Sensoric applications based on plasmonic effects at metal nanoparticles

Localized surface plasmons (LSPs) are charge density oscillations caused by an interaction of the external electromagnetic waves with the interface between metallic nanostructures (e. g. noble metal nanoparticles) and a dielectric medium. Intensity and frequency of the resulting SP absorption bands are characteristic for the type of material and depends on the size, shape and surrounding environments of the nanostructures. We have designed core/shell-nanostructures with a defined Au-core and increasing Ag-shell thickness as previously described [17]. We have used AFM measurement and dark-field microscopy to characterize the nanoparticles, which were immobilized via silane chemistry on glass substrates. The plasmon band of selected particles was investigated by single particle spectroscopy (SPS) in transmission and reflection mode. Their potential as optical biosensor was demonstrated by immobilization of a protein and a protein specific antibody leading to a refractive index change in the local environment of metal nanoparticles, which causes a characteristic shift of the SP absorption band maximum.