Colloidal Arrays Research Articles

Bioinspired Ultra‐Stretchable and Highly Sensitive Structural Color Electronic Skins

AbstractOrganisms possess remarkably adaptive ability to complex environments. For example, chameleons can alter their skin color to adapt to varying environments, which has inspired significant advances in bioinspired soft electronic skins (E‐skins), and their wide applications in wearable sensors, intelligent robots, and health monitoring. However, current bioinspired E‐skins face challenges in ultra‐stretchability, high sensitivity, and long‐term stability owing to the intrinsic limitations associated with their mismatched interface between soft matrix and hard conductive fillers, hindering their practical applications. Here, it is reported that bioinspired structural color electronic skins (SC E‐skins) that consist of liquid metal particles (LMPs), periodical ordered colloidal crystal arrays, and ultra‐stretchable hydrogel, imparting synergistic and durable electrical–optical sensing capabilities. Such SC E‐skins demonstrate outstanding performances including superior flexibility (elongation at break > 1100%), high sensitivity (gauge factor = 3.26), fast synergetic electric–optical response time (≈100 ms), outstanding durability (over 1500 cycles), and high accuracy (R2 > 99.5%). These bioinspired SC E‐skins with excellent capability of converting mechanical signals into synergetic electrical–optical outputs hold great promise for smart wearable devices, affording a new horizon in developing advanced health monitoring technologies.

Polymerization-induced ultrafast and massive growth of colloidal photonic crystals on hydrogel surface

Structural color materials based on colloidal photonic crystals (CPCs) have been extensively investigated since they can be prepared efficiently. Commonly, photonic hydrogels are prepared by a polymerizing pre-gel solution, in which colloids are self-assembled by passive methods. Except for magnetic colloids, the process of forming colloidal photonic crystals in a pre-gel solution requires hours to days, and it is almost impossible to assemble the colloids directly in hydrogels. Here, we present a mild strategy to prepare hydrogels with surface structural color, ordered colloidal arrays are formed at the air-hydrogel interface actively during the polymerization process, and bright structural color forms in minutes on a large scale. Polymer exclusion is the key driving force for the assembly of the colloids, other factors, such as evaporation flux, can also promote the colloids to assemble. Significantly, heterogeneous structural color patterns can be produced easily by exposing the hydrogel surface to air sequentially using a mask during the polymerization process. The simple and fast method provides a general route for preparing structural colored surfaces, which may be suitable for various applications.

Carbon dot-loaded Fe3O4 as photonic pigments for multilevel anti-counterfeiting

Amorphous arrays assembled from colloidal microspheres are a way that obtains angle-independent structural colors. In order to obtain additional properties, colloidal microspheres, which are constituent units, can be modified with other materials. Here, we utilized the silane-functionalized carbon quantum dots (SiCDs) by incorporating them into the Stöber reaction to fabricate Fe3O4@SiO2/SiCDs nanospheres with a core-shell structure. Amorphous colloidal arrays (ACAs) were constructed on commercial printing paper using Fe3O4@SiO2/SiCDs nanoparticles as structural units by a simple permeation assembly. Macroscopically, the prepared ACAs exhibit the magnetic properties of Fe3O4, while under sunlight, they display bright, angle-independent structural colors. Under ultraviolet light, the array shows significant fluorescence. This enables the presentation of multidimensional information under varying magnetic and lighting conditions. By adjusting the thickness of the outer SiO2/SiCDs composite layer, the optical properties and magnetism can be controlled easily. Moreover, due to the strong light absorption capability and high refractive index of Fe3O4, the digital patterns constructed with Fe3O4@SiO2/SiCDs nanospheres demonstrate excellent multi-level anti-counterfeiting characteristics, even under water exposure. The magnetic properties of Fe3O4@SiO2/SiCDs nanospheres, along with their distinct display characteristics under different optical environments, suggest their wide applicability in the fields of multifunctional anti-counterfeiting pigments, bioimaging, and sensing displays.

