notes+on+serology

 **__Forensic Characterization of Bloodstains__** Three questions to answer: 1. Is it blood? 2. From what species did the blood originate? 3. If the blood is human, how closely can it be associated with a particular individual?

1. IS IT BLOOD? - suggests but does not confirm the presence of blood; indicates that other tests should be performed - negative result means the substance IS NOT blood - positive result means the substance IS LIKELY blood (could be)
 * Presumptive Tests**

__Types of Tests__
 * 1. Catalytic Tests- Presumptive**

- tests based on the fact that heme from hemoblogin can catalyze breakdown of hydrogen peroxide //hemoglobin// - Fe containing molecule in RBC that binds oxygen and carries it from the lungs to tissues Blood contains hemoglobin (carries oxygen and makes blood red) which contains a heme group which contains an Fe which can catalyze the breakdown of hydrogen peroxide - sensitivity: 1:100,000

[| hemoglobin.bmp]

- usually produces a color change - specificity: some vegetable materials such as potatoes and horseradish will also turn the test pink - PROBLEM WHEN OUTDOORS - also, some metals interfere (Cu and Fe) - PROBLEM IF TESTING A VEHICLE - if test is negative and blood is NOT present; if positive then might be blood Iron binds oxygen and carries it through out the blood, soo iron is super important

__Catalytic Detection of Visible Blood Stains__
 * Kastle-Meyer Test** aka the phenolphthalein/peroxidase test

- when a blood stain, hydrogen peroxide and phenolphthalein reagent are mixed, the oxidation of the hemoglobin in the blood produces a deep pink color - sensitivity: 1:10,000 (if 1 drop of blood were present in a bucket with 10,000 drops of water, the PHTH test would still turn pink)

- Testing Method: swab the stain with a q-tip or some filter paper, add a drop of PHTH, add of drop of peroxide

- used in the field kit - suggest if dried sample is blood - positive result = green or yellow to blue-green - Plastic strip with filter paper on tip containing TMB and peroxidase
 * Sangur sticks/Hemastix**





Visible= Hemastix and Kastle MeyerNonVisible= Luminol

Catalytic Detection of non-visible Blood Stains - also a presumptive test - reaction between blood and luminol produces light instead of color - sensitivity: most sensitive presumptive test - detects bloodstains diluted up to 300,000 times - luminol reagent is sprayed onto items suspected to be blood and the room must be darkened - any blood stains present produce a faint blue glow - advantage: can screen large areas quickly and does not interfere with subsequent DNA testing
 * Luminol**



Reaction: Luminol is C8H7O3N3 - luminol powder is mixed with a liquid containing H2O2 and some other chemicals (H2O2 and luminol are the major players) - the reactions needs a catalyst to accelerate the process - in this case the Fe from hemoglobin is the catalyst - also an oxidation reaction - during the reaction, luminol loses N ad H and gains O to produce 3-aminophthalate - the reaction leaves the 3-aminophthalate in an energized state as the electrons in the O atoms are in higher energy orbitals - as the electrons fall to a lower energy level the extra energy is released in the form of light


 * [[image:http://www.piercenet.com/media/PD-Figure28.gif width="550" height="106" caption="Chemiluminescent Reaction Scheme"]] ||
 * Chemiluminescent Reaction Scheme ||

source: http://www.howstuffworks.com/luminol.htm


 * 2. Color Tests**/**Crystal Tests** - confirmation test

- heme from the hemoglobin molecule forms a crystal when reacted with certain substances

__Microcrystalline Tests__ - 2 common tests: **Teichmann Test and Takayama Test**

- small amount of blood added to microscope slide - chemical solution added - slide heated to form hemoglobin crystals (a pink crystal complex) - crystals can be viewed under a microscope

- positive results indicate blood - sensitivity: 0.001 mL of blood/0.1 mg hemoglobin - 20 year old blood stains have given positive results

IS IT HUMAN BLOOD???

__Precipitin Test__ - **Used to determine if the blood is of human or animal origin** - Basis: animals injected with human blood form antibodies against the blood- Bleed animal, collect in beaker, isolate antibodies. - the antibodies can be recovered by bleeding the animal and isolating the blood serum - the antibodies recovered from the animal blood interact with the antigens in the human blood and clump**
 * the serum is really //human antiserum//

Most common Precipitin Test is the Precipitin Ring test - human blood is layered on top of the animal serum containing the human blood antibodies - the interaction between the antibodies and the antigens forms a cloudy ring at the interface of the two liquids

[|http://diverge.hunter.cuny.edu/~weigang/Images/18-03_precipitin_1.jpg]

IS THE BLOOD RELATED TO THE CRIME OR A PARTICULAR INDIVIDUAL'S BLOOD? Gel Diffusion and DNA fingerprinting