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The quadrupolar field created by opposing magnets was used to assemble particles into chiral superstructures. 

Organizing the colloidal particles into 3D superstructures is a promising strategy for fabricating functional metamaterials with novel optical, electric, and catalytic properties. The rich surface properties of the colloidal particles provide many ways to manipulate their assembly behavior. Emulsion droplets are ideal microspaces for confining colloidal self-assembly, offering many advantages such as versatility, scalability, and controllability over size, shape, and composition. In this review, we first introduce recently developed strategies for the emulsion-confined assembly of colloidal particles into 3D superstructures by manipulating the interfacial properties of the emulsion droplets and colloidal particles, then demonstrate the novel collective properties of the assembled superstructures and highlight some of their unique optical and catalytic properties and applications in bioimaging, diagnosis, drug delivery, and therapy. 

Expensive instruments and complicated data processing are often required to discriminate solvents with similar structures and properties. Colorimetric sensors with high selectivity, low cost, and good portability are highly desirable to simplify such detection tasks. Herein, we report the fabrication of a photonic crystal sensor based on the self-assembled resorcinol formaldehyde (RF) hollow spheres to realize colorimetric sensing of polar solvents, including homologs and isomers based on the saturated diffusion time. The diffusion of solvent molecules through the photonic crystal film exhibits a unique three-step diffusion profile accompanied by a dynamic color change, as determined by the physicochemical properties of the solvent molecules and their interactions with the polymer shells, making it possible to accurately identify the solvent type based on the dynamic reflection spectra or visual perception. With its superior selectivity and sensitivity, this single-component colorimetric sensor represents a straightforward tool for convenient solvent detection and identification.