Poly(ionic liquid)s as a distinct receptor material to create a highly-integrated sensing platform for efficiently identifying numerous saccharides.

Saccharides have strong hydrophilicities, and are complex molecular structures with subtle structure differences, and tremendous structural variations. The creation of one sensing platform capable of efficiently identifying such target systems presents a huge challenge. Using the integration of unique multiple noncovalent interactions simultaneously occurring in poly(ionic liquid)s (PILs) with multiple signaling channels, in this research an aggregation-induced emission (AIE)-doped photonic structured PIL sphere is constructed. It is found that such a sphere can serve as a highly integrated platform to provide abundant fingerprints for directly sensing numerous saccharides with an unprecedented efficiency. As a demonstration, 23 saccharides can be conveniently identified using only one sphere. More importantly, by using simple ion-exchanges of PIL receptors or/and increasing the AIE signaling channels, this platform is able to perform, on demand, different sensing tasks very efficiently. This is demonstrated by using it for the detection of difficult targets, such as greatly extended saccharides as well as mixed targets, in real-life examples on one or two spheres. The findings show that this new class of platform is very promising for addressing the challenges of identifying saccharides.

Direct Determination of Redox Statuses in Biological Thiols and Disulfides with Noncovalent Interactions of Poly(ionic liquid)s.

The three most important redox couples, including cysteine (Cys)/cystine (Cyss), homocysteine (Hcys)/homocystine (Hcyss), and reduced glutathione (GSH)/glutathione disulfide (GSSG), are closely associated with human aging and many diseases. Thus, it is highly important to determine their redox statuses at the following two levels: (i) the redox identity in different thiols/disulfides and (ii) the redox ratio in a mixture of a specific couple. Herein, by using one single AIE-doped (AIE, aggregation-induced emission) photonic-structured poly(ionic liquid) (PIL) sphere as a virtual sensor array, we realize a direct determination of the redox status without a reducing pretreatment of disulfides, which will greatly promote the development of high-throughput and simple procedures. The pattern-recognition method uses the multiple noncovalent interactions of imidazolium-based PILs with these redox species to produce differential responses in both the photonic crystal and fluorescence dual channels. On the one hand, a single sphere enables the direct and simultaneous discrimination of the redox identities of Cys, Cyss, Hcys, Hcyss, GSH, and GSSG under the interference of other five commonly occurring thiols. On the other hand, this sphere also allows for not only a direct quantification of the GSH/GSSG ratios without previously determining the individual concentrations of GSH and GSSG but also the accurate prediction of the ratios in unknown redox samples. To further demonstrate applications of this method, redox mixtures in a biological sample are differentiated. Additionally, quantum calculations further support our assignments for interactions between the imidazolium-based PILs and these redox species.

Microfluidic synthesis of uniform single-crystalline MOF microcubes with a hierarchical porous structure.

Creating hierarchical porosity in MOFs and controlling their size and morphology have emerged as efficient means for achieving significant improvement of MOF properties, and are crucial for facilitating the practical implementation of their various applications. Although important advances in this respect have been made, the realization of a hierarchical pore structure in a single crystalline MOF particle with controlled size and shape is still a challenge, and highly desirable. In this work, based on droplet-based microfluidics in conjunction with evaporative crystallization, an efficient approach to large-scale synthesis of uniform single-crystalline HKUST-1 particles with a hierarchical pore structure is presented. It is found that the MOF crystallization in confined droplets could generate not only monodisperse single-crystalline microcubes with an engraved rich porous texture including bimodal or trimodal pore structures, but also the size and porosity of the resulting cubes as well as the introduced meso- or macropore size could be widely tailored by varying the preparation conditions. Importantly, through the simple addition of an active species into the formed droplets, the functionalization of the resulting pore structured HKUST-1 cubes could be facilely realized, affording a series of high-performance functional nanomaterials.

Molecular cage-bridged plasmonic structures with well-defined nanogaps as well as the capability of reversible and selective guest trapping.

Creating well-defined plasmonic hotspots with enormous field enhancements as well as the capability of selectively trapping targeted molecules into hotspots is of critical importance and a prerequisite for numerous plasmon-assisted applications, but it represents a great challenge. In this work, a robust molecular cage decorated with thioether moieties at the periphery was designed and synthesized. By using the synthesized cage as a linker, a series of molecular cage-bridged plasmonic structures with well-defined nanogaps (hotspots) were fabricated in an efficient and controllable fashion. It was found both experimentally and theoretically that the nanogaps of about 1.2 nm created by the molecular cage in the resultant plasmonic structures led to a strong plasmon coupling, thus inducing great field enhancement inside the nanogaps. More importantly, the embedded molecular cages endowed the formed hotspots with the capability of selectively trapping targeted molecules, offering huge opportunities for many emergent applications. As a demonstration, the hotspots constructed were used as a unique nanoreactor, and under mild conditions two types of plasmon-driven chemical transformation were successfully performed. All the results clearly indicate that the integration of the host-guest chemistry of the molecular cage with the plasmon-coupling effect of metal particles afforded a new class of plasmonic structures, showing great potential for facilitating a broad variety of plasmon-based applications.

