cvb215 Flashcards
Locard’s Exchange Principle
when two objects come together there is always an exchange of material
Factors that affect transfer and detection
force or pressure applied; nature of contact; types of surfaces; length of time of contact
What is the priority at a crime scene?
examine/process the deceased in order to remove body as quickly as possible (respect to the deceased, post mortem investigation
Common Knowledge Rule
information to help in understanding as opposed to relying on general knowledge and common sense
What is a negative test?
the substance tested is NOT the substance or too dilute or minute to detect
What are the limitations of trace DNA?
Unable to determine:
Source of DNA (from skin cells or blood?)
How trace DNA was deposited (primary or secondary transfer)
When trance DNA was deposited (persistence)
What are the three hair growth stages, and are they suitable for DNA analysis?
Anagen - active growth stage; suitable for nDNA analysis
Catagen - transitional growth stage; suitable for nDNA anlysis
Telogen - cessation of growth; may be suitable for nDNA analysis
What is primary transfer?
transfer from original source to object or person; implies direct association
What is secondary transfer?
transfer from original source to secondary source to object or person; implies indirect association
What is a positive test?
the substance tested MAY be the substance -> non confirmatory
What is a false positive?
an apparent positive test result; slower reaction time and different colour change
What are the presumptive tests used for blood?
TMB, Luminol, LCV
What are the presumptive tests used for seminal fluid?
AP (acid phosphate)
What is the presumptive test used for saliva?
Phadebas test
Trace DNA
cellular material transferred from a person to another object or person - located on objects contacted by skin
What are the types of transfer in trace DNA?
Rates of shedding (individuals vary in the rate they shed skin cells); Retention (depends on surface, environment, activity); Persistence (time since deposition is UNABLE to be determined)
Primary Crime Scene
A place where the offence occurred (e.g. house where murder occurred)
Secondary Crime Scene
A place other than where the offence occurred but where there is likely to be evidence relating to the offence (e.g. offenders vehicle, bushland where body was located)
What types of descriptions are used in impression evidence analysis?
partial or full impression; size and shape; description of class characteristics; description of any individual characteristics; substrate
Class Characteristics
intentional and unavoidable; repeat during the manufacturing process; shared by one or more shoes or tyres; include specific shapes, design, and size
Individual Characteristics
randomly occurring accidental damage; material randomly added or taken away from shoe outside or tyre; causes or contributes process and wear
Exclusion
The highest degree of non-association expressed in comparison examinations
Sufficient differences between characteristics in the impression and known item
The known item was not the source or and did not make the impression
Chromatography
separation technique that is based on the interaction of a compound with a stationary phase, and a mobile phase
Stationary Phase
a layer or coating on a supporting medium that interacts with the analyte
Mobile Phase
an inert gas or a solvent that flows through the supporting medium
Two types of Planar Chromatography
paper chromatography and thin layer chromatography
Two types of Planar Chromatography
paper chromatography and thin layer chromatography
How is Separation Achieved?
Components in the mixture interact with the stationary and mobile phases in different ways with the extent of interaction depending on physical properties of the compounds
Gas Chromatography
mobile phase is a gas; principal driving forces for separation is the difference in boiling points and polarities of compounds in the mixture
Liquid Chromatography
mobile phase is a liquid; driving force for separation is the solubility of the sample components in the mobile phase and their partitioning between this phase and the stationary phase (column)
Adsorption Chromatography
Separation is based on differences between the adsorption affinities of the sample components towards the surface of stationary phase.
Equation for Partitioning Coefficient
Kd=Cs(stationary phase)/Cm(mobile phase)
When is Partitioning Coefficient Optimum
With Kd value between 1 and 5; <1 separation is too poor; >10 separation is slow
Solute Retention
the strength of its interaction with the mobile and stationary phases
Capacity Factor
A universal measure of solute retention; k’=AreaVolume(stationary phase)/AreaVolume(mobile phase)
Retention Time (tr)
characteristic time that a particular analyte takes to pass through the system
Resolution (Rs)
measure of the separation
Peak Fronting Band Shape
High concentration of the sample is injected
Peak Tailing Band Shape
The analyte molecules are strongly retained on the stationary phase.
Eddy Diffusion
as solute molecules travel through the column, some take longer path than the others due to the imperfect packing of the stationary phase particles in the column. Causes band broadening
Longitudinal Diffusion
A band of analyte molecules contained in the injection solvent will tend to disperse in every direction due to the concentration gradient at the outer edges of the band; concentration of analyte is less at the edges of the band than at the center. This causes band broadening.
