Encoded silica colloidal crystal beads as supports for potential multiplex immunoassay

Multifunctional photonic microobjects with asymmetric response in radial direction and their anticounterfeiting performance

There are few explorations that have integrated multiple properties into photonic microobjects in a facile and controlled manner. In this work, we present a straightforward method to integrate different functions into individual photonic microobject. Droplet-based microfluidics was used to produce uniform droplets of an aqueous dispersion of monodispersed SiO2 nanoparticles (NPs). The droplets evolved into opal-structured photonic microballs upon complete evaporation of water. After infiltration of an aqueous solution of acrylamide (AAm) and acrylic acid (AAc) monomers into the interstices among SiO2 NPs, opal-structured SiO2 NPs/pAAm-co-AAc hydrogel composite photonic microballs were obtained upon UV irradiation. Afterwards, a wet etching process was introduced to etch the microballs in a controlled manner, yielding individual photonic microball composed of an SiO2 NPs/pAAm-co-AAc composite opal core and a neat pAAm-co-AAc shell. The pendant carboxylic acid groups in the skeleton of the hydrogel matrix were further utilized to react with positively charged compounds, such as Ruthenium compound containing fluorescent polymers. The resulting photonic microobjects eventually featured with localized stimulus-responsive properties and multiple colors under different modes. The multifunctional photonic microobjects were discovered to have fivefold of anticounterfeiting properties when used as building blocks for anticounterfeiting structures and may have other potential applications.

Communicating Supraparticles to Enable Perceptual, Information-Providing Matter

Materials are the fundament of the physical world, whereas information and its exchange are the centerpieces of the digital world. Their fruitful synergy offers countless opportunities for realizing desired digital transformation processes in the physical world of materials. Yet, to date, a perfect connection between these worlds is missing. From the perspective, this can be achieved by overcoming the paradigm of considering materials as passive objects and turning them into perceptual, information-providing matter. This matter is capable of communicating associated digitally stored information, for example, its origin, fate, and material type as well as its intactness on demand. Herein, the concept of realizing perceptual, information-providing matter by integrating customizable (sub-)micrometer-sized communicating supraparticles (CSPs) is presented. They are assembled from individual nanoparticulate and/or (macro)molecular building blocks with spectrally differentiable signals that are either robust or stimuli-susceptible. Their combination yields functional signal characteristics that provide an identification signature and one or multiple stimuli-recorder features. This enables CSPs to communicate associated digital information on the tagged material and its encountered stimuli histories upon signal readout anywhere across its life cycle. Ultimately, CSPs link the materials and digital worlds with numerous use cases thereof, in particular fostering the transition into an age of sustainability.

High-throughput fabrication of monodisperse spherical supraparticles through a reliable thin oil film and rapid water diffusion

A supraparticle is a spherical superstructure composed of fine building blocks, typically synthesized through colloidal assembly from evaporating and contracting suspension droplets. Microfluidic emulsification is known to be effective in producing large amounts of water-in-oil droplets. However, the process of supraparticle self-assembly has been limited by the evaporation of the oil that supports it and the sluggish shrinkage of water droplets. These are caused by the high volatility and low diffusion rates of water in the bulk oil layer, making the process last hours or even days. To address these challenges, we introduce a new system in this paper: the supraparticle reliable fabrication (SURF) system. This microfluidic-based system can quickly and reliably assemble spherical supraparticles in 20 min. The SURF system combines a conventional flow focusing device with a thinly layered low-volatile/water-soluble oil, and an open-microfluidic droplet evaporator. This setup facilitates the creation of uniform supraparticles with various materials and diameters (coefficient of variation: <3.5%). As a proof-of-concept for potential biochemical applications, we demonstrate a sensitive chemical reaction on the fabricated supraparticles, emphasizing the effectiveness of the SURF system as an alternative to traditional supraparticle synthesis and particle-based applications.

Encoded Fusion-Mediated MicroRNA Signature Profiling of Tumor-Derived Extracellular Vesicles for Pancreatic Cancer Diagnosis

MicroRNAs (miRNAs) in tumor-derived extracellular vesicles (tEVs) are important cancer biomarkers for cancer screening and early diagnosis. Multiplex detection of miRNAs in tEVs facilitates accurate diagnosis but remains a challenge. Herein, we propose an encoded fusion strategy to profile the miRNA signature in tEVs for pancreatic cancer diagnosis. A panel of encoded-targeted-fusion beads was fabricated for the selective recognition and fusion of tEVs, with the turn-on fluorescence signals of molecule beacons for miRNA quantification and barcode signals for miRNA identification using readily accessible flow cytometers. Using this strategy, six types of pancreatic-cancer-associated miRNAs can be profiled in tEVs from 2 μL plasma samples (n = 36) in an isolation-free and lysis-free manner with only 2 h of processing, offering a high accuracy (98%) to discriminate pancreatic cancer, pancreatitis, and healthy donors. This encoded fusion strategy exhibits great potential for multiplex profiling of miRNA in tEVs, offering new avenues for cancer diagnosis and screening.

One-step fabrication of three-dimensional macropore copolymer-modified polycarbonate array by photo-crosslinking for protein immunoassay

A photocross-linked copolymer was prepared, and could rapidly form a macropore structure in phosphate buffer solution (PBS) without the addition of porogen. The photo-crosslinking process contained the crosslinking of the copolymer itself and that with the polycarbonate substrate. The three-dimensional (3D) surface was achieved through one-step photo-crosslinking of the macropore structure. The macropore structure can be finely regulated by multiple dimensions, including monomer structure of the copolymer, PBS and copolymer concentration. Compared with the two-dimensional (2D) surface, the 3D surface has a controllable structure, a high loading capacity (59 μg cm-2) and immobilization efficiency (92%), and the effect of inhibiting the coffee ring for protein immobilization. Immunoassay results show that a 3D surface immobilized by IgG has high sensitivity (LOD value of 5 ng mL-1) and broader dynamic range (0.005-50 μg mL-1). This simple and structure-controllable method for preparing 3D surfaces modified by macropore polymer has great potential applications in the fields of biochips and biosensing.

