A gold nanohole array is functionalized with a cortisol thiol derivative, and binding to a monoclonal antibody is conveniently detected using the sensitive shift in the 1060 nm transmission peak of the array. Detection is also enhanced 3-fold by the application of a secondary antibody-gold nanoparticle conjugate. This regenerable response represents a more sensitive shift than that obtained previously for higher affinity binding and opens the way to application of nanohole arrays in immunobiosensing of important biomolecules.