Recent Advances in Nanozyme Research

Single-atom catalysts with peroxidase-like activity boost gel-sol transition-based biosensing

Gel-sol transition-based biosensors are a promising and popular alternative for portable, cost-effective, and user-friendly point-of-care testing (POCT). However, the improvement of sensitivity and practicability is highly demanded. In this work, a Fe-NC single-atom catalyst (SAC) is successfully synthesized and used as a signal amplification element for highly sensitive gel-sol transition-based biosensing. The Fe-NC SAC owns excellent peroxidase-like activity of 188 U/mg due to its definite atomically active centers and maximum atomic utilization of active metal atoms. As a proof-of-concept, the Fe-NC SAC is uniformly encapsulated in gelatin hydrogel to obtain a hydrogel sensor that allows colorimetric detection of trypsin based on gel-sol transition. The gelatin hydrogel network collapses derived from the hydrolysis by trypsin, and thereby the released Fe-NC SAC leads to the colorimetric sensing process. The designed hydrogel sensor offers a low detection limit of 1 ng/mL with a range from 1 to 100 ng/mL toward trypsin detection, exhibiting excellent selectivity and sensitivity, and well-performed practical detection in human serum. This work offers a successful paradigm for designing a promising SACs-related detection strategy and paves a new way to develop high-performance gel-sol transition-based sensors and various POCT applications.

Controllable synthesis of MoS2@TiO2 nanocomposites for visual detection of dopamine secretion with highly-efficient enzymatic activity

Dopamine (DA) plays an essential role in dopaminergic neuronal behavior and disease. However, current detection methods for discriminating the secretion of DA are hampered by the limitations of the requirement for bulky instrumentation and non-intuitive signals. Herein, we have controllably and proportionately integrated molybdenum disulfide (MoS₂) with titanium dioxide (TiO₂) to prepare MoS₂@TiO₂ nanocomposites (MoS₂@TiO₂ NCs) via a facile synthesis method. MoS₂@TiO₂ NCs with a certain reactant mass ratio have shown a significant enhancement in peroxidase-like activity with superiority of the nanocomposite structure compared to single MoS₂ or natural enzyme. The method for catalyzing the decomposition of H₂O₂ by MoS₂@TiO₂ NCs and competition for hydroxyl radicals (˙OH) between the chromogenic agent and DA enable a sensitive, specific, and colorimetric DA analysis with a low detection limit of 0.194 μM and a wide linear detection range (0.8 to 100 μM). Because of the favorable detection performance, we were encouraged to explore and finally realize the visual detection of cellular DA secretion that is stimulated in a High-K⁺ neurocyte environment. Collectively, this method will provide a promising strategy for basic research in neuroscience with its portable, sensitive, and naked-eye detectable performance.

Cooperative Amplification of Au@FeCo as Mimetic Catalytic Nanozymes and Bicycled Hairpin Assembly for Ultrasensitive Electrochemical Biosensing

Exploring the cooperative amplification of peroxidase-like metal nanocomposites and cycled hairpin assembly is intriguing for sensitive bioanalysis. Herein, we report the first design of a unique electrochemical biosensor based on mimicking Au@FeCo nanozymes and bicycled hairpin assembly (BHA) for synergistic signal amplification. By loading the enzyme-like FeCo alloy in Au nanoparticles (AuNPs), the as-synthesized Au@FeCo hybrids display great improvement of electronic conductivity and active surface area and excellent mimic catalase activity to H₂O₂ decomposition into ^•OH radicals. The immobilization of Au@FeCo in an electrode sensing interface is stabilized via the resulting electrodeposition in HAuCl₄ while efficiently accelerating the electron transfer of electroactive ferrocene (Fc). Upon the immobilization of a helping hairpin (HH) via Au-S bonds, a specific DNA trigger (T*) is introduced to activate BHA operation through competitive strand displacement reactions among recognizing hairpin (RH), signaling hairpin (SH), and HH. T* and RH are rationally released to catalyze two cycles, in which the transient depletion of dsDNA intermediates rapidly drives the progressive hairpin assemblies to output more products SH·HH. Thus, the efficient amplification of Au@FeCo mimic catalase activity combined with BHA leads to a significantly increased current signal of Fc dependent on miRNA-21 analogous to T*, thereby directing the creation of a highly sensitive electrochemical biosensor having applicable potential in actual samples.

