Colour-barcoded magnetic microparticles for multiplexed bioassays

Gradient-Wrinkled Microparticle with Grayscale Lithography Controlling the Cross-Linking Densities for High Security Level Anti-Counterfeiting Strategies

Physical unclonable functions (PUFs) enable different characteristics according to the purpose, such as easy to access identification, high security level, and high code capacity, against counterfeiting a product. However, most multiplex approaches have been implemented by embedding several security features rather than one feature. In this paper, we present a high security level anti-counterfeiting strategy using only labyrinth wrinkle patterns with different complexities, which can be used as unique and unclonable codes. To generate codes with different levels in a microtaggant, we fabricated wrinkle patterns with characteristic wavelength gradients using grayscale lithography. The elastic modulus of the polymer substrate and corresponding wavelength after the wrinkling process were controlled by designing the gray level of each subcode region in a gray-level mask image for photopolymerization of the microparticle substrate. We then verified the uniqueness of the extracted minutia codes through a cross-correlation analysis. Finally, we demonstrated the authentication strategies by decoding different minutia codes according to the scanning resolution during the decoding. Overall, the presented patterning method can be widely used in security code generation.

Shear Stress-Triggered Deformation of Microparticles in a Tapered Microchannel

We demonstrate that it is possible to produce microparticles with high deformability while maintaining a high effective volume. For significant particle deformation, a particle must have a void region. The void fraction of the particle allows its deformation under shear stress. Owing to the importance of the void fraction in particle deformation, we defined an effective volume index (V*) that indicates the ratio of the particle’s total volume to the volumes of the void and material structures. We chose polyethylene glycol diacrylate (Mn ~ 700) for the fabrication of the microparticles and focused on the design of the particles rather than the intrinsic softness of the material (E). We fabricated microparticles with four distinct shapes: discotic, ring, horseshoe, and spiral, with various effective volume indexes. The microparticles were subjected to shear stress as they were pushed through a tapered microfluidic channel to measure their deformability. The deformation ratio R was introduced as R = 1−W_deformed/D_original to compare the deformability of the microparticles. We measured the deformation ratio by increasing the applied pressure. The spiral-shaped microparticles showed a higher deformation ratio (0.901) than those of the other microparticles at the same effective volume index.

Integrated Assembly and Flexible Movement of Microparts Using Multifunctional Bubble Microrobots

Industrial robots have been widely used for manufacturing and assembly in factories. However, at the microscale, most assembly technologies can only pattern the micromodules together loosely and can hardly combine the micromodules to directly form an entity that cannot be easily dispersed. In this study, surface bubbles are made to function as microrobots on a chip. These microrobots can move, fix, lift, and drop microparts and integratively assemble them into a tightly connected entity. As an example, the assembly of a pair of microparts with dovetails is considered. A jacklike bubble robot is used to lift and drop a micropart with a tail, whereas a mobile microrobot is used to push the other micropart with the corresponding socket to the proper position so that the tail can be inserted into the socket. The assembled microparts with the tail-socket joint can move as an entity without separation. Similarly, different types of parts are integratively assembled to form various structures such as gears, snake-shaped chains, and vehicles, which are then driven by bubble microrobots to perform different forms of movement. This assembly technology is simple and efficient and is expected to play an important role in micro-operation, modular assembly, and tissue engineering.

Scanning two-photon continuous flow lithography for the fabrication of multi-functional microparticles

In this work, we demonstrate the high-throughput fabrication of 3D microparticles using a scanning two-photon continuous flow lithography (STP-CFL) technique in which microparticles are shaped by scanning the laser beam at the interface of laminar co-flows. The results demonstrate the ability of STP-CFL to manufacture high-resolution complex geometries of cell carriers that possess distinct regions with different functionalities. A new approach is presented for printing out-of-plane features on the microparticles. The approach eliminates the use of axial scanning stages, which are not favorable since they induce fluctuations in the flowing polymer media and their scanning speed is slower than the speed of galvanometer mirror scanners.