Enhancement of pH imaging of light addressable potentiometric sensor by colloidal spherical lens array

Visualizing the distribution of pH in a solution is an important basis for monitoring reaction processes and metabolic changes in micro-biochemical species. Light addressable potentiometric sensor (LAPS), as a simple structure, flexible imaging, low-cost and label-free electrochemical sensor, has been widely used to pH imaging. However, its spatiotemporal resolution is greatly affected by the frequency of modulation light, thus limiting its imaging performance. In this study, LAPS device modified by well-ordered and low-cost polystyrene (PS) colloidal monolayer as spherical lens array is proposed to obtain higher available modulation frequency of the maximum photoresponse. The morphology, optical properties and the electric field distribution of PS colloidal spherical lens array were tested and analyzed. pH sensing, imaging of uniform pH solution, the spatiotemporal pH imaging and dynamic imaging of enzymatic reactions of LAPS modified by PS colloidal spherical lens array were tested and evaluated. The experimental results show that LAPS modified by PS colloidal spherical lens array not only has acceptable pH sensing, but also widens the modulation frequency of the maximum photoresponse to 40 kHz. LAPS modified by colloidal spherical lens array modulated at the frequency of 40 kHz shows acceptable sensitivity and linearity, good reproducibility and stability, high SNR and high-spatiotemporal pH imaging capability. This work can be suitable for high-spatiotemporal monitoring of the changes in electrolyte environmental pH caused by the reaction and metabolism of the biochemical species.

Regulating two-dimensional colloidal crystal assembly through contactless acoustic annealing

Two-dimensional colloidal crystals assembled from polystyrene nanospheres have emerged as a pivotal foundation for fabricating large-area nano-functional surfaces. These assemblies, defined by their hexagonal close-packed configuration and interlaced with grain boundaries, have garnered significant attention for applications in plasmonic structures, catalysts, photonic crystals, and inverse opals. Nonetheless, achieving consistent large-scale regularity has proven challenging due to unpredictable crystal growth and the introduction of defects. Utilizing acoustic waves excited from the airside, our experiments demonstrate the significant effects of such waves on the self-assembly process, leading to larger crystal domains and reduced defects. In comparison to the extensively studied water-end excitation techniques, our air-end excitation method introduces a novel dynamic in regulating colloidal monolayer crystallization and presents a comprehensive analysis of varying acoustic parameters, frequency, amplitude, and waveform. These findings reveal the potential of airside acoustic annealing in refining the structure of two-dimensional colloidal arrays. To elucidate our experimental observations, we delve into the theoretical underpinnings of particle dynamics, driven by classical hydromechanical constraints like surface tension and gravity. Using a qualitative estimate, we shed light on the resonant excitations and their potential role in optimizing the self-assembly process, especially focusing on resonances pertinent for enhancing cluster enlargements. Conclusively, our research, steeped in robust theoretical frameworks and groundbreaking experimental techniques, offers a multifaceted solution for perfecting two-dimensional colloidal arrays. This combined approach not only broadens the scope of acoustically induced crystallization but also charts a path for its adoption across diverse environments, signaling transformative prospects for nanomanufacturing and optical research.

Dynamic Photonic Janus Colloids with Axially Stacked Structural Layers.

Diblock copolymer (dBCP) particles capable of dynamic shape and color changes have gained significant attention due to their versatility in programmable shapes and intricate nanostructures. However, their application in photonic systems remains limited due to challenges in achieving a sufficient number of defect-free photonic layers over a tens-of-micrometer scale. In this study, we present a pioneering demonstration of photonic dBCP particles featuring over 300 axially stacked photonic layers with responsive color- and shape-transforming capabilities. Our approach leverages the complex interplay between the macrophase separation of multiple incompatible components and the microphase separation of dBCP from solvent-evaporative microemulsions. Specifically, continuous phase separation of silicone oil from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP), triggered by solvent evaporation, promotes the anisotropic growth of PS-b-P2VP layers. This results in the formation of Janus colloids, where an oil droplet merges with a nanostructured polymer cone and lamellar structures align along the long axis of the cone. We highlight the capability to precisely adjust the particle morphology and the corresponding orientation, dispersion, and structural color window by modulating both the molecular weight of PS-b-P2VP and the volume ratio between PS-b-P2VP and silicone oil. Furthermore, reversible swelling/deswelling of photonic colloids is visualized and correlated with their structural colors. Finally, we demonstrate the potential of this study by presenting a multicolor-patterned array of photonic colloids, highlighting the possibilities for applications in smart photonic ink and devices.

