Santanu,

Antibodies generally do not bind on their own to a bare Au surface; you
will need a linker. I suggest this paper:

@Article{thiol-protocol,
  author =       {Nikin Patel and Martyn C. Davies and Mark Hartshorne and
                  Richard J. Heaton and Clive J. Roberts and Saul
                  J. B. Tendler and Philip M. Williams },
  title =        {Immobilization of Protein Molecules onto Homogeneous
                  and Mixed Carboxylate-Terminated Self-Assembled
                  Monolayers},
  journal =      {Langmuir},
  year =         1997,
  volume =       13,
  number =       24,
  pages =        {6485-90}
}