Precisely analyzing molecular chirality is one of the important issues in a wide range of biochemical principles, as majority of biochemical interactions and resulting reactions are highly dependent on the molecular chirality. The early stage of chirality analysis was led by spectroscopic techniques such as circular dichroism (CD) or optical rotatory dispersion (ORD) using the inherent chiro-optic response of molecules at the far UV range. However, the weak light-matter interactions result in lower sensitivity which makes inevitable to use highly concentrated analytes and long integration time. Here, we periodically assembled chiral plasmonic nanoparticles (432 helicoid III nanoparticles) which can sustain chirality even in the 3 dimensions for inducing uniform chiral fields. Plasmonic nanostructures or chiral metamaterials provides a new route to achieve ultrasensitive characterization of molecular chirality as it can enhance chiral light-matter interactions in the vicinity (local hot-spot) of nanostructures. While local nature of conventional approaches yields error-prone results depending on the relative orientation of molecules and local concentrations, uniform and enhanced chiral field of assembled chiral nanostructures intensify local light-matter interactions to offer viable route to overcome these limitations. Illumination of circularly polarized light (CPL) collectively excites helicoids in assembled structure (2D helicoid crystal) forming collective resonance (CR) mode and circular dichroism. Importantly, the effective dipole retrieval of helicoids revealed that the dipole of helicoid in 2D helicoid crystal collectively spin to the same direction with illuminated CPL. This collective behavior leads to uniform enhancement of chiral fields on the 2D helicoid surface. The 2D helicoid crystal exhibited highly sensitive response to the change in molecular chirality at millimolar (mM) scale supported by distinct polarization resolved color distribution of 2D helicoid crystals in different enantiomeric solutions. Furthermore, integration of 2D helicoid crystal in microfluidic systems enabled monitoring of few µM to pM concentrate change in sample chirality of nucleotides (microRNA-21) and proteins (SNARE complexes). We believe that our collective circular dichroism-based strategy offers a new paradigm and rational design rules of chiral plasmonic structures for robust enantioselective sensing.

Collective circular dichroism of 2D helicoid crystals for ultrasensitive molecular chirality analysis

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.