Recent advancements in metal-organic frameworks composites based electrochemical (bio)sensors.

Metal-organic frameworks (MOFs) are a novel class of crystalline materials which find widespread applications in the field of microporous conductors, catalysis, separation, biomedical engineering, and electrochemical sensing. With a specific emphasis on the MOF composites for electrochemical sensor applications, this review summarizes the recent construction strategies on the development of conductive MOF composites (post-synthetic modification of MOFs, in situ synthesis of functional materials@MOFs composites, and incorporating electroactive ligands). The developed composites are revealed to have excellent electrochemical sensing activity better than their pristine forms. Notably, the applicable functionalized MOFs to electrochemical sensing/biosensing of various target species are discussed. Finally, we highlight the perspectives and challenges in the field of electrochemical sensors and biosensors for potential directions of future development.

Regulating Interfacial Li-Ion Transport via an Integrated Corrugated 3D Skeleton in Solid Composite Electrolyte for All-Solid-State Lithium Metal Batteries.

Although solid composite electrolytes show tremendous potential for the practical solid-state lithium metal batteries, searching for a straightforward tactic to promote the ion conduction at electrolyte/electrode interface, especially settling lithium dendrites formation caused by the concentration gradient polarization, are still long-standing problems. Here, the authors report a corrugated 3D nanowires-bulk ceramic-nanowires (NCN) skeleton reinforced composite electrolyte with regulated interfacial Li-ion transport behavior. The special and integrated NCN skeleton endows the electrolyte with fast Li-ion transfer and solves the Li+ concentration polarization at electrode/electrolyte interface, thereby eliminating the energy barrier originated from the redistribution of charge carriers and offering homogeneous interfacial Li-ion flux on lithium anode. As a "double insurance", the bulk ceramic sheet in 3D framework enables the electrolyte to block the mobility of anions. The rational designed NCN composite electrolyte exhibits excellent ionic conductivity and the assembled all-solid-state battery possesses 90.2% capacity retention after 500 cycles. The proposed strategy affords a special insight in designing high-performance solid composite electrolytes.

In-Situ Intermolecular Interaction in Composite Polymer Electrolyte for Ultralong Life Quasi-Solid-State Lithium Metal Batteries.

Solid-state lithium metal batteries built with composite polymer electrolytes using cubic garnets as active fillers are particularly attractive owing to their high energy density, easy manufacturing and inherent safety. However, the uncontrollable formation of intractable contaminant on garnet surface usually aggravates poor interfacial contact with polymer matrix and deteriorates Li+ pathways. Here we report a rational designed intermolecular interaction in composite electrolytes that utilizing contaminants as reaction initiator to generate Li+ conducting ether oligomers, which further emerge as molecular cross-linkers between inorganic fillers and polymer matrix, creating dense and homogeneous interfacial Li+ immigration channels in the composite electrolytes. The delicate design results in a remarkable ionic conductivity of 1.43×10-3  S cm-1 and an unprecedented 1000 cycles with 90 % capacity retention at room temperature is achieved for the assembled solid-state batteries.

Interfacial jamming reinforced Pickering emulgel for arbitrary architected nanocomposite with connected nanomaterial matrix.

Three-dimensional (3D) nanocomposite (NC) printing has emerged as a major approach to translate nanomaterial physical properties to 3D geometries. However, 3D printing of conventional NCs with polymer matrix lacks control over nanomaterial connection that facilitates maximizing nanomaterial advantages. Thus, a printable NC that features nanomaterials matrix necessitates development, nevertheless, faces a challenge in preparation because of the trade-off between viscosity and interfacial stability. Here, we develop viscoelastic Pickering emulgels as NC inks through jamming nanomaterials on interfaces and in continuous phase. Emulgel composed of multiphases allow a vast range of composition options and superior printability. The excellent attributes initiate NC with spatial control over geometrics and functions through 3D printing of graphene oxide/phase-change materials emulgel, for instance. This versatile approach provides the means for architecting NCs with nanomaterial continuous phase whose performance does not constrain the vast array of available nanomaterials and allows for arbitrary hybridization and patterns.