Block Copolymer-Templated Approach to Nanopatterned Metal-Organic Framework Films.

The fabrication of patterned metal-organic framework (MOF) films with precisely controlled nanoscale resolution has been a fundamental challenge in nanoscience and nanotechnology. In this study, nanopatterned MOF films were fabricated using a layer-by-layer (LBL) growth method on functional templates (such as a bicontinuous nanoporous membrane or a structure with highly long-range-ordered nanoscopic channels parallel to the underlying substrate) generated by the microphase separation of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymers. HKUST-1 can be directly deposited on the templates without any chemical modification because the pyridine groups in P2VP interact with metal ions via metal-BCP complexes. As a result, nanopatterned HKUST-1 films with feature sizes below 50 nm and controllable thicknesses can be fabricated by controlling the number of LBL growth cycles. The proposed fabrication method further extends the applications of MOFs in various fields.

Facile fabrication of highly controllable gating systems based on the combination of inverse opal structure and dynamic covalent chemistry.

A three-dimensional (3D) inverse opal with periodic and porous structures has shown great potential for applications not only in optics and optoelectronics, but also in functional membranes. In this work, the benzaldehyde group was initially introduced into a 3D nanoporous inverse opal, serving as a platform for fabricating functional membranes. By employing the dynamic covalent approach, a highly controllable gating system was facilely fabricated to achieve modulable and reversible transport features. It was found that the physical/chemical properties and pore size of the gating system could easily be regulated through post-modification with amines. As a demonstration, the gated nanopores were modified with three kinds of amines to control the wettability, surface charge and nanopore size which in turn was exploited to achieve selective mass transport, including hydrophobic molecules, cations and anions, and the transport with respect to the physical steric hindrance. In particular, the gating system showed extraordinary reversibility and could recover to its pristine state by simply changing pH values. Due to the unlimited variety provided by the Schiff base reaction, the inverse opal described here exhibits a significant extendibility and could be easily post-modified with stimuli-responsive molecules for special purposes. Furthermore, this work can be extended to employ other dynamic covalent routes, for example Diels-Alder, ester exchange and disulfide exchange-based routes.

Guanidinium-Based Polymerizable Surfactant as a Multifunctional Molecule for Controlled Synthesis of Nanostructured Materials with Tunable Morphologies.

Rationally and efficiently controlling the morphology of nanomaterials plays a crucial role in significantly enhancing their functional properties and expending their applications. In this work, a strategy for controlled synthesis of diverse nanostructured materials with tunable morphologies was developed using a guanidinium-based surfactant with a polymerizable pyrrole unit as a multifunctional molecule that can serve not only as a structure-directing agent for mesostucture formation but also as a monomer and carbon source. The unique self-assembly behavior of the guanidinium head group under different conditions allows the synthesized surfactants to form different aggregates and thus to produce silica nanomaterials with multiple morphologies (such as sphere, disk, fiber, and cocoon) in conjunction with sol-gel chemistry. Besides the mesostructured silicates, by further exploring the polymerization and carbonization features of pyrrole units that were densely packed in the formed silica nanochannels, diverse nanostructured materials such as mesostructured conducting polymers, carbon materials, and metal-nanoparticle (NP)-decorated forms could also be easily obtained in one-pot fashion for various applications, such as energy storage and catalysis. As a demonstration, carbon nanotubes and Pd-NP-doped hollow carbon spheres were fabricated, which exhibited good specific capacitance (101.7 F g-1) at the scan rates of 5 mV s-1 and excellent catalytic performance (100% conversion for three cycles) in the Suzuki C-C coupling reaction, respectively. All of the results indicate that our strategy may open a new avenue for efficiently accessing diverse nanostructured materials with tunable morphologies for wide applications.

Controlled Fabrication of Functional Capsules Based on the Synergistic Interaction between Polyphenols and MOFs under Weak Basic Condition.

