A Multi-stopband Photonic-Crystal Microchip for High-Performance Metal-Ion Recognition Based on Fluorescent Detection

Visual Gustation via Regulable Elastic Photonic Crystals

The unique structural sensitivity of photonic crystals (PCs) endows them with stretchable or elastic tunability for light propagation and spontaneous emission modulation. Hydrogel PCs have been demonstrated to have biocompatibility and flexibility for potential human health detection and environmental security monitoring. However, current elastic PCs still possess a fixed elastic modulus and uncontrollable structural colors based on a tunable elastic modulus, posing considerable challenges for in situ detection, particularly in wearable or portable sensing devices. In this work, we introduced a novel chemo-mechanical transduction mechanism embedded within a photonic crystal nanomatrix, leading to the creation of structural colors and giving rise to a visual gustation sensing experience. By utilizing the captivating structural colors generated by the hydrogel PC, we employ abundant optical information to identify various analytes. The finite element analysis proved the electric field distribution in the PC matrix during stretch operations. The elastic-optical behaviors with various chemical cosolvents, including cations, anions, saccharides, or organic acids, were investigated. The mechanism of the Hofmeister effect regulating the elasticity of hydrogels was demonstrated with the network nanostructure of the hydrogels. The hydrogel PC matrix demonstrates remarkable capability in efficiently distinguishing a wide range of cations, anions, saccharides, and organic acids across various concentrations, mixtures, and even real food samples, such as tastes and soups. Through comprehensive research, a precise relationship between the structural colors and the elastic modulus of hydrogel PCs has been established, contributing to the biomatching elastic-optics platform for wearable devices, a dynamic environment, and clinical or health monitoring auxiliary.

Omnidirectional Photodetectors Based on Spatial Resonance Asymmetric Facade via a 3D Self-Standing Strategy

Integration of photovoltaic materials directly into 3D light-matter resonance architectures can extend their functionality beyond traditional optoelectronics. Semiconductor structures at subwavelength scale naturally possess optical resonances, which provides the possibility to manipulate light-matter interactions. In this work, a structure and function integrated printing method to remodel 2D film to 3D self-standing facade between predesigned gold electrodes, realizing the advancement of structure and function from 2D to 3D, is demonstrated. Due to the enlarged cross section in the 3D asymmetric rectangular structure, the facade photodetectors possess sensitive light-matter interaction. The single 3D facade photodetectors can measure the incident angle of light in 3D space with a 10° angular resolution. The resonance interaction of the incident light at different illumination angles and the 3D subwavelength photosensitive facade is analyzed by the simulated light flow in the facade. The 3D facade structure enhances the manipulation of the light-matter interaction and extends metasurface nanophotonics to a wider range of materials. The monitoring of dynamic variation is achieved in a single facade photodetector. Together with the flexibility of structure and function integrated printing strategy, three and four branched photodetectors extend the angle detection to omnidirectional ranges, which will be significant for the development of 3D angle-sensing devices.

Detection of Homologue and Isomer Vapors through Dynamic Reflection Spectra of Hollow Mesoporous Silica Sphere Photonic Crystals

Vapors of homologues and isomers with very similar refractive indices can be easily distinguished by using dynamic reflection spectra (DRS) of hollow mesoporous silica sphere (HMSS) photonic crystals (PCs). Different diffusion behaviors render the HMSS PCs with a distinct response to different chemicals vapors, leading to diversity in the evolution of the reflection spectra and their DRS patterns. Therefore, by studying the geometric characteristics and color changes of color-filled contour maps, as well as the reflection peak shift speeds at different stages, even isomers such as n-butanol and iso-butanol, with a refractive index difference of only 0.001, can be recognized. The reflection peak shift speed depends on both the refractive index and the diffusion speed of chemicals. The proposed strategy provides a convenient, accurate, and low-cost method to detect vapors of homologues and isomers.

Patterned Colloidal Photonic Crystals

Colloidal photonic crystals (PCs) have been well developed because they are easy to prepare, cost-effective, and versatile with regards to modification and functionalization. Patterned colloidal PCs contribute a novel approach to constructing high-performance PC devices with unique structures and specific functions. In this review, an overview of the strategies for fabricating patterned colloidal PCs, including patterned substrate-induced assembly, inkjet printing, and selective immobilization and modification, is presented. The advantages of patterned PC devices are also discussed in detail, for example, improved detection sensitivity and response speed of the sensors, control over the flow direction and wicking rate of microfluidic channels, recognition of cross-reactive molecules through an array-patterned microchip, fabrication of display devices with tunable patterns, well-arranged RGB units, and wide viewing-angles, and the ability to construct anti-counterfeiting devices with different security strategies. Finally, the perspective of future developments and challenges is presented.