Shape-Preserving Transformation of Electrodeposited Macroporous Microparticles for Single-Particle SERS Applications

Microparticles composed of bicontinuous and ordered macropores are important in many applications. However, rational integration of ordered macropores into a single crystalline microparticle remains a challenge. Here, we report a method to prepare three-dimensionally ordered macroporous (3DOM) Ag₇O₈NO₃ micropyramids via selectively cementing the colloidal crystal templates via an electrochemical method and their shape-preserving transformation into 3DOM Ag micropryamids formed by Ag nanoparticles via a chemical reduction process. The interconnected macropores facilitated the transportation and enrichment of the analyte molecules into the 3DOM Ag micropyramids. The dense Ag nanoparticles on the skeletons of the 3DOM Ag micropyramids provided strong electromagnetic fields. Taken together, a 3DOM Ag micropyramid as a kind of single-particle surface-enhanced Raman scattering (SERS) sensing substrate demonstrated high SERS sensitivity and outstanding SERS signal reproducibility. We explored the application of 3DOM Ag micropyramids in SERS detection of biomolecules (e.g., adenosine, adenine, hemoglobin bovine, and lysozyme) and proved their potentials in distinguishing exosomes from tumor and non-tumor cells. The method can be extended to prepared 3DOM structures of other materials with promising applications in sensing, separation, and catalytic fields.

Microfluidic preparation of optical sensors for biomedical applications

Optical biosensors are platforms that translate biological information into detectable optical signals, and have extensive applications in various fields due to their characteristics of high sensitivity, high specificity, dynamic sensing, etc. The development of optical sensing materials is an important part of optical sensors. In this review, we emphasize the role of microfluidic technology in the preparation of optical sensing materials and the application of the derived optical sensors in the biomedical field. We first present some common optical sensing mechanisms and the functional responsive materials involved. Then, we describe the preparation of these sensing materials by microfluidics. Afterward, we enumerate the biomedical applications of these optical materials as biosensors in disease diagnosis, drug evaluation, and organ-on-a-chip. Finally, we discuss the challenges and prospects in this field.

Encoding microcarriers for biomedicine

High throughput biological analysis has become an important topic in modern biomedical research and clinical diagnosis. The flow encoding scheme based on the encoding microcarriers provides a feasible strategy for the multiplexed biological analysis. Different encoding characteristics invest the microcarriers with different encoding mechanisms. Biosensor analysis, drug screening, cell culture, and the construction and evaluation of bionic organ chips can be realized by decoding the microcarriers and quantifying the detection signal intensity. In this review, the encoding strategy of microcarriers was divided into the optical and non-optical encoding approaches according to their encoding elements, and the research progress of the microcarrier encoding strategy was elaborated. Finally, we summarized the biomedical applications and predicted their future prospects.

Pollen-Inspired Photonic Barcodes with Prickly Surface for Multiplex Exosome Capturing and Screening

Exosomes, which play an important role in intercellular communication, are closely related to the pathogenesis of disease. However, their effective capture and multiplex screening are still challenging. Here, inspired by the unique structure of pollens, we present novel photonic crystal (PhC) barcodes with prickly surface by hydrothermal synthesis for multiplex exosome capturing and screening. These pollen-inspired PhC barcodes are imparted with extremely high specific surface area and excellent prickly surface nanostructures, which can improve the capture rate and detection sensitivity of exosomes. As the internal periodic structures are kept during the hydrothermal synthesis process, the pollen-inspired PhC barcodes exhibit obvious and stable structural colors for identification, which enables multiplex detection of exosomes. Thus, the pollen-inspired PhC barcodes can not only effectively capture and enrich cancer-related exosomes but also support multiplex screening of exosomes with high sensitivity. These features make the prickly PhC barcodes ideal for the analysis of exosomes in medical diagnosis.

Designing photonic microparticles with droplet microfluidics

Photonic materials with a periodic change of refractive index show unique optical properties through wavelength-selective diffraction and modulation of the optical density of state, which is promising for various optical applications. In particular, photonic structures have been produced in the format of microparticles using emulsion templates to achieve advanced properties and applications beyond those of a conventional film format. Photonic microparticles can be used as a building block to construct macroscopic photonic materials, and the individual microparticles can serve as miniaturized photonic devices. Droplet microfluidics enables the production of emulsion drops with a controlled size, composition, and configuration that serve as the optimal confining geometry for designing photonic microparticles. This feature article reviews the recent progress and current state of the art in the field of photonic microparticles, covering all aspects of microfluidic production methods, microparticle geometries, optical properties, and applications. Two distinct bottom-up approaches based on colloidal assembly and liquid crystals are, respectively, discussed and compared.

Periodic Surface-Enhanced Raman Scattering-Encoded Magnetic Beads for Reliable Quantitative Surface-Enhanced Raman Scattering-Based Multiplex Bioassay

Surface-enhanced Raman scattering (SERS)-based immunoassay on encoded beads is highly attractive with the advantages of ultrasensitivity, multiplex and high throughput. However, it was a great challenge to screen out in-focus signals of the immunoconjugated SERS nanoprobes on spherical bead conveniently. Here, periodic SERS-encoded magnetic beads (PSE-MBs) were developed through droplet optofluidic technique by using monodisperse SERS-encoded magnetic nanospheres as building blocks. The designed PSE-MBs not only exhibit huge coding capacity, but also provide the strongest and reproducible SERS coding signals as "in-focus beacons". When PSE-MBs are used as capture carriers in SERS-based immunoassay, both multiple target analytes and in-focus signals of SERS nanoprobes could be easily identified according to the collected SERS coding signals. Thus, reliable quantitative analysis of multiple target analytes could be conveniently achieved by such detection protocol. Additionally, the magnetic ingredient in PSE-MBs made the operation easily during the bioassay. The multiple advantages of PSE-MBs including large coding capacity, in-focus beacons and magnetic operation endorse them to be robust capture carriers in reliable quantitative SERS-based multiplex immunoassay.