Laminar Flow-Based Fiber Fabrication and Encoding via Two-Photon Lithography

In recent years, flow photolithography (FL) has emerged as a powerful synthetic tool for the creation of barcoded microparticles with complex morphologies and chemical compositions which have been shown to be useful in a range of multiplexed bioassay applications. More specifically, FL has been highly successful in producing micron-sized, encoded particles of bespoke shape, size, and color. That said, to date, FL has been restricted to generating barcoded microparticles and has lacked the ability to produce hybrid fibers which are structurally and spectrally encoded. To this end, we herein present a method that combines a continuous flow microfluidic system with two-photon polymerization (2PP) to fabricate microscale-encoded fibers and Janus strips in a high-throughput manner. Specifically, two co-flow liquid streams containing a monomer and initiator are introduced through a Y-shape channel to form a stable interface in the center of a microfluidic channel. The flow containing the (fluorescently labeled) monomer is then patterned by scanning the voxel of the 2PP laser across the interface to selectively polymerize different regions of the forming fiber/particle. Such a process allows for rapid spectral encoding at the single fiber level, with the resulting structurally coded fibers having obvious application in the fields of security identification and anticounterfeiting.

MRBLES 2.0: High-throughput generation of chemically functionalized spectrally and magnetically encoded hydrogel beads using a simple single-layer microfluidic device

The widespread adoption of bead-based multiplexed bioassays requires the ability to easily synthesize encoded microspheres and conjugate analytes of interest to their surface. Here, we present a simple method (MRBLEs 2.0) for the efficient high-throughput generation of microspheres with ratiometric barcode lanthanide encoding (MRBLEs) that bear functional groups for downstream surface bioconjugation. Bead production in MRBLEs 2.0 relies on the manual mixing of lanthanide/polymer mixtures (each of which comprises a unique spectral code) followed by droplet generation using single-layer, parallel flow-focusing devices and the off-chip batch polymerization of droplets into beads. To streamline downstream analyte coupling, MRBLEs 2.0 crosslinks copolymers bearing functional groups on the bead surface during bead generation. Using the MRBLEs 2.0 pipeline, we generate monodisperse MRBLEs containing 48 distinct well-resolved spectral codes with high throughput (>150,000/min and can be boosted to 450,000/min). We further demonstrate the efficient conjugation of oligonucleotides and entire proteins to carboxyl MRBLEs and of biotin to amino MRBLEs. Finally, we show that MRBLEs can also be magnetized via the simultaneous incorporation of magnetic nanoparticles with only a minor decrease in the potential code space. With the advantages of dramatically simplified device fabrication, elimination of the need for custom-made equipment, and the ability to produce spectrally and magnetically encoded beads with direct surface functionalization with high throughput, MRBLEs 2.0 can be directly applied by many labs towards a wide variety of downstream assays, from basic biology to diagnostics and other translational research.

Discontinuous Dewetting in a Degassed Mold for Fabrication of Homogeneous Polymeric Microparticles

Discontinuous dewetting (DD) is an attractive technique that enables the production of large liquid arrays in microwells and is applicable to the synthesis of anisotropic microparticles with complex morphologies. However, such loading of liquids into microwells presents a significant challenge, as the liquids used in this technique should exhibit low mold surface wettability. This study introduces DD in a degassed mold (DM), a simple yet powerful technique that achieves uniform loading of microparticle precursors into large microwell arrays within 1 min. Using this technique, hydrogel microparticles are produced by different polymerization mechanisms with various shapes and sizes, ranging from a few micrometers to hundreds of micrometers. Hydrophobic oil microparticles are produced by the simple plasma treatment of the DM, and agarose microparticles encapsulating bovine serum albumin (in a well-dispersed state) are produced by submerging the DM in fluorinated oil. To demonstrate additional functionality of microparticles using this technique, high concentrations of magnetic nanoparticles are loaded into microparticles for particle-based immunoassays performed in a microwell plate, and the immunoassay performance is comparable to that of ELISA.

Responsive Photonic Crystal Microcapsules of Block Copolymers with Enhanced Monochromaticity

Self-assembly of block copolymers (BCPs) has been developed as a promising approach for constructing photonic crystal (PC) microspheres for dynamic optical modulation. However, high curvature in the center of microspheres usually distorts the periodic core structure, leading to an inconsistency of photonic bandgap and poor monochromaticity of structural color. Herein, we report a simple yet robust strategy for fabricating responsive PC microcapsules of polystyrene-b-poly(2-vinylpyridine) through self-emulsification strategy. Interestingly, the microcapsules exhibit bright structural color with significantly enhanced monochromaticity, compared to their solid counterpart, since the microcapsules have no irregular cores. The structural colors of the PC microcapsules not only exhibit a variability through binary mixing of BCPs but also show a responsiveness to pH value. As a colored microcarrier, the PC microcapsules show a potential for visualizing the pH-dependent release behavior of encapsulated hydrophilic cargos on account of pH-responsive structural color.