A Versatile and Ultrasensitive Electrochemical Sensing Platform for Detection of Chlorpromazine Based on Nitrogen-Doped Carbon Dots/Cuprous Oxide Composite.

The excessive intake of chlorpromazine (CPZ) adversely affects human health profoundly, leading to a series of severe diseases such as hepatomegaly and dyskinesia. The rapid and precise detection of CPZ in real samples is of great significance for its effective surveillance. Herein, a versatile and sensitive electrochemical sensor was developed for the detection of antipsychotic drug CPZ based on a Nafion (Nf)-supported nitrogen-doped carbon dots/cuprous oxide (N-CDs/Cu2O) composite. The as-synthesized N-CDs/Cu2O composite was systematically characterized using various physicochemical techniques. The developed composite-based sensor displayed excellent performance towards CPZ determination in a dynamic linear range of 0.001-230 µM with the detection limit of 25 nM. Remarkably, the developed sensor displayed good performance in terms of sensitivity and selectivity. Furthermore, good anti-interference properties toward CPZ determination were attained despite the presence of highly concentrated interfering compounds. Therefore, this composite could be a notable potential modifier to enhance electrocatalytic activity onto the surface of the electrode. Finally, N-CDs/Cu2O/Nf-based sensor was effectively applied for quantification of CPZ in human urine and pharmaceutical formulation samples.

Versatile Strategy for Realizing Flexible Room-Temperature All-Solid-State Battery through a Synergistic Combination of Salt Affluent PEO and Li6.75La3Zr1.75Ta0.25O12 Nanofibers.

All-solid-state lithium metal batteries are highly attractive because of their high energy density and inherent safety. However, it is still a great challenge to design the solid electrolytes with high ionic conductivity at room temperature and good electrode/electrolyte interfacial compatibility simultaneously in a facile and scalable way. In this work, for the first time, the combination of salt affluent Poly(ethylene oxide) with Li6.75La3Zr1.75Ta0.25O12 nanofibers was designed and intensively evaluated. The synergistic effect of each component in the electrolyte enhances the ionic conductivity to 2.13 × 10-4 S cm-1 at 25 °C and exhibits a high transference number of 0.57. The composite electrolyte possesses superior interfacial stability against Li metal for over 680 h in Li symmetric cells even at a relatively high current density of 2 mA cm-2. The all-solid-state batteries employing the solid electrolytes exhibit excellent cycling stability at room temperature and superior safety performance. This work proposes a brand-new strategy to design and fabricate solid electrolytes in a versatile way for room-temperature all-solid-state batteries.

Magnetic recyclable CoFe2O4@PPy prepared by in situ Fenton oxidization polymerization with advanced photo-Fenton performance.

Here we present a magnetic recyclable photo-Fenton catalyst CoFe2O4@PPy with uniform morphology and excellent dispersibility prepared via simple in situ Fenton oxidization polymerization. The CoFe2O4 core provides good magnetic recyclability for the catalysts as well as the ion source for catalyzed decomposition of H2O2 in PPy coating. The optimal catalytic effect can be obtained by adjusting the ratio of CoFe2O4 and PPy. Methylene blue, Methyl orange and Rhodamine B (RhB) employed as model pollutants certificated that the catalyst exhibits a wide range of photodegradability. The decoloration rates reach nearly 100% in the photodegradation of 10 mg L-1 RhB after 2 h visible-light irradiation and only low toxicity small molecules are detected by LC-MS. Moreover, the catalytic activity remains after 5 cycles with decoloration rates up to 90%. The degradation measurement in the presence of scavengers of reactive species reveals that the positive holes (h+) and hydroxyl radical (·OH) are the main reactive oxygen species in the CoFe2O4@PPy system. The performance enhancement may be attributed to the combination of improved Fenton activity by coordinated Fe2+ and PPy redox pairs and photo-catalytic activity by broaden adsorption and photo-generated charge separation.

HfS2/MoTe2 vdW heterostructure: bandstructure and strain engineering based on first-principles calculation.

