Enhanced Nanoparticle Response From Coupled Dipole Excitation for Plasmon Sensors

Regular lattices of metallic nanoparticles exhibit extraordinary spectral features that arise from electromagnetic coupling between the dipole component of localized surface plasmons and constructive interference from diffracted far-field radiation. The present work introduces this coupled dipole excitation as an additional method to perform refractive index-based sensing using gold nanoparticle arrays. These arrays exhibit an aggregate sensitivity of 31 nm·RIU^-1 using the coupled dipole peak in transmission UV-vis spectroscopy. This aggregate sensitivity is in good agreement with values predicted by three models for coupled dipole excitation: an analytical coupled dipole approximation, a discrete dipole approximation, and finite difference time domain. A particle-based sensitivity, S NP , of 389 nm·RIU^-1 was determined for a fabricated array. Plasmon sensing based on the coupled dipole excitation in a gold nanoparticle array was possible even when the local surface plasmon signal from individual nanoparticles was indistinguishable from noise. Further increases in sensitivity and signal-to-noise are predicted as coupled dipole excitation parameters are optimized in high-precision fabrication of nanoparticle arrays.