Multidimensional Anisotropic Architectures on Polymeric Microparticles

Next generation life science technologies will require the integration of building blocks with tunable physical and chemical architectures at the microscale. A central issue is to govern the multidimensional anisotropic space that defines these microparticle attributes. However, this control is limited to one or few dimensions due to profound fabrication tradeoffs, a problem that is exacerbated by miniaturization. Here, a vast number of anisotropic dimensions are integrated combining SU-8 photolithography with (bio)chemical modifications via soft-lithography. Microparticles in a 15-D anisotropic space are demonstrated, covering branching, faceting, fiducial, topography, size, aspect ratio, stiffness, (bio)molecular and quantum dot printing, top/bottom surface coverage, and quasi-0D, 1D, 2D, and 3D surface patterning. The strategy permits controlled miniaturization on physical dimensions below 1 µm and molecular patterns below 1 µm² . By combining building blocks, anisotropic microparticles detect pH changes, form the basis for a DNA-assay recognition platform, and obtain an extraordinary volumetric barcoding density up to 1093 codes µm^-3 in a 3 × 12 × 0.5 µm³ volume.

Monodisperse drops templated by 3D-structured microparticles

The ability to create uniform subnanoliter compartments using microfluidic control has enabled new approaches for analysis of single cells and molecules. However, specialized instruments or expertise has been required, slowing the adoption of these cutting-edge applications. Here, we show that three dimensional-structured microparticles with sculpted surface chemistries template uniformly sized aqueous drops when simply mixed with two immiscible fluid phases. In contrast to traditional emulsions, particle-templated drops of a controlled volume occupy a minimum in the interfacial energy of the system, such that a stable monodisperse state results with simple and reproducible formation conditions. We describe techniques to manufacture microscale drop-carrier particles and show that emulsions created with these particles prevent molecular exchange, concentrating reactions within the drops, laying a foundation for sensitive compartmentalized molecular and cell-based assays with minimal instrumentation.

Fabrication of 3D concentric amphiphilic microparticles to form uniform nanoliter reaction volumes for amplified affinity assays

Reactions performed in uniform microscale volumes have enabled numerous applications in the analysis of rare entities (e.g. cells and molecules). Here, highly monodisperse aqueous droplets are formed by simply mixing microscale multi-material particles, consisting of concentric hydrophobic outer and hydrophilic inner layers, with oil and water. The particles are manufactured in batch using a 3D printed device to co-flow four concentric streams of polymer precursors which are polymerized with UV light. The cross-sectional shapes of the particles are altered by microfluidic nozzle design in the 3D printed device. Once a particle encapsulates an aqueous volume, each "dropicle" provides uniform compartmentalization and customizable shape-coding for each sample volume to enable multiplexing of uniform reactions in a scalable manner. We implement an enzymatically-amplified immunoassay using the dropicle system, yielding a detection limit of <1 pM with a dynamic range of at least 3 orders of magnitude. Multiplexing using two types of shape-coded particles was demonstrated without cross talk, laying a foundation for democratized single-entity assays.

Faithful Fabrication of Biocompatible Multicompartmental Memomicrospheres for Digitally Color-Tunable Barcoding

Barcodes have attracted widespread attention, especially for the multiplexed bioassays and anti-counterfeiting used toward medical and biomedical applications. An enabling gas-shearing approach is presented for generating 10-faced microspherical barcodes with precise control over the properties of each compartment. As such, the color of each compartment could be programmatically adjusted in the 10-faced memomicrospheres by using pregel solutions containing different combinations of fluorescent nanoparticles. During the process, three primary colors (red, green, and blue) are adopted to obtain up to seven merged fluorescent colors for constituting a large amount of coding as well as a magnetic compartment, capable of effective and robust high-throughput information-storage. More importantly, by using the biocompatible sodium alginate to construct the multicolor microspherical barcodes, the proposed technology is likely to advance the fields of food and pharmaceutics anti-counterfeiting. These remarkable properties point to the potential value of gas-shearing in engineering microspherical barcodes for biomedical applications in the future.

