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Colloidal photonic crystals (PCs), consisting of highly ordered monodisperse nanoparticles, have been carried out a great deal of research in recent decades due to the attributes of readable signal, easy modification and low cost. With these unique features, colloidal PCs have also gradually become a focus of candidates applied in sensing fields. In this review, an overview of recent advances in colloidal PCs including self-assemblies and sensing applications is illustrated. With respect to the development in self-assemblies of colloidal PCs, the review concentrates on the summary of responsive mechanisms, detection methods, responsive materials, unit cells and fabrication methods. In terms of advances in sensing application of colloidal PCs, various types of sensors are summarized based on the kinds and applications of target analytes. Furthermore, the current limitations and potential future directions of colloidal PCs in self-assemblies and sensing areas are also discussed. Image 1 • Colloidal PCs have come to the fore due to the unique feature of structures. • Recent developments in self-assemblies of colloidal PCs are highlighted. • Recent advances in sensing applications of colloidal PCs are introduced. • The prospect and current limitation of colloidal PCs are summarized. [ABSTRACT FROM AUTHOR]

G-series nerve agents, such as sarin, tabun, and soman, would cause tremendous harm in military and terrorist attacks, so it is necessary to develop a simple method for the rapid and efficient detection of these hazardous substances. We have developed a tunable acetylcholinesterase (AChE)-functionalized two-dimensional photonic crystal (2D PhC) for the detection of a real nerve agent, sarin. In accordance with the 2D PhC previously prepared by our group, the AChE-functionalized 2D PhC was optimized by adjustment of the amount of monomer in the hydrogel, which not only increased the sensitivity of the 2D PhC, with the detection limit decreasing by two orders of magnitude, but also ensured the structural color spanned the whole visible region in the detection range. A linear relationship between the logarithm of the sarin concentration and the particle spacing of the AChE-functionalized 2D PhC was observed from 7.1 × 10-17 to 7.1 × 10-4 mol/L. The AChE-functionalized 2D PhC also responded to mimics of G-series nerve agents, including dimethyl methylphosphonate, diisopropyl methylphosphonate, and isodipropyl methylphosphonate, to various degrees. The proposed 2D-PhC hydrogel has potential for low-cost, trace-level, and on-site monitoring of other G-series nerve agents. Graphical abstract [ABSTRACT FROM AUTHOR]

The indiscriminate use of nerve agents by terrorist groups has attracted attention of the scientific communities toward the development of novel sensor technique for these deadly chemicals. A photonic crystal (PhC) hydrogel immobilized with butyrylcholinesterase (BuChE) was firstly prepared for the sensing of Sarin agents. Periodic polystyrene colloidal (240 nm) array was embedded inside an acrylamide hydrogel, and then BuChE was immobilized inside the hydrogel matrix via condensation with 3-(diethoxyphosphoryloxy)−1,2,3-benzotriazin-4(3 h)-one (DEPBT). It indicated that a total of 3.7 units of BuChE were immobilized onto the PhC hydrogel. The functionalized hydrogel recognized the Sarin agent and then shrunk, thus the diffraction of PhC hydrogel blue shifted significantly, and a limit of detection (LOD) of 10 −15 mol L −1 was achieved. [ABSTRACT FROM AUTHOR]

Chiral hybrid organic–inorganic metal halides have attracted wide attention owing to their superior chiroptoelectronic and chirospintronic properties. Here, a new class of chiral lead‐free metal halides, (R/S‐MBA)3Ru2Br9 (MBA = methylbenzylammonium), with unique magnetic properties is reported. (R/S‐MBA)3Ru2Br9 is composed of a surface‐shared octahedron dimer separated by chiral cations and crystallizes into the Sohncke space group of P212121. The crystal structures, chiroptical, magnetic properties, and magnetic circular dichroism of (R/S‐MBA)3Ru2Br9 are systematically investigated. Owing to the strong antiferromagnetic coupling between the Ru atom through bromine bridge in the [Ru2Br9]3− dimer and the weak ferromagnetic coupling between the neighboring [Ru2Br9]3− dimer, (R/S‐MBA)3Ru2Br9 exhibits antiferromagnetic property with Néel temperature at 7 K. Considering the unique magnetic property of ruthenium, together with the rapid progress of antiferromagnetic spintronics and optospintronics recently, this work provides a novel multifunctional lead‐free chiral magnetic candidate toward chiral optoelectronics and antiferromagnetic spintronics. [ABSTRACT FROM AUTHOR]

A simple method was developed to prepare ultra-thin, large-area, free-standing two-dimensional (2D) polymethylmethacrylate (PMMA) colloidal crystal array monolayers by assembling PMMA colloids suspended in toluene on water surface. Diffraction of the free-standing films could be adjusted through the particle size or operation time. [ABSTRACT FROM AUTHOR]

Chiral semiconductor nanostructures have received enormous attention due to their emerging circularly polarized luminescence (CPL) properties. However, compared with well‐studied photoluminescence (PL), the reported CPL is much weaker and more challenging to be modulated. Herein, we describe a new approach for acquiring the intense and tunable CPL from inorganic chiral photonic crystals (CPCs) doped with semiconductor quantum dots (QDs). Unprecedentedly, the sign, position and intensity of CPL peaks can be precisely controlled by manipulating either the photonic band gap of CPCs or luminescence wavelength of QDs and a giant absolute dissymmetry factor |glum| up to 0.25 is obtained. More importantly, the origin of the CPL modulation is clearly elucidated by both experiment and theory. This work lays the foundation for the construction of next‐generation high‐performance CPL‐based devices. [ABSTRACT FROM AUTHOR]

