Depletion interaction of added additional polymer latex was reported to drive self-aggregation of particles in suspension or on a hard wall (Yodh, A. G.; Lin, K. H.; Crocker, J. C.; Dinsmore, A. D.; Verma, R.; Kaplan, P. D. Philos. Trans. R. Soc. London A 2001, 359, 921). We describe an experimental investigation of controlling the optimal geometrical arrangement for the adsorbed molecules by depletion interaction between the adsorbent and the metal wall. Bipyridine and a polymer of amino acid were found to form ordered structures that covered silver after adding a depletant of low molecular weight poly(ethylene glycol) (PEG) into their solutions in ethanol. The adsorbed molecules were investigated by surface enhanced Raman scattering (SERS) spectroscopy, which provided information about morphology at the molecular level. The PEG-mediated depletion interaction with the wall contributed to the entropic force for supramolecular assembling of these adsorbents on substrate.