Study on the Twisted and Coiled Polymer Actuator with Strain Self-Sensing Ability

Twisted and coiled polymer actuators (TCAs) are a kind of efficient artificial muscles, which have good prospects for application in soft robots, bionic devices, and biological, medical, and other high-tech fields. However, the inability to dynamically sense and adjust the strain of the actuator will lead to uncertainty in the accuracy of deformation and strain, resulting in imprecise target action. Herein, TCAs with strain self-sensing ability (TCASA) are prepared by integrating the stretchable optomechanical film (SOMF) sensors into TCAs, which provides a simple strategy for dynamical strain sensing. These SOMFs have a wide range of color changes during deformation of TCAs, and the strain is perceived by observing the color change according to the corresponding relationship between color change and strain. Furthermore, the proposed TCASA maintain excellent cycling stability of strain self-sensing during cyclic tests (200 cycles) and excellent strain self-sensing performance to perform strain control compared to TCAs without SOMFs. The results indicate that the proposed structure is a promising soft actuator with excellent strain self-sensing ability, which is well suited for soft robots, bionic devices, biological and medical fields, smart wearable technologies, and so forth, especially when controlled, repetitive deformations are required.

Structural Color Materials for Optical Anticounterfeiting

The counterfeiting of goods is growing worldwide, affecting practically any marketable item ranging from consumer goods to human health. Anticounterfeiting is essential for authentication, currency, and security. Anticounterfeiting tags based on structural color materials have enjoyed worldwide and long-term commercial success due to their inexpensive production and exceptional ease of percept. However, conventional anticounterfeiting tags of holographic gratings can be readily copied or imitated. Much progress has been made recently to overcome this limitation by employing sufficient complexity and stimuli-responsive ability into the structural color materials. Moreover, traditional processing methods of structural color tags are mainly based on photolithography and nanoimprinting, while new processing methods such as the inkless printing and additive manufacturing have been developed, enabling massive scale up fabrication of novel structural color security engineering. This review presents recent breakthroughs in structural color materials, and their applications in optical encryption and anticounterfeiting are discussed in detail. Special attention is given to the unique structures for optical anticounterfeiting techniques and their optical aspects for encryption. Finally, emerging research directions and current challenges in optical encryption technologies using structural color materials is presented.

Color-tunable ultralong organic room temperature phosphorescence from a multicomponent copolymer

Functional materials displaying tunable emission and long-lived luminescence have recently emerged as a powerful tool for applications in information encryption, organic electronics and bioelectronics. Herein, we present a design strategy to achieve color-tunable ultralong organic room temperature phosphorescence (UOP) in polymers through radical multicomponent cross-linked copolymerization. Our experiments reveal that by changing the excitation wavelength from 254 to 370 nm, these polymers display multicolor luminescence spanning from blue to yellow with a long-lived lifetime of 1.2 s and a maximum phosphorescence quantum yield of 37.5% under ambient conditions. Moreover, we explore the application of these polymers in multilevel information encryption based on the color-tunable UOP property. This strategy paves the way for the development of multicolor bio-labels and smart luminescent materials with long-lived emission at room temperature.

Functional materials displaying tunable emission and long-lived luminescence are a powerful tool in information encryption, organic electronics and bioelectronics. Here the authors design a color-tunable ultralong organic room temperature phosphorescence polymer through radical multiple component cross-linked copolymerization.

A clustering-triggered emission strategy for tunable multicolor persistent phosphorescence

A clustering-triggered emission (CTE) strategy, namely the formation of heterogeneous clustered chromophores and conformation rigidification, for achieving tunable multicolor phosphorescence in single-component compounds is proposed. Non-conventional luminophores comprising just oxygen functionalities and free of π-bonding, i.e., d-(+)-xylose (d-Xyl), pentaerythritol (PER), d-fructose (d-Fru) and d-galactose (d-Gal), were adopted as a simple model system with an explicit structure and molecular packing to address the hypothesis. Their concentrated solutions and crystals at 77 K or under ambient conditions demonstrate remarkable multicolor phosphorescence afterglows in response to varying excitation wavelengths, because of the formation of diverse oxygen clusters with sufficiently rigid conformations. The intra- and inter-molecular O⋯O interactions were definitely illustrated by both single crystal structure analysis and theoretical calculations. These findings shed new light on the origin and simple achievement of tunable multicolor phosphorescence in single-component pure organics, and in turn, have strong implications for the emission mechanism of non-conventional luminophores.

