Iridium nanoparticles supported on polyaniline nanotubes for peroxidase mimicking towards total antioxidant capacity assay of fruits and vegetables

In this study, a straightforward approach is presented for the first time to anchor Ir nanoparticles on the surface of uniform polyaniline (PANi) nanotubes (NTs), which can be used as an efficient peroxidase (POD)-like catalyst. The morphology and chemical structure of the PANi-Ir nanocomposite are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), Raman and X-ray photoelectron spectroscopy (XPS) measurements. Owing to the strong interaction between Ir nanoparticles and PANi, a remarkable catalytic enhancement is achieved compared to the bare Ir black catalyst and individual PANi NTs, dominating withan electron transfer mechanism. Furthermore, an efficient colorimetric sensor for ascorbic acid (AA) is developed with a low detection limit of 1.0 μM (S/N = 3), and a total antioxidant capacity (TAC) sensing platform is also constructed for the rigorous detection and analysis of fruits and vegetables.

Fe3O4 nanoparticles entrapped in the inner surfaces of N-doped carbon microtubes with enhanced biomimetic activity

Tubular structured composites have attracted great interest in catalysis research owing to their void-confinement effects. In this work, we synthesized a pair of hollow N-doped carbon microtubes (NCMTs) with Fe3O4 nanoparticles (NPs) encapsulated inside NCMTs (Fe3O4@NCMTs) and supported outside NCMTs (NCMTs@Fe3O4) while keeping other structural features the same. The impact of structural effects on the catalytic activities was investigated by comparing a pair of hollow-structured nanocomposites. It was found that the Fe3O4@NCMTs possessed a higher peroxidase-like activity when compared with NCMTs@Fe3O4, demonstrating structural superiority of Fe3O4@NCMTs. Based on the excellent peroxidase-like catalytic activity and stability of Fe3O4@NCMTs, an ultra-sensitive colorimetric method was developed for the detection of H2O2 and GSH with detection limits of 0.15 μM and 0.49 μM, respectively, which has potential application value in biological sciences and biotechnology.

Research Progress in Iron-Based Nanozymes: Catalytic Mechanisms, Classification, and Biomedical Applications

Natural enzymes are crucial in biological systems and widely used in biology and medicine, but their disadvantages, such as insufficient stability and high-cost, have limited their wide application. Since Fe₃O₄ nanoparticles were found to show peroxidase-like activity, researchers have designed and developed a growing number of nanozymes that mimic the activity of natural enzymes. Nanozymes can compensate for the defects of natural enzymes and show higher stability with lower cost. Iron, a nontoxic and low-cost transition metal, has been used to synthesize a variety of iron-based nanozymes with unique structural and physicochemical properties to obtain different enzymes mimicking catalytic properties. In this perspective, catalytic mechanisms, activity modulation, and their recent research progress in sensing, tumor therapy, and antibacterial and anti-inflammatory applications are systematically presented. The challenges and perspectives on the development of iron-based nanozymes are also analyzed and discussed.

A novel TMD-based peroxidase-mimicking nanozyme: From naked eye detection of leukocytosis-related diseases to sensing different bioanalytes

Being emerged as alternatives to natural enzymes, nanozymes have recently drawn much attention in sensing. Herein, the first multicomponent transition metal dicalchogenide (TMD)-based nanozyme (MCFS/rGO) was synthesized by a facile hydrothermal method and characterized. This peroxidase-mimic nanozyme follows the typical Michaelis-Menten kinetics, showing a higher affinity for H₂O₂ substrate (K_m = 9 μM) compared to that of natural peroxidase (K_m = 3700 μM). The remarkable potential of the MCFS/rGO nanozyme to detect H₂O₂ provided us with a great opportunity to design some simple and fast colorimetric sensing systems. Coupling the efficient peroxidase-mimicking activity of the nanozyme with the H₂O₂ production capacity of white blood cells (WBCs) leads to the development of a novel, simple, rapid, and efficient colorimetric method to distinguish leukocytosis-related patients from healthy people by the naked eye. This pioneering diagnostic technique can also be utilized to quantitatively measure the WBC count. Moreover, we coupled the mentioned nanozyme-based system with the activity of glucose oxidase enzyme available in different types of honey samples, an innovative mechanism proved to be an effective quality indicator of the samples. Last but not least, the MCFS/rGO nanozyme is also able to determine the quantity of some biologically significant analytes, including glutathione (GSH), ascorbic acid (AA), and mercury ions (Hg²⁺), of which the limit of detection (LOD) was 9.3 nM, 22.5 nM, and 0.32 μM, respectively. Our results, however, demonstrated the superior performance of the MCFS/rGO nanozyme to determine the first two mentioned bioanalytes compared with other TMDs. Overall, this novel nanozyme-based sensor system can be considered a suitable candidate for developing multipurpose biosensors for medical and biochemical applications.

