Molecularly imprinted polymer hollow spheres (MIHSs) were produced by using hexanitrohexaazaisowurtzitane (HNIW or CL-20) as a template, silica nanospheres as a sacrificial matrix, acrylamide as a functional monomer, ethylene glycol dimethacrylate as a cross-linker and acetonitrile as a porogen at 4 °C under UV irradiation. This sorbent was applied to the selective solid-phase extraction (SPE) of several explosives simultaneously by using a newly-developed SPE procedure. For the first time, 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) and CL-20 were selectively extracted and determined simultaneously from simulated post-blast samples prepared from motor oil and vacuum pump oil. The matrix effects were successfully eliminated and accurate quantization was achieved. When the loading amounts of HMX, RDX, TNT and CL-20 were, respectively, below 10, 2, 5 and 20 nmol for 100 mg of MIHS, these explosives were almost retrieved completely (above 98%). For the MIHSs and non-imprinted polymer hollow spheres (NIHSs), in acetonitrile and methanol, the imprinting factors (IFs) of CL-20 and tetraacetyldibenzylhexaazaisowurtzitane (TADB, a structural analogue of CL-20) changed dramatically, from 7.75 to 1.57 and 0.88 to 2.39, respectively. It highlighted the significant effect of solvents on imprinted sites.

Three-dimensional photonic crystal sensors are attractive platforms for autonomous chemical sensing and colorimetric bioassays. At present, the photonic crystal sensors with inverse opal structure were extensively studied, which swells or shrinks in response to the analytes. However, the fabrication of inverse opal sensors still remains a major challenge. Herein, we propose a simple and versatile approach to fabricate 3D opal photonic sensors. This photonic crystal is fabricated via assembly of monodispersed silica particles grafted with linear polymeric ligands (SiO2@LPs). Acrylic acid (negatively charged monomer) and N-tert-butylacrylamide (hydrophobic monomer) were incorporated with N-isopropylacrylamide to achieve strong affinity between the designed polymer ligands and proteins. The proposed photonic crystal displays a maximum redshift of 23 nm in response to 2 mg/mL lysozyme, accompanied by the structure color change from blue to green. Compared to the cross-linked polymers, the linear polymer with flexible structure allows the colloidal array to recognize lysozyme with higher sensitivity (as low as 5 μg/mL) and broader linearity (from 5 to 2000 μg/mL in aqueous media). In the future, this photonic crystal sensor can be used as universal tools for the detection of a broad range of analytes.

Eight molecularly imprinted polymers (MIPs) for CL-20 were synthesized by precipitation polymerization in acetonitrile. The amounts and types of functional monomers and crosslinkers and the polymerization temperature were taken into account. The imprinting effect and selectivity of the MIPs were evaluated by static adsorption experiments. The results showed that the MIPs prepared at 4 °C had a better imprinting effect. MIP 4, which was prepared with acrylamide (AAm) as the functional monomer and ethyleneglycol dimethacrylate (EGDMA) as the crosslinker, was the optimal MIP. When the molar ratio of the template (CL-20), functional monomer and crosslinker was 1/6/24, the MIP possessed optimal absorbability and selectivity. Its specificity parameter (SP) to TADB, HMX and RDX was 15.27, 17.66 and 15.05, respectively. The binding capacity (Qmax) of MIP 4 for CL-20 was 115.7 μg g−1 and the adsorption reached equilibration within 10 min. MIP 4 as a selective sorbent was used to extract CL-20, using SPE from the mixed solution of its precursor compound, its analogues and soil samples. Acetonitrile was used as a sample solvent, and methanol was used as a washing solvent. Then CL-20 was successively eluted with acetonitrile and methanol/acetic acid (4/1, v/v), and the recovery of CL-20 was 95%. After 5 SPE cycles, the extraction ability of the cartridge for soil samples did not decrease obviously.

•A PhC sensor was firstly utilized to detect a real chemical warfare, Sarin agent, with high sensitivity.•BuChE, which is cheaper and has better immobilization ability compared with AChE, was immobilized onto PhC sensor.•DEPBT was used as a condensation agent for the condensation of BuChE with PhC hydrogel.•The technique developed in this research also represented a potential in the detection of other nerve agents.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.A photonic crystal (PhC) biosensor immobilized with butyrylcholinesterase (BuChE) was firstly developed for the detection of Sarin agent, and the relationship between the concentration of Sarin agent and diffraction peak was also calculated. The functionalized PhC realized a simple and cheap method for the detection of real nerve agent.

