Surface plasmon resonance studies of gold and silver nanoparticles linked to gold and silver substrates by 2-aminoethanethiol and 1,6-hexanedithiol

Self-assembled monolayers (SAMs) of 2-aminoethanethiol (AET) or 1,6-hexaned ithiol (HDT) are formed on An and Ag substrates, and colloidal An (13.6 +/- 2.0 nm diameter) and Ag (30.0 +/- 10 nm diameter) nanoparticles are deposi ted onto these SAM surfaces. The resulting multilayered nanostructures, pre pared with different combinations of the substrate, SAM, and nanoparticles, are studied with surface plasmon resonance (SPR) measurements. Under certa in circumstances, the SPR sensitivity of the bare metal is considerably enh anced by the presence of the metal particles. Both the occurrence and the d egree of this effect depend strongly on the choice of the combination of ma terials in the multilayered system. The substrate/SAM/nanoparticles systems that exhibit the enhanced SPR sensitivity include Au/AET/Au, Au/HDT/Au, Au /AET/Ag, and Ag/AET/Ag. On the other hand, the effects of the nanoparticles are relatively week for Au/HDT/Ag, Ag/HDT/Ag, Ag/ AET/Au, and Ag/HDT/Au. T he observed system-selective nature of the nanoparticle induced SPR enhance ment is discussed using Fresnel equations in a six-phase model. The results demonstrate how the interactions within and among the different components of a nanoparticle based SPR sensor affect the performance of such a sensor . These results also demonstrate the potential utility of the SPR technique in the investigation of structural and optical properties of self-assemble d nanostructured materials.