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

Abstract

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.