In this study, a multilayered van der Waals (vdW) heterostructure, HfS2/MoTe2, was modeled and simulated using density functional theory (DFT). It was found that the multilayers (up to 7 layers) are typical indirect bandgap semiconductors with an indirect band gap varying from 0.35 eV to 0.51 eV. The maximum energy value of the valence band (VBM) and the minimum energy value of the conduction band (CBM) of the heterostructure were found to be dominated by the MoTe2 layer and the HfS2 layer, respectively, characterized as type-II band alignment, leading to potential photovoltaic applications. Optical spectra analysis also revealed that the materials have strong absorption coefficients in the visible and ultraviolet regions, which can be used in the detection of visible and ultraviolet light. Under an external strain perpendicular to the layer plane, the heterostructure exhibits a general transition from semiconductor to metal at a critical interlayer-distance of 2.54 Å. The carrier effective mass and optical properties of the heterostructures can also be modulated under external strain, indicating a good piezoelectric effect in the heterostructure.

Robust, Reprocessable, and Reconfigurable Cellulose-Based Multiple Shape Memory Polymer Enabled by Dynamic Metal-Ligand Bonds.

Smart materials with multiple shape memory capacities have gradually attracted the interest of a lot of researchers due to their potential application in textiles, smart actuators, and aerospace engineering. However, the design and sustainable synthesis of multiple shape memory polymers (SMPs) simultaneously possessing robust mechanical strength, reprocessability, and reconfigurability still remain full of challenges. Starting from a readily available biomass material cellulose, a well-defined SMP, cellulose-graft-poly(n-butyl acrylate-co-1-vinylimidazole) copolymer (Cell-g-(BA-co-VI)) was facilely synthesized by addition-fragmentation chain transfer polymerization (RAFT) and the subsequent metallosupramolecular cross-linking. Taking advantage of the dynamic bonding, i.e., the rapid reversible fragmentation and the formation of metal ion-imidazole coordination, polymer networks with highly tunable mechanical properties, excellent solid-state plasticity, and quadruple-shape memory capacity are handily attainable. Microscopically, the metal-ligand clusters have a strong tendency to phase segregate from the soft grafted copolymers indicated by atomic force microscopy (AFM), and these serve as netpoints to construct novel SMPs. This article represents our new exploration of the next-generation SMPs based on cellulose backbone where carrying with supramolecular cross-linked soft grafted copolymers. This architecture design allows achieving robust, reprocessable, and reconfigurable thermoplastic SMPs that are difficult to realize by many other methods. Integrating these properties into one system in a synergetic manner also provides a novel approach to the high value addition application of cellulose in the fabrication of advanced functional materials.

One-Step Generation of Multistimuli-Responsive Microcapsules via the Multilevel Interfacial Assembly of Polymeric Complexes.

Efforts to develop microcapsules that respond to different stimuli derive from the incorporation of multiple dynamic assemblies of diverse functional species to the capsule shells. However, this usually involves complicated preparation processes that ultimately hinder the integration of multiple functionalities in a single material. This is addressed in the present work by proposing a multilevel interfacial assembly approach involving polymeric complexes that facilitate the fabrication of multistimuli-responsive microcapsules based on one-step Pickering emulsification using oppositely charged polycation-graphene oxide (GO) and polyanion-surfactant complexes prepared in immiscible liquid solutions. The complexes initially stabilize the emulsion based on electrostatic interactions. Subsequently, the highly dynamic bonding between the polymeric complexes facilitates the rearrangement of components at the oil/water interface to form a continuous interfacial shell membrane. The integrity of the microcapsule shells is sensitive to near-infrared irradiation owing to the GO component and is also sensitive to NaCl content because the assemblies between nanoparticles and polyelectrolytes are bonded through electrostatic interactions. The generality of the proposed strategy is demonstrated by the interfacial assembly of polycation-Fe3O4 complexes and polyanion-surfactant complexes. The resulting microcapsules exhibit salt responsiveness, pH responsiveness, and the ability to be positioned controllably by the application of an external magnetic field. This work provides a promising approach for the preparation of multistimuli-responsive microcapsules.

Salt-Triggered Release of Hydrophobic Agents from Polyelectrolyte Capsules Generated via One-Step Interfacial Multilevel and Multicomponent Assembly.

