Controlled etching-assisted microfluidic fabrication of magnetic photonic crystal microspheres with tailored structures and functions

The integration of photonic crystal (PC) architectures with magnetic responsiveness offers a compelling route toward smart micro-materials. However, achieving precise structural control over such composite microspheres via simple fabrication methods remains elusive. Here, we report a facile strategy combining simplified T-junction microfluidics with a concept of controlled HF etching to generate a series of hierarchically porous magnetic photonic crystal microspheres (MPhCMs) with tailored architectures. Crucially, by precisely regulating the etching extent, we achieve two functionally distinct yet structurally related outcomes. Complete etching transforms the spheres into hierarchically porous adsorbents exhibiting an adsorption rate of 92.33%, owing to the effect of etching-induced micropores. Conversely, partial etching yields symmetric Janus MPhCMs with an asymmetric fluorescent-magnetic barcode. These Janus microspheres demonstrate a magnetically driven fluorescence switching behavior, making them ideal candidates for advanced anti-counterfeiting. Thus, the same controllable etching strategy enables a seamless transition from high-performance absorbents to smart optical barcodes. This work presents a versatile platform for designing multifunctional microparticles, bridging the gap between structural engineering and high-performance applications in environmental remediation and optical security. Graphical