Templated gold nanocaps for surface-enhanced Raman scattering (SERS) sensors based on monolayer polystyrene colloidal arrays

Gold nanocaps modified with Ag nanoparticles exhibit superior SERS signals when compared to gold nanocaps and a silicon substrate, for the detection of rhodamine 6G molecules.

High-Sensitivity Mechanochromic Sensor Using Core-Shell Colloidal Crystals

The Colloidal Crystals-based mechanochromic sensor changes color as the arrangement of colloidal particles changes in response to mechanical deformation, which can be detected through optical measurement. This type of sensor can be used in various applications, such as automobile collision detection, structural deformation detection, and medical equipment, among others. In this study, we prepared a stretchable film by dispersing surface-functionalized colloidal particles in an elastic polymer matrix. Surface of silica colloidal particle was modified with an initiator for Atom Transfer Radical Polymerization (ATRP), followed by surface-initiated ATRP of poly(t-butyl methacrylate) (PtBMA). The core-shell colloidal particles were composited with various acrylic monomers, to fabricate crystalline colloidal array which transforms to elastic film by photopolymerization exhibiting structural color. The prepared film showed a clear color change for deformation within 10%, and the peak reflectance showed more than 30%.

Optically Transparent and Color-Stable Elastomer with Structural Coloration under Elongation.

Optically transparent and colored elastomers with high toughness are expected to play an important role in the construction of advanced medical materials, wearable displays, and soft robots. In this study, we found that composite elastomers consisting of amorphous SiO2 particles homogeneously dispersed in high concentrations within a biocompatible acrylic polymer network exhibit optical transparency and bright structural colors. In the composite elastomers, the system in which the SiO2 particles form a colloidal amorphous array hardly changes its structural color hue despite deformation due to elongation. Furthermore, the composite elastomer of the SiO2 particles with the acrylic polymer network also results in high mechanical toughness. In summary, we have shown that the elastomer that exhibits fade-resistant structural coloration formed from safe materials can combine stable coloration and mechanical strength independent of their shape. This is expected to have new potential in future technologies to support our daily life.

High Q-Factor Plasmonic Surface Lattice Resonances in Colloidal Nanoparticle Arrays.

Surface lattice resonances (SLRs) sustained by ordered metal arrays are characterized by their narrow spectral features, remarkable quality factors, and the ability to tune their spectral properties based on the periodicity of the array. However, the majority of these structures are fabricated using classical lithographic processes or require postannealing steps at high temperatures to enhance the quality of the metal. These limitations hinder the widespread utilization of these periodic metal arrays in various applications. In this work, we use the scalable technique of template-assisted assembly of metal colloids to produce plasmonic supercrystals over centimeter areas capable of sustaining SLRs with high Q factors reaching up to 270. Our approach obviates the need for any postprocessing, offering a streamlined and efficient fabrication route. Furthermore, our method enables extensive tunability across the entire visible and near-infrared spectral ranges, empowering the design of tailored plasmonic resonant structures for a wide range of applications.

Designing color controllable SiO2 amorphous colloidal arrays

Amorphous assembling of SiO2 colloidal spheres is a convenient strategy to obtain amorphous photonic structure, such structure, referred to as SiO2 amorphous colloidal arrays (ACAs), can demonstrate angle-independent structural color owing to constructive interference. To date, an empirical equation for materials researchers to design the color of SiO2 ACAs remains vacant, and several influence factors concerning with the color of SiO2 ACAs are still ignored and uninvestigated. Herein, based on single scattering model, we have proposed an empirical equation to predict the reflection peak of SiO2 ACAs to design their color, and influence factors including background and thickness on the color of SiO2 ACAs were also investigated. By preparing spheres within the designed range as building blocks, SiO2 ACAs with colors varying from blue to red were achieved whose reflection peaks position fits well with the empirical equation. This study can help materials researchers to design and manipulate structural color of SiO2 ACAs while providing insight to understand the origin of structural color of SiO2 ACAs.

Construction of Steady Amorphous Colloidal Array Patterns via Infiltration-Driven Assembly of Core-Shell Microparticles followed by Short-Time Heating.

