High Carbonization Temperature to Trigger Enzyme Mimicking Activities of Silk-Derived Nanosheets

Relay-Type Catalysis by a Dual-Metal Single-Atom System in a Waste Biomass Derivative Host for High-Rate and Durable Li-S Batteries

An environmental-friendly and sustainable carbon-based host is one of the most competitive strategies for achieving high loading and practicality of Li-S batteries. However, the polysulfide conversion reaction kinetics is still limited by the nonuniform or monofunctional catalyst configuration in the carbon host. In this work, we propose a catalysis mode based on "relay-type" co-operation by adjacent dual-metal single atoms for high-rate and durable Li-S batteries. A discarded sericin fabric-derived porous N-doped carbon with a stacked schistose structure is prepared as the high-loading sulfur (84 wt %) host by a facile ionothermal method, which further enables the uniform anchoring of Fe/Co dual-metal single atoms. This multifunctional host enables superior lithiophilic-sulfiphilic and electrocatalytic capabilities contributed by the "relay-type" single-atom modulation effects on different conversion stages of liquid polysulfides and solid Li2S2/Li2S, leading to the suppression of the "shuttle effect", alleviation of nucleation and decomposition barriers of Li2Sx, and acceleration of polysulfide conversion kinetics. The corresponding Li-S batteries exhibit a high specific capacity of 1399.0 mA h g-1, high-rate performance up to 10 C, and excellent cycling stability over 1000 cycles. They can also endure the high sulfur loading of 8.5 mg cm-2 and the lean electrolyte condition and yield an areal capacity as high as 8.6 mA h cm-2. This work evidentially demonstrates the potential of waste biomass reutilization coupled with the design of a single-atom system for practical Li-S batteries with high energy density.

Multienzyme-Like Nanozymes: Regulation, Rational Design, and Application

Nanomaterials with more than one enzyme-like activity are termed multienzymic nanozymes, and they have received increasing attention in recent years and hold huge potential to be applied in diverse fields, especially for biosensing and therapeutics. Compared to single enzyme-like nanozymes, multienzymic nanozymes offer various unique advantages, including synergistic effects, cascaded reactions, and environmentally responsive selectivity. Nevertheless, along with these merits, the catalytic mechanism and rational design of multienzymic nanozymes are more complicated and elusive as compared to single-enzymic nanozymes. In this review, the multienzymic nanozymes classification scheme based on the numbers/types of activities, the internal and external factors regulating the multienzymatic activities, the rational design based on chemical, biomimetic, and computer-aided strategies, and recent progress in applications attributed to the advantages of multicatalytic activities are systematically discussed. Finally, current challenges and future perspectives regarding the development and application of multienzymatic nanozymes are suggested. This review aims to deepen the understanding and inspire the research in multienzymic nanozymes to a greater extent.

Molybdenum Disulfide-Integrated Iron Organic Framework Hybrid Nanozyme-Based Aptasensor for Colorimetric Detection of Exosomes

Tumor-derived exosomes are considered as a potential marker in liquid biopsy for malignant tumor screening. The development of a sensitive, specific, rapid, and cost-effective detection strategy for tumor-derived exosomes is still a challenge. Herein, a visualized and easy detection method for exosomes was established based on a molybdenum disulfide nanoflower decorated iron organic framework (MoS2-MIL-101(Fe)) hybrid nanozyme-based CD63 aptamer sensor. The CD63 aptamer, which can specifically recognize and capture tumor-derived exosomes, enhanced the peroxidase activity of the hybrid nanozyme and helped to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2 system to generate a stronger colorimetric signal, with its surface modification on the hybrid nanozyme. With the existence of exosomes, CD63 aptamer recognized and adsorbed them on the surface of the nanozyme, which rescued the enhanced peroxidase activity of the aptamer-modified nanozyme, resulting in a deep-to-moderate color change in the TMB-H2O2 system where the change is visible and can be monitored with ultraviolet-visible spectroscopy. In the context of optimal circumstances, the linear range of this exosome detection method is measured to be 1.6 × 104 to 1.6 × 106 particles/μL with a limit of detection as 3.37 × 103 particles/μL. Generally, a simple and accessible approach to exosome detection is constructed, and a nanozyme-based colorimetric aptamer sensor is proposed, which sheds light on novel oncological biomarker measurements in the field of biosensors.

Using Wool Keratin Derived Metallo-Nanozymes as a Robust Antioxidant Catalyst to Scavenge Reactive Oxygen Species Generated by Smoking

Self-assembled nanostructures based on biomolecules (e.g., proteins and amino acids) and metal ions have promising applications in mimicking the nanostructure, properties, and functions of natural enzymes. Herein, a metal ion-mediated self-assembly method for constructing catalytically active Cu-wool-keratin (CuWK) two-dimensional nanozymes is presented. Specifically, by introducing copper ions as abiological cofactors, WK can serve as a protein scaffold to design and create Cu catalytic sites. The optimized hybrids with Cu-WK coordination framework exhibit significant superoxide dismutases-like activity, catalase-like activity, and hydroxyl radical scavenging ability. These combined antioxidant activities make CuWK a robust nanozyme to effectively remove various reactive oxygen species (ROS). In this work, the as-prepared CuWK as a new additive can be integrated into a cigarette filter system to effectively remove the produced ROS from the burning of tobacco. More importantly, the CuWK nanozymes as a critical element can be further utilized to construct a recycling cigarette holder. Therefore, the present work shows that nanozymes with advanced catalytic capabilities can be constructed by self-assembly of metal ions and proteins, thus facilitating the rational design and discovery of this kind of artificial metalloenzymes.

