What is the ELISA test?


What is the ELISA test?

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Very generally, ELISA is an assay that allows for you to detect/quantify the presence of an antigen or an antibody, depending on the specific test used/purpose. Usually, ELISA diagnostic tests will adsorb an antigen of interest and patient serum is applied to determine whether an antibody specific to that antigen is present. For lab research, ELISAs can be handy to quantify antibody titres for experiments (which is what I use ELISAs for) among other things

Enzyme-linked immunosorbent assays (ELISAs) are a biochemical lab technique where you first capture an antigen or antibody from the sample, and then quantify the bound amount via an enzyme-driven colour-changing reaction. Usually that’s the enzyme HRP with its substrate TMB, but I’m sure there are other enzyme-substrate pairs that can be made to work.

The preceding reactions make sure that an amount of HRP proportional to the analyte you’re looking for gets bound. Thus, when you add a fixed amount of TMB and allow the reaction to proceed for a fixed time before stopping it with sulfuric acid, the amount of TMB that has been processed by HRP is again proportional to your original analyte concentration. And because processing by HRP turns TMB from colourless to bright blue, you can measure the exact “blueness” with a photospectrometer. You take that optical density value, do a bit of math, and out comes your original analyte concentration.

*actually trying to explain to a…12 year old, if not 5 year old*

An ELISA is a way to measure how much of a biological chemical you have in a liquid / solution. For example, if you want to measure how much “X protein” is in someone’s blood, the way it works is:

1. You have a tiny plastic container coated with something sticky – usually a special sticky substance that only X proteins will stick to.

2. You pour some plasma from blood into the coated plastic container and let it sit so any X proteins in the plasma have time to stick to the coating in the container (You’re “capturing” all the X protein molecules).

3. Pour out the remaining plasma liquid and now add some special chemicals into the container that will react and produce color only if protein X is present in the container.

Usually ELISA’s are done in plastic plates containing 96 tiny wells. In our example, only wells that had “captured” any protein X would become colored at the end. If someone’s blood didn’t contain protein X, the well containing their plasma would not be colored. The more protein X, the darker the color.

For learning about lab techniques, usually watching videos on youtube is most helpful.