home pregnancy tests

Frank DrHeasley at Chemistry.com
Wed Dec 18 19:09:32 EST 1996


On 5 Dec 1996 16:56:22 GMT, jimt12 at aol.com wrote:

>My name is Leticia. I am a senior at Alabama A&M University working on my
>senior chemical research project.  I am trying to determine the chemistry
>behind home pregnancy tests.  Any information and assistance will be
>greatly appreciated.

I designed Answer Plus, one of the very first enzyme immunoassay
consumer pregnancy tests, for Carter-Wallace Inc.

All consumer pregnancy tests use antibodies to detect human chorionic
gonadotropin, a hormone produced during pregnancy.

The early tests took about an hour and were based on hemagglutination
inhibition.  The endpoint was either a mat (negative) or a ring or dot
(positive) of red blood cells on the bottom of a small test tube.

Enzyme immunoassays also used antibodies, but detected binding with an
enzyme which interacted with a substrate to give a color reaction.

Tests which were based on gold sols came next.  Colloidal gold was
sensitized with antibodies, which caused the particles to agglutinate
in the presence of hCG.  This agglutination caused the normally red
sol to turn first blue then clear.

Particle based labelling methods were then combined with various
filtration media to produce tests similar to those widely used now.

Most of the current consumer tests are based on antibody sensitized
dyed particles which travel in a filter medium, encountering
immobilized antibodies.  If hCG is present, the particles stick to the
medium, resulting in a pattern.

Hope this helps.


Frank Heasley, Ph.D.
Principal
FSG Online - Careers in Science, Biotechnology and Medicine
http://www.chemistry.com



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