Rational Design of Conducting Polymer-Derived Tubular Carbon Nanoreactors for Enhanced Enzyme-like Catalysis and Total Antioxidant Capacity Bioassay Application

The design of void-confined tubular nanostructures has aroused significant interest for catalytic applications because of their distinct microenvironment to modulate the reaction kinetics. Herein, we propose a facile wrapping-pyrolysis strategy to confine Fe⁰ nanoparticles (Fe NPs) inside N-doped carbon nanotubes (Fe@NC NTs) derived from Fe₂O₃@polypyrrole (PPy) core-sheath nanofibers (NFs). The resultant Fe@NC NTs can act as efficient enzyme mimics and exhibit a significantly higher peroxidase (POD)-like catalytic activity than unconfined Fe NPs and bare NC NTs. Kinetic experiments demonstrate that the optimized void structure benefits the affinity with the POD substrates and achieves excellent catalytic efficiency. The mechanism study reveals that the generation of ^•OH from H₂O₂ endows Fe@NC NTs with excellent POD-like performance. Furthermore, we develop a total antioxidant capacity (TAC) sensing platform on account of this efficient POD-like system, expanding their applications in the field of food safety and human healthcare.

Tumor Microenvironment Activated Nanoenzyme-based Agents for Enhanced MRI-Guided Photothermal Therapy in NIR-II Window

We report a nanoenzyme-based photothermal agent, in which the nanoenzyme acts as a peroxidase, prodrug carrier, and MRI contrast agent. The formation of dimer by the prodrug under the catalysis...

Recent technological advances in mechanism, toxicity, and food perspectives of enzyme-mediated aflatoxin degradation

Aflatoxins are carcinogenic secondary metabolites produced by Aspergillus section Flavi that contaminates a wide variety of food and feed products and is responsible for serious health and economic consequences. Fermented foods are prepared with a wide variety of substrates over a long fermentation time and are thus vulnerable to contamination by aflatoxin-producing fungi, leading to the production of aflatoxin B1. The mitigation and control of aflatoxin is currently a prime focus for developing safe aflatoxin-free food. This review summarizes the role of major aflatoxin-degrading enzymes such as laccase, peroxidase, and lactonase, and microorganisms in the context of their application in food. A putative mechanism of enzyme-mediated aflatoxin degradation and toxicity evaluation of the degraded products are also extensively discussed to evaluate the safety of degradation processes for food applications. The review also describes aflatoxin-degrading microorganisms isolated from fermented products and investigates their applicability in food as aflatoxin preventing agents. Furthermore, a summary of recent technological advancements in protein engineering, nanozymes, in silico and statistical optimization approaches are explored to improve the industrial applicability of aflatoxin-degrading enzymes.

AgCu@CuO aerogels with peroxidase-like activities and photoelectric responses for sensitive biosensing

Photoelectrochemical (PEC) enzymatic biosensors integrate the excellent selectivity of enzymes and high sensitivity of PEC bioanalysis, but the drawbacks such as high cost, poor stability, and tedious immobilization of natural enzymes on photoelectrodes severely suppress their applications. AgCu@CuO aerogel-based photoelectrode materials with both remarkable enzyme-like activities and outstanding photoelectric properties were innovatively designed and synthesized to evaluate the activity of xanthine oxidase with a wide linear detection range and a low limit of detection.

Template-Regulated Bimetallic Sulfide Nanozymes with High Specificity and Activity for Visual Colorimetric Detection of Cellular H2O2

For the past several decades, most of the research studies on nanozymes have been aimed at improving their catalytic activity and diversity; however, developing nanozymes with strong catalytic activity and great specificity remains a challenge. Herein, a simple and efficient template synthesis method was used to synthesize bimetallic sulfide nanoparticles, NiCo₂S₄ NPs, and prove that they have excellent peroxidase-like activity with good specificity. By regulating polyvinyl pyrrolidone (PVP) and hexadecyl trimethyl ammonium bromide as the templating agent, we have obtained the NiCo₂S₄ (PVP) NPs with a high Ni/Co ratio, thus exhibiting superior peroxidase activity. In addition, the NiCo₂S₄ NPs selectively catalyzed and oxidized colorless 3,3,5,5-tetramethylbenzidine (TMB). On being treated with H₂O₂, TMB turns blue while other substrates did not undergo the oxidation reaction under the same conditions, such as 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium (ABTS) and dopamine. The high specificity of NiCo₂S₄ NPs is due to the strong electrostatic driving coordination between negatively charged NiCo₂S₄ NPs and positively charged TMB. Due to the peroxidase activity of the developed NiCo₂S₄ NPs, a simple, low-cost, and reliable colorimetric method was established. Simultaneously, this method for in situ quantitative monitoring of H₂O₂ produced by MDA-MB-231 cells was also achieved. This study has provided a theoretical basis for the improvement of the activity and specificity of bimetallic sulfide nanozymes and may offer guidance for the further reasonable design of related materials.

