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There is a demand for simple, selective, and efficient assays for the determination of clinically important metabolites such as creatinine for healthcare. Creatinine is the by-product of muscle energy metabolism and is excreted by the kidneys. To measure creatinine in the human serum, a creatinine imprinted photonic crystal hydrogel (CIPC hydrogel) for naked-eye detection is developed. CIPC hydrogel utilizes polystyrene-based two-dimensional (2D) photonic crystal colloidal arrays (PCs-array) embedded in the polyacrylamide hydrogel containing methacrylic acid which imprinted the creatinine template. The nanocavities in the hydrogel produced after the removal of the template bind to and recognize creatinine in the serum samples. The binding is selective and specific for creatinine. The binding is observed as shrinkage of the hydrogel volume and a decrease in the particle spacing which is monitored through changes in the Debye diffraction ring diameter and a visible blue-green to blue color shift. The binding event and the mechanism are investigated by molecular dockings. The CIPC sensor demonstrates a limit of detection (LOD) of 2.45 ± 1.6 µM, a linear detection range (25–500 µM), and recovery from 85.6 % to 99.9 % in the serum samples. CIPC hydrogel is available for the rapid and quantitative onsite detection of creatinine in the human serum sample. [ABSTRACT FROM AUTHOR]

Mono-dispersed molecularly imprinted hollow spheres (MIHSs) for hemoglobin (Hb) were prepared by employing silica nanospheres as the sacrificial templates. The obtained hollow spheres with uniform particle size of 360 nm in diameter were characterized by transmission electron microscopy. The outstanding affinities of these MIHSs to the target protein were confirmed by adsorption experiment in aqueous solution. Adsorption equilibrium was achieved within 10 min while the binding capacity ( Qmax) of Hb was 8.84 µmol g-1 at pH7.0. Furthermore, the MIHSs were successfully assembled into a closely-packed 3D colloidal array. The molecularly imprinted hollow sphere array (MIHSA) can selectively recognize Hb. As the concentration of Hb increased, the structure color of the MIHSA changed from blue to green, and turn to white finally with maximum red shift for 43 nm. The MIHSA showed promising potential for the naked-eye detection of target Hb. [ABSTRACT FROM AUTHOR]

A cross-responsive molecularly imprinted photonic crystal (MIPC) sensor array was established for the detection of RDX, HMX, CL-20 and TNT. The MIPC sensor red shifted and the structural color changed with the increasing concentration of the analytes. Using Pattern Recognition (PR) and principal component analysis (PCA), the sensor array could discriminate four different explosives. • Nitramine explosives were visually detected by molecularly imprinted photonic crystal (MIPC) sensors. • Nitramine explosives could be discriminated by pattern recognition. • Alkaline solution softened MIPC, and improved the mass transfer and the sensitivity. Colorimetric, selective and sensitive screening of explosives is important not only to military action but also to public security. Normal explosives detection is mainly targeted for nitroaromatic compounds, however, ntiramine explosive is used more widely due to its outstanding performance. Herein, molecularly imprinted photonic crystal (MIPC) sensors were made to detect typical nitramine explosives: 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), cyclotetramethylenete-tranitramine (HMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20). And 2,4,6-trinitrotoluene (TNT) templated MIPC was also made to discriminate not only nitramines but also nitrobenzene explosives. With explosives concentration increase, the diffraction peak and structure color of MIPC sensors both red shifted within 5 min. By adding alkaline solution, the MIPC sensors were softened, and the mass transfer and the sensitivity were improved. The MIPC sensors could respond to lower than 0.05 mM explosives with the limit of detection of 0.01 mM. A MIPC sensor array with the above MIPCs was constructed to achieve a semi-quantitative detection, and Pattern Recognition with a 48 × 4 multivariate data matrix was using to discriminate different explosive molecules. According to principal component analysis, the response of RDX, HMX, CL-20 and TNT scattered in separate areas, and the sensor array could discriminate with a LOD of 1 mM. [ABSTRACT FROM AUTHOR]