Microspinning: Local Surface Mixing via Rotation of Magnetic Microparticles for Efficient Small-Volume Bioassays

The need for high-throughput screening has led to the miniaturization of the reaction volume of the chamber in bioassays. As the reactor gets smaller, surface tension dominates the gravitational or inertial force, and mixing efficiency decreases in small-scale reactions. Because passive mixing by simple diffusion in tens of microliter-scale volumes takes a long time, active mixing is needed. Here, we report an efficient micromixing method using magnetically rotating microparticles with patterned magnetization induced by magnetic nanoparticle chains. Because the microparticles have magnetization patterning due to fabrication with magnetic nanoparticle chains, the microparticles can rotate along the external rotating magnetic field, causing micromixing. We validated the reaction efficiency by comparing this micromixing method with other mixing methods such as simple diffusion and the use of a rocking shaker at various working volumes. This method has the potential to be widely utilized in suspension assay technology as an efficient mixing strategy.

Electronic classification of barcoded particles for multiplexed detection using supervised machine learning analysis

Wearable biosensors are of great interest in recent years due to their potential in health related applications. Multiplex biomarker analysis is needed in wearable devices to improve the sensitivity and reliability. Electronic barcoding of micro-particles has the possibility to enable multiplexed biomarker analysis. Compared with traditional optical and plasmonic methods for barcoding, electronically barcoded particles can be classified using ultra-compact electronic readout platforms. Nano-electronic barcoding works by depositing a thin layer of oxide on the top half of a micro-particle. The thickness and dielectric property of the oxide layer can be tuned to modulate the frequency dependent impedance signature of the particles. A one to one correspondence between a target biomarker and each barcoded particle can potentially be established using this technique. The barcoded particles could be tested with wearable devices to enable multiplex analysis for portable point-of-care diagnostics and real-time monitoring. In this work, we fabricated nine barcoded particles by forming oxide layers of different thicknesses and different dielectric materials using atomic layer deposition and assessed the ability to accurately classify particle barcodes using multi-frequency impedance cytometry in conjunction with supervised machine learning.

Slip Molding for Precision Fabrication of Microparts

Microparts with precise sizes, custom shapes, and a wide selection of materials have various applications, including biomedical microelectromechanical systems (MEMS), drug delivery, single-cell studies, and tissue engineering. Janus microparts containing multiple components are also demonstrated for biomolecule analysis, cell-cell interaction studies, and self-assembly. Small-footprint, affordable, and rapid technologies to fabricate microparts with customized morphologies and a wide selection of materials are highly desired. This paper reports on a SlipChip-based microfluidic molding method to control the interface for the synthesis of microparts-on-demand (mPods) with fast and easy loading-slipping-solidification operations that do not require pumps, masks, or other auxiliary fluidic control instruments. This method is based on the relative movement of two microfluidic plates that are in close contact, and the size and shape of the microparts can be accurately controlled by the geometry of the microcavities imprinted on the contacting surfaces of these microfluidic plates. To demonstrate the capability of this method, mPods of different sizes and various shapes are presented with photosensitive resin via a photopolymerization reaction. The synthesis of two-layer Janus microparts is also demonstrated by a slip overmolding method. This SlipChip-based molding method can offer new opportunities for producing customized microparts with great flexibility for a broad spectrum of applications.

Degassed micromolding lithography for rapid fabrication of anisotropic hydrogel microparticles with high-resolution and high uniformity

Replica molding techniques, which are used to synthesize microparticles inside anisotropic micromolds, have been developed to enable the mass production of hydrogel particles. However, these techniques are limited in their ability to synthesize only a narrow range of particle compositions and shapes because of the difficulty in loading precursors into the micromolds as well as the low particle homogeneity due to the uneven evaporation of the precursors. Herein, we describe a simple yet powerful technique, called degassed micromolding lithography, which can load precursors within 1 min regardless of the wettability. This technique is based on the gas-solubility of a degassed micromold that acts as a suction pump to completely fill the mold by drawing precursor liquids in. The semi-closed system within the micromold prevents the uneven evaporation of the precursor, which is essential for the production of homogeneous particles. Furthermore, controlled uniformity of the hydrogel microparticles (C.V. < 2%) can be achieved by engineering the design of the micromold array.