One-step assembly of barcoded planar microparticles for efficient readout of multiplexed immunoassay

Barcoded planar microparticles are suitable for developing cost-efficient multiplexed assays, but the robustness and efficiency of the readout process still needs improvement. Here, we designed a one-step microparticle assembling chip that produces efficient and accurate multiplex immunoassay readout results. Our design was also compatible with injection molding for mass production.

Covalently Attaching Hollow Silica Nanoparticles on a COC Surface for the Fabrication of a Three-Dimensional Protein Microarray

Compared to traditional two-dimensional (2D) biochips, three-dimensional (3D) biochips exhibit the advantages of higher probe density and detection sensitivity due to their designable surface microstructure as well as enlarged surface area. In the study, we proposed an approach to prepare a 3D protein chip by deposition of a monolayer of functionalized hollow silica nanoparticles (HSNs) on an activated cyclic olefin copolymer (COC) substrate. First, the COC substrate was chemically modified through the photografting technique to tether poly[3-(trimethoxysilyl) propyl methacrylate] (PTMSPMA) brushes on it. Then, a monolayer of HSNs was deposited on the modified COC and covalently attached via a condensation reaction between the hydrolyzed pendant siloxane groups of PTMSPMA and the Si-OH groups of HSNs. The roughness of the COC substrate significantly increased to 50.3 nm after depositing a monolayer of HSNs (ranging from 100 to 700 nm), while it only caused a negligible reduction in the light transmittance of COC. The HSN-modified COC was further functionalized with epoxide groups by a silane coupling agent for binding proteins. Immunoglobulin G could be effectively immobilized on this substrate with the highest immobilization efficiency of 75.2% and a maximum immobilization density of 1.236 μg/cm², while the highest immobilization efficiency on a 2D epoxide group-modified glass slide was only 57.4%. Moreover, immunoassay results confirmed a competitive limit of detection (LOD) (1.06 ng/mL) and a linear detection range (1-100 ng/mL) of the 3D protein chip. This facile and effective approach for fabricating nanoparticle-based 3D protein microarrays has great potential in the field of biorelated detection.

CdSe/ZnS quantum dot-encoded maleic anhydride-grafted PLA microspheres prepared through membrane emulsification for multiplexed immunoassays of tumor markers

Early diagnosis of tumor markers is of great importance for the successful treatment of cancer. As a high-throughput and high-sensitivity detection technology, liquid suspension biochips based on quantum dot (QD) encoded microspheres have been widely used in the immunodetection of tumor markers. In this work, maleic anhydride grafted PLA (PLA-MA) microspheres based on quantum dot encoding were used as carriers for liquid phase suspension biochips for the immunoassay of tumor markers. PLA-MA fluorescent beads are prepared by embedding CdSe/ZnS quantum dots in PLA-MA using Shirasu porous glass (SPG) membrane emulsification technology, which has high fluorescence intensity, good stability, and good dispersion. Fluorescent immunoassays on dipsticks found that PLA-MA microspheres have high biological activity and good stability, which is conducive to immunoassays. Based on this, using the characteristics of CdSe/ZnS quantum dots and flow cytometry, monochromatic and two-color coding methods were developed, and 9 distinguishable coding beads were prepared. The results showed that PLA-MA fluorescent microspheres exhibited good biocompatibility, stable coding signals, low background noise, and low detection limits when performing quaternary immunoassays on tumor markers CA125, CA199, CA724, and CEA by CdSe/ZnS QD-encoded PLA-MA microsphere binding flow cytometry.

Photonic crystal barcodes assembled from dendritic silica nanoparticles for the multiplex immunoassays of ovarian cancer biomarkers

The combined detection of CA125, CEA and AFP is of great significance in the diagnosis of ovarian cancer. Photonic crystal (PhC) barcodes have apparent advantages in multiplex immunoassays of ovarian cancer markers. In this paper, a novel PhC barcode was assembled from dendritic silica nanoparticles (dSiO₂) for multiplex detection of ovarian cancer biomarkers. The interconnected macroporous structure of the dSiO₂ PhC beads and the open porous topography of dendritic silica particles could increase the surface area to volume ratio for antibody immobilization. We simultaneously detected multiple ovarian cancer markers in one test tube using the sandwich immunization method by utilizing dSiO₂ PhC beads as a barcode and CdTe QDs as a detection signal. The detection limits of the three ovarian cancer markers, AFP, CEA and CA125, were 0.52 ng mL^-1, 0.64 ng mL^-1 and 0.79 U mL^-1, respectively (the signal-to-noise ratio was 3). Compared with the classic silica colloidal crystal bead (SCCB) suspension array, the sensitivity of the dSiO₂ PhC bead suspension array was increased. In addition, the results showed that this barcode suspension array had acceptable accuracy and good reproducibility.

Three-dimensional protein microarrays fabricated on reactive microsphere modified COC substrates

Fabrication of three-dimensional (3D) surface structures for the high density immobilization of biomolecules is an effective way to prepare highly sensitive biochips. In this work, a strategy to attach polymeric microspheres on a cyclic olefin copolymer (COC) substrate for the preparation of a 3D protein chip was developed. The COC surface was firstly functionalized by the photograft technique with epoxy groups, which were subsequently converted to amine groups. Then monodisperse poly(styrene-alt-maleic anhydride) (PSM) copolymer microspheres were prepared by self-stabilized precipitation polymerization and deposited as a single layer on a modified COC surface to form a 3D surface texture. The surface roughness of the COC support undergoes a significant increase from 1.4 nm to 37.1 nm after deposition of PSM microspheres with a size of 460 nm, and the modified COC still maintains a transmittance of more than 63% at the fluorescence excitation wavelengths (555 nm and 647 nm). The immobilization efficiency of immunoglobulin G (IgG) on the 3D surface reached 75.6% and the immobilization density was calculated to be 0.255 μg cm^-2, at a probe protein concentration of 200 μg mL^-1. The 3D protein microarray can be rapidly blocked by gaseous ethylenediamine within 10 minutes due to the high reactivity of anhydride groups in PSM microspheres. Immunoassay results show that the 3D protein microarray achieved specific identification of the target protein with a linear detection range from 6.25 ng mL^-1 to 250 ng mL^-1 (R² > 0.99) and a limit of detection of 8.87 ng mL^-1. This strategy offers a novel way to develop high performance polymer-based 3D protein chips.

