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=                              Bioassay                              =
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                            Introduction
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A bioassay is an analytical method to determine concentration or
potency of a substance by its effect on living cells or tissues.
Bioassays are quantitative biological assays used to estimate the
potency of agents by observing their effects on living animals ('in
vivo') or tissue/cell culture systems ('in vitro').

A bioassay experiment can either be qualitative or quantitative,
direct or indirect. If the measured response is binary, the assay is
qualititative, if not, it is quantitative.

Bioassay is used to detect biological hazards or give a quality
assessment of a mixture. Bioassay is often used to monitor water
quality and also sewage discharge and its impact on surrounding. It is
also used to assess the environmental impact and safety of new
technologies and facilities.


                             Principle
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Bioassay is a biochemical test to estimate the relative potency of a
sample compound to a standard compound. Typical bioassay involves a
'stimulus' (ex. drugs) applied to a 'subject' (ex. animals, tissues,
plants) and a 'response' (ex. death) of the subject is triggered and
measured. The intensity of stimulus is varied by doses and depending
on this intensity of stimulus, a change/response will be followed by a
subject..


                              History
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The first uses of bioassay dates back to as early as the late 19th
century, when the foundation of bioassays was laid down by a German
physician, Paul Ehrlich. He introduced the concept of standardization
by the reactions of living matter. His bioassay on diphtheria
antitoxin was the first bioassay to receive recognition. His use of
bioassay was able to discover that administration of gradually
increasing dose of diphteria in animals stimulated production of
antiserum.

Many of the early bioassays consisted of using animals to test
carcinogenicity of chemicals. One well known example is a "canary in
the coal mine" experiment. To test for methane, miners would take
methane-sensitive canaries to coal mines to ensure safe air. In 1915,
Yamaigiwa Katsusaburo and Koichi Ichikawa tested the carcinogenicity
of coal tar using inner surface of rabbit's ears.

Through 1940s and 1960s, animal bioassay was primarily used to test
for toxicity and safety of drugs, food additives and pesticides.

In late 1960s and 1970s, reliance on bioassay increased as the public
concern for occupational and environmental hazards increased. While
before this health risks of certain chemicals such as pesticide was
tested in animal bioassay, it was still rare and testing was not seen
often.


Direct assay
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- The stimulus/standard sufficiently produces measurable and specific
response. The response must be clear, easily recognized, and directly
measured.


Indirect assay based on quantitative response
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- The relationship between the dose and the response is first
ascertained. Then the dose corresponding to a given response is
obtained from the relation for each preparation separately.


Indirect assay based on quantal response
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- The assay involves 'all or none' response (ex. life or death). The
response is produced by threshold effect.


[[ELISA]] (Enzyme-linked immunosorbent assay)
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- quantitative analytical method that measures absorbance of color
change from antigen-antibody reaction (ex. Direct, indirect, sandwich,
competitive). ELISA is used to measure variety of substances in human
body from cortisol levels for stress to glucose level for diabetes.


Home pregnancy test
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Home pregnancy test involves ELISA to detect the increase of human
chorionic gonadotropin (hCG) during pregnancy.


HIV test
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HIV test also uses indirect ELISA to detect HIV antibody caused by
infection.


                              See also
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* Assay
* Immunoassay


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