We use digital holographic microscopy and Mie scattering theory to simultaneously characterize and track individual colloidal particles. Each holographic snapshot provides enough information to measure a colloidal sphere's radius and refractive index to within 1%, and simultaneously to measure its three-dimensional position with nanometer in-plane precision and 10 nanometer axial resolution.

A s dielectric structures with a submicrometer length scale can interact strongly with light, various remarkable optical responses can be designed and tailored depending on the types and parameters of their structures. Over the past few decades, the unusual optical properties of the periodic dielectric structures called photonic crystals have been investigated intensively [1]. Many research groups have endeavored to engineer the optical properties of photonic crystals, including photonic bandgaps, 'slow' photons, negative refraction and other properties, or to use them in practical applications. Two-dimensional (2D) structures, which are mostly prepared by conventional lithographic processes, were demonstrated initially, in which total internal refl ections were adopted for confi ning the light in a nonperiodic third direction, and their use has been investigated in some limited applications [2]. Th ree-dimensional (3D) structures have also been investigated intensively because of their complete photonic bandgaps in certain structures, a critical property for controlling light in 3D space. Research on such structures has been supported by the recent development of facile fabrication methods, including the selfassembly of simple monodisperse particles, also known as colloidal self-assembly [3], block copolymer self-assembly [4], the auto-cloning process [5] and holographic lithography [6]. Of these methods, colloidal self-assembly is the most promising for the low-cost production of 2D and 3D photonic crystals over large areas or with various shapes [7,8]. Schematic diagrams of the basic colloidal crystal structure along with inverse and short-range-ordered scattering structures for photonic applications are shown in Figure 1. Disordered dielectric structures of monodisperse particles called photonic glasses have begun to be investigated as another class of photonic nanostructures that can manifest some unusual optical phenomena such as random lasing, strong light localization and long-range intensity correlations. In this review article, we describe self-assembled colloidal photonic nanostructures in brief and summarize recent achievements in the fi eld of colloidal photonic nanostructures and their applications. Fabrication of photonic nanostructures by colloidal assembly Colloidal crystalsSince Vanderhoff 's serendipitous discovery of a synthetic method for preparing monodisperse polymer colloids [9], the method has been extended to the preparation of a variety of polymeric colloids and also to the processing of inorganic colloidal particles such as silica, titania and iron oxide. As long as particles are stable in liquid and their size distribution is suffi ciently narrow, they can be crystallized in a facecentered cubic (fcc) lattice by increasing their volume fraction through any concentration process, such as controlled evaporation, sedimentation or fi ltration. In general, the interparticle forces can be described by summing over the various potentials from diff erent origins, including intermolecular for...

Chameleons use a non-close-packed array of guanine nanocrystals in iridophores to develop and tune skin colors in the full visible range. Inspired by the biological process uncovered in panther chameleons, we designed photonic films containing a non-close-packed face-centered-cubic array of silica particles embedded in an elastomer. The non-close-packed array is formed by interparticle repulsion exerted by solvation layers on the particle surface, which is rapidly captured in the elastomer by photocuring of the dispersion medium. The artificial skin exhibits a structural color that shifts from red to blue under stretching or compression. The separation between inelastic particles enables tuning without experiencing significant rearrangement of particles, providing elastic deformation and reversible color change, as chameleons do. The simple fabrication procedure consists of film casting and UV irradiation, potentially enabling the continuous high-throughput production. The mechanochromic property of the photonic films enables the visualization of deformation or stress with colors, which is potentially beneficial for various applications, including mechanical sensors, sound-vision transformers, and color display.

Long-term storage and controlled release of multiple components while avoiding cross-contamination have potentially important applications for pharmaceuticals and cosmetics. Polymersomes are very promising delivery vehicles but cannot be used to encapsulate multiple independent components and release them in a controlled manner. Here, we report a microfluidic approach to produce multiple polymersomes, or polymersomes-in-polymersome by design, enabling encapsulation and programmed release of multiple components. Monodisperse polymersomes are prepared from templates of double-emulsion drops, which in turn are injected as the innermost phase to form the second level of double-emulsion drops, producing double polymersomes. Using the same strategy, higher-order polymersomes are also prepared. In addition, incorporation of hydrophobic homopolymer into the different bilayers of the multiple polymersomes enables controlled and sequential dissociation of the different bilayer membranes in a programmed fashion. The high encapsulation efficiency of this microfluidic approach, as well as its programmability and the biocompatibility of the materials used to form the polymersomes, will provide new opportunities for practical delivery systems of multiple components.

How droplet microfluidics can be used to fabricate solid-shelled microcapsules having precisely controlled release behavior is described. Glass capillary devices enable the production of monodisperse double emulsion drops, which can then be used as templates for microcapsule formation. The exquisite control afforded by microfluidics can be used to tune the compositions and geometrical characteristics of the microcapsules with exceptional precision. The use of this approach to fabricate microcapsules that only release their contents when exposed to a specific stimulus--such as a change in temperature, exposure to light, a change in the chemical environment, or an external stress--only after a prescribed time delay, and at a prescribed rate is reviewed.