Transcript 12.2 Notes - Techniques - Trimble County Schools

12.2 Notes - Techniques
Objectives
Understand the concept of antigenantibody interactions and how it is
applied to species identification and
drug identification
List and describe forensics tests used
to characterize a stain as blood
Immunoassay Techniques
Used for typing blood
Also used for detecting drugs
Combine the drug with a protein and
inject it back to the individual causing it to
produce antibodies
EMIT - Enzyme Multiplied
Immunoassay Technique
Used to detect drugs in urine
Antibodies added to sample
If present, specific drug is bound to the antibody
Enzyme labeled drug is added to urine and More
antibodies bind to that
Measure amount of enzyme labeled drug that is
bound
Value of the unbound antibodies is then used to
determine the concentration of the drug originally
in the urine
EMIT continued
Screening for marijuana (THC)
THC breaks down to substances
more easily excreted
Major metabolite is THC -9carboxylic acid
EMIT is used for that specific
metabolite
RIA – radioimmunoassay
Uses drugs with radioactive tags
Neither EMIT or RIA are drug
specific and must be used with a
reliable confirmation test
Characterization of Bloodstains
Is it blood?
From what species did it come?
If it is human, can it be
associated to a particular
individual?
Determination – Color Test
Benzidine color test discontinued
because of carcinogenic effect
Currently uses phenolphthalein
called the Kastle-Meyer
Based on the peroxidase like activity
of hemoglobin which produces a deep
pink color when applied to blood
Hemastix strips – turns green with
blood
Determination – Light Test
Luminol – produces light
rather than color when viewed
in dark area (luminescence)
Luminol extremely sensitive
Can be diluted 300,000 times
Will not interfere with DNA
testing
Determination cont.
Precipitin test – used to determine
if blood is animal or human
Animals produce human antiserum
when injected with human antigens
Gel diffusion – antibodies and
antigen will diffuse toward one
another in an agar gel plane
forming a precipitation line or by
electrophoresis
Determination = Human origin
Further tests to determine
identity
Historically used ABO and
polymorphic enzymes
Currently uses DNA
12.2 Questions
1. What happens when serum containing B antibodies is added to red blood
cells carrying the B antigen? Will the same thing happen if serum
containing B antibodies is added to red blood cells containing A antigen?
Explain your answer
2. What is serology and what is its most widespread application? In what
other areas related to forensic science is it finding application?
3. What is the difference between monoclonal and polyclonal antibodies?
4. Briefly describe how antibodies capable of reacting with drugs are produced
in animals.
5. What immunoassay technique has gained widespread popularity among
toxicologists because of its speed and high sensitivity for detecting drugs in
urine? What drug is this technique frequently used to screen for?
6. What three questions must the criminalist answer when examining dried
blood?
7. Name the most common color test for blood and describe how it
identifies bloodstains.
8. Describe how luminal is used to detect bloodstains.
9. Name two reasons why color tests are superior to microcrystalline
tests for identifying blood.
10. What is the standard test used to determine whether blood is of