Search

Background: Nanozymes are a kind of emerging nanomaterials that can mimic the catalytic activity of natural enzymes with good stability. Objective: Benefited by the unique coordination structure and constitution, metal-organic frameworks (MOFs) have been widely exploited as novel nanozymes. Importantly, various MOFs engineered with fascinating functions provide great opportunities to enhance their enzyme-like activity and improve their applied performance, achieving the goal of vividly mimicking natural enzymes. Conclusion: This review summarized recent advances in the fabrication of the MOFs-based nanozymes and their applications in biosensing. First, MOFs-based nanomaterials containing pristine MOFs, functionalized MOFs, MOFs-based composites and MOFs derivatives are introduced, where the design strategy, enzyme-like activity and the catalytic mechanisms are highlighted systematically. Then, their applications in various target assays are summarized. Finally, the challenges and possible research directions for the development and application of MOFs-based nanozymes are provided.

A unique metallic IrxPb network structure with high Ir atomic utilization and enhanced performance for oxygen evolution.

Cost-effective and highly efficient Fe–N–C single-atom catalysts (SACs) have been considered to be one of the most promising potential Pt substitutes for the cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Nevertheless, they are subject to severe oxidative corrosion originating from the Fenton reaction, leading to poor long-time durability of PEMFCs. Herein, we propose a MnOx engineered Fe–N–C SAC (Mn–Fe–N–C SAC) to reduce and even eliminate the stability issue, as MnOx accelerates the degradation of the H2O2 by-product via a disproportionation reaction to weaken the Fenton reaction. As a result, the Mn–Fe–N–C SAC shows an ultralow H2O2 yield and a negligible half-wave potential shift after 10 000 continuous potential cycles, demonstrating excellent ORR stability. Besides, the Mn–Fe–N–C SAC also shows an improved ORR activity compared to the common Fe–N–C SAC. Results show that the MnOx interacts with the Fe–Nx site, possibly forming Fe–Mn or Fe–O–Mn bonds, and enhances the intrinsic activity of single iron sites. This work provides a method to overcome the stability problem of Fe–N–C SACs while still yielding excellent catalytic activity, thus showing great promise for application in PEMFCs.

Single-particle-layer sulfur electrodes are designed to build low-tortuosity through-pores across both vertical and planar directions of an electrode, enabling operation of low-porosity cathodes under practical conditions.

Currently, gas chromatography–mass spectrometry (GC–MS) and liquid chromatography–MS (LC–MS) are the primary methods used to detect pesticides and their metabolites for biomonitoring of exposure. Although GC–MS and LC–MS can provide accurate and sensitive measurements, these techniques are not suitable for point-of-care or in-field biomonitoring applications. The objective of this work is to develop a smartphone-based dual-channel immunochromatographic test strip (ICTS) for on-site biomonitoring of exposure to cypermethrin by simultaneous detection of cypermethrin and its metabolite, 3-phenoxybenzoic acid (3-PBA). Polymer carbon dots (PCDs) with ultrahigh fluorescent brightness were synthesized and used as a signal amplifier in ICTS assay. Cypermethrin (a representative pyrethroid pesticide) and its major metabolite 3-PBA were simultaneously detected to provide more comprehensive analysis of cypermethrin exposure. After competitive immunoreactions between the target sample and the coating antigens preloaded on the test line, the tracer antibody (PCD-conjugated antibody) was quantitatively captured on the test lines. The captured PCDs were inversely proportional to the amount of the target compound in the sample. The red fluorescence on the test line was then recorded using a smartphone-based device capable of conducting image analysis and recording. Under optimal conditions, the sensor showed excellent linear responses for detecting cypermethrin and 3-PBA ranging from 1 to 100 ng/mL and from 0.1 to 100 ng/mL, respectively, and the limits of detection were calculated to be ~0.35 ng/mL for cypermethrin and ~0.04 ng/mL for 3-PBA. The results demonstrate that the ICTS device is promising for accurate point-of-care biomonitoring of pesticide exposure.

Electrocatalytic CO2 reduction (ECR) can convert CO2 into various value-added fuels or chemicals, thus becoming a promising route for balancing the carbon cycle and realizing the low-carbon economy. Recently, the single-atom catalysts (SACs) have emerged and flourished in the field of ECR due to their unsurpassed atom utilization efficiency and unexpected high catalytic performance. Analogy to the recipe for cuisine, this review gives a comprehensive description of the methods to prepare SACs for ECR, and outlines the pathway from CO2 to target products. Moreover, the SACs that exhibit high catalytic performance towards ECR are systematically summarized in the aspects of support material, ligands, coordination number, porous structure, and position, just like regulating the “ingredients” of soup base for transforming CO2. Finally, the challenge and perspective for further upgrading SACs in the ECR domain are expounded. It is hoped that this review would give a general recipe to develop highly efficient (delicious) SACs in ECR.