Although core-shell microparticles with a hard core and soft shell are often used to fabricate photonic crystal films, they are rarely applied to construct steady amorphous colloidal array (ACA) patterns. In this work, a series of monodisperse core-shell microparticles with a polystyrene (PS) core and poly(methyl methacrylate-butyl acrylate) (P(MMA-BA)) shell have been successfully synthesized, and the glass transition temperatures (Tg) of the shell layer have been well regulated. The synthesized core-shell microparticles were then used to fabricate ACA patterns via a convenient infiltration-driven assembly method. The results showed that the Tg of the shell significantly affected the microstructure of the amorphous colloidal arrays (ACAs). During the assembly process, the microparticles quickly contacted each other and the lower-Tg shells could merge with each other to form a continuous film. In this situation, the PS core was embedded and ranked in the P(MMA-BA) film, and both the refractive index contrast and order degree of the colloidal array became relatively low, resulting in a poor structural color. However, when the Tg of the shell layer was moderately high, a short-range ordered array was prepared via infiltration-driven assembly, thereby displaying a bright structural color. More importantly, the shell layers could merge with each other to some extent after short-time heating, resulting in fine mechanical stability. In brief, this study provides a facile and environmental approach to construct steady ACA patterns, which is promising in printing and painting industries.

Lattice Transformation-Induced Retroreflective Structural Colors.

Retroreflective structural colors can usually be achieved based on interference combined with a total internal reflection mechanism or diffraction of a monolayer hexagonal two-dimensional (2D) colloidal array. Here, a novel retroreflective structural color was generated based on a hexagonal-parallelogram lattice transformation by stretching 3D photonic crystals with nonclosely packed long-range order. Compared to previous retroreflective colors, this new retroreflective color exhibits two unique off/on color switches: (1) a strain-dependent off/on color switch along the stretching direction and (2) a sample horizontal rotation angle-dependent off/on color switch under the fixed strain. These strain-responsive retroreflective colors are ideal candidates for visually sensing kinesio tapes' strain in practical applications and anticounterfeiting. This work reveals a new structural color regulation mechanism and will advance potential applications in anticounterfeiting, sensing, displays, etc.

Flexible and broadband colloidal quantum dots photodiode array for pixel-level X-ray to near-infrared image fusion

Combining information from multispectral images into a fused image is informative and beneficial for human or machine perception. Currently, multiple photodetectors with different response bands are used, which require complicated algorithms and systems to solve the pixel and position mismatch problem. An ideal solution would be pixel-level multispectral image fusion, which involves multispectral image using the same photodetector and circumventing the mismatch problem. Here we presented the potential of pixel-level multispectral image fusion utilizing colloidal quantum dots photodiode array, with a broadband response range from X-ray to near infrared and excellent tolerance for bending and X-ray irradiation. The colloidal quantum dots photodiode array showed a specific detectivity exceeding 1012 Jones in visible and near infrared range and a favorable volume sensitivity of approximately 2 × 105 μC Gy−1 cm−3 for X-ray irradiation. To showcase the advantages of pixel-level multispectral image fusion, we imaged a capsule enfolding an iron wire and soft plastic, successfully revealing internal information through an X-ray to near infrared fused image.

Mercury telluride colloidal quantum-dot focal plane array with planar p-n junctions enabled by in situ electric field–activated doping

Colloidal quantum dot (CQD)–based photodetectors are promising alternatives to bulk semiconductor-based detectors to be monolithically integrated with complementary metal-oxide semiconductor readout integrated circuits avoiding high-cost epitaxial growth methods and complicated flip-bonding processes. To date, photovoltaic (PV) single-pixel detectors have led to the best performance with background-limit infrared photodetection performance. However, the nonuniform and uncontrollable doping methods and complex device configuration restrict the focal plane array (FPA) imagers to operate in PV mode. Here, we propose a controllable in situ electric field–activated doping method to construct lateral p-n junctions in the short-wave infrared (SWIR) mercury telluride (HgTe) CQD–based photodetectors with a simple planar configuration. The planar p-n junction FPA imagers with 640 × 512 pixels (15-μm pixel pitch) are fabricated and exhibit substantially improved performance compared with photoconductor imagers before activation. High-resolution SWIR infrared imaging is demonstrated with great potential for various applications including semiconductor inspection, food safety, and chemical analysis.

