Correlative microscopy of single self-assembled nanorod dimers for refractometric sensing

Single metallic particles and dimers of nanospheres have been used extensively for sensing, but dimers of particles provide attractive advantages because they exhibit multiple modes that can be tuned by the dimer geometry. Here, we employ correlative microscopy of single self-assembled dimers of gold nanorods to study their performance as refractometric sensors. The correlation between atomic force microscopy and single-particle white-light spectroscopy allows us to relate the measured sensitivity to numerical simulations taking into account the exact geometry of the construct. The sensitivity of the antibonding mode is in good agreement with simulations, whereas the bonding mode exhibits a reduced sensitivity related to the accessibility of the gap region between the particles. We find that the figure of merit is a trade-off between the resonance linewidth and its refractive index sensitivity, which depend in opposite ways on the interparticle angle. The presence of two narrow plasmon resonances in the visible to near-infrared wavelength regime makes nanorod dimers exciting candidates for multicolor and multiplexed sensing.