Wavelength-Tunable Single-Mode Microlasers Based on Photoresponsive Pitch Modulation of Liquid Crystals for Information Encryption

Information encryption and decryption have attracted particular attention; however, the applications are frequently restricted by limited coding capacity due to the indistinguishable broad photoluminescence band of conventional stimuli-responsive fluorescent materials. Here, we present a concept of confidential information encryption with photoresponsive liquid crystal (LC) lasing materials, which were used to fabricate ordered microlaser arrays through a microtemplate-assisted inkjet printing method. LC microlasers exhibit narrow-bandwidth single-mode emissions, and the wavelength of LC microlasers was reversibly modulated based on the optical isomerization of the chiral dopant in LCs. On this basis, we demonstrate phototunable information authentication on LC microlaser arrays using the wavelength of LC microlasers as primary codes. These results provide enlightenment for the implementation of microlaser-based cryptographic primitives for information encryption and anticounterfeiting applications.

Interfacial Assembly of Amphiphilic Tiles for Reconfigurable Photonic Surfaces

Nature has created photonic structures in cells and assembled them to make photonic layers for a living. Inspired from nature, we design amphiphilic photonic tiles and assemble them at air-water interface to compose highly reconfigurable photonic layers. The photonic tiles are prepared by photolithographically defining the shape of the disc using a photocurable dispersion of repulsive particles. The tiles are further treated by directional dry etching to selectively render top and side surfaces of the discs hydrophobic. The amphiphilic photonic tiles deform the air-water interface by gravity, which causes a strong attractive force driven by capillarity. Therefore, the tiles form two-dimensional (2D) dense-packing, which rapidly adapts dynamic fluctuation and shape change of the interface, providing highly reconfigurable photonic layers. In addition, the assembly can be transferred into target solid surfaces through the Langmuir-Blodgett method to make photonic coatings. Moreover, the amphiphilic tiles can be assembled on the surface of water drops, forming a photonic shell on liquid marbles which resembles photonic structures in nature. We believe that our strategy based on a 2D tile assembly at the free interface will provide a simple yet useful means to create photonic layers on various purposes.

Excitation-Dependent Long-Life Luminescent Polymeric Systems under Ambient Conditions

Organic room temperature luminescent materials present a unique phosphorescence emission with a long lifetime. However, many of these materials only emit single blue or green color in spite of external stimulation, and their color tunability is limited. Herein, we report a rational design to extend the emission color range from blue to red by controlling the doping of simple pyrene derivatives into a robust polymer matrix. The integration of these pyrene molecules into the polymer films enhances the intersystem crossing pathway, decreases the first triplet level of the system, and ensures the films show a sensitive response to excitation energy, finally yielding excitation-dependent long-life luminescent polymeric systems under ambient conditions. These materials were used to construct anti-counterfeiting patterns with multicolor interconversion, presenting a promising application potential in the field of information security.

Perspective of Molecular Diagnosis in Healthcare: From Barcode to Pattern Recognition

Barcode technology has a broad spectrum of applications including healthcare, food security, and environmental monitoring, due to its ability to encode large amounts of information. With the rapid development of modern molecular research, barcodes are utilized as a reporter with different molecular combinations to label many biomolecular targets, including genomic and metabolic elements, even with multiplex targeting. Along with the advancements in barcoded bioassay, the improvements of various designs of barcode components, encoding and decoding strategies, and their portable adoption are indispensable in satisfying multiple purposes, such as medical confirmation and point-of-care (POC) testing. This perspective briefly discusses the current direction and progress of barcodes development and provides a hypothesis for barcoded bioassay in the near future.

Microfluidics tubing as a synthesizer for ordered microgel networks

Ordered microgel networks have undergone extensive research and shown translational promise in tissue engineering, precision and regenerative medicine, controlled delivery, optics and electronics, etc. Here, we introduce a new low-cost and efficient synthesizer for ordered microgel networks. The gel precursor microdroplets are formulated and incubated in a microfluidics tubing system to obtain tailorable and reproducible microgels, which are then patterned into networks under the precise spatiotemporal control of the tubing system and integrated either by crosslinking the microgel interfaces or by forming lipid bilayers at the interfaces. The system can synthesize ordered networks out of heterogeneous microgels by withdrawing multi-phase cell-laden or acellular gel precursors into the tubing and gelation, or out of homogeneous microgels by simultaneously injecting gel precursors and immiscible oil into the tubing and gelation. The ordered gel networks are synthesized at the tubing outlet or within a piece of enlarging tubing, where the microgels are collided and glued in defined sequences.

