Etching-assisted fabrication of photonic microparticles with tunable dual and quadruple stopbands from mono-sized and...

The integration of multiple photonic stopbands into a single microparticle is a coveted goal for advancing multiplexed sensing and high-capacity information encryption. However, conventional fabrication methods typically rely on the complex integration of different colloidal building blocks in terms of sizes or compositions, which increases cost and limits scalability. Herein, we report a facile and scalable strategy for fabricating cylindrical photonic microparticles with tunable dual stopbands from a single photonic composition, thereby eliminating the reliance on different colloidal building blocks. Our approach synergistically combines micromolding with a magnetic field-assisted selective etching process. The incorporation of ferromagnetic barium ferrite nanoparticles (BaFe₁₂O₁₉ NPs) enables precise orientation control of the microparticles, which is pivotal for the site-specific protection and etching that integrates both opal and inverse opal structures into a single microparticle. The ratio between these two distinct photonic regions can be readily tuned, allowing for customizable photonic properties and structural colors. Furthermore, we demonstrate the extensibility of this method by creating multi-segment photonic microparticles with more than two stopbands. Due to the different wettability between the opal and inverse opal regions, the microparticle array exhibits adjustable hydrophilicity and hydrophobicity and potentially possesses antifouling capability. These programmable microparticles, with their anisotropic and tunable optical characteristics, together with tunable hydrophobicity, offer significant potential for developing next-generation information encoding platforms, anti-counterfeiting technologies and displays, and even antifouling pigments.