Highlights A facile ion-imprinting method (IIM) is used to synthesize the isolated Fe-N-C single-atomic site catalyst (IIM-Fe-SASC), which mimics the natural enzyme-like active site and shows excellent peroxidase-like activity.The ion-imprinting process can precisely control ion at the atomic level and form numerous well-defined single-atomic Fe-N-C sites.The IIM-Fe-SASC has been successfully used as the nanoprobe for in situ H2O2 detection generated from MDA-MB-231 cells. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00661-z., Fe-based single-atomic site catalysts (SASCs), with the natural metalloproteases-like active site structure, have attracted widespread attention in biocatalysis and biosensing. Precisely, controlling the isolated single-atom Fe-N-C active site structure is crucial to improve the SASCs’ performance. In this work, we use a facile ion-imprinting method (IIM) to synthesize isolated Fe-N-C single-atomic site catalysts (IIM-Fe-SASC). With this method, the ion-imprinting process can precisely control ion at the atomic level and form numerous well-defined single-atomic Fe-N-C sites. The IIM-Fe-SASC shows better peroxidase-like activities than that of non-imprinted references. Due to its excellent properties, IIM-Fe-SASC is an ideal nanoprobe used in the colorimetric biosensing of hydrogen peroxide (H2O2). Using IIM-Fe-SASC as the nanoprobe, in situ detection of H2O2 generated from MDA-MB-231 cells has been successfully demonstrated with satisfactory sensitivity and specificity. This work opens a novel and easy route in designing advanced SASC and provides a sensitive tool for intracellular H2O2 detection. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00661-z.

With high activity and specificity to conduct catalysis under mild conditions, enzymes show great promise in many fields. However, they are not acclimatized to environments in practice after leaving the familiar biological conditions. Aiming at this issue, nanobiocatalysis, a fresh area integrating nanotechnology and enzymatic catalysis, is expected to design biocatalysis based on materials science. Specifically, nano-integrated biocatalysis and bio-inspired nanocatalysis are considered as two effective nanobiocatalytic systems to meet different design needs. Notably, both systems are not entirely separated, and the combination of both further sparks more possibilities. This review summarizes the type, construction, and function of nanobiocatalytic systems, analyzing the pros and cons of different strategies. Moreover, the corresponding applications in bioassay, biotherapy, and environmental remediation are highlighted. We hope that the advent of nanobiocatalysis will help in grasping the inherence of biocatalysis and propel biocatalytic applications.

Multifunctional nanozymes can benefit biochemical analysis via expanding sensing modes and enhancing analytical performance, but designing multifunctional nanozymes to realize the desired sensing of targets is challenging. In this work, single-atomic iron doped carbon dots (SA Fe-CDs) are designed and synthesized via a facile in situ pyrolysis process. The small-sized CDs not only maintain their tunable fluorescence, but also serve as a support for loading dispersed active sites. Monoatomic Fe offers SA Fe-CDs exceptional oxidase-mimetic activity to catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation with fast response (V

Highly efficient noble-metal-free electrocatalysts for oxygen reduction reaction (ORR) are essential to reduce the costs of fuel cells and metal-air batteries. Herein, a single-atom Ce-N-C catalyst, constructed of atomically dispersed Ce anchored on N-doped porous carbon nanowires, is proposed to boost the ORR. This catalyst has a high Ce content of 8.55 wt % and a high activity with ORR half-wave potentials of 0.88 V in alkaline media and 0.75 V in acidic electrolytes, which are comparable to widely studied Fe-N-C catalysts. A Zn-air battery based on this material shows excellent performance and durability. Density functional theory calculations reveal that atomically dispersed Ce with adsorbed hydroxyl species (OH) can significantly reduce the energy barrier of the rate-determining step resulting in an improved ORR activity.

