Structured bio-polymers for optical and photonic applications

Photonic technologies such as metamaterials, metasurfaces, and photonic crystals are increasingly exploring biodegradable alternatives to solid-state components. Among them, the Luria-Bertani Agar (LBA) growth medium has recently emerged as a promising bio-polymer, offering the unique advantage of sustaining fluorescent-protein-expressing bacteria, enabling a new class of biological and eco-friendly optical sources. In this study, we successfully implemented micro-and nano-photonic structures in functionalized LBA, used as planar and cell-compatible alternative to traditional bulk solid-state resonators. We replicated three distinct structures, a photonic crystal, a quasi-crystal and a metasurface, demonstrating their potential as templates for advanced photonic applications. We inoculated LBA with E. coli expressing Green Fluorescent Protein (GFP), confirming both cell survival and photoluminescence performance. Furthermore, we addressed LBA's intrinsic optical limitations due to its high scattering properties. Modified LBA formulations demonstrated that decreasing nutrient content significantly enhances the optical properties, reducing absorption and scattering while improving diffraction efficiency, without compromising cell viability. Additionally, we propose a sustainable approach to long-lifetime photoemissive metasurfaces based on an ethyl-cellulose (EC) matrix doped with Ir(III). This system combines outstanding phosphorescent properties with EC compatibility, towards hybrid metasurfaces with long-lifetime enhanced photoluminescence (PL). The approach will be integrated also with the possibility to use cellulose (extracted from broom) and other bio-polymers, like chitosan (extracted from agri-food wastes, like crustacean shells), both products abundant in the regions of southern Italy, as biodegradable alternatives to conventional plastics. Their use will be implemented in the framework of Physical Unclonable Functions (PUFs) for the fabrication of full-biodegradable anti-counterfeiting labels.