Quantum dots (QDs) have unique optical properties and several advantages over conventional organic dyes. The ability to make QDs water soluble allows for use in various biological applications. Smooth metallic surfaces are known to quench the fluorescence of both organic dyes and of certain QDs. This paper provides a comparative study of the quenching ability of an unmodified and a poly(ethyleneglycol) (PEG)-modified Au surface, of the emission from an organic dye and from CdSe/ZnS QDs. PEG is a biocompatible molecule widely used for modification of different surfaces when protein resistance is required. Fluorescence measurements show that both an unmodified and a PEG-modified Au surface are able to quench the emission from the dye and the QDs. Some interactions between the QDs and the unmodified An surface were also observed, although the interactions are significantly suppressed by the presence of PEG. The PEG-modified Au surface is suitable for further applications, involving biomolecules, where its efficient quenching ability and protein resistivity can be utilized. (c) 2007 Elsevier B.V. All rights reserved.