Enzyme cascade reactions in biological systems can effectively improve the catalytic performances owing to their high local concentration, efficient mass transfer and reduced intermediate decomposition. However, the disadvantages of high cost, low stability, and easy inactivation limit their practical applications in harsh environments. Nanozymes as the substitutes for enzymes not only have enzyme-like activities but also possess high stability, tunable catalytic property, and high pH/temperature tolerance, which have been intensively investigated for the establishment of biomimetic catalysis systems. In this review, we first summarized the recent development of the construction and advantage of the nanozyme-involved cascade reaction system. Then, the biomedical applications of the nanozyme-enhanced biomimetic cascade catalytic systems, including biosensing, therapies and antioxidation, were highlighted in detail. Finally, current challenges and future perspectives for nanozyme-activated cascade reactions are discussed and outlooked.

Free-standing two-dimensional (2D) organic nanomaterials are highly attractive for biological applications because of their unique structural properties and high biocompatibility. Herein, we design...

Advanced protein-based nanomaterials and nanosystems (PNNS) have attracted considerable scientific interest in recent decades due to their potential in bio-applications. Nowadays, the constructed PNNS exhibit different properties for various special applications based on the characteristics of different proteins. Herein, in this review article, a systematic summary and discussion focusing on designing multi-functional PNNS are presented. The latest developments in unique synthesis strategies and detailed classification of PNNS are reviewed. The functions of proteins in PNNS for biomedical applications, such as targeting proteins, carriers, enzymes, and fluorescent indicators, are summarized. Finally, the challenges and forward-looking perspectives of PNNS research are provided.

Paper-based rapid diagnostic tests, such as immunochromatographic assays, namely lateral flow immunoassay (LFA), are valuable alternatives for biomarker detection compared to traditional laboratory-based tests, but these assays need further refinement to consolidate their biosensing capabilities. Nanozyme integration into LFA systems may provide a reliable means of improving the analytic sensitivity of LFA tests. Due to the involvement of multiple liquid-handling steps, the quantitative accuracy is compromised, hence hindering the use of untrained personnel point-of-care use. Self-assembling allochroic nanocatalyst (SAN) assemblies satisfy these LFA quality measures by optimizing analyte-antibody reporting performance and by intrinsically catalyzing chromogen activation, thereby reducing the number of liquid handling steps involved during sample analysis. In SANs, the hydrophobic chromogens serve as peroxidase substrates that self-assemble into nanoparticles at high loading fractions. These features demonstrate the potential for SAN-LFAs to be a valuable patient point-of-care (POC) test. Herein, we describe the SAN fabrication process and employ SAN-LFAs to detect cardiac troponin I-troponin C (cTnI-TnC) and myoglobin (Myo) levels present in plasma samples. Using SAN-LFAs, the limits of detection for cTnI-TnC and Myo were 0.012 ng/mL and 0.2 ng/mL respectively. We also demonstrate SAN compatibility with blood samples and stability under long-term storage conditions. The successful utlization of SANs in LFA-based biomarker detection may inspire these nanocatalysts to be integrated into similar immunochromatographic testing methods.

Single-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO2 reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN2O2 sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO2 to CH4 with current density of 40 mA·cm-2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN2O2 active sites are due to the proper elevated CH4 and H2 energy barrier and fine-tuned electronic structure of Cu active sites. Single-atom catalysts (SACs) are promising candidates to catalyze CO2 reduction for the formation of high value hydrocarbons but most of the reactions yield CO. Here, the authors show a low-temperature calcining process to fabricate a carbon-dots-based SAC to efficiently convert CO2 to methane.

All-inorganic lead halide perovskites have become promising alternatives to traditional semiconductor electrochemiluminescence (ECL) emitters because of their appealing optoelectronic attributes, but major challenges remain in improving their stability and enhancing charge injection/transfer capacities. Herein, a self-sustaining suprastructure was constructed by successively loading aminated carbon dots (NCDs) and CsPbBr3 perovskite quantum dots (PeQDs) in situ into hierarchical zeolite imidazole framework-8 (HZIF-8). The elaborated architecture guarantees not only improved stability via the peripheral HZIF-8 protective barrier but also accelerated charge transport and efficient self-enhanced ECL between PeQDs and the surrounding NCDs in a confined structure. As a result, the ternary nanocomposite is endowed with greatly improved stability and ECL efficiency. Based on this ternary nanocomposite as an electrode substrate, a novel ECL sensing strategy is further proposed for the first time to evaluate T4 polynucleotide kinase activity and screen its inhibitors. This work opens an avenue for the advancement of perovskite-based ECL emitters as well as the development of corresponding applications in the ECL domain.