Dynamic photonic perovskite light-emitting diodes with post-treatment-enhanced crystallization as writable and wipeable inscribers

Controllable photonic patterns have attracted great attention for various applications in displays, smart sensors, and communications. Conventional patterned light-emitting-diode (LED) systems require complicated design, complex procedure, and advanced equipment. Moreover, permanent properties of the fabricated patterns on LED restrict it from various important applications. Herein, we present an innovative writable and wipeable perovskite light-emitting-diode (WWPeLED) device, which tactfully utilizes the large variation of turn-on voltage originating from the external quantum efficiency (EQE) difference under controllable thermal treatment. The turn-on voltages with/without thermal-treatment devices exhibit a large gap of over 5 V, and the thermal-treatment electroluminescence intensity is more than 10 times higher than that of non-thermal-treatment devices. The new phenomena open up an effective way of controlling illumination with desired pattern designs. Additionally, the distinct handwriting fonts and habits as well as printing patterns with illumination WWPeLED are also realized. Furthermore, these written and printed features can be totally wiped out with an 11 V cleaning voltage, turning the devices as a regular fully bright PeLED. The stability and repeatability tests prove the robustness of WWPeLED in both mechanical and electroluminescence performance after a long period of operations. The innovative WWPeLED devices may find prospective applications in various optoelectronic devices and flexible integrated systems.

Functional Micro-/Nanomaterials for Multiplexed Biodetection

When analyzing biological phenomena and processes, multiplexed biodetection has many advantages over single-factor biodetection and is highly relevant to both human health issues and advancements in the life sciences. However, many key problems with current multiplexed biodetection strategies remain unresolved. Herein, the main issues are analyzed and summarized: 1) generating sufficient signal to label targets, 2) improving the signal-to-noise ratio to ensure total detection sensitivity, and 3) simplifying the detection process to reduce the time and labor costs of multiple target detection. Then, available solutions made possible by designing and controlling the properties of micro- and nanomaterials are introduced. The aim is to emphasize the role that micro-/nanomaterials can play in the improvement of multiplexed biodetection strategies. Through analyzing existing problems, introducing state-of-the-art developments regarding relevant materials, and discussing future directions of the field, it is hopeful to help promote necessary developments in multiplexed biodetection and associated scientific research.

Bottom-Up Assembled Photonic Crystals for Structure-Enabled Label-Free Sensing

Photonic crystals (PhCs) display photonic stop bands (PSBs) and at the edges of these PSBs transport light with reduced velocity, enabling the PhCs to confine and manipulate incident light with enhanced light-matter interaction. Intense research has been devoted to leveraging the optical properties of PhCs for the development of optical sensors for bioassays, diagnosis, and environmental monitoring. These applications have furthermore benefited from the inherently large surface area of PhCs, giving rise to high analyte adsorption and the wide range of options for structural variations of the PhCs leading to enhanced light-matter interaction. Here, we focus on bottom-up assembled PhCs and review the significant advances that have been made in their use as label-free sensors. We describe their potential for point-of-care devices and in the review include their structural design, constituent materials, fabrication strategy, and sensing working principles. We thereby classify them according to five sensing principles: sensing of refractive index variations, sensing by lattice spacing variations, enhanced fluorescence spectroscopy, surface-enhanced Raman spectroscopy, and configuration transitions.

From colloidal particles to photonic crystals: advances in self-assembly and their emerging applications

Over the last three decades, photonic crystals (PhCs) have attracted intense interests thanks to their broad potential applications in optics and photonics. Generally, these structures can be fabricated via either "top-down" lithographic or "bottom-up" self-assembly approaches. The self-assembly approaches have attracted particular attention due to their low cost, simple fabrication processes, relative convenience of scaling up, and the ease of creating complex structures with nanometer precision. The self-assembled colloidal crystals (CCs), which are good candidates for PhCs, have offered unprecedented opportunities for photonics, optics, optoelectronics, sensing, energy harvesting, environmental remediation, pigments, and many other applications. The creation of high-quality CCs and their mass fabrication over large areas are the critical limiting factors for real-world applications. This paper reviews the state-of-the-art techniques in the self-assembly of colloidal particles for the fabrication of large-area high-quality CCs and CCs with unique symmetries. The first part of this review summarizes the types of defects commonly encountered in the fabrication process and their effects on the optical properties of the resultant CCs. Next, the mechanisms of the formation of cracks/defects are discussed, and a range of versatile fabrication methods to create large-area crack/defect-free two-dimensional and three-dimensional CCs are described. Meanwhile, we also shed light on both the advantages and limitations of these advanced approaches developed to fabricate high-quality CCs. The self-assembly routes and achievements in the fabrication of CCs with the ability to open a complete photonic bandgap, such as cubic diamond and pyrochlore structure CCs, are discussed as well. Then emerging applications of large-area high-quality CCs and unique photonic structures enabled by the advanced self-assembly methods are illustrated. At the end of this review, we outlook the future approaches in the fabrication of perfect CCs and highlight their novel real-world applications.