The Fabrication of Amino Acid Incorporated Nanoflowers with Intrinsic Peroxidase-like Activity and Its Application for Efficiently Determining Glutathione with TMB Radical Cation as Indicator

The assessment of glutathione (GSH) levels is associated with early diagnostics and pathological analysis for various disorders. Among all kinds of techniques for detecting GSH, the colorimetric assay relying on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) catalyzed by many nanomaterials with peroxidase-like activity attracts increasing attention owing to its outstanding merits, such as high sensitivity and high selectivity. However, the aggregation between the nanomaterials severely hinders the entrance of TMB into the “active site” of these peroxidase mimics. To address this problem, the D-amino acid incorporated nanoflowers possessing peroxidase-like activity with a diameter of 10–15 μm, TMB and H₂O₂ were employed to establish the detection system for determining the level of glutathione. The larger diameter size of the hybrid nanoflowers substantially averts the aggregation between them. The results confirm that the hybrid nanoflowers detection system presents a low limit of detection, wide linear range, perfect selectivity, good storage stability and desired operational stability for the detection of GSH relying on the intrinsic peroxidase-like activity and favorable mechanical stability of the hybrid nanoflowers, indicating that the hybrid nanoflowers detection system has tremendous application potential in clinical diagnosis and treatment.

Electrospun One-Dimensional Electrocatalysts for Oxygen Reduction Reaction: Insights into Structure-Activity Relationship

Oxygen reduction reaction (ORR) is an efficiency-determining process at the cathode in several energy storage and conversion devices, typically such as metal-air batteries and fuel cells. To date, a considerable amount of ORR electrocatalysts have been purposely exploited to address the key issues of high overpotentials and sluggish electrochemical kinetics. Electrospinning is a popular additive manufacturing technology, enabling the production of one-dimensional (1D) electrocatalysts with outstanding chemical stability and structural diversity. However, compared with the well-studied composite/structural design as well as performance advancement, insights into structure-activity relationship are yet to be settled. To clarify this key issue, herein, a dedicated review on the structure-activity relationship between the 1D architectures of electrospun electrocatalysts and their catalytic ORR property is presented. First, the development and principles of electrospinning technique, the composition regulation- and structure design-oriented fundamentals are summarized by imputing the perspectives of mechanistic understanding. Then, the typical examples of nanofiber-shaped and nanofiber-supported electrocatalysts with different compositions and structures for ORR are implemented to establish different structure-activity relationship by comparative studies. Finally, we also identify some ongoing challenges and present future perspectives to direct the precise manipulation of structure-activity relationship for further activation and optimization of electrospun 1D electrocatalysts.

Graphene encapsuled Ru nanocrystal with highly-efficient peroxidase-like activity for glutathione detection at near-physiological pH

A novel nanozyme comprised of graphene encapsuled Ru nanocrystals (Ru@G) with effective and stable peroxidase-like activity prepared using a chemical vapor deposition (CVD) method was used for the detection of glutathione at near-physiological pH.

Transition metal sulfides meet electrospinning: versatile synthesis, distinct properties and prospective applications

One-dimensional (1D) electrospun nanomaterials have attracted significant attention due to their unique structures and outstanding chemical and physical properties such as large specific surface area, distinct electronic and mass transport, and mechanical flexibility. Over the past years, the integration of metal sulfides with electrospun nanomaterials has emerged as an exciting research topic owing to the synergistic effects between the two components, leading to novel and interesting properties in energy, optics and catalysis research fields for example. In this review, we focus on the recent development of the preparation of electrospun nanomaterials integrated with functional metal sulfides with distinct nanostructures. These functional materials have been prepared via two efficient strategies, namely direct electrospinning and post-synthesis modification of electrospun nanomaterials. In this review, we systematically present the chemical and physical properties of the electrospun nanomaterials integrated with metal sulfides and their application in electronic and optoelectronic devices, sensing, catalysis, energy conversion and storage, thermal shielding, adsorption and separation, and biomedical technology. Additionally, challenges and further research opportunities in the preparation and application of these novel functional materials are also discussed.