Background Single-atom catalyst (SAC) is one of the newest catalysts, and attracting people’s wide attention in cancer therapy based on their characteristics of maximum specific catalytic activity and high stability. Methods This study designed and synthesized a Fe-N decorated graphene nanosheet (Fe-N5/GN SAC) with the coordination number of five. Its material characteristics were detected by different methods including scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Also, its enzyme-like properties were calculated based on Density functional theory (DFT). In addition, 3D cancer cell models were constructed and cytotoxic effects of Fe-N5/GN SAC were tested by flow cytometry and RT-PCR. Results Through enzymology and theoretical calculations, the Fe-N5/GN SAC has outstanding intrinsic peroxidase-like catalytic activity due to single-atom Fe site with five-N-coordination structure. It could kill human lung adenocarcinoma cells (A549) by decomposing hydrogen peroxide (H2O2) into toxic ROS under acidic microenvironment condition to induce the cell apoptosis in 3D lung cancer cell model. Conclusion Our study synthesized a novel SAC with peroxidase-like catalytic activity for tumor therapy. And it demonstrates a promising application of SAC with highly efficient single-atom catalytic sites for cancer treatment.

Smart materials, also known as intelligent materials, which are responsive to the external stimuli including heat, moisture, stress, pH, and magnetic fields, have found extensive applications in sensors, actuators, soft robots, medical devices and artificial muscles. Using three-dimensional (3D) printing techniques for fabrication of smart devices allows for complex designs and well-controlled manufacturing processes. 4D printing is attributed to the 3D printing of smart materials that can be significantly transformed over time. Herein the smart materials including hydrogels and polymeric nanocomposites used in 4D printing were reviewed and the fundamental mechanisms responsible for the functionalities were discussed in detail. In this report, 4D printing of smart systems and their applications in sensors, actuators and biomedical devices were reviewed to provide a deeper understanding of the current development and the future outlook.

During past decades, a variety of two-dimensional (2D) nanomaterials have been developed through molecular self-assembly. Among them, those assembled from sequence-defined polymers have received pa...

Electrochemical reduction of CO2 into value-added products is an effective approach to relieve environmental and energetic issues. Herein, EDTA anion-modified porous hollow copper microspheres (H-Cu MPs) were constructed by EDTA-2Na-assisted electrodeposition. The faradic efficiency (FE) of ethylene doubled from 23.3% to 50.1% at -0.82 V vs RHE in nearly neutral 0.1 M KHCO3 solution, one of the highest values among copper-based electrodeposited catalysts. Apart from the favorable influence from morphology regulated by EDTA-2Na, theoretical calculations revealed that the adsorbed EDTA anions were able to create a local charged copper surface to stabilize the transition state and dimer and to assist in the stabilization by interacting with OCCO adsorbate synergistically, which contributed to the outstanding catalytic performance together.

Atrazine is a widely used herbicide in the United States; however, the Environmental Protection Agency (EPA) has issued warnings about atrazine because of its reported potential harmful effects on animals and humans. Therefore, developing efficient ways to detect this herbicide’s residue are critically important. The competitive ELISA is a useful method for detecting chemicals for which antibodies exist due to its high sensitivity, specificity, and efficiency. However, the assay typically requires a separate application of a secondary antibody linked to an enzyme that catalyzes conversion of a non-colored organic to a detectable colored product. In this study, we used the recently developed peroxidase-like mesoporous core–shell palladium@platinum (Pd@Pt) nanoparticle which can easily be bound directly to primary antibody, thereby eliminating the need for a secondary antibody conjugate. We report a first instance in which this technique is applied for use in a competitive assay for small molecules, in this case the herbicide atrazine. Due to their high-surface area and mesoporous structure, Pd@Pt nanoparticles enable fast mass transfer for reaction with excellent catalytic activity. This leads to high sensitivity in our immunoassay with a limit of detection of 0.5 ng mL−1 defined by selecting an IC10 concentration, i.e., the analyte concentration at which 10% of the available Pd@Pt nanoparticle-labeled antibody is inhibited from binding to a plate coated with a bovine serum albumin-atrazine conjugate. We applied our method to well-water and pond water samples spiked with atrazine. Our tests at 5, 10, and 20 ng mL−1 yielded recoveries of 99 – 115%, offering strong supporting evidence that atrazine and other low molecular weight herbicides and pesticides can be detected using this immunoassay approach. Detection with this method is expected to lead to its use in a wide spectrum of applications in agriculture, medical, and biotechnology arenas.