Robust Carbonated Structural Color Barcodes with Ultralow Ontology Fluorescence as Biomimic Culture Platform

Photonic crystal (PC) barcodes are a new type of spectrum-encoding microcarriers used in multiplex high-throughput bioassays, such as broad analysis of biomarkers for clinical diagnosis, gene expression, and cell culture. Unfortunately, most of these existing PC barcodes suffered from undesired features, including difficult spectrum-signal acquisition, weak mechanical strength, and high ontology fluorescence, which limited their development to real applications. To address these limitations, we report a new type of structural color-encoded PC barcodes. The barcodes are fabricated by the assembly of monodisperse polydopamine- (PDA-) coated silica (PDA@SiO₂) nanoparticles using a droplet-based microfluidic technique and followed by pyrolysis of PDA@SiO₂ (C@SiO₂) barcodes. Because of the templated carbonization of adhesive PDA, the prepared C@SiO₂ PC beads were endowed with simultaneous easy-to-identify structural color, high mechanical strength, and ultralow ontology fluorescence. We demonstrated that the structural colored C@SiO₂ barcodes not only maintained a high structural stability and good biocompatibility during the coculturing with fibroblasts and tumor cells capture but also achieved an enhanced fluorescent-reading signal-to-noise ratio in the fluorescence-reading detection. These features make the C@SiO₂ PC barcodes versatile for expansive application in fluorescence-reading-based multibioassays.

Precisely Encoded Barcodes through the Structure-Fluorescence Combinational Strategy: A Flexible, Robust, and Versatile Multiplexed Biodetection Platform with Ultrahigh Encoding Capacities

With the rapid development of suspension array technology, microbeads-based barcodes as the core element with sufficient encoding capacity are urgently required for high-throughput multiplexed detection. Here, a novel structure-fluorescence combinational encoding strategy is proposed for the first time to establish a barcode library with ultrahigh encoding capacities. Based on the never revealed transformability of the structural parameters (e.g., porosity and matrix component) of mesoporous microbeads into scattering signals in flow cytometry, the enlargement of codes number has been successfully realized in combination with two other fluorescent elements of fluorescein isothiocyanate isomer I (FITC) and quantum dots (QDs). The barcodes are constructed with precise architectures including FITC encapsulated within mesopores and magnetic nanoparticles as well as QDs immobilized on the outer surface to achieve the ultrahigh encoding level of 300 accompanied with superparamagnetism. To the best of knowledge, it is the highest record of single excitation laser-based encoding capacity up to now. Moreover, a ten-plexed tumor markers bioassay based on the tailored-designed barcodes has been evaluated to confirm their feasibility and effectiveness, and the results indicate that the barcodes platform is a promising and robust tool for practical multiplexed biodetection.

Biomimetic design of photonic materials for biomedical applications

Photonic crystal (PC) materials with bio-inspired structure colors have drawn increasing attention as their potentials have been rapidly progressed in the field of biomedicine. After elaborate integration with smart materials or preparations through advanced techniques, PC materials have shown significant advantages in biosensing, bio-probing, bio-screening, tissue engineering, and so forth. In this review, we first introduced the fundamentals of PC materials as well as their fabrication strategies with different dimensional outputs. Based on these diversified PC materials, their biomedical potentials as biosensing elements, cell carriers, drug delivery systems, screening methods, cell scaffolds for tissue engineering, cell imaging probes, as well as the monitoring means for biological processes were then highlighted. In addition to these, we finally listed and discussed some emerging applications of PCs integrated with functional materials and newly developed material engineering technologies. In short, this review will provide a panoramic view of PCs-based biomedicines, and moreover, the progressive discussions from fundamentals to advanced applications in this review may also encourage researchers to innovate PC materials or devices for broader biomedical applications.

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.

Photonic Janus Balls with Controlled Magnetic Moment and Density Asymmetry

Colloidal crystals show structural colors through wavelength-selective diffraction at photonic stopbands. Here, we design photonic Janus balls with a controlled magnetic moment for programmable structural color switching. The Janus balls are produced from microfluidically produced paired drops of two distinct photocurable resins. The lighter resin contains magnetic nanoparticles and carbon black, whereas heavier one contains silica particles at a high volume fraction. The paired drops spontaneously align vertically due to the density asymmetry. The magnetic moment is assigned in the vertically aligned drops by aligning magnetic nanoparticles with an external field and capturing them through photopolymerization. Silica particles in the heavier compartment spontaneously form crystalline arrays due to interparticle repulsion, developing structural colors. The resulting photonic Janus balls vertically align without an external field, like a roly-poly toy, so that carbon-black-laden compartments face upward. With an external magnetic field, the Janus balls align their magnetic moment to the field and display structural colors. Importantly, the direction of the magnetic moment is set by the direction of the external field during photopolymerization, which enables the simultaneous manipulation of orientations of distinct photonic Janus balls in a programmed manner. These photonic Janus balls are potentially useful as active color inks for anti-counterfeiting tags.

Plasmonic Janus Microspheres Created from Pickering Emulsion Drops

Metal nanostructures have been created in a film format to develop unique plasmonic properties. Here, well-defined metal nanostructures are designed on the surface of microspheres to provide plasmonic microgranules. As conventional techniques are inadequate for nanofabrication on spherical surfaces, photocurable emulsion drops with a regular array of silica particles are employed at the interface to create periodic nanostructures. The silica particles, originating from the dispersed phase, fully cover the interface by forming a non-close-packed hexagonal array after drop generation, and slowly protrude to the continuous phase during aging while their interparticle separation decreases. Therefore, hexagonal arrays of spherical dimples with controlled geometry and separation are created on the surface of microspheres by photocuring the drops and removing the particles. Directional deposition of either aluminum or gold results in a continuous film with a hexagonal array of holes on the outermost surface and isolated curved disks in dimples, which renders the hemisphere of microspheres plasmonically colored. The resonant wavelength is controlled by adjusting the aging time, metal thickness, and size of silica particles, providing various plasmonic colors. This granular format of the plasmonic Janus microspheres will open a new avenue of optical applications including active color pixels, optical barcodes, and microsensors.

