Detecting Antibody–Antigen Interactions with Chiral Plasmons: Factors Influencing Chiral Plasmonic Sensing

Abstract

Chiral near fields possessing enhanced asymmetry (superchirality), created by the interaction of light with (chiral) nanostructures, potentially provide a route to novel sensing and metrology technologies for biophysical applications. However, the mechanisms by which these near fields lead to the detection of chiral media is still poorly understood. Using a combination of numerical modeling and experimental measurements on an antibody–antigen exemplar system, important factors that influence the efficacy of chiral sensing are illustrated. It is demonstrated that localized and lattice chiral resonances display enantiomeric sensitivity. However, only the localized resonances show a strong dependency on the structure of the chiral media detected. This can be attributed to the ability of birefringent chiral layers to strongly modify the properties of near fields by acting as a sink/source of optical chirality, and hence alter inductive coupling between nanostructure elements. In addition, it is highlighted that surface morphology/defects may amplify sensing capabilities of localized chiral plasmonic modes by mediating inductive coupling.

Tuning dipolar and multipolar resonances of chiral silicon nanostructures for control of near field superchirality

“…Using a curve smoothing function over this wavelength range on the simulated spectra, which previously has been used to mimic the effects of structural heterogeneity, would improve the level of agreement with experiment. 30 The observed levels of CD are of a similar magnitude to plasmonic 2D chiral geometries 18,31 and are much greater those produced from colloidal nanoparticle arrangements, however the latter is advantageously more suitable for mass production. 32,33…”

Lithography‐Free Fabrication of Terahertz Chiral Metamaterials and Their Chirality Enhancement for Enantiomer Sensing

“…Previously, researchers using other chiral geometries have found it difficult to achieve these characteristics. [45,51] For instance, 3D helices show discontinuous spatial distribution of the optical chirality with inversion of the signs, [45,51,52] 2D gammadions have the same-signed optical chirality for both of the circular polarization states, [53] planar spirals show spatial mismatch in the optical chirality region when the polarization state is switched, [54] and chiral oligomers provide chirality hot spots located inside the structure that limit access. [55] Therefore, the unique chiral geometry of CHAM is beneficial for the utilization of near-field optical chirality with changes in the polarization state.…”

Probing Interactions between Chiral Plasmonic Nanoparticles and Biomolecules

“…Binding of the antigen resulted in an alteration of the real component of the effective refractive index of the biomolecular layer, which was amplified by the presence of a strong plasmonic field. [84] Link and co-workers studied a different type ii) The collective CD mode either decreases or increases in intensity depending on the sign of the enhanced optical chirality of the chiral molecular layer. Reproduced with permission from ref.…”

“…Kadodwala and co‐workers fabricated an antibody‐antigen biosensing system, where antibodies were immobilized on an optically chiral substrate. Binding of the antigen resulted in an alteration of the real component of the effective refractive index of the biomolecular layer, which was amplified by the presence of a strong plasmonic field [84] . Link and co‐workers studied a different type of system, where the absorption component of κ for chromophore biomolecules was amplified by coupling to the plasmon mode of a gold nanosphere [85] .…”