Nanophotonic Chiral Sensing: How Does it Actually Work?

Abstract

Nanophotonic chiral sensing has recently attracted a lot of attention. The idea is to exploit the strong light-matter interaction in nanophotonic resonators to determine the concentration of chiral molecules at ultra-low thresholds, which is highly attractive for numerous applications in life science and chemistry. However, a thorough understanding of the underlying interactions is still missing. The theoretical description relies on either simple approximations or on purely numerical approaches. We close this gap and present a general theory of chiral light-matter interactions in arbitrary resonators. Our theory describes the chiral interaction as a perturbation of the resonator modes, also known as resonant states or quasinormal modes. We observe two dominant contributions: A chirality-induced resonance shift and changes in the modes excitation and emission efficiencies. Our theory brings new and deep insights for tailoring and enhancing chiral lightmatter interactions. Furthermore, it allows to predict spectra much more efficiently in comparison to conventional approaches. This is particularly true as chiral interactions are inherently weak and therefore perturbation theory fits extremely well for this problem.

Chiral Plasmonic Shells: High-Performance Metamaterials for Sensitive Chiral Biomolecule Detection

“…But in contrast, κ owns opposite signs for L-and D-tryptophan solutions, and this makes a specified interaction with CMs of opposite handedness through modifying the chiral field and the accompanying chiroptical resonance. 51 These enhanced chiral fields (Figure 6c,f) near CPSs are exclusively of one sign across the entire patch, which greatly enhances this handshake interaction and confers excellent chiral sensor performance.…”

Neural-Network-Enabled Design of a Chiral Plasmonic Nanodimer for Target-Specific Chirality Sensing

“…As reported by several pioneering works, Δn and Δκ in the vicinity of the plasmonic resonator redistribute the resonant energy of the plasmonic resonator and result in a shift in resonance frequency of an individual mode. 60−62 Herein, the magnitude of spectral shift as a result of the dielectric 60,61 and chiral perturbation 62 (Δω 0,n and Δω 0,κ ) at the eigenfrequency ω 0 can be readily written in terms of the electric field E, magnetic field H, and the optical helicity density h = Im{E•H*}/2ω:…”

Resonant Plasmonic–Biomolecular Chiral Interactions in the Far-Ultraviolet: Enantiomeric Discrimination of sub-10 nm Amino Acid Films

“…The net OA enhancement can arise due to multiple mechanisms, among them are resonance shifts and modifications in the excitation and emission of the resonator modes. 53 These individual calculations are, however, beyond the scope of this work.…”

“…Re{κ} can modify the CD response of plasmonic−biomolecular systems. 53 When the film has a purely imaginary κ, the lack of mirror symmetry is more substantial (Figure 1c, blue curves), even after considering the background biomolecular chiroptical signal. The same observations are valid for the CB signals (Figure 1d).…”

“…For real biomolecules, with dispersive n and κ, we expect to see the largest deviations from the reference spectra, when the CD (or CB) response of the plasmonic nanostructure spectrally overlaps with the respective chiral signal of the biomolecule. Recently, Both et al 53 theoretically described the multiple mechanisms contributing to the CD signal of chiral plasmonic nanostructures interacting with a chiral medium. We expect the same effects to be present in our work because both nanostructure and biomolecular films are chiral.…”