fibers and hairs

Dr. Sangeetha BalakrishnanPG Department of ChemistryWomen’s Christian College

Chennai – 600 006

Fibers and Hair

4 February, 2017

Forensic Science PCH/NM/01

Fibers• Fibers are a trace evidence.• Direct Transfer: Transfer of fibers directly

from victim to suspect or suspect to victim.Eg: fiber from woolen sweater of victim attacker

• Secondary Transfer: Fibers are transferred from the original source to a suspect and then to a victim. Eg: carpet fiber victim attacker

Classification of FibersFibers

Natural Synthetic Mineral

AnimalAnimal PlantSilk – silkwormCashmere – goatsAngora – rabbits

Obtained from hair/fur of the animals.Animal fibers are made of proteins.

Plant fibers are made of cellulose.

Seeds - cotton

Fruits – Coir (coconut)

Stems – hemp, jute, flax

Leaves – banana, manila

(man-made fibers)Mineral fibers are neither made of proteins nor of cellulose.

They are obtained fromnaturally occurring minerals.

Asbestos fiber

Banana Tree

ManilaTree

Manila envelope Manila envelope Manila twine

Asbestos Fiber

Fiber Characteristics

Fiber AnalysisCharacteristic features of fiber forensic analysis:

1. Size

2. Cross Section

3. Colour

4. Crimp

Analysis of Fibers1. Observation of Fiber Cross Section -

Microscopy• Type of cross section helps identify the fiber.• Fibers made with end use in mind!

Trilobal cross-section: more volume, sheen and better resilience.True delta cross-section: extra brightness and shine.Round cross-section: smooth silky luster.Hollow cross-section: light weight and improved insulation.

2. Diameter• Round fibers: one diameter• Many fibers are not round! • Oval and elongated fibers have more

than one diameter!• Both the diameters are recorded!

3. Delusterants• Finely ground materials added to the

chemical mixture from which the fiber is made.

• Act to reduce the fiber's shine, by scattering light.

• Eg: Titanium dioxide• Delusterants of different shapes and sizesadded to the pre-fabrix mix.• Observation of these delusterants in the

unknown evidence and known evidence.

4. Refractive Index• Submersion Method.• The shape of the fiber may cause it to

have more than one refractive index.• Reason: light travels at different speeds in

the fiber depending on whether it travels through the length and diameter of the fiber.

RI1

RI2

5. Colour• Naked eye observation: subjective! • Metamerism.Visible Spectrophotometer.• Dyes: even, uniform colouration• Pigments: Uneven colouration.

Chemical Analysis of Fibers1) Fourier Transform Infrared

Spectroscopy (FT-IR)• non-destructive fiber analysis• identifies the chemical composition of

fibers.• not just the class, but also the sub-class to

which the fibers belong!• Nylon 6-6 and Nylon 6-12.

2) Pyrolysis Gas Chromatography

• Requirement: Just about 1/8th of a fiber.• Destructive analysis mode.• Betterthan FT-IR in distinguishing closely

related fibers.

HAIR IN FORENSIC ANALYSIS

Hair• Also a trace evidence. Like fiber.• Importance to forensic scientists: Easily transferred.Multiple transfers; help create a trail.It is stable; can be found years after

someone is buried in a casket.Mostly resistant to chemical attack.Has mitochondrial DNA. Unique

identification!

What is hair?

• Hair is found only in mammals.• Hair is an outgrowth of the epidermis.• Hair originates at follicles.• As hair begins to grow, it is soft. When it reaches the epidermis, it hardens into keratin.• Papilla: present at the end of the follicle. Supplies nutrients to hair.• Sebaceous gland: secretes oil tokeep hair conditioned.

Hair - The Basics (cont'd)• Hair absorbs nutrients and "materials" at

follicle as it grows. These are supplied by the blood vessels.

• At the surface of the skin, hair is keratinised; it is dead. It no longer receives supplies from the blood vessels.

• Hair growth: hair is "pushed up".• "material" absorbed by hair at follicle

remains in hair as it is "pushed up", and until the hair is cut or falls out.

• Example: Tetrahydrocannabinol absorbed from marijuana. --->Drug analysis on hair!

The Structure of Human Hair• Root: widest end of the hair.It is the part that was growing in the follicle.• Shaft: From the root to the tip, it tapers.• Tip: End of the hair away from the root.Hair is narrowest at the tip.

Hair has different diameters depending on where it is measured.

The Structure of Human Hair (cont'd)cuticle• outermost layer• made of keratin• not smooth• overlapping scales.

cortex• middle layer• humans: most prominent• made of spindle cells• melanin: here!

medulla• innermost layer• in humans: 4 types found.

Microscopic Image of Hair

Cuticle of human hair showing overlapping scales.

Five types of human medullae

The Life Cycle of Hair• 1st Stage: Anagen Stage lasts around 1,000 days~90% of human hair is in this stage. period of active growth; follicles divide, deposit

materialwithin the hair.

• 2nd Stage: Catagen Stage hair grows and changes (grey!)~ 2% of hair in this stage.

• 3rd Stage: Telogen stagehair follicle is dormant; hairs easily lost.~ 10 - 18% of hair in this stage.

Racial Differences in Human Hair

Life is interesting!

Human vs. Non Human HairCharacteristic Human Hair Animal Hair

Pigmentation pattern Denser toward the cuticle

Denser toward the medulla.Often found in solid massses called ovoid bodies.

Colour Usually one colour along the length

Abrupt colour change in banded patterns.

Medulla Small Larger

Medullary Index(dia of medulla/dia of entire hair)

0.33 or less 0.5 or greater

Cuticle flat, narrow, uneven.

rodents, bats: coronal cuticle(stack of crowns)cats,seals: spinous(like petals)

Hair in a Forensic Investigation• Hair collection: plucking, shaking, scraping, placing

tape.• Objective: unknown to known evidence (!)• Most cases: hair is a class evidence.• Except: DNA profiling.• Great degree of variation on different parts of the

same head!

• Hair can be:1) Head hair, 2) eyebrows and eyelashes, 3) beard

and moustache, 4) underarm hair, 5) body hair, and 6) pubic hair.

Needed: About 2 dozen hairs for comparison!Known sample: include dyed, bleached, grey hair!

Hair Analysis.1) Human or animal hair.2) Macroscopic Investigation: length,

colour and curliness.3)Microscopic Investigation: pattern of the

medulla, pigmentation of the cortex, types of scales on the cuticle, refractive index.

Use: Comparison Microscope.

Locard's Principle at work.

Hair Analysis...cont'd• Microscopic Investigation:Phase contrast microscopy: finer details;

better contrast.Fluorescence Microscope: hair that has

been treated with dyes.Electron Microscopes: about 50,000 times

magnification.surface or interior of hair sample.

Substances in the hair shaftNeutron activation Analysis:• 14 different elements in a 2 cm long hair strand• antimony, argon, bromine, copper, gold,manganese,

silver etc: identify and quantify.• Individualisation!!!• Probability of two people having the same

concentration of all the elements is RARE!

When hair is plucked - blood and tissue; identify blood type.

DNA Analysis:• Hair follicle contains mitochondrial DNA.