Controlled release of hydrophobic agents from salt-responsive capsules is hindered by the hydrophilic shell and interfacial tension between inner oil and surrounding water. Rupturing shells in salt solution is another effective way. However, the densely entangled polyelectrolytes (PEs) in shells determined that the rupture requires extremely high ion-strength. Herein, salt-responsive capsules with double-network shells including a continuous PE-nanocrystal network and interfacial ion pairs are proposed and revealed via a one-step interfacial multilevel and multicomponent assembly (IMMA) method. Rigid nanocrystals can weaken the entanglements of PE chains and reduce the critical salt-concentration. Interfacial ion pairs are responsible for maintaining the stability of the shells. Such double networks enable the disintegration of capsules in an applicable salt-concentration without damaging the stability of capsules. In addition, hydrophobic domains assemblied by surfactants and PE-nanocrystal network supply transport pathway for oil to across hydrophilic shells and subsequently produce inverse micelle to carry oil into water. The mechanism of formation and release of capsules is systematically investigated, which further demonstrates IMMA to be a typical method for creation of sophisticated structures in a brief way.

Liquefaction of water on the surface of anisotropic two-dimensional atomic layered black phosphorus.

The growth and wetting of water on two-dimensional(2D) materials are important to understand the development of 2D material based electronic, optoelectronic, and nanomechanical devices. Here, we visualize the liquefaction processes of water on the surface of graphene, MoS2 and black phosphorus (BP) via optical microscopy. We show that the shape of the water droplets forming on the surface of BP, which is anisotropic, is elliptical. In contrast, droplets are rounded when they form on the surface of graphene or MoS2, which do not possess orthometric anisotropy. Molecular simulations show that the anisotropic liquefaction process of water on the surface of BP is attributed to the different binding energies of H2O molecules on BP along the armchair and zigzag directions. The results not only reveal the anisotropic nature of water liquefaction on the BP surface but also provide a way for fast and nondestructive determination of the crystalline orientation of BP.

Facile and scalable fabrication of self-assembled Cu architecture with superior antioxidative properties and improved sinterability as a conductive ink for flexible electronics.

The inherent susceptibility to oxidation and poor sinterability significantly limit the practical application of Cu-based conductive inks. Most methodologies employed for the inks like organic polymer coatings and inorganic metal deposition are generally ineffective. Herein, we report the design of a novel hierarchical Cu architecture to simultaneously improve the antioxidative and sinterability via a self-passivation mechanism and loose interior structures. The hierarchical Cu architecture was prepared using copper hydroxide, L-ascorbic acid, and polyvinylpyrrolidone in aqueous solution; 40 g Cu were prepared in a scale-up experiment. A possible growth mechanism is proposed, involving the Cu2O-templated and mediated nucleation and growth of Cu nanocrystals, followed by the PVP-directed electrostatic self-assembly of Cu nanocrystals. The synthesized Cu shows high oxidation resistance after stored in ambient environment for 90 d by self-passivation, wherein the dense oxidized external layer prevented further oxidation of Cu, unlike other antioxidative strategies. In addition, the structure became 2D flake after a simple ball-milling for 10 min of 2000r, thus forming a good conductive network at the temperature of 180 °C. Importantly, no obvious decline in the electrical performance after severe surface oxidation. Although the structure cannot offer excellent conductive performance, but it proposes a new solution for the balance of antioxidative capabilities and good sinterability in Cu nanomaterials, thus facilitating greater utilization of Cu-based conductive inks for emerging flexible electronic applications.

Acid Environment-improved fluorescence sensing performance: A quinoline Schiff base-containing sensor for Cd2+ with high sensitivity and selectivity.

