Coupling of multiple LSP and SPP resonances: interactions between an elongated nanoparticle and a thin metallic film.

We study the coupling interactions between a progressively elongated silver nanoparticle and a silver film on a glass substrate. Specifically, we investigate how the coupling between localized surface plasmons (LSPs) and propagating surface plasmon polaritons (SPPs) is influenced by nanoparticle length. Although the multiple resonances supported by the nanoparticle are effectively standing wave surface plasmons, their interaction with the SPP continuum of the underlying Ag film indicates that their spectral response is still localized in nature. It is found that these LSP-SPP interactions are not limited to small particles, but that they are present as well for extremely long particles, with a transition to the SPP coupling interactions of a bilayer metallic film system beginning at a particle length of approximately 5 µm.

Biotinylated synthetic chemokines: their use for the development of nonradioactive whole-cell binding assays.

A chemokine binding assay on whole cells was developed using biotinylated synthetic CCL22 as a model ligand. CCL22 analogues were produced by a chemical route, resulting in > 97% homogeneous and defined polypeptides. First, the 5 biotinylated CCL22 analogues synthesized were captured by agarose-immobilized streptavidin, indicating that the biotin molecules introduced in positions G1, K27, K49, K61, and K66 of CCL22 were accessible for binding. Then, it was established using a migration assay that the biotinylated chemokines were at least as biologically active as the unmodified CCL22 form. Subsequently, the biotinylated chemokines were evaluated in an FACS-based whole-cell binding assay. Surprisingly, only the CCL22 analogue with the biotin in position K66 constituted a suitable staining reagent for CCR4-positive cells. Finally, binding characteristics and reproducibility of the binding assay were outlined for the CCL22 analogue with the biotin in position K66. These results exemplified that biotinylated synthetic chemokines constitute promising ligands for the development of chemokine receptor-binding assays on whole cells, provided the position of the biotin moiety introduced along the sequence is adequately chosen.