Jackson Immuno Research Inc.
specializing in secondary antibodies and conjugates
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Whole IgG Affinity-Purified Secondary Antibodies

"I have used a wide variety of secondaries and Jackson ImmunoResearch has consistently been the best. The fluorophores are bright and stable and their selective (x reactivity removed) secondaries have always shown species specificity in multiple labeling."

Janet Duerr, Ohio University

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Blocking & Control Reagents from Jackson ImmunoResearch

Blocking and Control Reagents

We provide a range of reagents to optimise immunotechniques including Normal Serums, Bovine Serum Albumin and ChromPure™ Purified Proteins. These reagents can be used either for blocking, to minimise unwanted background signal, or as controls for experimental validation. Our blog article on selecting controls and blocking reagents provides a detailed overview.


ChromPure™ purified proteins from normal serums - experimental controls and blocking reagents.

ChromPure proteins are primarily used as experimental controls for either primary or secondary antibodies. They are available conjugated to a range of fluorescent dyes and reporter enzymes, allowing the isolation of signal derived from non-specific interactions. ChromPure purified proteins may also be used as blocking reagents for Western blotting, IHC, and IF.

Normal Serums

Normal serums are obtained from non-immunized animals and consequently do not detect any specific antigen. Normal serum is recommended for use as a blocking agent to reduce background from non-specific, conserved- sequence, and/or Fc-receptor binding.

Gamma Globulins

Gamma globulins are derived from non-immunized animal serums and have been further purified by salt fractionation, ion-exchange chromatography, and gel filtration. Gamma globulins can be used as blocking reagents and as controls. View our product list here.

Bovine Serum Albumin (IgG-Free, Protease Free)

Bovine serum albumin (BSA) is used extensively as a carrier protein to dilute antibodies and as a general protein blocking agent in immunoassays and immunodetection protocols.

Monovalent Fab Fragments

Fab fragments can enable the blocking of endogenous immunoglobulins to reduce background staining and for multiple labeling assays when primary antibodies are derived from the same host species. Learn more with our blocking protocols.

Cautions: When using a labeled secondary antibody for detection, never block with normal serum or IgG from the host species of the primary antibody. If immunoglobulins in normal serum bind to the specimen of interest, they will be recognized by the labeled secondary antibody, resulting in higher background.

Bovine serum albumin (BSA) and dry milk, both commonly used for blocking, may contain bovine IgG. With the exception of bovine anti-goat IgG, many secondary antibodies such as anti-bovine, anti-goat, anti-horse and anti-sheep will react strongly with bovine IgG. Therefore, use of BSA or dry milk for blocking or diluting these antibodies may significantly increase background and/or reduce antibody titer. For blocking, use normal serum (5% v/v) from the host species of the labeled secondary antibody.

Nitrocellulose membranes being blocked on a rocker


Blocking reagents and controls may be required for experimental protocols depending on the immunotechniques undertaken. Here we detail a selection of common problems solved with appropriate blocking, diluents or control reagents.

Western blotting

Problem Solution Indicated Product
Background (non-specific signal obscuring bands of interest) Use appropriate blocking reagent to block membrane prior to incubating with primary. Normal Serums
BSA (IgG- and protease-free)
Avoid using milk or BSA if primary antibodies are derived from goat, horse or sheep. Normal Serums
Detection of reduced immunoprecipitating (IP) antibody at 50 or 25 kDa To avoid detecting IP antibody heavy chains at 50 kDa, use conjugated anti-light chain specific antibody. Anti-light chain specific antibodies
To avoid detecting IP antibody light chains at 25 kDa, probe blot with conjugated anti-IgG, Fc fragment after blocking with monovalent Fab fragment anti-Fc. Whole IgG Antibodies
Fab fragments

View our Western Blotting page for additional information.


Problem Solution Indicated Product
Confirmation that primary antibody binding is due to antigen specificity To demonstrate specific binding of the primary antibody, use an isotype negative control (nonspecific IgG from the same species as the primary antibody). ChromPure™ proteins
Background (general) Block endogenous binding sites which may interact with experimental reagents. Normal Serums
Background (homologous Ig recognition) Block endogenous immunoglobulins. Fab Fragments
Multiple label primary antibodies from same host species Utilize Fab fragments in suggested protocols to accomplish multiple labeling. Fab Fragments
Immunolabel primary antibody prior to incubation. FabuLight
Endogenous enzymes Inactivate endogenous peroxidase with hydrogen peroxide. Selecting Control, Diluent and Blocking Reagents Guide
Use levamisole to inactivate endogenous phosphatases.
Endogenous biotin Block endogenous biotin. Incubate with streptavidin, followed by free biotin.
Ionic interactions Include detergent in buffers, optimize salt concentrations and pH. Tween®‑20 and/or Triton™ X‑100.

View our IHC/ICC/IF page for additional information.

Flow cytometry

Problem Solution Indicated Product
Background from antibodies binding Fc receptors. Block Fc receptors. Normal Serums
Use F(ab')2 format secondary antibody to avoid entrapment by Fc receptors. F(ab')2 Secondary Antibodies
Confirmation that primary antibody binding is due to antigen specificity Use an isotype negative control (non-specific IgG from the same species as the primary antibody) to demonstrate specific binding of the primary antibody. ChromPure™ Purified Proteins

View our Flow Cytometry page for additional information.


Problem Solution Indicated Product
Background Use an appropriate blocking reagent to block wells prior to incubating with the primary antibody. Normal Serums Page
BSA (IgG-free and protease-free)
No Signal Use a positive control to demonstrate activity of the labeled secondary antibody: coat with primary antibody isotype and detect directly with secondary. Chrompure Proteins

View our ELISA page for additional information.