Yue Lan

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.

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.

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.

Maleimide-containing polymer inverse opals: a new kind of reactive photonic structure with significant extendibility

In this work, maleimide-containing polymer inverse opals have been successfully prepared by utilization of an acrylate monomer bearing a masked (protected) maleimide unit. As an ideal clickable functional group, maleimide can promote the Michael addition of thiol-containing molecules and the thermoreversible Diels–Alder reaction of furan derivatives, providing tremendous opportunities to produce various functional materials from one maleimide-containing polymer. As a demonstration, four chemical systems were facilely evolved from the prepared maleimide-containing inverse opal. By exploiting the nucleophilic thiol–ene reaction of maleimide, the zwitterionic pH-responsive inverse opal and electroactive inverse opal were first fabricated by reacting with cysteine and thiol-containing ferrocene derivatives, respectively. Based on the same reaction, it was also found that the maleimide-containing inverse opal could serve as a self-reporting sensing platform to sensitively detect the reduction of oxidized glutathione by specific enzymes. On the other hand, the thermoreversible nature of the Diels–Alder reaction of the maleimide groups made it possible to construct a dynamic molecule gating system by reacting with alkyl-chain-substituted furan derivatives from the prepared interconnected macroporous film. In fact, due to the unlimited variety provided by the two kinds of reactions mentioned above, the described photonic material exhibits a significant extendibility and could be easily post-modified for special purposes with maintenance of the opaline structure. Thus, this novel clickable maleimide-containing polymer inverse opal could serve as a reactive platform for producing a variety of functional photonic materials.

Ultrasensitive detection of aliphatic nitro-organics based on “turn-on” fluorescent sensor array

The broad class of explosives includes nitro aromatics as well as challenging aliphatic nitro-organics whose detection is important from counter-terrorism and national security perspectives. Here we report a turn-on fluorescent sensor array based on aggregation-induced emission (AIE) fluorophores as receptors. To achieve a good sensing system with fast response, good sensitivity and low detection limit, three receptors with abundant chemical diversities for target analytes were synthesized. The turn-on response of the individual receptor showed highly variable and cross-reactive analyte-dependent changes in fluorescence. The excellent ability to identify a variety of explosives, especially the challenging aliphatic nitro-organics (2,3-dimethyl-2,3-dinitrobutane (DMNB), 1,3,5-trinitro-1,3,5-triazinane (RDX), cyclotetramethylene tetranitramine (HMX) and entaerythritol tetranitrate (PETN)), was demonstrated in qualitative and quantitative analyses with 100% accuracy. The fluorescence signal amplification in the presence of explosives allows for application of these receptors in a sensor microarray suitable for high-throughput screening. These results suggested that the cross-reactive sensor array based on AIE fluorophores could find a wide range of applications for sensing various analytes or complex mixtures.

Self-assembled main-chain poly(bile acid) membranes that wrinkle

With prospects for application in much scientific research, wrinkle patterns have attracted much attention. Several delicate methods, including a pre-patterning process and a controlled stress release procedure, have been developed to fabricate well-controlled wrinkle patterns. In this work, we discovered accidentally that unsophisticated mechanical scratching can also lead to ordered wrinkle structures. Combining experiment results and theoretical models as well as the folding properties of bile acid derivatives, it is revealed that ordered spring-like structures and their organized aggregates (multi-lamellar membranes), which are all based on unique amphiphilicity and rigid steroid skeletons, play a crucial role in the formation of well-organized wrinkle patterns. As far as we know, this is the first attempt to explain polymer wrinkle phenomena on a molecular level. Furthermore, due to their excellent biocompatibility, these polymers may serve as new wrinkling materials and exhibit potential uses in the field of bioengineering.

Electrothermally Driven Fluorescence Switching by Liquid Crystal Elastomers Based On Dimensional Photonic Crystals

In this article, the fabrication of an active organic-inorganic one-dimensional photonic crystal structure to offer electrothermal fluorescence switching is described. The film is obtained by spin-coating of liquid crystal elastomers (LCEs) and TiO2 nanoparticles alternatively. By utilizing the property of LCEs that can change their size and shape reversibly under external thermal stimulations, the λmax of the photonic band gap of these films is tuned by voltage through electrothermal conversion. The shifted photonic band gap further changes the matching degree between the photonic band gap of the film and the emission spectrum of organic dye mounting on the film. With rhodamine B as an example, the enhancement factor of its fluorescence emission is controlled by varying the matching degree. Thus, the fluorescence intensity is actively switched by voltage applied on the system, in a fast, adjustable, and reversible manner. The control chain of using the electrothermal stimulus to adjust fluorescence intensity via controlling the photonic band gap is proved by a scanning electron microscope (SEM) and UV-vis reflectance. This mechanism also corresponded to the results from the finite-difference time-domain (FDTD) simulation. The comprehensive usage of photonic crystals and liquid crystal elastomers opened a new possibility for active optical devices.

Pyrrole-Terminated Ionic Liquid Surfactant: One Molecule with Multiple Functions for Controlled Synthesis of Diverse Multispecies Co-Doped Porous Hollow Carbon Spheres.

Rationally and efficiently controlling chemical composition, microstructure, and morphology of carbon nanomaterials plays a crucial role in significantly enhancing their functional properties and expending their applications. In this work, a novel strategy for simultaneously controlling these structural parameters was developed on the base of a multifunctional precursor approach, in which the precursor not only serves as carbon source and structure-directing agent, but also contains two heteroatom doping sites. As exemplified by using pyrrole-terminated ionic liquid surfactant as such precursor, in conjunction with sol-gel chemistry this strategy allows for efficiently producing well-defined hollow carbon spheres with controlled microstructure and chemical compositions. Remarkably, the dual-doping sites in confined silica channels provide an exciting opportunity and flexibility to access various doped carbons through simply anion exchange or altering the used oxidative polymerization agent, especially the multispecies codoped materials by combination of the two doping modes. All the results indicate that the described strategy may open up a new avenue for efficiently synthesizing functional carbon materials with highly controllable capability.

Chemically Patterned Inverse Opal Created by a Selective Photolysis Modification Process.

Anisotropic photonic crystal materials have long been pursued for their broad applications. A novel method for creating chemically patterned inverse opals is proposed here. The patterning technique is based on selective photolysis of a photolabile polymer together with postmodification on released amine groups. The patterning method allows regioselective modification within an inverse opal structure, taking advantage of selective chemical reaction. Moreover, combined with the unique signal self-reporting feature of the photonic crystal, the fabricated structure is capable of various applications, including gradient photonic bandgap and dynamic chemical patterns. The proposed method provides the ability to extend the structural and chemical complexity of the photonic crystal, as well as its potential applications.