Sandwich Immunoassay
Definition
The detection architecture used by most lateral-flow strips for large antigens: the target antigen is captured between two antibodies, the conjugated detection antibody and the immobilised capture antibody at the test line. Both antibodies must bind simultaneously for a signal to appear.
- Format
- Antigen captured between two antibodies
- Common platform
- Lateral-flow strips
- Target size
- Large antigens
- Signal requirement
- Both antibodies must bind simultaneously
Common questions
Why is the sandwich format specifically suited to large antigens rather than small molecules?+
A sandwich format needs two antibodies binding two distinct sites on the same molecule at once, which requires enough surface area on the target; small molecules like many drugs of abuse typically lack room for two simultaneous binding sites, so they use competitive rather than sandwich formats.
What causes a false negative in a properly stored sandwich immunoassay strip?+
If the antigen concentration is extremely high, excess antigen can saturate both the capture and detection antibodies separately before they bind each other, a phenomenon called the hook effect, which paradoxically produces a weak or absent test line despite abundant target present.
How does the requirement for simultaneous double binding improve specificity over a single-antibody test?+
Requiring two independent antibody-antigen recognition events before a signal appears reduces the chance that a structurally similar but non-target molecule triggers a false positive, since it would need to satisfy both binding requirements at once.
Related terms
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