Fiber Optic Particle Plasmon Resonance-Based Immunoassay Using a Novel Multi-Microchannel Biochip

A novel multi-microchannel biochip fiber-optic particle plasmon resonance (FOPPR) sensor system for the simultaneous detection of multiple samples. The system integrates a novel photoelectric system, a lock-in module, and an all-in-one platform incorporating optical design and mechanical design together to improve system stability and the sensitivity of the FOPPR sensor. The multi-microchannel FOPPR biochip has been developed by constructing a multi-microchannel flow-cell composed of plastic material to monitor and analyze five samples simultaneously. The sensor system requires only 30 μL of sample for detection in each microchannel. Moreover, the total size of the multi-microchannel FOPPR sensor chip is merely 40 mm × 30 mm × 4 mm; thus, it is very compact and cost-effective. The analysis was based on calibration curves obtained from real-time sensor response data after injection of sucrose solution, streptavidin and anti-dinitrophenyl (anti-DNP) antibody of known concentrations over the chips. The results show that the multi-microchannel FOPPR sensor system not only has good reproducibility (coefficient of variation (CV) < 10%), but also excellent refractive index resolution (6.23 ± 0.10 × 10⁻⁶ refractive index unit (RIU)). The detection limits are 2.92 ± 0.28 × 10⁻⁸ g/mL (0.53 ± 0.01 nM) and 7.48 ± 0.40 × 10⁻⁸ g/mL (0.34 ± 0.002 nM) for streptavidin and anti-DNP antibody, respectively.

Facile Surface Functionalization of Cyclic Olefin Copolymer Film with Anhydride Groups for Protein Microarray Fabrication

Immobilization of protein at high efficiency is a challenge for fabricating polymer-based protein chips. Here, a simple but effective approach was developed to fabricate a cyclic olefin copolymer (COC)-based protein microarray with a high immobilization density. In this strategy, poly(maleic anhydride-co-vinyl acetate) (poly(MAH-co-VAc)) brushes were facilely attached on the COC surface via UV-induced graft copolymerization. The introduction of poly(MAH-co-VAc) brushes resulted in an obvious increase in the surface roughness of COC. The functionalized COC showed little reduction in transparency compared with pristine COC, indicating that the photografting treatment did not alter its optical property. The graft density of the anhydride groups on the modified COC could be tuned from 0.46 to 3.2 μmol/cm². The immobilization efficiency of immunoglobulin G (IgG) on functionalized COC reached 88% due to the high reactivity between anhydride groups and amine groups of IgGs. An immunoassay experiment demonstrated that the microarray showed high sensitivity to the target analyte.

Water Droplets Translocation and Fission in a 3D Bi-Planar Multifurcated T-Junction Microchannels

Droplet fission has gained notable interest in drug delivery applications due to its ability to perform parallel operations in single device. Hitherto, droplet flow behavior in a 3D constriction was scarcely investigated. This study aims to investigate droplets fission inside a 3D bi-planar multifurcated microfluidic device. The flow behavior and droplet size distribution were studied in trifurcated microchannels using distilled water as dispersed phase (1 mPa·s) and olive oil (68 mPa·s) as continuous phase. Various sizes of subordinate daughter droplets were manipulated passively through the modulation of flowrate ratio (Q) (0.15 < Q < 3.33). Overall, we found droplet size coefficient of variations (CV%) ranging from 0.72% to 69%. Highly monodispersed droplets were formed at the upstream T-junction (CV% < 2%) while the droplet fission process was unstable at higher flowrate ratio (Q > 0.4) as they travel downstream (1.5% < CV% < 69%) to splitting junctions. Complex responses to the non-monotonic behavior of mean droplet size was found at the downstream boundaries, which arose from the deformations under nonuniform flow condition. CFD was used as a tool to study the preliminary maximum velocity (Umax) profile for the symmetrical (0.01334 m/s < Umax < 0.0153 m/s) and asymmetrical branched channels (0.0223 m/s< Umax < 0.00438 m/s), thus complementing the experimental model studies.

Colloidal Crystals from Microfluidics

Colloidal crystals are of great interest to researchers because of their excellent optical properties and broad applications in barcodes, sensors, displays, drug delivery, and other fields. Therefore, the preparation of high quality colloidal crystals in large quantities with high speed is worth investigating. After decades of development, microfluidics have been developed that provide new choices for many fields, especially for the generation of functional materials in microscale. Through the design of microfluidic chips, colloidal crystals can be prepared controllably with the advantages of fast speed and low cost. In this Review, research progress on colloidal crystals from microfluidics is discussed. After summarizing the classifications, the generation of colloidal crystals from microfluidics is discussed, including basic colloidal particles preparation, and their assembly inside or outside of microfluidic devices. Then, applications of the achieved colloidal crystals from microfluidics are illustrated. Finally, the future development and prospects of microfluidic-based colloidal crystals are summarized.

Self-assembly of colloids based on microfluidics

Self-assembly of colloids provides a powerful way for the construction of complex multi-scale materials. Microfluidic techniques possess great potential to precisely control the assembly of micro- and nano-scale building blocks via the rational design of various microfluidic environments. In this review, we first discuss the self-assembly of colloids without templates by using the laminar microfluidic technique. The self-assembly of colloids based on a droplet as a template was subsequently summarized and discussed via droplet microfluidic technique. Moreover, the evaporation-driven self-assembly of colloids in microfluidic channels has been discussed and analysed. Finally, the representative applications in this field have been pointed out. The aim of this review is to summarize the state-of-art on the self-assembly of colloids based on various microfluidic techniques, exhibit their representative applications, and point out the current challenges in this field, hoping to inspire and guide future work.

Porous Hydrogel-Encapsulated Photonic Barcodes for Multiplex Detection of Cardiovascular Biomarkers

Early detection of cardiac troponin I (cTnI), B-type natriuretic peptide (BNP), and myoglobin (Myo) is essential for the diagnosis of acute myocardial infarction (AMI) and heart failure (HF). We designed a porous hydrogel-encapsulated photonic crystal (PhC) barcode-based suspension array for multiple cardiovascular marker detection. The hybrid hydrogel was composed of polyethylene glycol diacrylate (PEGDA) and gelatin, resulting in a porous and hydrophilic scaffold which ensured stability of the PhC in aqueous solutions. The encapsulated PhC barcodes had stable diffraction peaks for the corresponding markers. Using a sandwich format, the proposed suspension array was used for simultaneous multiplex detection of cardiovascular biomarkers in a single tube. The immunoassay results we tested on cTnI, BNP, and Myo could be assayed in the ranges of 0.01 to 1000 ng/mL, 0.1 to 10 000 pg/mL, and 1 to 10 000 ng/mL with limits of detection of 0.009 ng/mL, 0.084 pg/mL, and 0.68 ng/mL at 3σ, respectively. This method also showed acceptable accuracy and repeated detection, and the results were consistent with the results of conventional clinical methods for detecting actual clinical samples. Therefore, suspension arrays based on hydrogel-encapsulated PhC barcodes are highly promising for AMI diagnosis.

