Strong Near-Field Coupling for Enhancing Plasmonic Chirality Toward Single-Molecule Sensing

Abstract

Plasmonic chirality shows great potential in analytical chemistry, biomedicine, and life science due to the strong chiroptical response generated from metallic nanostructures. However, significant chiral effects are mainly realized in three-dimensional structures because of their high structural asymmetry and large plasmon mode volume. This paper describes planar plasmonic “τ”-shaped structure arrays that can obtain significantly enhanced chiroptical responses for single-molecule detection. The “τ”-shaped structure arrays based on a chiral–achiral coupling scheme are constructed to generate a large superchiral field and enhanced circular dichroism (CD). Numerical simulations show that the chiroptical responses can be efficiently manipulated by the near-field coupling strength of plasmons determined by the parameters of the arrays and the structural chirality of the unit cells. The planar “τ”-shaped structure arrays with a large CD signal and enhanced superchiral field enable ultrasensitive detection of single-molecule bovine serum albumin (BSA) protein.

Chiro-plasmon responses of x-shaped titanium nitride (TiN) nanoarrays by numerical simulations

“…This allows its adjustable localized surface plasmon resonance from visible to NIR band by the geometry of TiN nanostructure and dielectric environments [19][20][21][22][23]. Yet, literature reports about plasmonic chirality are noted to focus on noble metal metamaterials while TiN metamaterials are still limited [24][25][26][27][28]. Only in 2018, Sruthi group reported the CD properties of TiN core-shell nanohelices, which experimentally revealed a maximum g-factor ∼0.1 under NIR incidence.…”

Chiral Luminescence Quantum Efficiency Engineered by Plasmonic Antennas

“…The superscript ± indicates the right/left circularly polarized (RCP/LCP) emitter. Assuming that the collection efficiency remains constant when the chiral emitter is coupled to the nanostructure, the chiral detection sensitivity can be enhanced by nanostructures that generate near-field with increased local field intensity or chiral asymmetry. − For instance, recent studies have achieved chiral-sensitive enantiomeric discrimination in surface-enhanced Raman scattering response or luminescence from fluorescent species. − However, most previous works focused on the excitation enhancement during chiral sensing by engineering nanostructures to feature enhanced near-field optical chirality (OC). − To further understand the impact of the chiral near-field upon the emission process of molecules, we focus on the chiral response of luminescence QE in plasmonic nanostructures. Furthermore, the QE in TMDCs plasmonic hybrid differs for valley excitons with different spins. , Thus, chiral-dependent QE may improve the sensitivity of enantiomers’ chiral recognition.…”

Inversing Plasmonic Chirality through Locally Turning Building Blocks in a Trident-Shaped Nanostructure Array

“…L-shaped gold nanoantennas attained giant CD response from a multimode interference mechanism . “τ”-shaped structure array or trilayer tetramer array can obtain enhanced CD signal due to strong near-field coupling between the building blocks. , Previous designs focused on exploring the electric-field enhancement of the SPs to gain much larger chiroptical effects than their natural counterparts; however, the magnetic field part containing half light energy was typically weak and normally made a small contribution to CD enhancement. Moreover, inversing chiroptical responses that favor structure-sensitive applications, such as flipping the CD signals, can generally be observed in two enantiomers with distinct handedness , but rarely realized in a single planar chiral nanostructure.…”