•Large spherical solanesol MIPs were firstly synthesized as chromatographic adsorbents in Flash chromatography.•MIPS-Flash chromatography conditions were optimized.•MIPS-Flash chromatography was successfully applied in extraction of purified solanesol from tobacco leaves.•The method established is feasible to large scale extraction of other active ingredients from natural products.A novel solanesol extraction method based on molecularly imprinted polymer (MIP) as the Flash chromatography stationary phase was established and evaluated. Spherical MIP particles in a size range of 250–350 μm (d (0.5) = 320 μm) for solanesol were synthesized by suspension polymerization, with imprinting factor of 3.9. The MIP particles (5.5 g) were packed in common Teflon column as the stationary phase while the sample solution and elution solvent were confirmed as methanol and methanol/acetic acid solution (80/20, v/v), loading at 4 ml/min and eluting 8 ml/min, respectively. Under the optimal chromatographic conditions, the adsorption capacity of the MIP-Flash column was determined as 107.3 μmol/g, and in each process, 370.8 mg purified solanesol (98.4%) could be obtained from the extract (20 mM, 40 ml) of tobacco leaves (14.7 g), and the yield of solanesol was 2.5% of the dry weight of tobacco leaves. The results reported here confirm the feasibility to extract highly purified active ingredients directly from natural products on a large scale by MIP-Flash chromatography.

We developed a simple method to fabricate colloidal crystal heterostructures (CCHs) with two or three stacked poly(methyl methacrylate) (PMMA) particle two-dimensional (2D) colloidal monolayer arrays of different particle spacings that independently diffract light. The 2D colloidal monolayer arrays of PMMA were prepared by using the air/water interface self-assembly method we recently developed. Two- and three-layer CCHs were fabricated by successive deposition of 2D PMMA colloidal monolayer arrays of different particle sizes. The structure and optical properties of 2D monolayer arrays and 2D CCHs were characterized with SEM, reflectance spectra, their Debye diffraction rings and their diffracted wavelengths. The layers maintain their spacing and ordering as they are transferred from the air/water interface onto the substrate. The 2D CCHs diffraction measurements suggest that the optical properties of the colloidal crystal heterostructures arise mainly from the independent diffraction of the individual 2D colloidal arrays. This enables selective combination of particular light wavelengths through diffraction of the 2D CCHs.

•Monodispersed molecularly imprinted hollow spheres (MIHSs) were synthesized.•Silica nanospheres (290 nm) was the sacrificial matrix for MIHSs.•MIHSs extraction of β-estradiol from aqueous solution was efficient and selective.•MIHSs can be reused for at least six repeated rounds.•MIHSs extraction recovering for β-estradiol from surface water was more than 90.42%.Solid phase extraction (SPE) is widely used in many different areas, such as environmental, biological, and food analysis, where cleaning and pre-concentration of samples are key steps in the analytical protocol. New materials have significant impact on the development of solid phase extraction. In this paper, mono-dispersed molecularly imprinted hollow spheres (MIHSs) of β-estradiol (E2) were synthesized using silica nanospheres particles as the sacrificial matrix. Compared to the corresponding non-imprinted hollow spheres (NIHSs), the MIHSs with uniform size of 290 nm have outstanding affinity in aqueous solution. Static saturation adsorption required only 15 min to achieve equilibrium, with a binding capacity (Qmax) of 44.5 μmol g−1. The extraction of E2, ethinyl estradiol (EE), diethylstilbestrol (DES), ethisterone (ES) and estrone (E1) from water samples by MIHSs was also investigated. In the spiked samples of tap water, Qinghe river water and Zhanjiang river water, more than 90.42% of E2, but less than 79% of EE, DES, ES and E1 were recovered. The limits of detection (LOD) ranged from 0.1 to 0.26 µmol L−1 after solid phase extraction by MIHSs and HPLC–UV analysis. The adsorption capacity of the MIHSs showed no significant deterioration after six rounds of regeneration.Monodispersed molecularly imprinted hollow spheres (MIHSs) with a diameter of 290 nm for β-estradiol (E2) were synthesized by using silica nanospheres as the sacrificial matrix. The MIHSs showed outstanding affinity, selectivity, good site accessibility and quick mass transfer toward β-estradiol in aqueous solution.

A label-free and easy-to-prepare biosensor for the fast and naked-eye detection of proteins was developed in this study. A closely packed crystalline array was self-assembled in ethanol–water (1:1, v/v) from the surface imprinted silica (SIS) colloid for hemoglobin bovine (Hb). The reflection of the molecular imprinted colloidal array (MICA) red shifted by 23 nm in response to 1.0 mg mL−1 of Hb at pH 7.0. Compared with the non-imprinted colloidal array (NICA), MICA has a higher selectivity towards the target protein, and can recognize the target protein via an “induced-fit” mechanism.

A novel 2-D photonic crystal (PC) sensing material for the visual detection of glucose with high selectivity at a physiological ionic strength (150 mM) is developed. A monolayer polystyrene crystalline colloidal array (CCA) is embedded in a phenylboronic acid (PBA) functionalized hydrogel film to diffract light to sensitively report on the hydrogel surface area. This 2-D PC sensor is superior to the previously reported 3-D PC sensors due to its fast preparation and simple detection. The binding of glucose would increase the cross-linking of the hydrogel that could shrink the hydrogel to increase the Debye diffraction ring diameter. At a physiological ionic strength of 150 mM, the 2-D PC sensor exhibits significant sensitivity for glucose across the entire human physiological glucose range. Additionally, the 2-D PC sensor shows high selectivity for glucose rather than other sugars (fructose and galactose). The diffraction color change of the 2-D PC sensor can be observed. For validation, the prepared 2-D PC hydrogel sensor is applied for the sensing of glucose in the artificial tear fluid.

