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

Abstract

Resonant plasmonic–molecular chiral interactions are a promising route to enhanced biosensing. However, biomolecular optical activity primarily exists in the far-ultraviolet regime, posing significant challenges for spectral overlap with current nano-optical platforms. We demonstrate experimentally and computationally the enhanced chiral sensing of a resonant plasmonic–biomolecular system operating in the far-UV. We develop a full-wave model of biomolecular films on Al gammadion arrays using experimentally derived chirality parameters. Our calculations show that detectable enhancements in the chiroptical signals from small amounts of biomolecules are possible only when tight spectral overlap exists between the plasmonic and biomolecular chiral responses. We support this conclusion experimentally by using Al gammadion arrays to enantiomerically discriminate ultrathin (<10 nm thick) films of tyrosine. Notably, the chiroptical signals of the bare films were within instrumental noise. Our results demonstrate the importance of using far-UV active metasurfaces for enhancing natural optical activity.

Achiral Magnetic Photonic Antenna as a Tunable Nanosource of Chiral Light

“…Therefore, by demodulating the signal, the NS gives access to a very large spectral range covering about 300 nm, centered on the resonance wavelength, whose sign of the chirality density can be fully controlled over this range. Moreover, by changing the NS's length or material, the whole visible spectrum can be covered, as well as the ultraviolet, where chiral biomolecules efficiently absorb light 49 (see Figures S4, S16, and S17). Also, fabrication defects of the NS, such as rounded corners, would only marginally affect the optical and chiral response of the nanostructure (Figure S5).…”

Can we still measure circular dichroism with circular dichroism spectrometers: The dangers of anisotropic artifacts

“…1,35 But as the chiral nanomaterials community engineers materials with strong linear anisotropy and g-factors approaching the theoretical limit, this second-order expansion is insufficient and may be relaying inaccurate approximations of the true, underlying contributions to the signal. [23][24][25][26][27][36][37][38][39][40] In this work, we derive expressions for the measured CD (I CD ) using the differential Stokes-Mueller formalism with first-, second-, and third-order Taylor series expansions and consider the differences in the resultant expressions. After reinforcing the presence of second-order LDLB artifacts in linearly anisotropic samples, we find that the third-order expansion introduces terms that can make noticeable contributions to the simulated CD spectra in strongly linearly and circularly dichroic media.…”

“…For the most part, modeling the measured CD using expansions to the second‐order is sufficient 1,35 . But as the chiral nanomaterials community engineers materials with strong linear anisotropy and g‐factors approaching the theoretical limit, this second‐order expansion is insufficient and may be relaying inaccurate approximations of the true, underlying contributions to the signal 23–27,36–40 . In this work, we derive expressions for the measured CD ( ) using the differential Stokes–Mueller formalism with first‐, second‐, and third‐order Taylor series expansions and consider the differences in the resultant expressions.…”

Controlled synthetic chirality in macroscopic assemblies of carbon nanotubes

“…Furthermore, in contrast to chiral metamaterials that require sophisticated nanofabrication processes to engineer conventional metallic and dielectric materials, the demonstrated synthetic chiral matter consisting of ordered CNTs can be prepared through simple and scalable procedures. Especially in the DUV range, the CNT-based chiral platform is advantageous over chiral metamaterials because the available DUV metallic and dielectric materials are limited to only a few candidates, including magnesium [35], aluminum [36][37][38], and titanium dioxide [39], and the ultrasmall feature sizes and sophisticated geometries of metamaterials make their fabrication extremely challenging. In addition, the demonstrated synthetic chiral matter is fundamentally different from ordinary metamaterials because CNTs are not simple metallic or dielectric rods.…”