A Bi-functionalized core-shell photonic microcapsules: Killing two “birds” with one controllably etched “stone”

Core-shell photonic microcapsules (PhMCs) have the advantage of rich structural color compared with homogeneous photonic crystal microspheres, and thus have higher application value. How to prepare structurally color controllable PhMCs with responsive functions is increasingly urgent, which is related to the possibility of further expanding their applications. In this report, we integrate microfluidic and controlled etching techniques to conveniently prepare structurally color controllable responsive PhMCs and successfully apply them in the fields of metal ion detection and optical anti-counterfeiting. Microfluidics endows PhMCs with controllable and homogeneous dimensions. Meanwhile, controlled etching gives PhMCs shells a controllable ratio of opal/inverse-opal structures. The fully-etched PhMCs were designed as metal ion detectors to identify the existence of metal ions in the solution through the change of structural color. Notably, the partially etched PhMCs have three structural colors of red/green/yellow, which is the first time that triple stop band gaps PhMCs have been prepared based on two materials. The triple information has been switched by adjusting the transmission/reflection modes and the temperature to explore the function of an optical anti-counterfeiting model. Our study provides a new path for the construction of functionalized PhMCs, and further expands its potential application value.