Forensic Serology- FINAL L11

THE MAJOR BODY FLUIDS

• Blood

• Semen

• Saliva

GENETIC MARKERS

ABO Blood Group

BLOOD’S PRESUMPTIVE TESTS

• React with the hemoglobin present in blood

• Colorimetry, Fluorescence, or Chemiluminescence

COLORIMETRIC TESTS

The testing chemical is added to the suspected stain and then an oxidant is added, usually 3% hydrogen peroxide

CATALYTIC COLOR TESTS

• Phenolphthalein

• Benzidine

• Leucomalachite green

• Tetramethylbenzidine (TMB)

LUMINOL AND FLUORESCEIN

Predominantly used for largescale serology testing.

LUMINOL

• Very sensitive to hemoglobin and will detect blood in dilutions of 1 in 5,000,000.

• Does not affect polymerase chain reaction (PCR) of DNA.

FLUORESCEIN

• Prepared much in the same way as luminol except that the commercial preparation contains a thickener

• Stays on the surface better than luminol, making it easier to use on walls and other vertical surfaces

• Produces fluorescence and must be illuminated at 450 nanometers

CONFIRMATORY TESTS FOR BLOOD

Formation of crystals through the application of heat and testing chemicals

EXAMPLE OF CONFIRMATORY TESTS FOR BLOOD

Takayama test (also known as the hemochromogen test)

TAKAYAMA TEST

1. Sample of the presumptive stain is placed under a cover slip.

2. Sample is heated briefly and observed through a microscope.

3. If blood is present, salmon-colored crystals form.

NOTE FOR BLOOD

Practically speaking, most forensic laboratories today do not conduct confirmatory tests for blood—the sample, if presumptively positive, will go straight to the DNA unit.

PRESUMPTIVE TESTS FOR SEMEN

Detection of acid phosphatase

EXAMPLE OF PRESUMPTIVE TESTS FOR SEMEN

• Most common test is Brentamine Fast Blue B applied to the sample on an alphanaphthyl phosphate substrate

• (+) Reaction – Purple Color

CONFIRMATORY TESTS FOR SEMEN

Detection of acid phosphatase

CHRISTMAS TREE STAIN

Traditional method for sperm identification

CHRISTMAS TREE STAIN

• (+) Sperm head turns pink, middle portion blue, tail yellow-green

• Skin cells will stain green to blue-green.

SALIVA

Bite marks, licked adhesives (like envelopes and stamps), eating and drink surfaces, or even expectoration (spitting) can yield important DNA evidence

ENZYME AMYLASE

Occurs in saliva, and tests exist for amylase; amylase also occurs in many other body fluids