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In sandwich ELISA the Fc region of primary antibody bind to the polystyrene coated well. But what are the specific interactions (like 'hydrophobic interaction' or 'van der waals force') happen between well and Fc region?

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    $\begingroup$ My understanding of a 'sandwich' Elisa is that the primary antibody binds to the polystyrene plate. After 'blocking' of non-specific sites, the antigen-containing fraction is presented to the coated well. Then, to complete the 'sandwich', a second antibody also directed against the antigen is coated onto the Elisa plate. If the antigen binds directly to the polystyrene plate, this is a 'direct' Elisa $\endgroup$ – user1136 Jan 14 '17 at 11:40
  • $\begingroup$ @xusr seen both use, don't know which corect. In few notebooks, "direct ELISA" used to mean direct binding of antigens into the well. but most sources treat "Direct ELISA" is where the primary antibody is itself tagged, so it "directly" gives signal of detection of antigen. Whereas in indirect ELISA the labelled secondary antibody (capable to direct bind only to primary antibody) indirectly indicates antigen. This question and Wilson-Walker seems to use second usage. $\endgroup$ – Always Confused Apr 1 '18 at 12:24
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This page from Cole-Parmer includes everything you could possibly want to know about the adsorption of biomolecules to polystyrene. To summarize:

  • binding is neither covalent nor ionic, but
  • it is generally mediated by non-specific intermolecular van der Waals interactions, which generally are about 100X weaker than ionic or covalent bonds
  • the exception is some hydrogen bonds, which can be 10X stronger than the other types
  • Intermolecular attraction forces are based on intramolecular electric polarities of which two types can be distinguished: alternating polarities (AP) and stationary polarities (SP), i.e. dipoles.

  • these interactions can be both hydrophobic and hydrophilic, depending on the surface chemistry of the polystyrene

If you're interested in the specific chemistry of everything, feel free to read the entire thing, it's quite detailed.

I would to note one thing from your question. In the absence of a specific binding partner like Protein A, antibodies bind to polystyrene completely non-specifically, meaning that not only does the Fc region bind, but Fab as well, including the CDRs (antigen binding domains). An ELISA depends on the fact that not all antibody molecules bind this way, so many or a majority of them have their antigen binding sites available to capture their target.

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  • $\begingroup$ Cole-Parmer is a great reference. $\endgroup$ – user1136 Jan 14 '17 at 20:16

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