Gas-Shearing Fabrication of Multicompartmental Microspheres: A One-Step and Oil-Free Approach

Multicompartmental microparticles (MCMs) have attracted considerable attention in biomedical engineering and materials sciences, as they can carry multiple materials in the separated phases of a single particle. However, the robust fabrication of monodisperse, highly compartmental MCMs at the micro- and nanoscales remains challenging. Here, a simple one-step and oil-free process, based on the gas-flow-assisted formation of microdroplets ("gas-shearing"), is established for the scalable production of monodisperse MCMs. By changing the configuration of the needle system and gas flow in the spray ejector device, the oil-free gas-shearing process easily allows the design of microparticles consisting of two, four, six, and even eight compartments with a precise control over the properties of each compartment. As oils and surfactants are not used, the gas-shearing method is highly cytocompatible. The versatile applications of such MCMs are demonstrated by producing a magnetic microrobot and a biocompatible carrier for the coculturing of cells. This research suggests that the oil-free gas-shearing strategy is a reliable, scalable, and biofriendly process for producing MCMs that may become attractive materials for biomedical applications.

Designing Structural-Color Patterns Composed of Colloidal Arrays

Structural coloration provides a great potential for various applications due to unique optical properties distinguished from conventional pigment colors. Structural colors are nonfading, iridescent, and tunable, which is difficult to achieve with pigments. In addition, structural color is potentially less toxic than pigments. However, it is challenging to develop structural colors because elaborate nanostructures are a prerequisite for the coloration. Furthermore, it is highly suggested the nanostructures be patterned at various length scales on a large area to provide practical formats. There have been intensive studies to develop pragmatic methods for producing structural-color patterns in a controlled manner using either colloidal crystals or glasses. This article reviews the current state of the art in the structural-color patterning based on the colloidal arrays. We first discuss common and different features between colloidal crystals and glasses. We then categorize colloidal arrays into six distinct structures of 3D opals, inverse opals, non-close-packed arrays, 2D colloidal crystals, 1D colloidal strings, and 3D amorphous arrays and study various methods to make them patterned from recent key contributions. Finally, we outline the current challenges and future perspectives of the structural-color patterns.

Self-Organization of Fluids in a Multienzymatic Pump System

The nascent field of microscale flow chemistry focuses on harnessing flowing fluids to optimize chemical reactions in microchambers and establish new routes for chemical synthesis. With enzymes and other catalysts anchored to the surface of microchambers, the catalytic reactions can act as pumps and propel the fluids through the containers. Hence, the flows not only affect the catalytic reactions, but these reactions also affect the flows. Understanding this dynamic interplay is vital to enhancing the accuracy and utility of flow technology. Through experiments and simulation, we design a system of three different enzymes, immobilized in separate gels, on the surface of a microchamber; with the appropriate reactants in the solution, each enzyme-filled gel acts as a pump. The system also exploits a reaction cascade that controls the temporal interactions between two pumps. With three pumps in a triangular arrangement, the spatio-temporal interactions among the chemical reactions become highly coordinated and produce well-defined fluid streams, which transport chemicals and form a fluidic "circuit". The circuit layout and flow direction of each constituent stream can be controlled through the number and placement of the gels and the types of catalysts localized in the gels. These studies provide a new route for forming self-organizing and bifurcating fluids that can yield fundamental insight into nonequilibrium, dynamical systems. Because the flows and fluidic circuits are generated by internal chemical reactions, the fluids can autonomously transport cargo to specific locations in the device. Hence, the findings also provide guidelines to facilitate further automation of microfluidic devices.

Hollow Colloid Assembled Photonic Crystal Clusters as Suspension Barcodes for Multiplex Bioassays

Barcode particles have a demonstrated value for multiplexed high-throughput bioassays. Here, a novel photonic crystal (PhC) barcode is presented that consists of hollow colloidal nanospheres assembled through microfluidic droplet templates. Due to their gas-filled core, the resultant barcode particles not only show increased refractive index contrast, but also remain in suspension by adjusting the overall density of the PhC to match that of a detection solution. In addition, magnetic nanoparticles can be integrated to give the barcodes a magnetically controllable motion ability. The encoding ability of the barcodes is demonstrated in microRNA detection with high specificity and sensitivity, and the excellent features of the barcodes make them potentially very useful for biomedical applications.