The development of acid environment-applicable fluorescence sensor is challenging but attractive topic, which can achieve the rapid and comprehensive evaluation of total soluble heavy metal content in natural water. In this work, a quinoline-containing Schiff base, AMQD, was utilized as fluorescence probe for Cd2+. Interestingly, the obtained chemosensor exhibited much better fluorescence detection sensitivity and selectivity toward Cd2+ in acidic 10% methanol aqueous solution (pH 4) comparing to those in neutral environment. Initially, the fluorescence emission of AMQD was almost invisible with the absence of metal ions, while a significant turn-on fluorescence response (~425 nm) can be observed with the addition of Cd2+. The fluorescence detection possesses excellent selectivity without the interference of any other metal cation. The recognition ratio between the fluorescence sensor AMQD and Cd2+ was confirmed to be 1:1, and the detection limit was calculated to be 2.4 nM.

Enzyme and pH dual-responsive hyaluronic acid nanoparticles mediated combination of photodynamic therapy and chemotherapy.

Hyaluronic acid (HA) is a natural biopolymer that can target to tumor cells due to CD44 receptors overexpressed in tumor cells. Here, a theranostic nanoparticle HA-Ce6 (DOX) with enzyme and pH dual-responsive is presented, which combined HA and a highly promised photosensitizer chlorin e6 (Ce6) using adipic dihydrazide (ADH) as a linker. The hydrazide group on its surface can efficiently conjugate doxorubicin to form HA-Ce6 (DOX) nanoparticles through the pH-sensitive hydrazone bond. In this study, the dual-response of HA-Ce6 (DOX) nanoparticles in the tumor cell are discussed. The HA-Ce6 (DOX) nanoparticles showed an average size of 90 nm with a uniform spherical morphology. In vitro drug release studies showed that HA-Ce6 (DOX) accomplished rapid drug release under acid conditions and enzyme stimulating. Confocal images revealed that the nanoparticles enhance the cellular accumulation of DOX and Ce6 in A549 cells. The therapeutic efficacy of HA-Ce6 (DOX) nanoparticles in A549 cells in vitro was evaluated through the MTT assay. The results showed that the therapeutic efficacy of HA-Ce6 (DOX) nanoparticles against A549 cells was remarkably enhanced compared with free DOX and free Ce6. These results indicate that the HA-Ce6 (DOX) nanoparticles could be a promising delivery system for photodynamic therapy and chemotherapy.

Near infrared photothermal-responsive poly(vinyl alcohol)/black phosphorus composite hydrogels with excellent on-demand drug release capacity.

Owing to their excellent tissue-penetration ability, near-infrared (NIR) photothermal-responsive intelligent materials show remarkable advantages in biomedical applications. However, the majority the previously reported NIR-absorbing agents are metal- and carbon-based nanoparticles, both of which possess low photothermal conversion efficiency and poor biocompatibility. Herein, polydopamine modified black phosphorus (pBP) nanosheet-containing poly(vinyl alcohol) (PVA) composite hydrogels are facilely fabricated via a freezing/thawing approach. Taking advantage of the high photothermal conversion efficiency of pBP, the prepared composite hydrogels exhibit a fascinating on-demand NIR-responsive drug release behavior. An in vitro cell culture study demonstrates that these composite hydrogels present good biocompatibility and cellular interaction. Moreover, since the incorporated pBP nanosheets can form a strong hydrogen bonding interaction within the PVA matrix, the composite hydrogels also show enhanced mechanical properties. We believe that the robust mechanical properties and excellent biocompatibility accompanied by the highly controllable NIR-responsive drug release performance of the obtained composite hydrogel augur well for its diverse future applications in the biomedical field.

Surface functionality density regulated in situ reduction of nanosilver on hierarchial wrinkled mesoporous silica nanoparticles and their antibacterial activity.

Hierarchical wrinkled mesoporous silica nanoparticles (WMS NPs) bedecked with diverse functionality density of amino groups (WMSs-N2, WMSs-NN and WMSs-NNN) were first synthesized via typical Sol-Gel method, and then utilized for the in situ reduction of nanosilver with sodium borohydride. Elegantly distributed Ag NPs (ca. 7-10 nm, 3-5 nm) on WMSs-N2 and WMSs-NN without any agglomeration were obtained respectively, while Ag NPs (ca. 50 nm) dispersed on WMSs-NNN were obviously larger and slightly agglomerated. Compared to pure Ag NPs, all the obtained Ag@WMSs composites were durable and displayed much better antibacterial performance, with a minimal inhibitory concentration of 12-80 mg L-1 and a minimal bactericidal concentration of 24-108 mg L-1, respectively. Moreover, it was found that the functionality density of amino groups and the specific surface area of WMSs played a crucial role for the antibacterial performance of the obtained nanocomposites. Because WMSs-NN had higher specific surface area and surface amino density than WMSs-N2, the size and dispersion of Ag NPs on WMSs-NN were smaller and superior to those of Ag NPs on WMSs-N2, respectively. Accordingly, Ag@WMSs-NN displayed a better antibacterial capacity than Ag@WMSs-N2. As for Ag@WMSs-NNN, owing to the high loading content of Ag NPs, they exhibited the best antibacterial and bactericidal properties.

