An analytical formalism is proposed to calculate polarizability of surface immobilized gold nanospheres (SIGNs) above a gold surface. Using this formalism, we can evaluate the gap distance and its distribution in the SIGN system under various conditions. Experimental results show that the gap distance is much smaller than the thickness of the gap-supporting layer with no adsorbed gold nanospheres. This means that the layer under the nanosphere is collapsed or disordered, stemming from the existence of the SIGNs. (C) 2009 Elsevier B. V. All rights reserved.