Jiecheng Cui

Metal–Organic Frameworks with a Three-Dimensional Ordered Macroporous Structure: Dynamic Photonic Materials†

Tuning MOFs: When a metal-organic framework (MOF) with an ordered three-dimensional macroporous structure is integrated into a film, the resulting materials have an additional optical element, which can be used as a general and effective signal transducer. This, in combination with the hierarchical pore structure, makes these films interesting dynamic photonic materials with potential applications in sensors.

Inverse Opal Spheres Based on Polyionic Liquids as Functional Microspheres with Tunable Optical Properties and Molecular Recognition Capabilities

Based on the combination of the unique features of both polyionic liquids and spherical colloidal crystals, a new class of inverse opaline spheres with a series of distinct properties was fabricated. It was found that such photonic spheres could not only be used as stimuli-responsive photonic microgels, but also serve as multifunctional microspheres that mimic the main characteristics of conventional molecules, including intrinsic optical properties, specific molecular recognition, reactivity and derivatization, and anisotropy.

Polydopamine-coated nanofibrous mats as a versatile platform for producing porous functional membranes

In this work, polydopamine-coated electrospun polystyrene (PS) nanofibrous mats were successfully prepared by simply immersing the PS mats into dopamine alkaline Tris buffer solution for 24 h. The successful growth of polydopamine (Pdop) was confirmed with X-ray photoelectron spectroscopy (XPS). The thickness of the Pdop layer was about 20 nm observed by transmission electron microscope (TEM). The wetting behavior was changed tremendously into superhydrophilicity. Combining the unique characteristics of Pdop as active secondary reaction sites and electrospun mat as a flexible porous support, this hierarchically structured nanofibrous mat can serve as a useful platform for developing porous functional membranes. As demonstrated, oil/water separation and molecule gating membranes were fabricated by using the Michael reaction of Pdop coating with undecanethiol (UT) or 11-mercaptoundecanoic acid (MUA), respectively. As an oil/water separation membrane, the long alkyl chains of UT anchored on the membrane surface increased the contact angle (CA) of water distinctly, and water was blockaded completely while oil smoothly passed through the membrane. Similarly, a molecule gating membrane was constructed based on the pH-induced deprotonation of the carboxyl group of MUA, and its permeation selectivity was confirmed by cyclic voltammetry (CV) with an electrochemical probe. Moreover, the reductive property of the Pdop coating was also utilized to facilely introduce various metal nanoparticles into membrane systems for potential applications, for example, a silver nanoparticle-decorated membrane can be used as an effective antibacterial film as confirmed by the modified Kirby-Bauer method. All performed experiments demonstrate that polydopamine-coated nanofibrous mats can serve as a versatile platform for producing porous functional membranes.

Reactive photonic film for label-free and selective sensing of cyanide.

Three-dimensional ordered inverse-opal films bearing a reactive trifluoroacetyl group are successfully constructed. Through the specific reaction between cyanide and trifluoroacetyl, the photonic films can selectively detect sub-micromolar levels of cyanide by distinct structural color change. Labeled molecules are not necessary for the sensing mechanism.

Highly Sensitive Assay for Acetylcholinesterase Activity and Inhibition Based on a Specifically Reactive Photonic Nanostructure

Assays for acetylcholinesterase (AChE) with high sensitivity and high selectivity as well as facile manipulation have been urgently required in various fields. In this work, a reaction-based photonic strategy was developed for the efficient assay of AChE activity and inhibition based on the synergetic combination of the specific thiol-maleimide addition reaction with photonic porous structure. It was found that various applications including detection of AChE activity, measurement of the related enzymatic kinetics, and screening of inhibitors could be efficiently implemented using such strategy. Remarkably, the unique photonic nanostructure endows the constructed sensing platform with high sensitivity with a limit of detection (LOD) of 5 mU/mL for AChE activity, high selectivity, and self-reporting signaling. Moreover, the label-free solid film-based sensing approach described here has advantages of facile manipulation and bare-eye readout, compared with conventional liquid-phase methods, exhibiting promising potential in practical application for the AChE assay.

CB[8]-based rotaxane as a useful platform for sensitive detection and discrimination of explosives

Based on a naphthalene-threaded cucurbit[8]uril (CB[8]) rotaxane structure on a solid substrate, a new strategy for rapid, fully reversible, and highly sensitive detection of a broad class of explosives was developed by using one receptor. Due to the unique confinement effect and size exclusion of the CB[8] cavity, it is found that the intercalation of an explosive compound in the constructed rotaxane can significantly influence the photophysical property of the naphthalene core in the confined nanocavity of CB[8]. Dependent on the electronic structures and the sizes of explosive compounds, the fluorescence of the naphthalene core would be quenched or enhanced to different extents, leading to the direct detection and discrimination of distinctively different groups of trace explosives in the vapor phase, especially including the challenging aliphatic nitro-organics (RDX, HMX and PETN). Control experiments were performed to show the different sensing behaviors between the common organic vapors and nitrate-based explosives, which made it easy to realize the discrimination between target analytes and interferents. Due to the surface-attached sensing elements, a rapid response was also achieved in this system. Moreover, the non-covalent nature of the resulting heteroternary complex indicates that the trapped target molecules in the rotaxane structure are facilely removable by simply washing, demonstrating an excellent regeneration of the constructed explosive sensors for real-world application. The performed experiments suggested that the rotaxane structure-based sensing protocol opened a new way to develop a new kind of explosive sensors enabling a richer identification of threats.