Multienzymes activity of metals and metal oxide nanomaterials: applications from biotechnology to medicine and environmental engineering

With the rapid advancement and progress of nanotechnology, nanomaterials with enzyme-like catalytic activity have fascinated the remarkable attention of researchers, due to their low cost, high operational stability, adjustable catalytic activity, and ease of recycling and reuse. Nanozymes can catalyze the same reactions as performed by enzymes in nature. In contrast the intrinsic shortcomings of natural enzymes such as high manufacturing cost, low operational stability, production complexity, harsh catalytic conditions and difficulties of recycling, did not limit their wide applications. The broad interest in enzymatic nanomaterial relies on their outstanding properties such as stability, high activity, and rigidity to harsh environments, long-term storage and easy preparation, which make them a convenient substitute instead of the native enzyme. These abilities make the nanozymes suitable for multiple applications in sensing and imaging, tissue engineering, environmental protection, satisfactory tumor diagnostic and therapeutic, because of distinguished properties compared with other artificial enzymes such as high biocompatibility, low toxicity, size dependent catalytic activities, large surface area for further bioconjugation or modification and also smart response to external stimuli. This review summarizes and highlights latest progress in applications of metal and metal oxide nanomaterials with enzyme/multienzyme mimicking activities. We cover the applications of sensing, cancer therapy, water treatment and anti-bacterial efficacy. We also put forward the current challenges and prospects in this research area, hoping to extension of this emerging field. In addition to therapeutic potential of nanozymes for disease prevention, their practical effects in diagnostics, to monitor the presence of SARS-CoV-2 and related biomarkers for future pandemics will be predicted.

Recent advances in nanomaterials for colorimetric cancer detection

The early diagnosis of cancer can significantly improve patient survival rates. Colorimetric methods for real-time naked-eye detection have aroused growing interest owing to their low cost, simplicity, and practicability. With the rapid development of nanotechnology, compared with conventional diagnostic methods, nanomaterials with unique physical and chemical properties were applied to improve selectivity and sensitivity in colorimetric detection of cancer biomarkers, such as MUC1 aptamer conjugated PtAuNPs to specifically recognize MUC1 proteins on the cancer cell surfaces, etching of silver nanoprisms to detect prostate-specific antigen, and aggregation or dispersion of AuNPs to sense prostate cancer antigen gene 3 or glutathione, by which the limit of detection (LOD) could approach values down to a few cancer cells per mL, several fg per mL proteins, several ng of nucleic acids, or even tens of nM of organic molecules. Herein, we review the recent progress achieved in developing colorimetric nanosensors for cancer diagnosis, particularly providing an overview of the sensing principles, target biomarkers, advanced nanomaterials employed in the fabrication of sensing platforms, and strategies for improving signal sensitivity and specificity. Finally, we sum up the nanomaterial-based colorimetric cancer detection as well as existing challenges that should be resolved to extend their clinical application.

Novel strategies for degradation of aflatoxins in food and feed: A review

Aflatoxins are toxic secondary metabolites mainly produced by Aspergillus fungi, posing high carcinogenic potency in humans and animals. Dietary exposure to aflatoxins is a global problem in both developed and developing countries especially where there is poor regulation of their levels in food and feed. Thus, academics have been striving over the decades to develop effective strategies for degrading aflatoxins in food and feed. These strategies are technologically diverse and based on physical, chemical, or biological principles. This review summarizes the recent progress on novel aflatoxin degradation strategies including irradiation, cold plasma, ozone, electrolyzed oxidizing water, organic acids, natural plant extracts, microorganisms and enzymes. A clear understanding of the detoxification efficiency, mechanism of action, degradation products, application potential and current limitations of these methods is presented. In addition, the development and future perspective of nanozymes in aflatoxins degradation are introduced.

