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 or tissue/cell culture systems. A bioassay experiment can either be qualitative or quantitative, direct or indirect. If the measured response is binary, the assay is qualitative, 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
Bioassay is a biochemical test to estimate the relative potency of a sample compound to a standard compound. Typical bioassay involves a stimulus applied to a subject and a response 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
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.
Classifications
Direct assay
- 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
- 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
- The assay involves 'all or none' response. The response is produced by threshold effect.
- quantitative analytical method that measures absorbance of color change from antigen-antibody reaction. ELISA is used to measure variety of substances in human body from cortisol levels for stress to glucose level for diabetes.
