Chiral Wrinkle Patterns in Nano- and Microscales and their Applications with Enantioselective Interactions

Abstract

Chiral materials are optical isomers, which have 3D symmetric breaking geometry and thus have unique optical properties. Enantiomeric structures can rotate light or have different interactions for left-handed and right-handed circularly polarized light (CPL). Chiral materials are ubiquitous around living things and can be easily found, such as amino acids, proteins, organs, hands, and feet, and sometimes their chirality determines life and death. By utilizing the unique structural and optical properties of artificial chiral materials, it can be used in various fields such as protein secondary structure analysis, biosensing, optoelectronic devices, and nanomedicine. Accordingly, researchers' interest in tailored artificial chiral material for chiroptical and chirally structural properties has grown over the past few decades. Artificial chiral materials were mainly manufactured by lithography-based methods and synthesis or self-assembly using chiral additives. However, these methods have drawbacks such as high cost and material compatibility issues, which hinder active research on chiral materials.

In this thesis, an overview of artificial chiral materials and their prospects, including fabrication and potential applications, were presented. Besides, buckling-based chiral wrinkle structures and their enantioselective application in nano- and micro scales were also introduced. Buckling process had advantage to construct 3D structure by controlling deformation in out-of-plane direction. So, biaxial asymmetric buckling as a facile fabrication was utilized for fusilli-like chiral wrinkles. Size and shape of chiral wrinkles were also adjusted with control parameters such as strain, oxidation, and stretching angle. Chiral micro-wrinkles could be utilized as THz chiral metamaterials and 3D chiral microenvironments for cells. Glancing angle deposition was applied to the chiral micro-wrinkle prepared buckling process to create 3D chiral microstrip patterns, and the chiroptical response at THz was measured and calculated by finite-difference time-domain simulation. Enantiomers were sensed with enhanced signals through superchiral field and electromagnetically coupling on the surface of chiral microstrip patterns. In addition, different alignments and differentiations of cells were observed through selective recognition of the innate chirality of cells and substrates. Chiral nano-wrinkles were exploit as a chiral template for chiral plasmonic patterns prepared by self-assembly method or vapor deposition. And their linear and circular anisotropic optical properties could induce enhancement of chiroptical response by obliquely stacking multilayer of chiral plasmonic patterns. In addition, due to the charge distribution of chiral plasmonic pattern induced differently by CPL, enantiomers could be adsorbed in different amounts. In summary, the buckling-based artificial chiral material in nano- and microscales is an easy chiral material manufacturing strategy, and potential applications are presented not only with amino acids but also with cellular chirality and enantioselective interactions. I hope that this thesis will open up the use of chiral materials in potential fields such as advanced chiral optics, disease diagnosis and chiral separation.