Self-assembled colloidal arrays for structural color

Structural color materials that are colloidally assembled as inspired by nature are attracting increased interest in a wide range of research fields. The assembly of colloidal particles provides a facile and cost-effective strategy for fabricating three-dimensional structural color materials. In this review, the generation mechanisms of structural colors from colloidally assembled photonic crystalline structures (PCSs) and photonic amorphous structures (PASs) are first presented, followed by the state-of-the-art and detailed technologies for their fabrication. The variable optical properties of PASs and PCSs are then discussed, focusing on their spatial long- and short-order structures and surface topography, followed by a detailed description of the modulation of structural color by refractive index and lattice distance. Finally, the current applications of structural color materials colloidally assembled in various fields including biomaterials, microfluidic chips, sensors, displays, and anticounterfeiting are reviewed, together with future applications and tasks to be accomplished.

Condensing-enriched magnetic photonic barcodes on superhydrophobic surface for ultrasensitive multiple detection

The ultrasensitive detection of multiple nucleic acids has great significance in a broad range of medical fields since nucleic acid samples are usually of small volumes and highly diluted. Herein, we present a novel magnetic photonic crystal (PhC) barcode-integrated condensing-enriched superhydrophobic platform for the ultrasensitive multiple miRNA detection. Droplets containing targets could suck the hydrogel PhC barcodes without losing their targets due to the difference in wettability between the hydrophilic PhC barcodes and hydrophobic substrate. During the evaporation of water from the droplet microreactors, these targets could be effectively enriched in the barcodes for achieving higher sensitivities. As the encoding signals of the PhC barcodes are the characteristic reflection peaks generated by their ordered physical nanostructures, the barcodes are stable and free from any fluorescent background and photobleaching; thus, they are accurate for distinguishing different targets. In addition, with the integration of magnetic nanoparticles into the hydrogel PhC barcodes, they could be imparted with the features of immobilization during change of medium and flexible movement for controlling the reaction, both of which could facilitate the detection processes. Based on this platform, we have demonstrated that the detection limit of multiple miRNAs is improved by about three orders. Thus, our platform is an ideal alternative for the ultrasensitive simultaneous multiplex analysis in medical fields.

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.

Molybdenum disulfide-integrated photonic barcodes for tumor markers screening

As a new class of two-dimensional (2D) materials, molybdenum disulfide (MoS₂) has huge potential in biomedical area; while its applications in multiplex bioassays are still a challenge. Here, we present novel MoS₂-integrated silica colloidal crystal barcode (SCCB) for multiplex microRNA (miRNA) screening. MoS₂ was adsorbed on SCCBs by electrostatic interaction, and quantum dots (QDs) decorated hairpin probes were coupled on MoS₂ by covalent linkage. As the MoS₂ could quench the QDs of the hairpin probes, they together formed a molecular beacon (MB) structure before the detection. When used in assays, target miRNA could form a double strand with the probe and made QDs keep away from MoS₂ sheets to recovery their fluorescence. Because the released QDs were positively correlated with the concentration of the hybridized nucleic acid, the target miRNAs could be quantified by measuring the fluorescence signal of the QDs on the SCCBs. In addition, by utilizing different MoS₂-integrated structural color encoded SCCBs, multiplexed miRNA quantification could also be realized. Based on this strategy, we have demonstrated that several pancreatic cancer-related miRNAs could be selectivity and sensitivity detected with a detection limit of 4.2 ± 0.3 nM. These features make the MoS₂-integrated SCCB ideal for many potential applications.

Barcoded point-of-care bioassays

Barcoded bioassays are ready to promote bioanalysis and biomedicine toward the point of care.

Rapid Self-Assembly of Au Nanoparticles on Rigid Mesoporous Yeast-Based Microspheres for Sensitive Immunoassay

A simple, rapid, inexpensive, eco-friendly, and high-throughput biological strategy for the preparation of functional microspheres on a yeast-cell platform was introduced. Microspheres prepared through the treatment of yeast cells with formaldehyde and decoating buffer exhibited excellent characteristics, such as superior mechanical strength, high sulfhydryl group content, and mesoporous structure. Au nanoparticles (NPs) easily and rapidly self-assembled onto the surfaces of the yeast-based microspheres within 5 min to form rigid yeast@Au microspheres with high monodispersity and uniformity. The rapid formation of yeast@Au microspheres mainly involved the enhancement of sulfhydryl groups and mesoporosity. The yeast@Au microspheres were successfully used in a flow cytometry immunoassay to detect Pseudorabies viral infection events. Signal-to-noise ratio was enhanced by approximately 49.4-fold. The presence of Au NPs on the yeast-based microspheres greatly improved sensitivity by decreasing noise through reducing nonspecific adsorption, highly enhancing the fluorescence signal caused by the surface plasmon resonance effect, and increasing the coupling efficiency of the capture protein. The presented method was used to analyze 81 clinical swine serum specimens. The results obtained by this developed method were compared to those of commercial diagnostic kits. The sensitivity, specificity, and efficiency of the developed method were 92.31, 88.24, and 88.89%, respectively. The excellent characteristics of the yeast@Au microspheres illustrate its great potential for high-throughput immunoassay applications in the fields of disease diagnosis, environmental analysis, and food safety.