Effect of oxidative stress from nanoscale TiO2 particles on a Physarum polycephalum macroplasmodium under dark conditions.

Information regarding the effect of nanoscale titanium dioxide particles (nTiO2) on the environment under dark conditions is scarce, and the effect of nTiO2 on fungi is largely unknown. Due to its huge size and high sensitivity to external stimuli, the slime mold fungi cell, Physarum polycephalum macroplasmodium, was utilized as a novel subject for the toxicity investigations in the present study, and oxidative stress from nTiO2 on the macroplasmodium was assessed under dark conditions. Short exposure (2-3 h) caused an intracellular reactive oxygen species (ROS) imbalance, and an anti-oxidative mechanism was activated from intermediate doses of nTiO2 (5-18 mg/mL). At long exposure times (~3 days), relatively low doses of nTiO2 (≤9 mg/mL) stimulated the growth of macroplasmodium and oxidative stress without DNA damage, whereas higher doses of nTiO2 (≥15 mg/mL) led to growth inhibition, significant DNA oxidative damage, and activation of the DNA single-strand repairing system. Although DNA oxidative damage was decreased to the same level as the control group by the supplementation of the anti-oxidant vitamin C, growth of the macroplasmodium failed to be completely restored. We inferred that nTiO2 induced a complicated toxicity effect on P. polycephalum in addition to DNA oxidative damage. Taken as a whole, the present study implied the probability of using P. polycephalum macroplasmodium for toxicity studies at the single-cell level, indicating that nTiO2 could induce oxidative stress or damage in P. polycephalum even under dark conditions and suggesting that the release of nTiO2 could lead to a growth imbalance of slime molds in the environment.

Two-dimensional hybrid layered materials: strain engineering on the band structure of MoS2/WSe2 hetero-multilayers.

In this paper, we report a comprehensive modeling and simulation study of constructing hybrid layered materials by alternately stacking MoS2 and WSe2 monolayers. Such hybrid MoS2/WSe2 hetero-multilayers exhibited direct bandgap semiconductor characteristics with bandgap energy (E g) in a range of 0.45-0.55 eV at room temperature, very attractive for optoelectronics (wavelength range 2.5-2.75 µm) based on thicker two-dimensional (2D) materials. It was also found that the interlayer distance has a significant impact on the electronic properties of the hetero-multilayers, for example a five orders of magnitude change in the conductance was observed. Three material phases, direct bandgap semiconductor, indirect bandgap semiconductor, and metal were observed in MoS2/WSe2 hetero-multilayers, as the interlayer distance decreased from its relaxed (i.e., equilibrium) value of about 6.73 Å down to 5.50 Å, representing a vertical pressure of about 0.8 GPa for the bilayer and 1.5 GPa for the trilayer. Such new hybrid layered materials are very interesting for future nanoelectronic pressure sensor and nanophotonic applications. This study describes a new approach to explore and engineer the construction and application of tunable 2D semiconductors.

A Thresholdless Tunable Raman Nanolaser using a ZnO-Graphene Superlattice.

A ZnO-graphene superlattice is synthesised via a spatially confined reaction. When illuminated by a pump laser, the Stokes' photons of the superlattice are greatly amplified by the surface plasmon at the interface of the graphene and the ZnO. Benefitting from the special geometry, the ZnO-graphene superlattice allows the generation of a tunable nanolaser that operates from the visible to near-infrared range at room temperature.