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What Is a Block Assay?

Assays, such as ELISA and Western Blot, use protein molecules to bind to the surface of other proteins or molecules. The interaction or the ability of these assays to perform binding of proteins is essential to the procedure; however, it is the non-specific binding of unwanted proteins during the assay that can cause detrimental effects to the assay results. To prevent the non-specific binding from occurring, blocking reagents can be added to the assay. There are different types of blocking assays that can be used, depending on the experiment.

Detergent Blockers
- Detergents are a type of blocking reagent, which are both ionic and non-ionic. This type of blocking reagent in an assay must be present in all of the solutions, including buffers. The detergent blockers can be removed through washing with water and buffers during the assay procedure. These types of blockers are commonly used in conjunction with protein blockers and are inexpensive and stable to store.
Protein Blockers
- Protein blockers block all non-occupied sites of the surface of molecules and stabilize molecules bound to the surface. This helps reduce denaturation of proteins during the assay procedure. In addition, protein blockers are permanent and only need to be added once during the procedure and will not wash off with water or buffer solution. The most common protein blockers are bovine serum albumin, non-fat dry milk, normal serum and fish gelatin.
Polymer Blockers
- Polymers, such as polyethyleneglycol (PEG), polyvinyl alcohol (PVA) and polyvinylpyrrolidone, are blocking reagents used for hydrophobic (water-disliking) molecules. It makes the surfaces of these molecules non-binding and hydrophilic (water-liking). A popular assay using this type of block is the over-the-counter pregnancy test.
Fish Protein Blocks
- Specific fish protein blocks designed for the immunoassays, such as ELISA, improve results by reducing non-specific binding of molecules. In addition, most of these types of blocks come in different strengths to either detect specific antigens (foreign particle) or coat non-specific binding sites that are inaccessible to other types of blocking reagents.

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