Chiral plasmonic properties arising from the metal nanostructures and their assemblies are desirable for a range of applications such as chiral biosensors, negative refractive materials, broadband circular polarizers. However, it remains a challenge to realize genuine chiroptical responses by arranging plasmonic nanoparticles in a large-scale solid-state material. The past research often uses the chiral nematic scaffolds provided by cellulose-nanocrystals (CNCs) self-assembly. The selective reflection of lefthanded circularly polarized light in the visible spectra range by the chiral CNC template strongly hinders the observation of chiroptical properties from plasmonic metal nanostructures. Here, we present a chiral plasmonic composite film composed of chitin nanocrystals (ChNCs) and silver nanoparticles (AgNPs) that exhibit genuine circular dichroism (CD) effects with a characteristic bisignate peak-and-dip line shape surrounding the plasmon resonance frequency of AgNPs. Our wet-chemistry synthetic route, which takes inspiration from the well-known silver mirror reaction, is relatively easy and low-cost, as chitin belongs to the family of reducing sugar that can reduce metal precursors. This synthetic route can be readily altered to tune the chiroptical properties, such as the intensity and spectra position of the CD signal, of the final composite material. Furthermore, the organization of plasmonic nanoparticles in the template is disordered but is still able to generate constant left-handed CD signals. The physical origin of the optical chirality of this disordered system will be discussed. In conclusion, our work provides a novel motif for realizing device-friendly chiral plasmonic materials, and bridges the relative fields of chemistry, physics, and material science due to its multidisciplinary nature.

Solid-state chiral plasmonic materials via chitin-nanocrystals self-assembly

ACS Spring 2022

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