Production of Photonic Supraballs Composed of Single-Crystalline Colloidal Arrays through Osmosis-Induced Consolidation

Production of Photonic Supraballs Composed of Single-Crystalline Colloidal Arrays through Osmosis-Induced Consolidation

Band edge induced plasmonic excitation in heterostructures consisting of rod hyperbolic metamaterials and colloidal photonic crystals

Heterostructures consisting of metal coated rod hyperbolic metamaterials (HMMs) and colloidal photonic crystals (PhCs) are proposed and fabricated. There are two different mechanisms for the reflection valleys induced from the excitation of plasmons in HMMs. Besides the common wave vector matching effects from colloidal gratings, band edge effects provide additional excitations in heterostructures. Slow light induced excitation is verified by separately modifying the photonic bandgap and grating parameters on HMMs using multilayer or monolayer colloidal crystals, 1D PhCs, or ellipsoid arrays, and by modifying the interval or metal thickness in heterostructures. Index-dependent sensitivity of the valleys is enhanced by the bandgap effect.

Adhesive photonic-ionic skins for visualizing wearable strain distributions

Photonic-ionic skins (PI-skins) inspired by natural skins with ion transduction and chromotropic traits have attracted tremendous attention. Although PI-skins with multiple signal synergistic outputs have been developed, incorporating strong adhesion for direct wearing and precise location of deformation remains highly desirable and challenging. Herein, a mechanochromic and electromechanical PI-skin with superior adhesion, sensitivity, stability, and self-healing ability is presented to visualize wearable strain distributions and monitor human motions. The PI-skin is constructed by integrating a close-packed carboxylated polystyrene (PS-COOH) colloidal array with polymerized deep eutectic solvent (PDES) via in-situ photopolymerization. The as-prepared PI-skin simultaneously exhibits sensitive dual-signal sensing of strain (gauge factor: 1.28, response time: 240 ms, mechanochromic sensitivity of 1.87 nm per percent strain) via adjusting the lattice spacing of the colloidal photonic arrays and resistance. Notably, thanks to the multiple hydrogen bond network of PDES, PI-skin has achieved remarkable adhesion (∼1.44 MPa on glass), mechanical strength, and self-healing performance. Furthermore, the excellent resilience of PDES endows the PI-skin with long-term electrical stability and reproducibility. The PDES contributed to high stretchability (∼1197.8 %), guaranteeing the application as a flexible sensor. The PI-skin promises direct and firm wearing as an interactive sensor for motion monitoring and visual mapping strain distribution.

A selectivity‐enhanced colloidal crystal array for ribavirin sensing based on the synergistic effect of covalent and non‐covalent interactions

AbstractRibavirin is an important antiviral with demonstrated activity against coronaviruses such as severe acute respiratory syndrome coronavirus and coronavirus disease 2019 virus. However, abuse of ribavirin will cause great environmental damage and threaten human health owing to its reproductive toxicity and teratogenicity. Therefore, an innovative detection method is demanded for simple and sensitive detection of ribavirin. This work reports an imprinted colloidal crystal array (ICCA) for ribavirin sensing. The building blocks of the ICCA are ribavirin imprinted spheres, which possess superior binding efficiency toward ribavirin. Benefiting from the highly ordered structure, the ICCA exhibits optical properties which change upon binding ribavirin. The changes in reflectance wavelength enable a fast and label‐free detection of ribavirin between 21 and 245 μmol L−1. Moreover, the sensor shows excellent selectivity for ribavirin detection in river water. Overall, all the results reported in this work demonstrate that the ICCA should be a promising detection tool for antivirals. © 2023 Society of Industrial Chemistry.

Easy Cell Detachment and Spheroid Formation of Induced Pluripotent Stem Cells Using Two-Dimensional Colloidal Arrays

Induced pluripotent stem cells (iPSCs) may develop into any form of cell and are being intensively investigated. The influence on iPSCs of nanostructures generated using two-dimensional colloidal arrays was examined in this study. Colloidal arrays were formed using the following procedure. First, core–shell colloids were adsorbed onto a glass substrate using a layer-by-layer method. Second, the colloids were immobilized via thermal fusion. Third, the surface of the colloids was modified by plasma treatment. By adjusting the number density of colloids, cultured iPSCs were easily detached from the substrate without manual cell scraping. In addition to planar culture, cell aggregation of iPSCs attached to the substrate was achieved by combining hydrophilic surface patterning on the colloidal array. Multilayered cell aggregates with approximately four layers were able be cultured. These findings imply that colloidal arrays might be an effective tool for controlling the strength of cell adhesion.