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.

We report on the synthesis of a label-free p-nitrophenol (PNP) responsive crystalline colloidal array (CCA) based on the combination of a photonic crystal and the molecular imprinting technique. This novel sensing material was prepared by a self-assembly approach using PNP imprinted colloidal spheres and was characterized by a three-dimensional (3D) ordered opal structure in which numerous recognition sites were created during imprinting. The PNP recognition swelled the colloidal spheres, leading to a red shift of the diffraction wavelength of the CCA due to the lattice spacing change and the effective diffractive index change. The relationship between the diffraction wavelength of the CCA and the size of the colloidal spheres were studied and the size of the molecularly imprinted colloidal spheres was optimized to 200 (±5) nm by adjusting the recipe composition during the emulsifier-free emulsion polymerization. As a result, color change due to the diffraction light shift which is related to PNP concentrations can be observed. The results showed that the diffraction wavelength of the molecularly imprinted colloidal array (MICA) red-shifted more than 50 nm in response to 30 mM of PNP with a detection limit of 1 mM PNP. The color change of the MICA from green to red was observed. The imprinting efficiency of the molecular imprinting, the effect of buffer pH and the selectivity were also investigated. We achieved a facile colorimetric detection method for PNP without sample treatment.

This review covers the concepts of photonic crystal (PhC) and its usage for the sensing of environmental pollutants. PhCs are composed of periodic and ordered nanostructures which can manipulate the diffraction or reflection of light propagation through the structures. If the light spectra locate in the visible range, the color of materials can be observed by naked eye. The optical properties of PhCs are determined by the lattice constant of the crystal or by the refractive index contrast between the colloids and the surrounding medium. Based on these features, responsive PhCs can be designed to detect the environmental pollutants. In this review, we primarily described the photonic crystals for the sensing of volatile organic compounds (VOCs), organophosphates (OPs), heavy metal ions and endocrine disrupting chemicals (EDCs), and these sensors exhibited excellent sensitivity and are promising for the on-site monitoring of pollutants.

A label-free and easy-to-prepare biosensor for the fast and naked-eye detection of proteins was developed in this study. A closely packed crystalline array was self-assembled in ethanol–water (1:1, v/v) from the surface imprinted silica (SIS) colloid for hemoglobin bovine (Hb). The reflection of the molecular imprinted colloidal array (MICA) red shifted by 23 nm in response to 1.0 mg mL−1 of Hb at pH 7.0. Compared with the non-imprinted colloidal array (NICA), MICA has a higher selectivity towards the target protein, and can recognize the target protein via an “induced-fit” mechanism.

A novel 2-D photonic crystal (PC) sensing material for the visual detection of glucose with high selectivity at a physiological ionic strength (150 mM) is developed. A monolayer polystyrene crystalline colloidal array (CCA) is embedded in a phenylboronic acid (PBA) functionalized hydrogel film to diffract light to sensitively report on the hydrogel surface area. This 2-D PC sensor is superior to the previously reported 3-D PC sensors due to its fast preparation and simple detection. The binding of glucose would increase the cross-linking of the hydrogel that could shrink the hydrogel to increase the Debye diffraction ring diameter. At a physiological ionic strength of 150 mM, the 2-D PC sensor exhibits significant sensitivity for glucose across the entire human physiological glucose range. Additionally, the 2-D PC sensor shows high selectivity for glucose rather than other sugars (fructose and galactose). The diffraction color change of the 2-D PC sensor can be observed. For validation, the prepared 2-D PC hydrogel sensor is applied for the sensing of glucose in the artificial tear fluid.

We report on the synthesis of a label-free p-nitrophenol (PNP) responsive crystalline colloidal array (CCA) based on the combination of a photonic crystal and the molecular imprinting technique. This novel sensing material was prepared by a self-assembly approach using PNP imprinted colloidal spheres and was characterized by a three-dimensional (3D) ordered opal structure in which numerous recognition sites were created during imprinting. The PNP recognition swelled the colloidal spheres, leading to a red shift of the diffraction wavelength of the CCA due to the lattice spacing change and the effective diffractive index change. The relationship between the diffraction wavelength of the CCA and the size of the colloidal spheres were studied and the size of the molecularly imprinted colloidal spheres was optimized to 200 (±5) nm by adjusting the recipe composition during the emulsifier-free emulsion polymerization. As a result, color change due to the diffraction light shift which is related to PNP concentrations can be observed. The results showed that the diffraction wavelength of the molecularly imprinted colloidal array (MICA) red-shifted more than 50 nm in response to 30 mM of PNP with a detection limit of 1 mM PNP. The color change of the MICA from green to red was observed. The imprinting efficiency of the molecular imprinting, the effect of buffer pH and the selectivity were also investigated. We achieved a facile colorimetric detection method for PNP without sample treatment.