12.2 Notes - Techniques

ObjectivesUnderstand 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

Immunoassay TechniquesUsed 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 boundValue of the unbound antibodies is then used to determine the concentration of the drug originally in the urine

EMIT continuedScreening 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

RIA – radioimmunoassayUses drugs with radioactive tags

Neither EMIT or RIA are drug specific and must be used with a reliable confirmation test

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

Determination – Color TestBenzidine 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 TestLuminol – produces light rather than color when viewed in dark area (luminescence)Luminol extremely sensitiveCan be diluted 300,000 timesWill not interfere with DNA testing

Determination cont.Precipitin test – used to determine if blood is animal or humanAnimals 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 identityHistorically used ABO and polymorphic enzymesCurrently uses DNA

12.2 Questions1. 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 human or animal origin and what is the principle underlying test?

11.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?

12. In what technique can antigens and antibodies be induced to move toward one another under the influence of an electrical field?