Chiral semiconductor nanostructures have received enormous attention due to their emerging circularly polarized luminescence (CPL) properties. However, compared with well‐studied photoluminescence (PL), the reported CPL is much weaker and more challenging to be modulated. Herein, we describe a new approach for acquiring the intense and tunable CPL from inorganic chiral photonic crystals (CPCs) doped with semiconductor quantum dots (QDs). Unprecedentedly, the sign, position and intensity of CPL peaks can be precisely controlled by manipulating either the photonic band gap of CPCs or luminescence wavelength of QDs and a giant absolute dissymmetry factor |glum| up to 0.25 is obtained. More importantly, the origin of the CPL modulation is clearly elucidated by both experiment and theory. This work lays the foundation for the construction of next‐generation high‐performance CPL‐based devices. [ABSTRACT FROM AUTHOR]

A novel hydrogel film with a highly ordered macropore monolayer on its surface was prepared by templated photo-polymerization of hydrogel monomers on a two-dimensional (2D) polystyrene colloidal array. The 2D inverse opal hydrogel has prominent advantages over traditional three-dimensional (3D) inverse opal hydrogels. First, the formation of the 2D array template through a self-assembly method is considerably faster and simpler. Second, the stable ordering structure of the 2D array template makes it easier to introduce the polymerization solution into the template. Third, a simple measurement, a Debye diffraction ring, is utilized to characterize the neighboring pore spacing of the 2D inverse opal hydrogel. Acrylic acid was copolymerized into the hydrogel; thus, the hydrogel responded to pH through volume change, which resulted from the formation of the Donnan potential. The 2D inverse opal hydrogel showed that the neighboring pore spacing increased by about 150 nm and diffracted color red-shifted from blue to red as the pH increased from pH 2 to 7. In addition, the pH response kinetics and ionic strength effect of this 2D mesoporous polymer film were also investigated. [ABSTRACT FROM AUTHOR]

It is always a hot research issue to get weak fault information from severely contaminated data before further analysis. Wavelet denoising methods have been widely applied by researchers in many different applications. This paper presents the application of the Bayesian wavelet packet method on mechanical equipment monitoring with an approach for selecting the wavelet decomposition levels based on the statistical autocorrelation function (ACF). Firstly, a reasonable decomposition level is selected; then, the degree of noise pollution of each wavelet coefficient can be got based on the Bayesian rule; finally, the estimated value of each wavelet coefficient can be obtained using the Bayesian hypothesis test. The denoising approach is compared with the conventional soft and hard threshold methods using signals simulated and obtained from track vibration test. The comparison result reveals the proposed method shows better denoising performance for weak information recognition. [ABSTRACT FROM AUTHOR]

As a typical antibiotic that is harmful to the health of human beings and widely used in animal husbandry, oxytetracycline (OTC) has a potential threat to the food safety. Therefore, the design of portable sensors for efficiently monitoring trace amounts of OTC in foods is vital to maintain safe food supply in our daily life. Herein, a two-dimensional (2D) molecularly imprinted photonic crystal hydrogel (MIPCH) sensor for the detection of OTC was fabricated by combining the photonic crystal (PC) method and molecular imprinting technique. In this regard, OTC was used as imprinted template to form the MIPCH sensor with specific binding sites during polymerization. After the removal of template, the obtained MIPCH possessed the specific nanocavities that were complementary to target compound, OTC. In addition, the response of the MIPCH to tetracyclines (TCs) in aqueous solution was monitored through a readable change of Debye diffraction ring, which is related to the particle spacing variation of MIPCH in response to the target molecules. As the concentration of OTC increased from 0 to 60 μM, the particle spacing of MIPCH sensor increased to about 94 nm and the structural color redshifted from blue to red. More importantly, the detection of OTC in milk sample by this portable, cost-effective MIPCH sensor has also been achieved at the same range of OTC. With the increasing concentration of OTC in milk sample, the particle spacing of MIPCH sensor increased about 92 nm and the structural color of MIPCH changed from blue through green to orange. Image 1 • A novel 2D molecularly imprinted PC was developed for the fast screening of trace level residues of OTC in milk. • The detection could be realized by naked eyes through observing the diffraction ring or structural color. • The sensor also showed advantages in easy preparation and specificity towards the targets. [ABSTRACT FROM AUTHOR]

A novel photonic crystal sensor, a cellulose film with a three dimensional (3D) colloidal array embedded inside, was fabricated by infiltrating the voids of a 3D poly methyl methacrylate (PMMA) colloidal array with methyl cellulose aqueous solution, followed by thermal curing. When the obtained cellulose photonic crystal film sensor (CPCFS) was immersed in alcohols, including ethanol, n-propanol, isopropanol and n-butanol, its lattice constant and mean effective refractive index increased, which led to the redshift of the reflection of incident light. The redshift of this sensor had linear response to the concentration of alcohol vapors, while its structural color changed from blue to green visually. This CPCFS demonstrates promising potential as an on-site monitoring sensor for alcohols and an inexpensive and minimally invasive breathalyzer in the future. [ABSTRACT FROM AUTHOR]

Chiral semiconductor nanostructures have received enormous attention due to their emerging circularly polarized luminescence (CPL) properties. However, compared with well‐studied photoluminescence (PL), the reported CPL is much weaker and more challenging to be modulated. Herein, we describe a new approach for acquiring the intense and tunable CPL from inorganic chiral photonic crystals (CPCs) doped with semiconductor quantum dots (QDs). Unprecedentedly, the sign, position and intensity of CPL peaks can be precisely controlled by manipulating either the photonic band gap of CPCs or luminescence wavelength of QDs and a giant absolute dissymmetry factor |glum| up to 0.25 is obtained. More importantly, the origin of the CPL modulation is clearly elucidated by both experiment and theory. This work lays the foundation for the construction of next‐generation high‐performance CPL‐based devices. [ABSTRACT FROM AUTHOR]