1-(2-Cyanoethyl)pyrrole enables excellent battery performance at high temperature via the synergistic effect of Lewis base and C[triple bond, length as m-dash]N functional groups

The electrolyte of a lithium ion battery is unstable and is easily decomposed at high temperature, which can lead to the degradation of battery performance. To solve this problem, herein a novel electrolyte additive 1-(2-cyanoethyl)pyrrole (CP) has been proposed to improve the electrochemical performance of LiFePO4 batteries at high temperature. The capacity retention of the battery with 1 wt% CP is 76.7%, while that of the battery without the additive is 38.1% after 200 cycles at 60 °C. Theoretical calculation results reveal that the binding energy of CP and PF5/HF is much higher than that of the solvents in the electrolyte. Surface analysis of the electrodes demonstrates that CP can reduce the decomposition of the electrolyte, and restrain the dissolution of transition metals in the electrolyte at high temperature. TEM/XPS results indicate that CP can modify the protective film on the surface of the cathode material and promote the formation of more regular and thinner CEI films. The promotion of the CP additive is of great significance for improving the high temperature performance of lithium ion batteries and is expected to be applied on a large scale.

Fe(III) bipyridyl or phenanthroline complexes with oxidase-like activity for sensitive colorimetric detection of glutathione

In this study, three types of Fe(III) bipyridyl or phenanthroline (Fe(III)-L₃ ) complex could directly catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to induce blue chromogenic changes without H₂ O₂ . Fe(III)-L₃ complex could induce a colour change in TMB directly after a short incubation time. Due to the high oxidase-like activity of the Fe(III)-L₃ complexes, superoxide anion radicals (O₂ ^•- ) were formed in solution. Intermediates radical involving oxo-iron species were then produced that oxidized TMB to its oxidation products (oxTMB), which had an absorbance maximum at 652 nm. Glutathione (GSH) could inhibit the oxidation reaction of the Fe(III)-L₃ complex-TMB system, a rapidly colorimetric method was established for the specific detection of GSH that had a detection limit of 0.1 μM. Furthermore, Fe(III)-L₃ complexes could catalyze TMB to oxTMB directly without H₂ O₂ . This fast and simple colorimetric method may open a new avenue for application in the point-of-care diagnosis field using the TMB chromogenic system.

Anodic hydrazine electrooxidation boosted overall water electrolysis by bifunctional porous nickel phosphide nanotubes on nickel foam

Water electrolysis is an environmentally friendly and sustainable technique for ultra-pure hydrogen production, while expensive electrode materials and high driving voltage have seriously hindered its commercialization process. Here, Earth-abundant bifunctional porous Ni2P hollow nanotubes on nickel foam (Ni2P-HNTs/NF) electrocatalysts are synthesized through a facile self-template method and a phosphating process, which are perfectly combined with the hydrazine electrooxidation reaction (HzOR) boosted water electrolysis. Benefiting from the unique structural characteristic of open-framework and abundant step atoms, Ni2P-HNTs/NF achieves 10 mA cm-2 at 91 mV (vs. RHE) for the cathodic hydrogen evolution reaction and 18 mV (vs. RHE) for the anodic HzOR in a three electrode system, respectively. The corresponding two-electrode hydrazine electrolyzer produces 10 mA cm-2 with a total voltage of only 152 mV for ultra-pure hydrogen production, highlighting a cost-effective and energy-saving water electrolysis mode.

CoSe2 hollow microspheres with superior oxidase-like activity for ultrasensitive colorimetric biosensing

As one of the transition metal dichalcogenide, CoSe₂ has received much attention because of its superior physicochemical properties. In this work, a self-templated approach was proposed for constructing CoSe₂ hollow microspheres by utilizing ZIF-67 hollow sphere as a template. In the followed selenylation process, selenium vapor reacts with cobalt ion in ZIF-67 to form CoSe₂ microspheres. The obtained CoSe₂ microspheres retain the cavity of the ZIF-67 and massive uniformly dispersed CoSe₂ nanoparticles are embedded throughout carbon walls. The hollow interior and porous structure of CoSe₂ microspheres provide an enhanced surface-volume ratio and short charge/mass transfer distance. The CoSe₂ microspheres show a typical oxidase-like property able to promote 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by dissolved oxygen to produce an intensive color reaction. Reactive oxygen species trials demonstrate that ·OH, ¹O₂ and O₂^•- radicals coexist in the TMB-CoSe₂ system. Based on its inhibitive role, a rapid and ultrasensitive determination of glutathione was reached, showing four orders of magnitude linear range from 0.005 to 10 μM and a limit of detection of 4.62 nM (S/N = 3). The assay has been successfully used to glutathione determination in practical samples.

Facile synthesis of covalent organic framework derived Fe-COFs composites as a peroxidase-mimicking artificial enzyme

An artificial catalyst (Fe-COFs) with peroxidase-like activity was successfully synthesized at room temperature and applied to catalyze the reaction between TMB and H₂O₂. This catalytic system can be used not only to detect residual hydrogen peroxide (H₂O₂) in milk efficiently, but also to degrade rhodamine B (RhB) in waste water.

