Five‐Level Structural Hierarchy: Microfluidically Supported Synthesis of Core–Shell Microparticles Containing Nested Set of Dispersed Metal and Polymer Micro and Nanoparticles

This study presents the development of a hierarchical design concept for the synthesis of multi‐scale polymer particles with up to five levels of organization. The synthesis of core–shell microparticles containing nested sets of dispersed metal and polymer micro‐ and nanoparticles is achieved through in situ photopolymerization using a double co‐axial capillaries microfluidic device. The flow rates of the carrier, shell, and core phases are optimized to control particle size and result in stable core–shell particles with well‐dispersed three‐level composites in the shell matrix. The robustness and reversibility of these core–shell particles are demonstrated through five cycles of drying and re‐swelling, showing that the size and structure of core–shell particles remain unchanged. Additionally, the permeability and mobility of dye molecules within the shell matrix are tested and showed that different molecular weight dyes have different penetration times. This study highlights the potential of microfluidics as a powerful tool for the controlled and precise synthesis of complex structured materials and demonstrates the versatility and potential of these core–shell particles for sensing applications as particle‐based surface‐enhanced Raman scattering (SERS).