A bioassay is an analytical method used to determine the potency of various substances on living cells or tissues; in vivo or in vitro. Bioassays are used to estimate the biological risks of a mixture. In simpler words, a bioassay is the assessment of biological molecules, and various companies like Scorpion have made this easy in the present age.
Principle:
The potency of a substance can only be measured by comparing it to another substance i-e by using a standard. A stimulus in the form of a drug or substance is applied to the subject, and the response is measured. The method used should be reliable and error-free to obtain correct results.
Types of Bioassays:
There are two major types of bioassays based on the method used. These types are:
- Direct Bioassay
- Indirect bioassay
The indirect bioassay is further divided into two types depending upon whether the response was binary or can be measured on a continuous scale.
Direct Bioassay:
In direct bioassay, a specific stimulus is applied, which is measurable. The response to that stimulus is recorded. The variable is the stimulus, which is moulded to achieve a particular reaction.
Indirect Assay:
A fixed stimulus is applied in the indirect assay, and the response is measured accordingly. The response obtained is the variable in the indirect assay.
The response obtained in the indirect assay can be further divided into two types:
- Quantitative response:
In this case, the response received can be measured on a continuous scale—for example, blood sugar concentration.
- Quantal Response:
In this case, the response is binary. It either is one or the other. It can not be measured on a direct scale. For example, the subject either died or stayed alive; there is no in between.
Examples of Bioassays:
- Enzyme-Linked Immunosorbent assay (ELISA):
ELISA is a powerful method to detect and identify a protein (antigen or an antibody)in a complex mixture. Enzyme labelled ELISA plates are available that bind antibodies or proteins. The unbound molecules are easily washed away from the surface of the plates, and then measurements are taken. ELISA can be done in several formats
- Direct ELISA
- Indirect ELISA
- Sandwich ELISA
- Competitive ELISA
All formats have their benefits and demerits. The format is selected according to the process you will perform, and the relevant substrate is chosen. ELIZA is used in cancer screening and detection of antibodies, food allergens, and viruses.
- Home Pregnancy Tests:
Bioassays have been used to detect pregnancy at home for decades now. In the past, people utilised bioassays to determine the concentration of enzyme human chorionic gonadotrophins in the urine of a female. The urine was administered to test animals like mice or rabbits. The disadvantage of that method was that it took two to four weeks to give the results, and by that time menstrual cycle was already missed. The other drawback was the unnecessary killing of animals. These bioassays are replaced by immunoassays today.
- Human Immunodeficiency Virus:
HIV antibodies can be detected by using indirect ELISA. Another bioassay based on trans-activation has been developed now, which sees the presence of HIV-1, and it is considered a huge achievement in the medical field.
Hence,
Bioassays are important techniques which have important applications in biochemistry, pathology, cell biology, molecular biology and biotechnology.