Nanozymes: A New Disease Imaging Strategy

Nanozymes are nanomaterials with intrinsic enzyme-like properties. They can specifically catalyze substrates of natural enzymes under physiological condition with similar catalytic mechanism and kinetics. Compared to natural enzymes, nanozymes exhibit the unique advantages including high catalytic activity, low cost, high stability, easy mass production, and tunable activity. In addition, as a new type of artificial enzymes, nanozymes not only have the enzyme-like catalytic activity, but also exhibit the unique physicochemical properties of nanomaterials, such as photothermal properties, superparamagnetism, and fluorescence, etc. By combining the unique physicochemical properties and enzyme-like catalytic activities, nanozymes have been widely developed for in vitro detection and in vivo disease monitoring and treatment. Here we mainly summarized the applications of nanozymes for disease imaging and detection to explore their potential application in disease diagnosis and precision medicine.

Self-template synthesis of defect-rich NiO nanotubes as efficient electrocatalysts for methanol oxidation reaction

Developing robust and inexpensive non-noble metal based anode electrocatalysts is highly desirable for alkaline direct methanol fuel cells (ADMFCs). Herein, we successfully develop a facile self-template synthetic strategy for gram-grade porous NiO nanotubes (NTs) by pyrolyzing a nanorod-like Ni-dimethylglyoxime complex. The pyrolysis temperature highly correlates with the morphology and crystallinity of NiO NTs. The optimal NiO NTs exhibit a large electrochemically active surface area, a fast catalytic kinetics, and a small charge transfer resistance, which induce an outstanding electrocatalytic activity for the methanol oxidation reaction (MOR). Compared with conventional NiO nanoparticles, NiO NTs achieve a 11.5-fold increase in mass activity at 1.5 V for the MOR due to nanotubal morphology and abundant non-vacancy defects on the NiO NT surface. Moreover, NiO NTs have a higher electrocatalytic activity for the intermediates of the MOR (such as formaldehyde and formate) than conventional NiO nanoparticles, which also contribute to MOR activity enhancement. Given the facile synthesis and enhanced electrocatalytic performance, NiO NTs may be promising anode electrocatalysts for ADMFCs.

Selectively monitoring glutathione in human serum and growth-associated living cells using gold nanoclusters

Glutathione (GSH) plays a variety of vital functions in biological systems. Growth-associated change of GSH level in cells might be critical for cell survival and monitoring of GSH in living cells are of great significance for understanding the dynamic link between GSH and some diseases. In this work, chitason micelles templated gold nanoclusters (CM-Au NCs) emitting red fluorescence were prepared with a simple and rapid method, which shows interesting phenomenon of aggregation induced emission (AIE) affected by the size of the chitosan micelles. The unique CM-Au NCs can be used to develop turn-off fluorescent probe for detecting GSH in human serum and living cells based on the reverse process of AIE of CM-Au NCs, completely different from the principle of aggregation caused quenching (ACQ) effect, which can distinguish GSH from other biothiols (cysteine and homocysteine) and quantitatively detect GSH concentration of human serum in healthy people and cancer patients with high sensitivity. The practical application of fluorescent CM-Au NCs for cellular imaging and detecting GSH level indicates ultra-trace changes of GSH levels in normal and cancer cells could be monitored at different growth stages, which reveals that the levels of GSH in cancer cells was always higher than that of normal cells. Compared with commercial GSH assay kits for detection GSH in human serum and living cells, the proposed method was verified to be accuracy and precision. The results not only reflect the changes of GSH during cell growth at different stages, but also demonstrate the feasibility of reverse process of AIE of CM-Au NCs for detection GSH. This strategy would provide a platform to understand the dynamic link between GSH and disease to clarify the disease mechanism.

A neoteric sandwich-configurational composite film offering synchronous conductive aeolotropy, superparamagnetism and dual-color fluorescence