Abstract With the development of infrared detection technology, the threat of infrared detection technology to military targets in the battlefield is becoming more and more serious. Novel infrared stealth materials are in urgent demand. Photonic crystals are promising infrared stealth materials because they can prohibit the propagation of electromagnetic waves in a certain frequency range. This paper outlines a simple and fast method to fabricate three-dimensional photonic crystals for stealth material. Monodisperse polystyrene colloid microspheres with a particle size of 2 μm were prepared and used in a gas–liquid interface self-assembly to form a three-dimensional photonic crystal infrared stealth material. The infrared absorption peak wavelengths of the material were 3.30 μm and 3.42 μm. The band gap is in good agreement with the photon forbidden band (3.24–3.44 μm) obtained from simulation and calculation using Rsoft software. The material meets the requirements of an infrared stealth material and realizes the modulation of the infrared radiation characteristics of the detectable band of 3–5 μm. The process provides a simple, economical, fast, and efficient new method for the preparation of large diameter, three-dimensional photonic crystal infrared stealth materials. [ABSTRACT FROM AUTHOR]

We developed a photonic crystal (PhC) sensor for the quantification of 2,4,6-trinitrotoluene (TNT) in solution. Monodisperse (210 nm in diameter) molecularly imprinted colloidal particles (MICs) for TNT were prepared by the emulsion polymerization of methyl methacrylate and acrylamide in the presence of TNT as a template. The MICs were then self-assembled into close-packed opal PhC films. The adsorption capacity of the MICs for TNT was 64 mg TNT/g. The diffraction from the PhC depended on the TNT concentration in a methanol/water (3/2, v/v) potassium dihydrogen phosphate buffer solution (pH = 7.0, 30 mM). The limit of detection (LOD) of the sensor was 1.03 μg. The color of the molecularly imprinted colloidal array (MICA) changed from green to red with an 84 nm diffraction red shift when the TNT concentration increased to 20 mM. The sensor response time was 3 min. The PhC sensor was selective for TNT compared to similar compounds such as 2,4,6-trinitrophenol, 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2-nitromesitylene, 4-nitrotoluene, 2-nitrotoluene, 1,3-dinitrobenzene, methylbenzene, 4-nitrophenol, 2-nitroaniline, 3-aminophenol and 3-nitroaniline. The sensor showed high stability with little response change after three years storage. This sensor technology might be useful for the visual determination of TNT. [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 label free and easy-to-prepare optical sensor with high mechanical strength for the fast and visible response to tension and pH variables was reported. An elastic nanocomposite hydrogel was successfully fabricated by in situ free-radical co-polymerization of N , N -dimethylacrylamide (DMAA), acrylic acid (AA) and aluminum oxide nanoparticles (Al 2 O 3 NPs). DMAA and AA could form effective cross-linkage with Al 2 O 3 NPs via hydrogen binding, electrostatic interaction and bidentate bridging. By encapsulating polymethyl methacrylate (PMMA) colloidal arrays into the hydrogels, the optical nanocomposite hydrogels (ONHs) can be easily obtained. This three-dimensionally ordered array exhibits a stop band, and the optical hydrogels can tune the bright color from blue to cyan, green, yellow green, yellow, orange and then finally red by mechanical stimulation of uniaxial tension within 50% strain following Bragg’s law. The mechanical and optical properties can be adjusted via changing the fraction of AA and polymerization time. Meanwhile, the mechanical and optical responses were reversible for more than 10 times without deterioration. Besides, this material has rapid response to the changing of pH and the full-color change was observed. Owing to the high biocompatibility of nanocomposite hydrogel (NC gel) system and the excellent mechanical strength and water-stability of these ONHs, this optical sensor has high potential to be applied in biomedical field as tension or pH sensor for the intraocular pressure measurement and tonometry and blood gas analysis. [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]

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]

