Dense Arrays of Nanohelices: Raman Scattering from Achiral Molecules Reveals the Near‐Field Enhancements at Chiral Metasurfaces

Abstract

Against the background of the current healthcare and climate emergencies, surface enhanced Raman scattering (SERS) is becoming a highly topical technique for identifying and fingerprinting molecules, e.g., within viruses, bacteria, drugs, and atmospheric aerosols. Crucial for SERS is the need for substrates with strong and reproducible enhancements of the Raman signal over large areas and with a low fabrication cost. Here, dense arrays of plasmonic nanohelices (≈100 nm in length), which are of interest for many advanced nanophotonics applications, are investigated, and they are shown to present excellent SERS properties. As an illustration, two new ways to probe near‐field enhancement generated with circular polarization at chiral metasurfaces are presented, first using the Raman spectra of achiral molecules (crystal violet) and second using a single, element‐specific, achiral molecular vibrational mode (i.e., a single Raman peak). The nanohelices can be fabricated over large areas at a low cost and they provide strong, robust and uniform Raman enhancement. It is anticipated that these advanced materials will find broad applications in surface enhanced Raman spectroscopies and material science.

Tunable Near-Infrared II Photosensitive Platforms of Plasmonic Ring Nanocone Arrays

“…NIR-based optical technologies have received extensive interest because of their various prospective applications in clinical diagnosis and medicament dispensing in cellular tissue and trace molecules’ detection. − Preparation of “hot spot” with a strong localized electric field from a small distance between plasmonic nanoparticles or the sharp tip of anisotropic nanostructure was acceptable as the main distribution to enhance Raman intensity. , However, random aggregation of plasmonic nanoparticles induced a significant redshift of surface plasmon resonance modes, and uncontrollable optical properties were the drawbacks of SERS reproducibility and sensitivity. , Much effort has been made to fabricate SERS substrates including lithography technology and nanoparticle self-assembly to improve SERS signal. − …”

Chiral Opto‐Fluidics and Plasmonic Nanostructures as a Functional Nanosystem for Manipulating Surface Deformations

“…For this task, a chiral system with inherent distinct absorption under circularly polarized light (CPL) can be prioritized. [ 13 ] Although the concept of chirality originates from chemistry, nowadays it gains ground on nanotechnology and nanophotonics by introducing chiral metastructures, [ 14 ] metasurfaces, [ 15 ] quantum emitters [ 16 ] and bio‐plasmonic conjugates. [ 17 ] The optoelectronic chirality of artificially designed meta‐objects finds large utilization in sensing, [ 18 ] photodetection, [ 19 ] and photochemistry.…”

“…[ 20 ] Chiral plasmonic systems exhibit differential electromagnetic absorption under CPL and consequent variable temperature generation introducing photothermal chirality. [ 15b ] Recently, we have studied the fluid convection induced by the chiral photothermal effect and first proposed the concept of chiral optofluidics. [ 21 ] However, in the previous work, natural convection flow of water driven by the thermal‐induced buoyancy suffered from extremely small velocity (≈10 −2 nm s −1 ).…”

Polymeric Carbon Nitride with Chirality Inherited from Supramolecular Assemblies

“…Discovering new methods to produce, control, identify, and separate chiral compounds can profoundly impact the development of pharmaceuticals, agrochemicals, and many other materials. [1][2][3][4] The synthesis of chiral compounds and chiral separation are among the most significant challenges in chemistry, and they play essential roles in the pharmaceutical industry.…”