We're back!! As you all know, #Macademics is my favorite time of the month and in light of me studying for my candidacy exam (pray for me), I decided to use what I'm learning and teach you all about immunoassay.
Immunoassay is a biochemical test that is used to determine the presence and/or concentration of a particular analyte - remember analyte is a molecule of interest. One of the biggest applications for immunoassay is disease detection - they also are good for a lot of clinical testing. Every disease typically has a biomarker specific to it and immunoassay platforms are used to detect these markers to let tracking both the detection and progression of the disease.
I'm not going to go into ALL of the details about immunoassay because that would take a while, but I will tell you about two of the ways you can you conduct this test and also about a few of the labels that are used in these techniques.
One Site, Noncompetitive Assay
This type of assay is like the one pictured for this post. The green circle is the analyte of interest and it binds with an antibody (Y shaped protein) that has a label on it. The unbound antibodies are washed away and the ones that captured analyte are measured. The intensity of the measured signal is directly proportional to the amount of analyte in the sample.
Two Site, Noncompetitive Assay
This type of immunoassay is normally called a "sandwich immunoassay" because the analyte is in between two antibodies, like in the picture to the left. Since there are two antibodies, they have different names and functions. The first antibody, called the capture antibody is immobilized on a surface and its job is to catch the analytes. Once that happens, unbound analytes are washed away and then the second antibody with a label, called the detection antibody, is added to the mix to complete the sandwich complex. Afterwards, the signal is measured and, like the one site assay, is directly proportional to the amount of analyte present.
Now you may be wondering what they label the antibodies with to generate a signal. One of the most popular labels for these assays are enzymes. In the presence of certain reagents, enzymes cause a color change, which makes it easy to tell whether or not the test was positive. Another type of label emits light in response to electric current, these are called electrochemiluminescent tags (long word, I know). Other assays detect DNA or radioactive isotopes, but I won't go into those.
Here's a fun fact for you before I end this. Pregnancy tests are immunoassays. They detect human chorionic gonadotropin (hCG) in urine which is a marker for pregnancy.
Hope you all learned a little something about immunoassays! Be sure to check out the site's new look.
See you next week.
-The Chemist
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