How do I choose the right secondary antibody?

There are three main factors you need to consider in order to choose the right secondary antibody for your application: 

• In which species the primary antibody was developed – Ideally, you’ll need a secondary antibody that is raised in a species that’s different from the host species of the primary antibody. For example, if your primary antibody is raised in a goat, you should use a secondary antibody raised in any species other than a goat. 
• Whether your primary antibody is monoclonal or polyclonal – For a monoclonal primary antibody with a single isotype of immunoglobulin, you must use a secondary antibody that recognizes that specific isotype. For a polyclonal primary antibody that contains a mix of different isotypes of immunoglobulin G, the best secondary antibody to use is one that is capable of recognizing all isotypes. 
• Type of application – Secondary antibody fragments, which can penetrate tissues more easily because of their smaller size, are the better option for applications such as immunofluorescence and immunohistochemistry. Whole secondary antibodies are good for use in most other applications.