Metal-organic coordination materials with controllable nanostructures are of widespread interest due to the coupled benefits of inorganic/organic building blocks and desired architectures. In this work, based on the finding of a synergistic interaction between metal-organic frameworks (MOFs) and natural polyphenols under weak basic condition, a facile strategy has been developed for directly fabricating diverse phenolic-inspired functional materials or metal-phenolic frameworks (MPFs) with controlled hollow nanostructures (polyhedral core-shell, rattle-like, hollow cage, etc.) and controllable size, morphology, and roughness, as well as composition. By further incorporating the diverse functionalities of polyphenols such as low toxicity and therapeutic properties, catalytic activity, and ability to serve as carbon precursors, into the novel assemblies, diverse artificially designed nanoarchitectures with target functionalities have been generated for an array of applications.

Efficient Construction of Well-Defined Multicompartment Porous Systems in a Modular and Chemically Orthogonal Fashion.

A microfluidic assembly approach was developed for efficiently producing hydrogel spheres with reactive multidomains that can be employed as an advantageous platform to create spherical porous networks in a facile manner with well-defined multicompartments and spatiotemporally controlled functions. This strategy allows for not only large scale fabrication of various robust hydrogel microspheres with controlled size and porosity, but also the domains embedded in hydrogel network could be introduced in a modular manner. Additionally, the number of different domains and their ratio could be widely variable on demand. More importantly, the reactive groups distributed in individual domains could be used as anchor sites to further incorporate functional units in an orthogonal fashion, leading to well-defined multicompartment systems. The strategy provides a new and efficient route to construct well-defined functional multicompartment systems with great flexibility and extendibility.

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.

2D-ordered dielectric sub-micron bowls on a metal surface: a useful hybrid plasmonic-photonic structure.

Recently, it has been demonstrated that the combination of periodic dielectric structures with metallic structures provides an efficient means to yield a synergetic optical response or functionality in the resultant hybrid plasmonic-photonic systems. In this work, a new hybrid plasmonic-photonic structure of 2D-ordered dielectric sub-micron bowls on a flat gold surface was proposed, prepared, and theoretically and experimentally characterized. This hybrid structure supports two types of modes: surface plasmon polaritons bound at the metallic surface and waveguided mode of light confined in the cavity of bowls. Optical responses of this hybrid structure as well as the spatial electric field distribution of each mode are found to be strongly dependent on the structural parameters of this system, and thus could be widely modified on demand. Importantly, compared to the widely studied hybrid systems, namely the flat metallic surface coated with a monolayer array of latex spheres, the waveguided mode with strong field enhancement appearing in the cavities of bowls is more facilely accessible and thus suitable for practical use. For demonstration, a 2D-ordered silica sub-micron bowl array deposited on a flat gold surface was fabricated and used as a regenerable platform for fluorescence enhancement by simply accommodating emitters in bowls. All the simulation and experiment results indicate that the 2D-ordered dielectric sub-micron bowls on a metal surface should be a useful hybrid plasmonic-photonic system with great potential for applications such as sensors or tunable emitting devices if appropriate periods and materials are employed.

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.

Emulsion droplets as a dynamic interface for the direct and large-scale synthesis of ultrathin free-standing mesoporous silica films as well as 2D polymeric and carbon nanomaterials.

The efficient synthesis of free-standing mesostructured two-dimensional (2D) nanofilms with high-yield as well as good control of composite, mesophase structure, orientation of the pore channel and thickness represents a big challenge. In this work, it was serendipitously found that microemulsion droplets of tetraethylorthosilicate (TEOS) could serve as a novel dynamic interface for continuous growth of nanofilms. Based on this finding, a general, efficient strategy for the direct and large-scale synthesis of free-standing mesoporous silica films (FSMSFs) was developed. Remarkably, with the careful control of the synthesis conditions, the FSMSFs with high-yield as well as good control of composite, mesophase structure, orientation of the pore channel and thickness could be efficiently achievable. More importantly, by using polymerizable surfactants the preorganized monomers in the nanochannels of the resultant silica films could be further converted into 2D polymers and carbon nanomaterials as well as metal particle-decorated forms, as exemplified by using pyrrole-terminated surfactants, demonstrating a powerful method to create 2D inorganic, organic or hybrid functional nanomaterials.

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.

AIE-induced fluorescent vesicles containing amphiphilic binding pockets and the FRET triggered by host-guest chemistry.

A series of tetraphenylethylene (TPE)-bile acid conjugates was described. It was found that the synergetic combination of the distinct properties of TPE and bile acid units could directly afford uniform fluorescent vesicles with amphiphilic binding pockets in the membrane. This structural features of such vesicles provides a unique opportunity for facile construction of functional chemical systems through host-guest chemistry.