if your antibody could be cysteine tagged, the cysteine will bind directly to clean gold in a non-tris buffer llike PBS or HEPES. If it doesn't attach well, a small amount of dithiothreitol (DTT) or 2-beta metcaptoethanol (BME) can hlep to ensure that the sulfur on the cysteine is accessible for imnobilization. However, this may also attach the antibody vian any other cysteines that may be present in your protein.

Another option is EDC/NHS cross-linking of the N-terminus to a carboxylated gold nanoparticle (e.g. using an alkane thiol such as 11-mercaptodecanoic acid (MUA) to form a self-assembled monolayer on your particle). The antibody should be in a buffer non-tris buffer such as acetyl acetonate, PBS or HEPES at about 1 pH point below the pI of the protein. The attached paper is for attachment to gold surfaces, but should work for nanoparticles, you would just have to dialyse or centrifugate and resuspend the particles after the protein attachment step to wash any unused reactant from the nanoparticles.

It is also possible to attach the c-terminus of a protein to an amide functionalized nanoparticle in a similar way, but I have not tried this as the N-terminal attachment always worked well. Gold nanoparticles can also be functionalised with alkane thiols that present an NTA or biotin functional group for effective protein immobilization if your antibody is a recombinant form with an affinity tag, but many of these molecules are expensive to buy.

You should use the copyright sign, if quoting someone else, see below:

https://www.researchgate.net/post/Does_anyone_know_a_protocol_binding_antibodies_to_gold_nanoparticles