Question

1. why is a blocking step necessary before adding antibodies?

Explanation:

In immunoassays (like ELISA), the blocking step (using a protein - rich solution like BSA or non - fat milk) is necessary to prevent non - specific binding of antibodies to the surface (e.g., the wells of a microplate). The surface has areas that can bind antibodies non - specifically. If we don't block these areas, the antibodies will bind to these non - target sites, which can lead to a high background signal. This high background can interfere with the detection of the specific antigen - antibody interaction, making the results inaccurate (e.g., false positives or inflated signal values that don't reflect the true amount of the target antigen).

Answer:

A blocking step is necessary before adding antibodies (e.g., in immunoassays) to prevent non - specific binding of antibodies to the surface (e.g., microplate wells), which would otherwise cause high background signal and inaccurate results by interfering with the specific antigen - antibody interaction.