Ligand assays measure the product of the chemical interaction between a molecule and a reactive substance or receptor. They can measure a variety of substances in the human body and are classified into competitive, non-competitive, and miniaturized microarray assays. The latter allows for the simultaneous measurement of multiple molecules from a small biological sample.
Assays are a method used in medicine to determine the presence and quantity of a molecule in a biological substance. There are several types of tests and they are indicated by their name. Ligand assays specifically refer to the group of assays that measure the product of the chemical interaction between the molecule to be measured and a reactive substance or receptor placed on the assay.
In the human body, a ligand is a signal-activating molecule that fits to specific receptor sites located on cell walls. When a ligand inserts itself into its specific receptor site, it causes the physical form of the receptor to change, thereby triggering the sending of a biological signal. In ligand assays, it is this cellular response that is measured.
Ligand tests can be used to measure a wide variety of substances in the human body, such as cells, drugs and hormones. Different types of biological ligand analyzes have been created, because the human body is very complex. The mechanism by which the measurement is made can be used to classify assays into three main classes, including competitive, non-competitive, and miniaturized microarray assays.
In a competitive test, both a radioactively labeled compound similar in structure to the test molecule and the receptor binding site are provided on the test. When the human sample is introduced to be measured in the assay, it must compete with radioactively labeled molecules already present in the assay to bind to the receptors provided. The amount by which the radioactively labeled molecules exceed binding to the sample receptor can provide medical professionals with information about the presence and quantity of the molecules in the sample. Competitive tests were first used in the mid-1950s to measure the concentration of human hormones, mainly thyroid hormone and breast cancer hormone receptor function.
A second type of ligand analysis is the non-competitive analysis. It works similar to that of the competitive assay, except that the radioactively labeled molecules on the assay are available in excess and therefore are already competing with the sample molecules. The degree to which sample molecules are able to bind to assay receptors can estimate the amount of the molecule present in the human sample. This analysis technology was widely used in the mid-1980s.
Competitive and non-competitive ligand assays allow investigation of one molecule at a time. The third class of assays allows for the simultaneous measurement of multiple molecules from a small biological sample. This is done through the use of a miniaturized chip loaded with multiple small areas of specific receptors. These are called miniaturized microarrays or microspots. This third class of test types offers the ability to measure more biological complexes from small samples and has become more widely used.
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