Done by: Rawan Abdullah Sanbou No.: Ghofran Bagher No:

All pregnancy tests work by detecting a certain hormone in the urine or blood that is only there when a woman is pregnant. This hormone is called human chorionic gonadotropin or hCG. It is also called the pregnancy hormone.

Blood sample Urine sample

 In the positive test, two of the three bands are colored, but in a negative test, only one is colored. This difference results from a lack of hCG in the women’s urine.

 The reaction zone contains: a type of antibody called anti-hCG antibody(Ab). These are mouse monoclonal antibody, which recognize a single molecular feature, or epitope, on hCG molecules.

 The test zone contains:  a polyclonal mixture of antibodies, which recognized a variety of epitope on hCG molecules.  dye molecules, which act as substrates for the enzymes currently in the reaction zone.

 The control zone contains:  The dye substrate  Antibodies, called anti-mouse antibodies, can recognize epitopes on the mouse monoclonal antibodies that are currently in the reaction zone.

 The test strip is dipped in the urine sample. The sample, which contains hCG, is drawn up the strip by capillary action and first arrives at the reaction zone, which contains the enzyme-linked anti-hCG antibodies.

 The enzyme-linked antibodies recognize parts of the hCG molecules and bind to these molecules from the urine. The complexes of the hCG and antibodies, as well as the unbound antibodies, dissolve in the fluid and detach from the capillary membrane. They are then carried along the test strip by the capillary flow.

 The complexes and free antibodes arrive at the test zone. The immobilized polyclonal antibodies bind to hCG molecules in the complexes. The free antibodies continue to flow along the strip.

 The mouse monoclonal antibodies that escaped binding in the test zone have reached the control zone. Here, anti-mouse antibodies that are affixed to the strip bind to these monoclonal antibodies.

 In the test zone, the enzyme-linked antibodies catalyze a reaction with the dye substrate and trigger a color reaction.  The same type of reaction occurs in the control zone.

 Because there are no hCG molecules, these mouse monoclonal antibodies have nothing to bind to and therefore migrate alone up the test strip.  The enzyme-linked antibodies arrive at the test zone, which contains a dye substratte and the immobilized polyclonal antibodies.

 Here, the enzyme-linked antibodies are not carrying hCG molecules, so the immobilized polyclonal antibodies are not able to snare them. All of the enzyme-linked antibodies continue to travel along the strip.

 The enzyme-linked, mouse monoclonal antibodies are captured in the control zone.  The control zone contains anti-mouse antibodies that bind to regions of the travelling antibodies and thereby immobilize them.

 The control zone is an important region that distinguish whether the strips are working correctly.  In the strip is working correctly and if the women is not pregnant, the control zone will produce a color reaction, but the test zone will not.

 et/pregnancy-tests.cfm#a  est.html  SOURCE: Purves, et al., Life: The Science of Biology, Seventh Edition, Sinauer Associates © 2004 Sinauer Associates, W. H. Freeman & Co., and Sumanas, IncSinauer Associates

Question?