In this paper, we report on experimental and theoretical studies of investigating how the structural properties of plasmonic nanodome array devices determine its optical properties and sensing performance. We focused on examining the effect of the interdome gap spacing within the plasmonic array structures on performance for label-free capture affinity biosensing applications. Optical sensing properties were characterized for nanodome array devices with interdome spacings (gap between edges of adjacent nanodomes) of 14 nm, 40 nm, and 79 nm, as well as a device where adjacent domes are in contact (zero spacing). For each interdome spacing, the resonance extinction spectrum was measured using a broadband reflection instrumentation and finite-difference-time-domain (FDTD) simulation was used to model the local electric field distribution associated with the resonances. Key aspects of the plasmonic nanodome arrays for label-free biosensing applications were investigated by measuring their sensitivities to bulk refractive index changes and surface binding effects using charged polyelectrolyte layers. We then characterized the surface sensitivity (sensitivity to molecular binding events or changes of refractive index within the detection region within 30 nm near the sensor surface) as a metric to predict the optimal interdome spacing for capture affinity-based biosensing measurements. Strong interdome near-field coupling achieved with smaller interdome spacing yielded higher electromagnetic field enhancement and bulk refractive index sensitivity. However, the smallest interdome spacing was not optimal for surface biosensing applications where a reduction in the surface sensitivity for the dipole mode was observed for device with interdome spacing below 14 nm.
Citation: Optics Express
Pub Type: Journals
Surface plasmon resonance, Nanodome array, Optical biosensor, Label-free capture affinity