Immunoassay Techniques

When a stain is encountered at a crime scene that appears to be blood, there are several questions that must be answered:

1. Is it blood?

2. If it is blood, is it human or some other species?

3. If it is human, can it be linked to a particular individual?

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Is it Blood?

A presumptive, or screening, test for blood often used in crime scenes is the spraying of suspected areas of blood staining with Luminol. If blood was present at some point, the luminol will react with the blood stain and cause the area that was covered with blood to fluoresce. Luminol is simply a chemical reaction in which the Luminol solution reacts with iron from the hemoglobin of blood to cause a faint blue fluorescence. Even tiny amounts of iron can cause Luminol to fluoresce, so it is quite reliable in detecting trace amounts of blood. Because Luminol is extremely sensitive, it can detect even diluted samples of blood that were cleaned up long before. If luminol is sprayed in an area suspected of being a cleaned up crime scene, it will still detect blood that has been diluted up to 300,000 times. If the stain is blood, luminol will not interfere with any subsequent DNA analysis that may be done though it may destroy other components for testing within the blood.

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Is it Blood?

Another presumptive test is called the Kastle-Meyer Color Test. The Kastle-Meyer Color Test uses a solution of phenolphthalein and hydrogen peroxide on a piece of filter paper to detect blood. When blood of any quantity is present and exposed to the testing paper or solution, it will turn pink.

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Is it Blood?

Another presumptive test is called the Kastle-Meyer Color Test. The Kastle-Meyer Color Test uses a solution of phenolphthalein and hydrogen peroxide on a piece of filter paper to detect blood. When blood of any quantity is present and exposed to the testing paper or solution, it will turn pink.

Subject | Subject

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