A new type of two-dimensional (2D) sandwich-configurational composite film offering electrically conductive aeolotropism, superparamagnetism and dual-color fluorescence was successfully fabricated via electrospinning. The composite film consists of a [polyaniline (PANI)/polymethylmethacrylate (PMMA)]//[Eu(BA)₃phen/PMMA] Janus nanobelt array aeolotropic conductive-fluorescent layer (first layer), a Fe₃O₄/polyvinylpyrrolidone (PVP) superparamagnetic nanofibers layer (second layer) and a Tb(BA)₃phen/polyacrylonitrile (PAN) fluorescent nanofiber layer (third layer), which have been tightly bonded together to form a sandwich-configurational composite film with trifunctionality. Because of the exceptive sandwich-like structure, electrically conductive, superparamagnetic, and fluorescent substances are mutually and efficaciously segregated. Thus, reciprocally pernicious interferences among them can be thoroughly avoided; thus, the sandwich-configurational composite film coinstantaneously possesses superior conductive aeolotropism, fluorescence and magnetism tri-functionality. Thus, the aeolotropic conductive-fluorescent layer and fluorescent layer respectively exhibit excellent red and green fluorescence properties. Further, the conductive aeolotropism and superparamagnetism of the composite film can be severally adjusted via regulating the contents of PANI and Fe₃O₄ NPs. Owing to the peculiar nanostructure made of Janus nanobelts in the aeolotropic conductive-fluorescent layer, the conduction ratio reaches 10⁸ times between conductive and insulating directions of the sandwich-configurational composite film. Under the excitation of 290 nm ultraviolet light, prominent red emission at 615 nm can be clearly observed in the aeolotropic conductive-fluorescent layer. Additionally, major green emission at 545 nm can be observed in the fluorescent layer under 314 nm light excitation. Furthermore, due to the exceptional sandwich structure, the properties of each layer of the whole film are relatively independent, the fluorescence intensities of the aeolotropic conductive-fluorescent layer and the fluorescent layer are hardly affected by the magnetic variation of the superparamagnetic layer, and the fluorescence intensity of the fluorescent layer is not influenced by the modulation of the PANI content of the aeolotropic conductive-fluorescent layer. The neoteric sandwich-configurational composite film with concurrent trifunctionality constructed by a facile method has potential applications in many fields. Overall, the academic design and manufacturing means will provide support for the design and construction of new-typed aeolotropic conductive films with multifunctionality.

Ultrathin NiS/Ni(OH)2 Nanosheets Filled within Ammonium Polyacrylate-Functionalized Polypyrrole Nanotubes as an Unique Nanoconfined System for Nonenzymatic Glucose Sensors

Ultrathin two-dimensional NiS/Ni(OH)₂ nanosheets (NiS/Ni(OH)₂ NSs) were successfully filled within the hollow interiors of ammonium polyacrylate-functionalized polypyrrole nanotubes (NH₄PA/PPyNTs) by a simple solvothermal method. This kind of novel hierarchical nanostructures with typical structural features of a nanoconfined system, denoted by NiS/Ni(OH)₂/NH₄PA/PPyNTs, were prepared by two main sections: polyacrylic acid (PAA) was first polymerized on PPyNTs containing vinyl groups, and the obtained PAA/PPyNTs exhibited a typical Janus structure, whose external surface was covered with carboxyl groups and the internal surface was still covered with PPy chains; second, Ni²⁺ ions as a precursor were facilely combined with -NH- segments in PPy chains by the coordination interaction under the solvothermal environment; therefore, NiS/Ni(OH)₂ NSs (<1 nm) were well distributed on the internal surface of NH₄PA/PPyNTs by the in situ growth. Because of the synergistic effects of ionizable NH₄PA, PPy with good conductivity, NiS and Ni(OH)₂ with electrocatalytical activity, as well as the nanoconfinement effect, the obtained NiS/Ni(OH)₂@NH₄PA/PPyNTs exhibited excellent electrocatalytic performance for detecting glucose. Sufficiently thin shells composed of ionizable NH₄PA and good conductive PPyNTs can not only promote the electronic transmission effectively during the electrochemical detection of glucose but also hardly limit the transport of glucose and products. In addition, ultrathin NiS/Ni(OH)₂ NSs may further enhance the electrocatalytic performance for glucose because of the more exposed active sites with the large surface area. Therefore, NiS/Ni(OH)₂@NH₄PA/PPyNTs can be applied as a good electrode material with stability and sensitivity for building a nonenzymatic glucose sensor.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

An efficient thin-walled Pd/polypyrrole hybrid nanotube biocatalyst for sensitive detection of ascorbic acid

Controllable fabrication of novel and uniform noble metal nanoparticles on a specific support with a superior catalytic or electrocatalytic performance is of significantly importance for practical applications. In this report, we demonstrated an effective way to fabricate uniform thin-walled Pd/polypyrrole (PPy) hollow nanotubes. The prepared Pd/PPy hybrid nanotubes exhibited an excellent peroxidase-like activity to oxidize a typical peroxidase substrate such as 3,3',5,5'-tetramethylbenzidine in comparison with traditional Pd/C and Pd black catalysts. The outstanding catalytic activity of the Pd/PPy hybrid nanotubes for peroxidase mimicking could be resulting from their unique hollow characteristic and an interfacial effect between PPy and Pd components. Based on the favorable catalytic property of the Pd/PPy hybrid nanotubes, a convenient and rapid colorimetric way to sensitively determine ascorbic acid has been presented. The detection limit was around 0.062 μM and an excellent selectivity was also achieved. The developed detection system in this study could be extended to the fields of bioscience and biotechnology with promising prospects.

