Multifunctional Photonic Janus Particles.

Photonic Janus particles with a sphere fused to a cone are created from the phase separation of dendronized brush block copolymers ( den -BBCP) and poly(4-vinylpyridine)- r -polystyrene (P4VP- r -PS) during the solvent evaporation of oil-in-water emulsions. Rapid self-assembly of den -BBCP generates well-ordered lamellar structures stacking along the long axis of the particles, producing structural colors that are dependent on the incident light angle. The colors are tunable over the visible spectrum by varying the molecular weight of den -BBCP. The P4VP- r -PS phase can undergo further surface modifications to produce multifunctional photonic Janus particles. Specifically, real-time magnetic control of the reflected color is achieved by coating the P4VP- r -PS phase with citric acid-capped Fe 3 O 4 nanoparticles. Charged biomolecules (i.e., antibodies) are electrostatically immobilized to the Fe 3 O 4 coating for potential applications in biosensing. As a demonstration, a new photonic sensor for the foodborne pathogen Salmonella is developed with antibody-modified photonic Janus particles, where the angle-dependent structural color plays a key role in the sensing mechanism.