Coordination‐Actuated Photonic Microparticles for Recyclable, High‐Resolution Heavy Metal Sensing Via Structural Color

Optical transduction of metal ion binding via macroscopic color changes enables non‐contact, equipment‐free environmental monitoring, yet achieving high sensitivity with reusable materials remains challenging. A recyclable microphotonic sensing platform is presented based on polypyrrole (PPy)‐integrated block copolymer microparticles that translate heavy metal coordination into quantifiable structural color shifts. Microparticles comprising polystyrene‐ b ‐poly(2‐vinylpyridine) (PS‐ b ‐P2VP) with well‐defined lamellar nanostructures are fabricated via emulsion‐evaporation‐induced self‐assembly, wherein the pyrrole monomers are selectively confined within the P2VP microdomains and polymerized in situ to form an interpenetrating PPy/P2VP coordination network that promotes rapid ion diffusion and cooperative binding. Upon exposure to heavy metal ions (Cu 2+ , Zn 2+ , Pb 2+ , and Cd 2+ ), cooperative coordination drives pronounced microdomain contraction, yielding blue shifts in Bragg reflection wavelengths observable to the naked eye. The platform achieves detection limits of ∼0.5 ppm for Cu 2+ ions with response times under 30 min at ambient temperature. The response is fully reversible upon acid treatment, with >95% optical recovery over 10 consecutive cycles. Integration of Fe 3 O 4 nanoparticles further enables facile recovery and reuse of the sensor colloids. Coupling reconfigurable coordination chemistry with photonic crystal engineering in a colloidal platform thus provides sensitive, reversible, and equipment‐free heavy metal detection suitable for field deployment.