Abstract: A label free molecularly imprinted photonic crystal (MIPC) was developed to detect the degradation product of nerve agents. Mono-dispersed poly-methyl methacrylate colloidal particles with the diameter of 280nm were used to fabricate a closely packed colloidal crystal array (CCA), and a methyl phosphonic acid (MPA) imprinted hydrogel was prepared within the CCA using 2-hydroxyethyl-methacrylate and N-isopropylacrylamide as monomers, ethyleneglycol dimethacrylate and N, N′-methylenebisacrylamide as cross-linkers, a mixture of n-octanol and acetonitrile as porogen. The diffraction intensity of the MIPC decreased significantly upon the MPA adsorption with a limit of detection (LOD) of 10−6 molL−1. Furthermore, the diffraction intensity decreased and blue shifted with the increase of temperature, decreased and red shifted with the increase of ionic strength. At higher pH, the diffraction intensity increased without obvious diffraction shift. The MIPC provides an indirect path to detect nerve agents (Sarin, Soman, VX and R-VX) by monitoring the MPA released from the hydrolysis of nerve agents, with LODs of 3.5×10−6 molL−1, 2.5×10−5 molL−1, 7.5×10−5 molL−1 and 7.5×10−5 molL−1 for Sarin, Soman, VX and R-VX, respectively. [Copyright &y& Elsevier]

• The sensitivity of the IOPC increases due to the inverse opal structure and the infiltration of dimethyl sulfoxide. • The sensing mechanism of the IOPC is simulated by RSoft, and the experimental results are highly consistent with the simulated experimental results. • The reflection wavelength redshift of the IOPC increases with the concentration of alcohol vapors. • The reflection-peak of IOPC shifted when exposed to acetone and hydrogen peroxide, which provide a potential method for the detection of peroxide explosives. Colorimetric sensors were fabricated by embedding three dimensional (3D) inverse opal photonic crystal (IOPC) structure inside a dimethyl sulfoxide (DMSO) infiltrated carboxymethyl cellulose membrane for gas sensing. The DMSO infiltrated IOPC (DMSO-IOPC) carboxymethyl cellulose sensors can perform visual, on-site monitoring for analytes including alcohols, acetone and hydrogen peroxide (H 2 O 2). After exposed to alcohols and acetone, the mean effective refractive index (RI) and lattice constant of DMSO-IOPCs were changed, which led to a redshift of diffraction peak of the incident light. Sequentially their structural color changed remarkably. The limit of detection (LOD) for methanol and ethanol vapors are 110 ppm and 102 ppm, respectively. The H 2 O 2 sensor is also achieved by using DMSO-IOPCs, and the diffraction blue-shifted when they were exposed to H 2 O 2 vapor. In addition, this DMSO-IOPC sensor shows excellent selectivity and reversibility. The sensing mechanism of the DMSO-IOPC membranes was explained and simulated using finite-different time-domain (FDTD) method, and the experimental results were consistent with the simulated results. The DMSO-IOPCs demonstrate promising potential for in-situ monitoring of alcohol vapors, and could be used for peroxides detection and as a cheap and minimally invasive breathalyzer. [ABSTRACT FROM AUTHOR]

Abstract For surface-enhanced Raman scattering (SERS) sensing technology, it is required that the SERS substrates should obtain not only high sensitivity but also outstanding signal stability and good affinity for the target analytes. In this work we designed a cellulose photonic crystal (PhC) modified with Ag-nanoparticles, which can enhance the Raman signal through the combination of the affinity of cellulose to target analyte in organic solvents, the plasmonic responses of Ag-nanoparticles and the trapping effect of PhC on light. As a result, the concentration of p -methylthiopheno down to 10−6 M can be detected quantitatively. The cellulose PhC SERS substrate has the good affinity for organic solvents, which is easy to prepare and preserve, and shows promising prospect in sensor techniques. Graphical abstract Unlabelled Image Highlights • A flexible cellulose photonic crystal film modified by Ag-nanoparticles can be used as a surface-enhanced Raman scattering substrate to enhance Raman scattering. • Two-dimensional photonic crystal methylcellulose film modified by Ag-nanoparticles has the best enhancement. • It can be used to detect the different analytes of concentrations down to 10−6 M in organic solvents. • There exists a linear relation between the concentration and signal intensity. [ABSTRACT FROM AUTHOR]