The synergistic therapy of chemotherapy and photothermal therapy (PTT) has been reported as a promising antitumor strategy. To achieve effective combination therapy, developing more suitable candidate nanomaterials with optimal photothermal property and high chemical drug loading capacity is very necessary. Herein, a bimetallic PtPd nanoparticle was synthesized with the merits of excellent photothermal effect and mesoporous structure for doxorubicin (DOX) loading. We further designed PtPd-ethylene glycol (PEG)-folic acid (FA)-doxorubicin (DOX) nanoparticle for chemo-photothermal therapy of MCF-7 tumor with folic acid engineering to achieve active targeting. Moreover, excellent photoacoustic (PA) imaging of PtPd-PEG-FA-DOX nanoparticles facilitated the precise in vivo tracking and further evaluation of nanoparticles’ targeting effect. The in vitro and in vivo results both demonstrated PtPd-PEG-FA-DOX nanoparticles serve as a safe and promising system for effective treatment of MCF-7 tumor.

O3-layered metal oxides are promising cathode materials for high-energy Na-ion batteries (SIBs); however, they suffer from fast capacity fade. Here, we develop a high-performance O3-NaNi0.68Mn0.22C...

Alkaline anion exchange membrane (AEM) electrolysers to produce hydrogen from water are still at an early stage of development, and their performance is far lower than that of systems based on proton exchange membranes. Here, we report an ammonium-enriched anion exchange ionomer that improves the performance of an AEM electrolyser to levels approaching that of state-of-the-art proton exchange membrane electrolysers. Using rotating-disk electrode experiments, we show that a high pH (>13) in the electrode binder is the critical factor for improving the activity of the hydrogen- and oxygen-evolution reactions in AEM electrolysers. Based on this observation, we prepared and tested several quaternized polystyrene electrode binders in an AEM electrolyser. Using the binder with the highest ionic concentration and a NiFe oxygen evolution catalyst, we demonstrated performance of 2.7 A cm−2 at 1.8 V without a corrosive circulating alkaline solution. The limited durability of the AEM electrolyser remains a challenge to be addressed in the future. Anion exchange membrane water electrolysers have potential cost advantages over proton exchange membrane electrolysers, but their performance has lagged behind. Here the authors investigate the cause of the poor performance of anion exchange membrane electrolysers and design ionomers that can overcome some of the challenges.

Lead halide perovskites have been promising electrochemiluminescence (ECL) candidates because of their excellent photophysical attributes, but their poor stability has severely restricted ECL applications. Herein, the in situ assembly of all-inorganic perovskite CsPbBr3 nanocrystals (CPB) into hollow graphitic carbon nitride nanospheres (HCNS) were described as a novel ECL emitter. The architecture guaranteed not only improved stability because of the peripheral HCNS protecting shell but also high-performance ECL of CPB because of a matching band-edge arrangement. Dual-ECL readouts were obtained from the nanocomposite including an anodic ECL from CPB and a cathodic ECL from HCNS. The former displayed prominent color purity to construct an efficient ECL resonance energy transfer system, and the latter served as an internal standard for a ratiometric analysis. A well-designed DNA probe was further utilized for the targeting of CD44 receptors on the MCF-7 cell surface and the double signal amplification. The sensing strategy exhibited good analytical performance for MCF-7 cells, ranging from 1.0 × 103 to 3.2 × 105 cells mL-1 with a detection limit of 320 cells mL-1. Sensitive and accurate evaluation of CD44 expression was finally achieved at 0.22 pM. This work is the first attempt to use halide perovskite for reliable ECL bioanalysis and provides a perspective to design a perovskite-based nanocomposite as a high-performance ECL emitter for its exclusive ECL system.

Atomically dispersed Fe–N–C materials recently hold great interest in costly Pt substitution for the cathodic oxygen reduction reaction of fuel cells. However, the heat treatment involved in the ma...

Two-dimensional (2D) graphene has been widely used as an ideal substrate for many functional materials. It is crucial to understand and control the growth of metal nanocrystals on the graphene surface. Herein we report a novel phenomenon that pre-synthesized palladium nanoparticles are spontaneously transformed into palladium nanostrings (Pd NSs) with nanoscale grain boundaries induced by the reduction of a graphene oxide substrate. A systematic study has been performed to explore the formation mechanism of Pd NSs, where the surface chemistry of 2D graphene is found to be the key factor. More importantly, these Pd NSs exhibit significantly enhanced stability and are among the most active catalysts for formic acid oxidation. Density-functional theory investigation further unravels that the formation of grain boundaries weakens the adsorption of formate and facilitates its subsequent oxidation.