Chitin is the 2nd most abundant biopolymer, produced by crustacean, insects, and fungi. With such diverse occurrence in nature, chitin assembled in many different nanostructures that leads to a number of striking optical effects such as antireflective arrays [1] in some insects and photonic bandgap structures that give rise to strong iridescence in beetles [2] and some fungi [3] or even gyroid structures in some butterflies [4]. We are interested to understand the helicoidal organization of chitin and studied Penaeus setiferus (King Prawn/Shrimp) which conforms into a chiral nematic structure with variable pitch values between 200 nm and a few microns. P.setiferus uses such helicoidal structure mainly to form a strong mechanical network as a part of the exoskeleton and the optical appearance of the shrimp seems to do not reveal the interesting chiral optics. However, when the proteins and Ca-minerals were removed from the shrimp exoskeleton, the residual chitin show quite remarkable iridescent appearance with strong circular polarization, Fig1. This helicoidal framework is highly porous and provides an exciting template for exploring chiral photonics using different deposition methods. With the goal of transferring this intricate network, the iridescent chitin shell is used in this study to decorate with Au nanoparticles using wet chemical methods. Our studies show that the helicoidal organization of the iridescent shrimp shells can be conformed and transferred into higher refractive index materials with a distinctive macroscopic combination of optical effects that causing circular dichroism. The interplay between the plasmonic states of Au and the chiral photonic structure of shrimp shell is characterized using optical microscopy, UV-Vis-NIR visible spectroscopy, and high-resolution SEM and TEM techniques

Understanding the structural diversity in chitins as a versatile template for optical biomimetics

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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