Short-range ordered photonic structures of lamellae-forming diblock copolymers for excitation-regulated fluorescence enhancement

Photonic crystals can be represented by periodic nanostructures with alternating refractive indices, which create artificial stop bands with the appearance of colors. In this regard, nanodomains of block copolymers and the corresponding structural colors have been intensively studied in the past. However, the practical application of photonic crystals of block copolymers has been limited to a large degree because of the presence of large defects and grain boundaries in the nanodomains of block copolymers. The present study focuses on the alternative opportunity of short-range ordered nanodomains of block copolymers for fluorescence enhancement, which also has a direct relevance to the development of fluorescence sensors or detectors. The enhancement mechanism was found to be interconnected with the excitation process rather than the alternation of the decay kinetics. In particular, we demonstrate that randomly oriented, but regular grains of lamellae of polystyrene-block-polyisoprene, PS-b-PI, diblock copolymers and their blend with PS homopolymers can behave as Bragg mirrors to induce multiple reflections of the excitation source inside the photonic structures. This process in turn significantly increases the effective absorption of the given fluorophores inside the polymeric photonic structures to amplify the fluorescence signal.

Nanoparticle Based Curve Arrays for Multirecognition Flexible Electronics

Assembly of nanoparticles into controllable micro or nanocurve circuits by a feasible strategy is demonstrated. The curves, with various tortuosity morphologies, have tunable resistive strain sensitivity, which can be integrated into a multi-analysis flexible sensor. The curve-based sensor can run complicated facial expression recognition, and may contribute practical applications on auxiliary apparatus for skin micromotion manipulation for paraplegics.

Three-dimensional multi-recognition flexible wearable sensor via graphene aerogel printing

Multi-response, multi-function and high integration are the critical pursuits of advanced electronic wearable sensors.

A photochromic sensor microchip for high-performance multiplex metal ions detection

Current multi-analytes chips are limited with requiring numbers of sensors, complex synthesis and compounds screen. It is expected to develop new principles and techniques to achieve high-performance multi-analytes testing with facile sensors. Here, we investigated the correlative multi-states properties of a photochromic sensor (spirooxazine), which is capable of a selective and cross-reactive sensor array for discriminated multi-analytes (11 metal ions) detection by just one sensing compound. The multi-testing sensor array performed in dark, ultraviolet or visual stimulation, corresponding to different molecular states of spirooxazine metal ions coordination. The facile photochromic microchip contributes a multi-states array sensing method, and will open new opportunities for the development of advanced discriminant analysis for complex analytes.

Bio-inspired vapor-responsive colloidal photonic crystal patterns by inkjet printing

Facile, fast, and cost-effective technology for patterning of responsive colloidal photonic crystals (CPCs) is of great importance for their practical applications. In this report, we develop a kind of responsive CPC patterns with multicolor shifting properties by inkjet printing mesoporous colloidal nanoparticle ink on both rigid and soft substrates. By adjusting the size and mesopores' proportion of nanoparticles, we can precisely control the original color and vapor-responsive color shift extent of mesoporous CPC. As a consequence, multicolor mesoporous CPCs patterns with complex vapor responsive color shifts or vapor-revealed implicit images are subsequently achieved. The complicated and reversible multicolor shifts of mesoporous CPC patterns are favorable for immediate recognition by naked eyes but hard to copy. This approach is favorable for integration of responsive CPCs with controllable responsive optical properties. Therefore, it is of great promise for developing advanced responsive CPC devices such as anticounterfeiting devices, multifunctional microchips, sensor arrays, or dynamic displays.

Bioinspired materials: from low to high dimensional structure

The surprising properties of biomaterials are the results of billions of years of evolution. Generally, biomaterials are assembled under mild conditions with very limited supply of constituents available for living organism, and their amazing properties largely result from the sophisticated hierarchical structures. Following the biomimetic principles to prepare manmade materials has drawn great research interests in materials science and engineering. In this review, we summarize the recent progress in fabricating bioinspired materials with the emphasis on mimicking the structure from one to three dimensions. Selected examples are described with a focus on the relationship between the structural characters and the corresponding functions. For one-dimensional materials, spider fibers, polar bear hair, multichannel plant roots and so on have been involved. Natural structure color and color shifting surfaces, and the antifouling, antireflective coatings of biomaterials are chosen as the typical examples of the two-dimensional biomimicking. The outstanding protection performance, and the stimuli responsive and self-healing functions of biomaterials based on the sophisticated hierarchical bulk structures are the emphases of the three-dimensional mimicking. Finally, a summary and outlook are given.