Molecular Bottlebrush-Stabilized Polymeric Microspheres by Photoinitiated RAFT Dispersion Polymerization for Bead-Based Immunoassays

Polymeric microspheres are indispensable in catalysis, coatings, and biomedical analysis, yet conventional dispersion polymerization requires high stabilizer loadings and often yields surfaces with limited functional accessibility. Here, we report a molecular bottlebrush strategy that overcomes these limitations by employing reversible addition–fragmentation chain transfer (RAFT)-derived macromonomers, followed by ring-opening metathesis polymerization (ROMP) to generate bottlebrush stabilizers for photoinitiated RAFT dispersion polymerization. These bottlebrushes afford robust steric stabilization at significantly reduced loadings and enrich microsphere surfaces with RAFT end groups, enabling facile postpolymerization modification. The resulting PMMA microspheres exhibit exceptional monodispersity, tunable diameters, and versatile surface functionality. Subsequent photoiniferter polymerization yields carboxyl-functionalized microspheres with grafted poly(acrylic acid) chains, providing a high density of accessible carboxyl groups for biomacromolecule conjugation. Optimization of the chain length reveals a critical balance between loading capacity and accessibility, leading to markedly improved performance in bead-based immunoassays. This bottlebrush-mediated approach thus establishes a general and scalable platform for producing size-controlled, surface-functional polymeric microspheres with enhanced bioanalytical utility.