Properties of a Good Detector
high sensitivity, universal response, fast response, low background noise, ease of operation
Flame Ionization Detector (FID)
GC detector; analyte molecules eluting from the column are burned in a flame and produce electrons. This electric current is amplified and measured; high sensitivity; destructive
Spectrophotometric Detectors
UV-VIS detector. Used in liquid chromatography (HPLC); Infrared detector. Used in GC;
Fluorescence detector. Used for analytes that give fluorescence
Bioactive Molecule
Any molecule that has a biological effect on a human or animal body, like amino acids, proteins, and peptides
Amino acid
Organic acids that have an amino group bonded to the α carbon atom, next to a carboxyl group. Always a chiral compound
Acid-Base Properties of Amino Acids
exist as dipolar ion (zwitterions) that have both formal positive and formal negative charges. The overall charge is neutral; amphoteric: they can react as either an acid or a base
Isoelectric Point
Point at which a compound is electrically neutral.
Electrophoresis
method to separate molecules on the basis of their charge and size; Positively charged molecules will move towards the cathode while negatively charged molecules move towards the anode.
What affects Migration Rate
Depends on the strength of the electric field; ionic strength, viscosity, and temperature of the medium in which the molecules are moving also affect the migration rate of the molecules
Equation for Migration Rate
v’=charge/mass
Paper electrophoresis
amino acid and nucleotides
Polyacrylamide gel (PAG) electrophoresis
proteins and nucleic acids
Agarose gel
very large proteins, DNA
Tracking Electrophoretic Movement
Proteins and DNA are negatively charged and will move to the anode. Bromophenol blue is added to the sample, it is a negatively charged dye and therefore migrates in the same direction as a protein or DNA and track the extent of the electrophoretic movement
DNA staining
Proteins and DNA are colourless, so visualising agent (dye) that binds to their structure is added to the buffer or the gel; for proteins - coomassie blue (binds to proteins), for DNA - ethidium bromide (binds to DNA helix)
Isoelectric Focusing
pH gradient formed during electrophoresis, so t a pH value, the protein reaches its isoelectric point (pI) and carries a zero net charge, the protein molecules stop moving and become focused in a narrow zone on the gel
Properties of Nanomaterials
enhanced electrical and heat conductivity; magnetic properties; optical properties - colour changes with size
Top Down Synthesis of Nanomaterials
size reduction from bulk materials
Bottom Up Synthesis of Nanomaterials
material synthesis from atomic level
Nanoparticle Synthesis
Colloidal chemical method
Colloidal Chemical Method
a metal salt is reduced leaving nanoparticles evenly dispersed in a liquid; aggregation is prevented by the introduction of a stabilising reagent that coats the particle surfaces; particle size ranges from 1-200nm
Preparation of Gold Nanoparticles
chemical reduction of tetrachloroaurate (HAuCl4) using a reducing agent such as sodium citrate (Na3C6H5O7); sodium citrate reduced the gold salt (Au3+) to metallic gold (Au0); neutral gold atoms aggregate into seed crystals; seed crystals continue to grow and eventually form gold nanoparticles
Preparation of Silver Nanoparticles
prepared by chemical reduction of silver nitrate; AgNO3 + NaBH4 -> Ag0 + 1/2H2 + 1/2B2H6 + NaNO3; different colours from the bulk silver metal due to the fact incident light create oscillation in the free electron cloud on the surface of nanoparticles and cause them to absorb electromagnetic radiation at different wavelengths
Carbon Nanotube Preparation
Prepared by arc discharge between carbon electrodes
what are Nanosensors
small devices made of nanomaterials that can detect optical or electronic signals
Biosensors use
can be functionalised with a recognition layer to selectively capture and detect target analytes. uses one monoclonal antibody, a secondary antibody and a magnetic nanoparticle
Magnetoresistive Sensors
made of conductive chips and were initially used as elements in computer hard drives; used for the detection of proteins in blood and saliva directly without extraction
BPA
Blood Pattern Analysis
ABC
Appearance, Behaviour, Context
Types of graviational Force
Drip Stain Drip Pattern Drip Trail Flow Pattern Pool- Bleed out Saturation Stain
Types of External Force patterns
Impact stain,
Splatter Stain
Expiration Stain
Cast off pattern
Transfer Stain
Transfer Stain,
Swipe Stain
Wipe Stain
Types of Altered Stain
Altered Stain
Blood clot
Serum Stain
What is a Void
An area that would be expected to be covered in blood however has an area of now blood
Partition Chromatography
Separation is based on difference in the solubility of the sample components into the mobile and the stationary phases; depends on partitioning coefficient (Kd) of the compound into the 2 phases
Affinity Chromatography
affinity ligand, specific for binding the target molecule, is attached to an inert matrix; stationary phase binds the target analyte selectively. All other sample components pass through the stationary phase
Ion-exchange Chromatography
Separation is based on the ion-exchange of the charged ions in the sample; stationary phase may have anions or cations covalently attached to its surface
