first two types of microscope often used in hair analysis
compound light
polarised light
in order to make comparisons how should the unknown and known hairs be visualised
under microscopes with the same settings and on the same mounting media
how can different mounting media affect the visualisation of hairs under microscopy
the difference in refractive index between the sample and the mounting media affects the contrast and therefore how well the sample is to be seen
what 9 features of hair can be seen under microscopes that help with the discriminative value of hair evidence
colour
cosmetic treatment
thickness range (micrometers)
cross sectional shape
shaft irregularities
general hair damage (split, frayed, broken)
biological damage = insect bites, fungal or bacterial activity
material adhered to it - blood, nits, particles/residues
non-root morphologies - cut, rounded or broken
what does microscopic analysis of the cuticle include
colour - indicates use of dyes
presence or absence of pigment granules
inner margin analysis
thickness - thin medium thick
damage
scale protrusion
what does microscopic analysis of the cortex include
pigment granules = size, shape, density, distribution
texture - fine, medium, coarse
ovoid bodies and cortical fusi
the presence of the medulla
what can be determined from the root if it is present (microscopically)
growth stage
follicular material
abnormalities
what type of microscopy should be used when deciding similarity between two hairs
comparison
all instrumental parameters need to be the same on either side
what type of hair have the most discriminative value and why
head hairs
as they tend to have more variation between individuals than other types
how should the secondary analysis of hair evidence be carried out
by a second examiner using a microscope that is blind to the conclusions from the first examiner
what type of analysis is done if microscopic analysis of hairs doesn’t give sufficient evidence
SEM analysis
elemental analysis
fluorescence analysis
DNA testing (not trace though)
what can hair analysis using SEM provide
higher resolution
gives surface analysis giving physical damage, scales on hair
what 3 modes of SEM can give elemental analysis of hairs and the residues on it
secondary electron
backscatter electron
EDX
what are IR and Raman spectroscopy used for in hair analysis
what is the name of the method used in the statistical analysis of IR and raman data
looking at hair treatments and chemical - can tell is hair is untreated
telling which dyes may have been used
upon comparisons with known samples
chemometrics
what information can be gathered from the mass spectrum of a hair
atomic mass
molecular formula
molecular weight
elemental presence
chemical structure (from fragmentation patterns)
what can information gathered from the mass spectrometry in criminal investigations
substance identification
tracking movements of people due to the substances present
info on trace amounts of things
what type of species are detected by mass spectrometry
charged species, this is achieved by ionisation in the first stage of mass spec
what are 4 types of ionisation in mass spec
electron = hard, good for structural determination due to fragmentation = volatile species
chemical = soft, good for molecular ion and M+H ion identification = volatile species
electrospray = non volatile species = good for multiply charged ions
MALDI (matrix assisted laser desorption ionisation) = highest mass - good for keratin identification = non volatile species
briefly explain ESI (electron spray ionisation)
analyte flows through a capillary into MS drawn into the mass analyser by a circular electrode
a voltage is applied between capillary tip and circular electrode
creates charged species that leave the capillary tip as a fine mist with a +ve or -ve charge
in mass spec what is DESI
desorption electrospray ionisation
spray onto the surface of the sample creating charged species that go into the MS inlet
doesn’t destroy sample
can detect surface contaminants
in mass spec what is LDESI
laser desorption electrospray ionisation
an IR laser used to ablate the sample creating a cloud of neutral molecules
cloud is then hit with electrospray = ionisation
ions collected in MS
no need for a matrix - can use live tissue
why is mass spec beneficial over IR and Raman but also why is it not?
good = ir and raman are likely to have a lot of noise to detect trace amounts
bad = destructive of sample
what is MALDI
sample is mixed with a matrix without making chemical changes to the sample
laser charges the matrix not the sample which passes charge onto analyte
not destructive of sample - structure is maintained
what are the three types of analyser most using in mass spec for hair analysis
quadrupole = reproducible and low cost relatively, portable, low resolution and mass discrimination
TOF - time of flight = best mass range, high accuracy, good LOD, measure speed of analyte, large instrument
magnetic sector = best resolution, high accuracy, expensive and large
what is Tandem Mass Spectrometry
also called mass spectrometry/mass spectrometry, MS/MS or MS^2
only allows a particular ion of interest through to analyser
do first mass analysis = parent ion is let through or selected
then excite this species so fragmentation occurs = daughter ions and neutral fragments
second mass analysis = then select the fragments you want to detect from daughter ions
cna also go further and do it 3 times = MS^3 or MS/MS/MS
what are the two types of tandem mass spectrometer
tandem in space
tandem in time
explain what is meant by a tandem in space mass spectrometer and why they are beneficial
the mass analysis stages (however many there is) are physically separated so they occur in different regions of the instrument
different types of analyser can be used at each stage depending on your goal
these instrument are a lot bigger than normal but have much greater mass spectra specificity
when is MS/MS often used
in analysis of drug concentration in hair as these are very low concentration compares to other matrices they are observed in e,g blood
why may two peak be seen for one element in the mass spectrum
due to different possible stable isotopes of that element
the peak height is the ratio of these isotopes in the mixture
what is the name of the peak slightly above the M+ ion peak
MH+ ion peak
the molecular ion peak plus a hydrogen atom - tends to happen in electron ionisation methods
what can looking at the isotope ratios of elements in the hair be used for
identifying the location an individual may have travelled based on the change in drinking water isotopes at different locations
a lot of chemical elements have more than one natural abundance
what are the three main conclusions that can be drawn from microscopical hair analysis
association = questioned can’t be distinguished from known
inconclusive = questioned hair has some similarities and some differences but there are limiting factors cause complications
exclusion = questioned hair has meaningful differences from known
what is the problem with hair evidence
hair can’t be individualised on the basis of physical characteristics alone - microscopy can’t determine if a hair come from a specific individual
why is hair evidence good
there is a large amount of morphological variation within individuals and between individuals which give discrimination potential of forensic hair comparisons
what factors strengthen and weaken the association conclusion
strengthen =
distinctive cosmetic treatment
abnormalities
weaken
short hairs
incomplete hairs
colourless not very pigmented
what is an example of something that can give an inconclusive conclusion
hairs being exposed to different environmental conditions e.g buried vs direct sunlight
how can the confidence in an exclusion conclusion be improved
by collecting many reference hairs from multiple sub areas in the person
what things affect the transfer of hair evidence
texture
hair loss rate
wear of hats
washing
artificial dying
secondary transfers
weather
substrate type
there are too many external principles to predict the number of hairs expected at a scene
what must a labs human hair reference collection include
different:
ancestral groups
cosmetic treatments
diseases
body locations
damage types
degradation types
to be used for comparisons and should be updated regularly
