Investigation of the structure of iron oxide nanoparticle assemblies in order to optimize the sensitivity of surface plasmon resonance-based sensors

Abstract

Surface plasmon resonance (SPR) biosensors based on metal thin films are very attractive for detection of biomolecules. Nanoparticle assemblies were recently demonstrated to significantly enhance sensitivity. Here, we show that the fine control of the structure of nanoparticle assemblies is critical to optimize the sensitivity. Iron oxide (Fe3-O4) nanoparticles were assembled onto a gold thin film by performing the Copper Catalyzed Alkyne-Azide cycloaddition (CuAAC) "click" reaction. A biotin derivative was grafted by CuAAC at the surface of nanoparticle assemblies in order to detect streptavidin (SA). The fine control of the size and of the density of nanoparticles allowed tuning the surface plasmon waves at the surface of the gold thin film in order to optimize the response of the sensors. The accessibility of biotin at the nanoparticle surface to SA was also investigated as a function of the interparticle distance. We show that the interplay between the volume fraction of iron oxide and the accessibility of biotin at the nanoparticle surface is critical to enhance the sensitivity of SPR sensors.