H2O2 generation enhancement by ultrasonic nebulisation with a zinc layer for spray disinfection

With the outbreak of COVID-19, microbial pollution has gained increasing attention as a threat to human health. Consequently, many research efforts are being devoted to the development of efficient disinfection methods. In this context, hydrogen peroxide (H₂O₂) stands out as a green and broad-spectrum disinfectant, which can be produced and sprayed in the air directly by cavitation in ultrasonic nebulisation. However, the yield of H₂O₂ obtained by ultrasonic nebulisation is too low to satisfy the requirements for disinfection by spraying and needs to be improved to achieve efficient disinfection of the air and objects. Herein, we report the introduction of a zinc layer into an ultrasonic nebuliser to improve the production of H₂O₂ and generate additional Zn²⁺ by self-corrosion, achieving good disinfecting performance. Specifically, a zinc layer was assembled on the oscillator plate of a commercial ultrasonic nebuliser, resulting in a 21-fold increase in the yield of H₂O₂ and the production of 4.75 μg/mL Zn²⁺ in the spraying droplets. When the generated water mist was used to treat a bottle polluted with Escherichia coli for 30 min, the sterilisation rate reached 93.53%. This ultrasonic nebulisation using a functional zinc layer successfully enhanced the production of H₂O₂ while generating Zn²⁺, providing a platform for the development of new methodologies of spray disinfection.

Engineering the Stability of Nanozyme-Catalyzed Product for Colorimetric Logic Gate Operations

Recently, the design and development of nanozyme-based logic gates have received much attention. In this work, by engineering the stability of the nanozyme-catalyzed product, we demonstrated that the chromogenic system of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) can act as a visual output signal for constructing various Boolean logic operations. Specifically, cerium oxide or ferroferric oxide-based nanozymes can catalyze the oxidation of colorless TMB to a blue color product (oxTMB). The blue-colored solution of oxTMB could become colorless by some reductants, including the reduced transition state of glucose oxidase and xanthine oxidase. As a result, by combining biocatalytic reactions, the color change of oxTMB could be controlled logically. In our logic systems, glucose oxidase, β-galactosidase, and xanthine oxidase acted as inputs, and the state of oxTMB solution was used as an output. The logic operation produced a colored solution as the readout signal, which was easily distinguished with the naked eye. More importantly, the study of such a decolorization process allows the transformation of previously designed AND and OR logic gates into NAND and NOR gates. We propose that this work may push forward the design of novel nanozyme-based biological gates and help us further understand complex physiological pathways in living systems.

Coconut-shell-derived activated carbon for NIR photo-activated synergistic photothermal-chemodynamic cancer therapy

Exploiting new non-metal-based peroxidase-mimic nanoenzymes for chemodynamic therapy (CDT) in cancer treatment is an active and challenging field. Here, we found that activated carbon nanoparticles (denoted as ANs) fabricated from coconut shell have satisfactory peroxidase-mimic nanoenzyme activity. Based on this positive result, gadodiamide, a clinically used nuclear magnetic imaging contrast agent, was loaded inside the AN pores and encapsulated by polyvinylpyrrolidone (PVP) to obtain Gd@PANs. PANs (ANs modified using PVP) efficiently catalyze the massive decomposition of endogenous hydrogen peroxide (H2O2) inside cancer cells to produce toxic oxidized hydroxyl radicals (˙OH) for the CDT treatment of cancer, but they showed no toxicity toward normal cells. Additionally, under 808 nm laser irradiation, the photothermal conversion efficiency of the PANs reaches 45.20%, ensuring their effective photothermal therapy (PTT) treatment functionality. Simultaneously, during PTT treatment, the heating effect significantly enhances the peroxidase-mimic activity of the PANs to achieve an ideal PTT-CDT synergistic therapeutic outcome. Gd@PANs can also be used for the T1-magnetic resonance imaging (MRI) of tumors to integrate treatment and diagnosis.

Carbonized zein nanosheets with intrinsic enzyme-mimicking activities and high photothermal conversion efficiency for synergistic cancer therapy

With the rapid development of biology and nanotechnology, designing nanomaterials with intrinsic enzyme-like activities has attracted huge attention in recent years. Herein, for the first time, we use zein as a new protein precursor to prepare N-rich carbonized zein nanosheets (C-Zein) via facile pyrolysis. Zein is an inert, biodegradable and sustainable natural biopolymer. After high-temperature carbonization, zein can be converted into highly catalytically active C-Zein, which can possess excellent peroxidase- and oxidase-like catalytic activities. Such intrinsic enzyme-like activities of C-Zein are closely related to its graphitization degree, the ratio of graphitic nitrogen and the formation of disordered graphene. Intriguingly, C-Zein also exhibits high photothermal conversion efficiency in the near-infrared (NIR) region. Coupling their unique photothermal and catalytic properties, the as-prepared C-Zein can act as a robust agent for synergistic photothermal-catalytic cancer treatment under the irradiation of NIR light. We expect that this work paves the way to use zein for designing efficient artificial enzymes and accelerate further growth in exploring its new biomedical and pharmaceutical applications.