1. 12.2 Notes - Techniques

2. Objectives
Understand the concept of antigen-antibody interactions and how it is applied to species identification and drug identification
List and describe forensics tests used to characterize a stain as blood

3. 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

4. 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

5. EMIT continued Screening for marijuana (THC)
THC breaks down to substances more easily excreted
Major metabolite is THC -9-carboxylic acid
EMIT is used for that specific metabolite

6. RIA – radioimmunoassay
Uses drugs with radioactive tags
Neither EMIT or RIA are drug specific and must be used with a reliable confirmation test

7. Characterization of Bloodstains
Is it blood?
From what species did it come?
If it is human, can it be associated to a particular individual?

8. 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

9. 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

10. 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

11. Determination = Human origin
Further tests to determine identity
Historically used ABO and polymorphic enzymes
Currently uses DNA

12. 12.2 Questions
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
What is serology and what is its most widespread application? In what other areas related to forensic science is it finding application?
What is the difference between monoclonal and polyclonal antibodies?
Briefly describe how antibodies capable of reacting with drugs are produced in animals.
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?
What three questions must the criminalist answer when examining dried blood?
Name the most common color test for blood and describe how it identifies bloodstains.
Describe how luminal is used to detect bloodstains.
Name two reasons why color tests are superior to microcrystalline tests for identifying blood.
What is the standard test used to determine whether blood is of human or animal origin and what is the principle underlying test?
Which technique takes advantage of the fact that antibodies and antigens move toward one another on a plate coated with a medium made from a natural polymer called agar?
In what technique can antigens and antibodies be induced to move toward one another under the influence of an electrical field?