Uniform Core–Shell Photonic Crystal Microbeads as Microcarriers for Optical Encoding

We demonstrate a rapid and robust method to fabricate uniform core–shell photonic crystal (PC) microbeads by the microfluidic and centrifugation–redispersion technique. Colored crystalline colloidal arrays (CCAs) were first prepared through centrifugation–redispersion approach by self-assembly of polystyrene–poly­(N-isopropylacrylamide) (PS–PNIPAm) core/shell nanoparticles (NPs). Different from the conventional NPs (e.g., charged PS or PNIPAm NPs), PS–PNIPAm NPs could easily self-assemble into well-ordered CCAs by only one purification step without laborious pretreatment (e.g., dialysis or ion exchange) or slow solvent-evaporation process. The CCAs is then encapsulated into a transparent polymer shell with functional groups (e.g., copolymer of ETPTA and butyl acrylate (BA)), triggering the formation of core–shell PC microbeads which can be used as optical encoding microcarriers. Importantly, this technique allows us to produce core–shell PC microbeads in a rapid and robust way, and the optical reflections of the PC microbeads appear highly stable to various external stimuli (e.g., temperature, pH value, and ionic strength) relying on the features of the CCAs core and protection of the polymer shell. Moreover, various probe biomolecules (e.g., proteins, antibodies, and so on) can be easily linked on the surface of the core–shell PC microbeads owing to the hydrophilic modification induced by the hydrolysis of BA on the microbead surface, enabling the multiplex biomolecular detection.