Flexible sandwich-shaped composite film with simultaneous double electrically conductive anisotropy, magnetism and dual-color fluorescence

Flexible sandwich-shaped composite film with simultaneous double electrically conductive anisotropy, magnetism and dual-color fluorescence was successfully constructed via electrospinning.

Janus nanofiber array pellicle: facile conjugate electrospinning construction, structure and bifunctionality of enhanced green fluorescence and adjustable magnetism

A [Fe₃O₄/polyvinyl pyrrolidone (PVP)]//[Tb(BA)₃phen/PVP] Janus nanofiber array pellicle (denoted JNAP) was successfully constructed by facile conjugate electrospinning without twisting for the first time. The JNAP offers the dual-functionality of fluorescence and magnetism. This technology entirely solves the dilemma of the magnetic spinning dope and fluorescent spinning dope being easily mixed together during the parallel electrospinning process, as it achieves complete segregation of magnetic nanoparticles and fluorescent molecules. Moreover, conjugate electrospinning without twisting has fewer requirements on the viscosity of the spinning dope compared with parallel electrospinning, in which the two spinning dopes should have the same viscosity. It was satisfactorily found that the JNAP has higher fluorescence intensity than the corresponding non-aligned Janus nanofiber pellicle. The magnetism of the JNAP could be tailored by changing the doping amount of the Fe₃O₄ NPs. The JNAP has potential applications in nanotechnology and biomedicine, etc., due to its enhanced green fluorescence and adjustable magnetism. In addition, this design concept and manufacturing process provide a facile way for preparing other one-dimensional Janus nanomaterials with multifunctionality.

A [Fe₃O₄/PVP]//[Tb(BA)₃phen/PVP] Janus nanofiber array pellicle with enhanced green fluorescence and adjustable magnetism dual-functionality was constructed via facile conjugate electrospinning.

Simulated enzyme inhibition-based strategy for ultrasensitive colorimetric biothiol detection based on nanoperoxidases

A simulated enzyme inhibition-based strategy based on a nanoperoxidase mimic was adopted for ultrasensitive colorimetric glutathione detection.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Advanced electrospun nanomaterials for highly efficient electrocatalysis

We highlight the recent developments of electrospun nanomaterials with controlled morphology, composition and architecture for highly efficient electrocatalysis.

Functional nanomaterials with unique enzyme-like characteristics for sensing applications

We highlight the recent developments in functional nanomaterials with unique enzyme-like characteristics for sensing applications.

Porous biochar composite assembled with ternary needle-like iron-manganese-sulphur hybrids for high-efficiency lead removal

Hierarchical porous biochar derived from corn straw containing ternary needle-like iron-manganese-sulphur composites (Fe-Mn-S@HCS) are fabricated, and their physicochemical characteristics and performance for Pb removal were examined in detail. Introduction of Mn (transition metal) into Fe-biochar composites can effectively alter the chemical state of Fe; simultaneous doping with S can enhance cation exchange for Pb removal. High uptake of Pb by Fe-Mn-S@HCS in a short time period was observed with the adsorption capacity of 181.5 mg g^-1 and the pseudo-second-order rate constant of 0.075 g mg^-1 h^-1. Complexation, reduction, and precipitation were found to be involved in the Pb removal by Fe-Mn-S@HCS based on the results of HRTEM, XPS, and XRD analyses. This study demonstrated the feasibility of Fe-Mn-S biochar composites for high-efficiency Pb removal from aqueous solution.

Co3O4 nanocrystals as an efficient catalase mimic for the colorimetric detection of glutathione

Co₃O₄ nanocrystals with ultrasmall size, excellent stability and catalytic activity were used as an efficient catalase mimic.

Assembling exceptionally-structured Janus nanoribbons into a highly anisotropic electrically conductive array film that exhibits red fluorescence and superparamagnetism

Exceptive-structured Janus nanoribbons and their array films demonstrating high conductive anisotropism, improved red fluorescence and superparamagnetism were constructed via electrospinning.