Chirality plays a fundamental role in natural sciences and pharmacology. Circularly polarized light, a type of light wave that propagates on a helical path, is routinely used in chemical and biochemical instrumental analysis to characterize the three-dimensional structure of molecules. The main problem is that the optical responses of chiral molecules are inherently weak and new types of engineered materials are needed to enhance the detection of molecular chirality. Chiral metamaterials, which exhibit extraordinary electromagnetic properties not observed in nature, are fabricated with repeating patterns capable of enhancing such interactions. In order for a metamaterial to interact with ultraviolet or visible light, the scale of the repeating patterns needs to be on the order of hundreds of nanometers or less, which is extremely difficult and costly to fabricate using currently available technologies. This represents a significant challenge to be addressed in metamaterials engineering for future optical devices.
The CELICOIDS project responds to this growing need for simpler metamaterial fabrication technologies and proposes the development of new types of chiral nanostructures to control light-matter interactions. The project focuses on self-assembly of nanoparticles, which is a bottom-up fabrication technique that relies simply on physical interactions between particles in order to form the desired pattern, without the need of complex and expensive equipment.
The objective of CELICOIDS is to investigate the bottom-up self-assembly of end-modified nanorods to fabricate a new class of metamaterial, metallic nanohelicoids. The nanorods are obtained from cellulose, a natural polysaccharide extracted from paper, cotton or other plant fibres. When a suspension of the end-modified cellulose nanorods is poured onto a surface or confined within microdroplets, they self-assemble to form helical structures as they dry. Once these structures are impregnated with metals such as gold, they will guide the formation of metallic nanohelicoids. After removing the modified cellulose template, the ultimate goal is to achieve new metallic helicoidal structures. This nanostructure, when combined in a solution of chiral molecules, will likely amplify the interactions between circularly polarized light and chiral molecules through their anticipated electromagnetic properties. These properties will open new prospects for optical instruments routinely used in chemistry, biochemistry and pharmacology.