Bioinspired Photonic Barcodes with Graphene Oxide Encapsulation for Multiplexed MicroRNA Quantification

Multiplexed microRNA (miRNA) quantification has a demonstrated value in clinical diagnosis. In this paper, novel mussel-inspired photonic crystal (PhC) barcodes with graphene oxide (GO) encapsulation for multiplexed miRNA detection are presented. Using the excellent adhesion capability of polydopamine, the dispersed GO particles can be immobilized on the surfaces of the PhC barcodes to form an additional functional layer. The GO-decorated PhC barcodes have constant characteristic reflection peaks because the GO immobilization process not only maintains their periodic microstructure but also enhances their stability and anti-incoherent light-scattering capability. The immobilized GO particles are shown to enable high-sensitivity miRNA screening on the surface of the PhC barcodes by integration with a hybridization chain reaction amplification strategy. Because the PhC barcodes have stable encoding reflection peaks, multiplexed low-abundance miRNA quantification can also be achieved rapidly, accurately, and reproducibly by employing different GO-decorated PhC barcodes. These features should make GO-encapsulated PhC barcodes ideal for many practical applications.

Binary colloidal crystals (BCCs): Interactions, fabrication, and applications

The organization of matter into hierarchical structures is a fundamental characteristic of functional materials and living organisms. Binary colloidal crystal (BCC) systems present a diversified range of nanotopographic structures where large and small colloidal particles simultaneously self-assemble into either 2D monolayer or 3D hierarchical crystal lattices. More importantly, understanding how BCCs form opens up the possibility to fabricate more complex systems such as ternary or quaternary colloidal crystals. Monolayer BCCs can also offer the possibility to achieve surface micro- and nano-topographies with heterogeneous chemistries, which can be challenging to achieve with other traditional fabrication tools. A number of fabrication methods have been reported that enable generation of BCC structures offering high accuracy in growth with controllable stoichiometries; however, it is still a challenge to make uniform BCC structures over large surface areas. Therefore, fully understand the mechanism of binary colloidal self-assembly is crucial and new/combinational methods are needed. In this review, we summarize the recent advances in BCC fabrication using particles made of different materials, shapes, and dispersion medium. Depending on the potential application, the degree of order and efficiency of crystal formation has to be determined in order to induce variability in the intended lattice structures. The mechanisms involved in the formation of highly ordered lattice structures from binary colloidal suspensions and applications are discussed. The generation of BCCs can be controlled by manipulation of their extensive phase behavior, which facilitates a wide range potential applications in the fields of both material and biointerfacial sciences including photonics, biosensors, chromatography, antifouling surfaces, biomedical devices, and cell culture tools.

Robust, Highly Visible, and Facile Bioconjugation Colloidal Crystal Beads for Bioassay

High mechanical strength, highly visible, and admirable grafting molecular ability is the key challenge for colloidal photonic crystal (CPC) barcode beads in multiplex analysis fields. To achieve this goal, we proposed self-adhesion particles, polydopamine-coated SiO₂ nanoparticles (PDA@SiO₂), to construct CPC barcode beads by droplet-based microfluidic approach. Because of the adhesion, broad absorption of light, and "active" functional groups of PDA, the beads are endowed with high robustness, visibility, and excellent biomolecule immobilization. Ultrasonic treatment and compression experiments demonstrated that PDA@SiO₂ CPC barcode beads have a high mechanical strength. Color analysis illustrated that PDA@SiO₂ CPC beads exhibited a high visibility in color. The verification of fluorescent-tagged biomolecule conjugation together with the antigen detection stated that PDA@SiO₂ CPC beads are capable of immobilizing biomolecule by covalent binding. With a sandwich format, the beads were applied to analyze the tumor makers including alpha fetal protein, carcinoembryonic antigen, and prostate specific antigen from practical clinical serum. The proposed suspension arrays using PDA@SiO₂ CPC beads as a barcode showed acceptable accuracy and detection reproducibility.

Three-dimensional poly(lactic-co-glycolic acid)/silica colloidal crystal microparticles for sustained drug release and visualized monitoring

In this paper, a three-dimensional (3D) poly(lactic-co-glycolic acid) (PLGA)/silica colloidal crystal drug delivery system with sustained drug release and visualized release monitoring was developed. This system had employed silica colloidal crystal microparticles as template skeleton, PLGA as drug carrier and dexamethasone (DEX) as therapeutic agent. The fabrication of the microparticle-based system included droplet formation based-on microfluidics, silica nanoparticle self-assembly and layer-by-layer deposition of PLGA containing DEX. In 370 μm droplets, the silica colloidal nanoparticles could self-assemble orderly into microparticles with a diameter of 187 μm, featuring red structure color. During the deposition of PLGA with the drug into the voids of the template microparticles, the reflection peak red-shifted and weakened until the voids were completely filled. Owing to the gradual degradation of PLGA, the release of DEX was triggered and sustained for 4 weeks with a cumulative release of 94.9%, while the structure color of the microparticles recovered during the release process. The color change could be recognized by the naked eyes, which would benefit the non-invasive monitoring of the drug release. The in vitro cytotoxicity and long-term inhibiting proliferation were investigated on retinal pigment epithelial cells. The inhibition effect of DEX released from the microparticles showed concentration-dependence from 40 to 200 μg mL^-1 and time-dependence within 7 days. As a sustained drug delivery system with self-reporting drug release, the particles have potential applications in treatment of intraocular diseases.

Responsive Block Copolymer Photonic Microspheres

Responsive photonic crystals (PCs) have attracted much attention due to their broad applications in the field of chemical and physical sensing through varying optical properties when exposed to external stimuli. In particular, assembly of block copolymers (BCPs) has proven to be a robust platform for constructing PCs in the form of films or bulk. Here, the generation of BCPs photonic microspheres is presented with 3D periodical concentric lamellar structures through confined self-assembly. The structural color of the spherical PCs can be tuned by selective swelling of one block, yielding large change of optical property through varying both layer thickness and refraction index of the domains. The as-formed spherical PCs demonstrate large reflection wavelength shift (≈400-700 nm) under organic solvent permeation and pH adjustment. Spherical shape and structural symmetry endow the formed spherical PCs with rotation independence and monochrome, which is potentially useful in the fields of displays, sensing, and diagnostics.