Surface Plasmons for Chiral Sensing

Chiral sensitive techniques have been used to probe the fundamental symmetries of the universe, study biomolecular structures, and even develop safe drugs. The traditional method for the measurement of chirality is through optical activity, however, chiroptical signals are inherently weak and often suppressed by large backgrounds. Different techniques have been proposed to overcome the limitations of traditionally used optical polarimetry, such as cavity- and/or nanophotonic-based schemes. In this chapter we demonstrate how surface plasmon resonance can be employed as a new research tool for chiral sensing, which we term here as CHIral Surface Plasmon Resonance (CHISPR). We present how surface plasmons at a metal-chiral interface are sensitive to the chirality parameter of the chiral medium and how their properties can be exploited to reveal information not easily accessible using standard polarimetric/nanophotonic approaches. We then present an experimental realisation of CHISPR, an angle-resolved measurement scheme, and demonstrate how can one detect the complete chirality (handedness and magnitude) of a chiral sample while being also sensitive to both the real and imaginary part of a chiral sample’s refractive index. We present analytical results and numerical simulations of CHISPR measurements, predicting signals in the mdeg range for chiral samples of \({<}\)100 nm thickness at visible wavelengths. Finally, we present a theoretical analysis that clarifies the underlying physics of the near-field chiral interactions and their far-field manifestation. In overall, CHISPR builds upon the strengths of standard SPR: does not require elaborate fabrication and has the advantage of being directly implementable on existing SPR instrumentation, making it, thus, an ideal modality for studying chirality dynamics on surfaces.