Distance control in-between plasmonic nanoparticles via biological and polymeric spacers

• The possibilities to produce precisely-controlled nanoparticle groupings by using biological and polymeric spacers are discussed.
• Experimental data are used to point out the current limits of forming gold nanoparticle dimers by using biological and polymeric spacers.
• Calculations were made to discuss the effect of the nanoparticle diameter and the inter-particle distance in the plasmonic coupling.

SummaryFor detailed experimental studies about the electromagnetic coupling between plasmonic nanoparticles, precisely-controlled nanoparticle groupings with adjustable inter-particle distance would be required. In the present review article, the possibilities of generating such groupings by using biological and polymeric spacers in between the nanoparticles are described. In particular, streptavidin–biotin and DNA are discussed as biological spacers, and layer-by-layer (LbL) assembled films as polymeric spacers. The concepts are visualized by experimental data, which also point out the pitfalls and current limits of such approaches. Calculation results reveal that while small variations in the diameter of plasmonic cores lead to small changes, small variations in the inter-particle distance due to soft linkers result in significant changes in plasmonic coupling. In the case of protein-based spacers, nonspecific adsorption has to be considered as an obstacle for the formation of controlled groupings.

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