Fe₃O₄ Nanoparticle-Based Janus Photonic Crystal Microbeads with Multiple Fluorescence Colors for Information Coding

In this study, we fabricate magnetic Janus photonic crystal microbeads with multiple fluorescence colors based on photonic crystals, Fe 3 O 4 nanoparticles, and fluorescent dyes by a microfluidic device. We mix the poly(styrene-methyl methacrylate-acrylic acid) (p(St-MMA-AA)) nanoparticles, the Fe 3 O 4 nanoparticles, and the fluorescent dyes. We use the mixture as the dispersed phase and the silicone oil as the continuous phase. We get the Janus photonic crystal microbeads after the self-assembly of the photonic crystals. Due to the greater density, the Fe 3 O 4 nanoparticles sink to the bottom of the Janus microbeads, which are made up of photonic crystals combined with p(St-MMA-AA) nanoparticles. The fluorescent dyes are distributed in the gaps of photonic crystals. The Janus photonic crystal microbeads could rotate upside down under the action of magnets because of the magnetism of the Fe 3 O 4 nanoparticles. Moreover, they can fluoresce under UV light due to the fluorescent dyes. We combine Janus photonic crystal microbeads into arrays of numbers, letters, symbols, and patterns for information coding and anti-counterfeiting. The Janus microbeads have enormous potential for use in array displays, information coding, and anti-counterfeiting.