No signal detected despite proper primary antibody binding. Secondary antibody fails to recognize or bind to the primary antibody, breaking the detection chain.
Common Causes
1Secondary antibody not raised against primary antibody host species
2Isotype mismatch between primary and secondary antibodies
3Secondary antibody conjugate incompatible with detection system
4Wrong secondary antibody selected for primary antibody class (IgG, IgM, etc.)
Solutions
1Ensure secondary antibody is raised against primary antibody species (e.g. anti-rabbit for rabbit primary)
2Verify isotype compatibility between primary and secondary antibodies
3Confirm secondary antibody conjugate matches detection method (HRP for DAB, fluorophore for IF)
4Check that secondary antibody recognizes primary antibody class (IgG, IgM, etc.)
5Run positive control with validated antibody pair to confirm detection system