Enantioselective Sensing by Collective Circular Dichroism of 2D Helicoid Crystals

Chiral plasmonic nanostructure 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 [1,2]. However, these approaches tend to be error-prone due to the spatially varying handedness of local hot-spots and stochasticity of the target molecular orientations, vibrations, and local concentrations [3]. In this regards, applying uniform and strong chiral field offers viable route to overcome these limitations. Previously, we presented a novel gold helicoid nanoparticle with 432 symmetry which can preserve their handedness in 3 dimensions by peptide-assisted method [4,5]. Based on the unique property of 432 helicoid III nanoparticles (helicoids), here, we demonstrate a collective circular dichroism from periodically assembled helicoids (2D helicoid crystal) for highly sensitive and robust enantioselective sensing. The collective resonance [6] of helicoids in crystal results in collective spinning of helicoid dipoles upon circularly polarized light (CPL) illumination and this collective behavior leads uniform boost up of chiral fields on the 2D helicoid surface. The 2D helicoid crystal exhibited highly sensitive response to the molecular chirality change at sub millimolar (mM) scale which was substantiated by distinct polarization resolved color distribution of 2D helicoid crystals in different enantiomeric solutions. Integration of 2D helicoid crystal in microfluidic systems enabled trace sample analysis and practical application of 2D helicoid crystal for the monitoring of chirality alteration in nucleotides (microRNA-21) and proteins (SNARE complexes). We believe that our collective circular dichroism based strategy offers a truly new paradigm and rational design rules of chiral plasmonic structures for robust enantioselective sensing.<br/><b>References</b><br/>[1] Tang, Y. et al., <b><i>Phys. Rev. Lett</i>.</b>, 104, 163901 (2010).<br/>[2] Ho, C. S. et al., <b><i>ACS Photonics</i></b>, 4, 197 (2017).<br/>[3] Hentschel, M. et al., <b><i>Sci. Adv</i>.</b>, 3, e1602735 (2017).<br/>[4] H.-E. Lee et al., <b><i>Nature</i></b>, 556, 360 (2018).<br/>[5] S.W. Im et al., <b><i>Adv. Mater.</i></b>, 32, 1905758 (2020).