All-Water-Based Nanofabrication of Multilayer Biopolymer/Inorganic Reflectors with Reconfigurable Structural Color Patterns

Achieving high performance nanoscale photonic functionalities remains extraordinarily challenging when using naturally derived biomaterials. The ability to manipulate ultrathin films of structural proteins─combined with photolithographic control of their polymorphism─unlocks a compelling route toward engineering biopolymer-based photonic crystals with precisely defined photonic bandgaps and reconfigurable structural colors. In this work, we describe a robust, water-based fabrication process for silk/inorganic hybrid one-dimensional (1D) photonic crystals that overcomes many of the conventional difficulties in ensuring reproducibility, uniformity, and reliability at the nanoscale. Through a carefully designed solution-processing strategy, sequentially stacked nanofilms with tunable sub-100 nm thicknesses are achieved, yielding silk/ZrO₂ photonic crystals with high reflectivity of up to 84% with 8 bilayers. Ultraviolet irradiation further modulates the structural conformation of the silk nanofilms within the multilayer, enabling both passive structural color tunability and dynamically reconfigurable patterns. Silk-based photonic crystals that embed encrypted, water-responsive structural color codes are illustrated as a proof-of-concept, underscoring the viability of more sophisticated nanoscale biomaterial-based photonic systems.