Molecularly Imprinted Photonic Polymers as Sensing Elements for the Creation of Cross‐Reactive Sensor Arrays

By combining molecular imprinting and colloidal crystal templating, molecularly imprinted inverse-opal photonic polymers (MIPPs) acting as sensing elements have been exploited to create sensor arrays for the first time. With this new strategy, abundant sensing elements with differential sensing abilities were easily accessible. Because of the unique hierarchical porous structure integrated in each sensing element, high sensitivity and selectivity, fast response and self-reporting (label-free) detection could be simultaneously achieved. All these fascinating features indicate that MIPPs are ideal sensing elements for creating sensor arrays. By integrating the individual sensing elements on a substrate, the formed array chip delivers better portability and high-throughput capability. As a demonstration, six kinds of contaminants were selected as analytes. The detection and discrimination of these analytes and even their mixtures in a wide range of concentrations, particularly trace amounts of analyte against a high background of other components, could be achieved, indicating the powerful capability of MIPPs-based sensor array for sensing. These results suggest that the described strategy opens a new route for sensor array creation and should find important applications in a wide range of areas.

Polydopamine-based photonic crystal structures

Active photonic crystals (PC) or photonic crystal heterostructures have many applications such as chemical and biological sensors, active colour displays, structural colour printing and fluorescence enhancement. However, photonic crystal structures with the different functions mentioned above require different preparation methods, and some of them require sophisticated instruments for specific production processes. Thus, development of a simple way or a useful platform for conveniently fabricating specific photonic crystal structures with different functions is highly desirable and significant. Herein, by exploiting the self-polymerization of dopamine, we successfully introduced polydopamine (PDA) into silica opaline templates and produced PDA photonic crystal structures. Based on the utilization of the unique properties of PDA such as reactivity, reductive ability, powerful adhesive capability as well as carbonizable feature, PDA-based photonic crystal structures provide a very useful platform for further convenient fabrication of multifunctional photonic crystal structures with a variety of potential applications. Due to the virtually unlimited variety provided by the active secondary reactions of PDA, the post-modification of PDA-based photonic crystals can readily afford photonic crystal based chemical or biological sensors. The reductive as well as adhesive ability of PDA provides another tremendous opportunity to produce photonic crystal heterostructures with various metals, metal oxides, polymer or semiconductor nanoparticles. As a demonstration, PDA/Ag/PDA and PDA/Pt/PDA opaline structures were prepared by PDA-assisted metallization or adsorption, respectively, which could find promising application in fluorescence enhancement of organic dyes or chemical solvent sensors. More importantly, the carbonizable feature of PDA allows for efficiently producing carbon inverse opaline films as well as metal particle doped carbon inverse opaline films by carbonizing the corresponding PDA, PDA/Ag/PDA or PDA/Pt/PDA photonic structures, which may show various potential applications in catalysis and energy conversion.

Poly(ionic liquid)-based monodisperse microgels as a unique platform for producing functional materials

In this work, we report the microfluidic preparation of monodisperse imidazolium-based poly(ionic liquid) (PIL) microgels with a controlled size and morphology, and show that the imidazolium units in the microgel network can be exploited as reactive sites to efficiently access desired functional materials by a simple counteranion-exchange or conversion reaction. Moreover, based on the counteranion-exchange reaction, spatio-temporal engineering of the surface of the PIL microgels could also be realized, and a new and simple strategy for the fabrication of diverse anisotropic microgels (patchy particles) with great flexibility was developed. In addition, by exploiting the convenient generation of carbene units from the imidazolium moieties, as well as the carbonizable feature of PIL, the prepared PIL microgels could be further converted into stable carbene spheres and monodisperse carbon particles. All the results show that these monodisperse PIL-based microgels can serve as a very useful platform for facilely accessing various functional materials.

Metal-free click approach for facile production of main chain poly(bile acid)s

In this work, a metal-free click polymerization approach was developed to facilely produce versatile main chain poly(bile acid)s with high efficiency. No metal catalysts and organic solvents are required for the polymerization process, which exhibits multiple advantages, including less toxicity, being environmentally friendly and economically sound. Remarkably, the polymerization can finish within several minutes when the reactive monomers are in a crystalline state. Although the monomers are amorphous, no more than one hour is needed for completing the polymerization. The conversion efficiency can reach up to nearly 100% with the polymer molecular weight up to 93 500 Da, which still shows good solubility in most common solvents. The described approach is applicable for various bile acid monomers with different linkages, including long flexible alkyl chains, amide groups, phenyl groups and sterically hindered structures. Probably due to the strengthened hydrogen bonding interactions, π–π stacking and the hindrance effect introduced by the linkage used, the molecular weight and properties of the resulting polymers are strongly dependent on the monomer structures. Notably, by introducing a steric effect on azide groups (4e and 4f), the regioselectivity of the 1,4-triazole linkers is significantly improved from 60% to 85%. All the obtained polymers are thermally stable and display high resistance to thermal degradation.