Optical sensing characteristics of nanostructures supporting multiple localized surface plasmon resonances

Noble metal nanoparticles supporting localized surface plasmon resonances (LSPR) have been extensively investigated for label free detection of various biological and chemical interactions. When compared to traditional propagating surface plasmon based sensors, LSPR sensors offer extensive wavelength tunability, greater electric field enhancement and sensing in reduced volumes. However, these sensors also suffer from a major disadvantage - LSPR sensors remain highly susceptible to interference because they respond to both solution refractive index changes and non-specific binding as well as specific binding of the target analyte. These interactions can compromise the measurement of the target analyte in a complex unknown media and hence limit the applicability and impact of the sensor. Despite the extensive amount of work done in this field, there has been an absence of optical techniques that make these sensors immune to interfering effects. Recently, our group experimentally demonstrated a multi-mode LSPR sensor that exploits three resonances of a U-shaped gold nanostructure to differentiate the target interaction from bulk and surface interfering effects. In this paper, we provide a comprehensive description of the electric field profiles of the three resonances of the U-shaped nanostructure. We will also evaluate the sensitivities of the nanostructure to the various bulk and surface interactions using numerical simulations.