Scheme 1. Schematic illustration of the physiochemical mechanisms and applications of chirality transfer from chiral molecules to plasmonic NPs.

We have devised a simple method to determine the absorption and radiative decay rates of surface plasmon polaritons in an Au nanohole array by combining polarization-resolved reflectivity spectroscopy and temporal coupled-mode theory. The dependence of two rates on wavelength has been measured and they are found to agree with finite-difference time-domain simulations. As both absorption and radiative decay rates play a key role in several plasmonic applications, our approach offers a simple and effective means in determining them.

Enhancing the circular dichroism signals of chiral plasmonic nanostructures is vital for realizing miniaturized functional chiroptical devices, such as ultrathin wave plates and high-performance chiral biosensors. Rationally assembling individual plasmonic metamolecules into coupled nanoclusters or periodic arrays provides an extra degree of freedom to effectively manipulate and leverage the intrinsic circular dichroism of the constituent structures. Here, we show that sophisticated manipulation over the geometric parameters of a plasmonic stereo-metamolecule array enables selective excitation of its surface lattice resonance mode either by left- or right-handed circularly polarized incidence through diffraction coupling, which can significantly amplify the differential absorption and hence the intrinsic circular dichroism. In particular, since the diffraction coupling requires no index-matching condition and its handedness can be switched by manipulating the refractive index of either the superstrate or the substrate, it is therefore possible to achieve dynamic tuning and active control of the intrinsic circular dichroism response without the need of modifying structure parameters. Our proposed system provides a versatile platform for ultrasensitive chiral plasmonics biosensing and light field manipulation.

We show the spectral figure-of-merit (FOM) from nanohole arrays can be larger than 1900/RIU by phase-based surface plasmon resonance. By using temporal coupled mode theory, we find the p-s polarization phase jump is the sharpest when both the absorption and radiative decay rates of surface plasmon polaritons are matched, yielding an extremely small spectral differential phase linewidth and thus superior FOM. The result is supported by numerical simulation and experiment. As a demonstration, we show the phase detection outperforms the conventional spectral counterpart significantly by sensing the binding of bovine serum albumin antibodies under identical condition.

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