Amorphous Fe-Containing Phosphotungstates Featuring Efficient Peroxidase-like Activity at Neutral pH: Toward Portable Swabs for Pesticide Detection with Tandem Catalytic Amplification

Peroxidase-mimetic materials are intensively applied to establish multienzyme systems because of their attractive merits. However, almost all of the nanozymes explored exhibit catalytic capacity only under acidic conditions. The pH mismatch between peroxidase mimics in acidic environments and bioenzymes under neutral conditions significantly restricts the development of enzyme-nanozyme catalytic systems especially for biochemical sensing. To solve this problem, here amorphous Fe-containing phosphotungstates (Fe-PTs) featuring high peroxidase activity at neutral pH were explored to fabricate portable multienzyme biosensors for pesticide detection. The strong attraction of negatively charged Fe-PTs to positively charged substrates as well as the accelerated regeneration of Fe²⁺ by the Fe/W bimetallic redox couples was demonstrated to play important roles in endowing the material with peroxidase-like activity in physiological environments. Consequently, integrating the developed Fe-PTs with acetylcholinesterase and choline oxidase led to an enzyme-nanozyme tandem platform with good catalytic efficiency at neutral pH for organophosphorus pesticide response. Furthermore, they were immobilized onto common medical swabs to fabricate portable sensors for paraoxon detection conveniently based on smartphone sensing, showing excellent sensitivity, good anti-interference capacity, and low detection limit (0.28 ng/mL). Our contribution expands the horizon of acquiring peroxidase activity at neutral pH, and it will also open avenues to construct portable and effective biosensors for pesticides and other analytes.

Effects of Au States in Thiol-Organosilica Nanoparticles on Enzyme-like Activity for X-ray Sensitizer Application: Focus on Reactive Oxygen Species Generation in Radiotherapy

In radiotherapy, the use of Au nanoparticles (Au NPs) has been proposed to enhance cell damage by X-ray irradiation. Although the role of Au in radiotherapy is not fully understood, the catalytic activity of Au has been actively studied in the industrial field. Moreover, owing to their enzyme-like activity and high biocompatibility in vitro and in vivo, Au NPs present significant potential for biological applications. In this study, we incorporated different Au states both on the surface and embedded in thiol-organosilica (thiol-OS/Au series) to investigate the efficiency of anticancer cell activity of Au in radiotherapy. The thiol-OS/Au series comprised different Au(I)/Au(0) ratios and Au NPs, and different sizes of Au NPs were embedded in thiol-OS/Au. These thiol-OS/Au series samples were evaluated for enzyme-like activities in reactive oxygen species (ROS) generation by X-ray irradiation. Thiol-OS/Au embedded with small Au NPs (AC600/thiol-OS/Au) exhibited peroxidase (POD)-like activity under acidic conditions. This POD-like activity improved ROS generation and cytotoxicity under X-ray irradiation. Furthermore, AC600/thiol-OS/Au exhibited catalase (CAT)-like activity under basic conditions and showed no cytotoxicity toward nonirradiated cells. These results revealed the efficiency of functionalizing with small Au NPs that possess pH-controlled POD- and CAT-like activity as a radiosensitizer. We compared the suitability of using Au with different states to obtain the thiol-OS/Au series samples for application as radiosensitizers. The findings of this study will aid the design of efficacious strategies for the Au nanostructure-based radiotherapy of cancer cells.

Two-Dimensional Ultrathin CeVO4 Nanozyme: Fabricated through Non-Oxidic Material

In recent years, the synthesis of materials in lower dimensions, like two-dimensional (2D) or ultrathin crystals, with distinctive characteristics has attracted substantial scientific attention. The mixed transition metal oxides (MTMOs) nanomaterials are the promising group of materials, which have been extensively utilized for various potential applications. Most of the MTMOs were explored as three-dimensional (3D) nanospheres, nanoparticles, one-dimensional (1D) nanorods, and nanotubes. However, these materials are not well explored in 2D morphology because of the difficulties in removing tightly woven thin oxide layers or exfoliations of 2D oxide layers, which hinder the exfoliation of beneficial features of MTMO. Here, through the exfoliation via Li⁺ ion intercalation and subsequent oxidation of CeVS₃ under hydrothermal condition, we have demonstrated a novel synthetic route for the fabrication of 2D ultrathin CeVO₄ NS. The as-synthesized CeVO₄ NS exhibit adequate stability and activity in a harsh reaction environment, which gives excellent peroxidase-mimicking activity with a K _M value of 0.04 mM, noticeably better than natural peroxidase and previously reported CeVO₄ nanoparticles. We have also used this enzyme mimic activity for the efficient detection of biomolecules like glutathione with a LOD of 53 nM.

Reactive oxygen species-upregulating nanomedicines towards enhanced cancer therapy

Reactive oxygen species (ROS) play a crucial role in physiological and pathological processes, emerging as a therapeutic target in cancer. Owing to the high concentration of ROS in solid tumor tissues, ROS-based treatments, such as photodynamic therapy and chemodynamic therapy, and ROS-responsive drug delivery systems have been widely explored to powerfully and specifically suppress tumors. However, their anticancer efficacy is still hampered by the heterogeneous ROS levels, and thus comprehensively upregulating the ROS levels in tumor tissues can ensure an enhanced therapeutic effect, which can further sensitize and/or synergize with other therapies to inhibit tumor growth and metastasis. Herein, we review the recently emerging drug delivery strategies and technologies for increasing the H₂O₂, ˙OH, ¹O₂, and ˙O₂^- concentrations in cancer cells, including the efficient delivery of natural enzymes, nanozymes, small molecular biological molecules, and nanoscale Fenton-reagents and semiconductors and neutralization of intracellular antioxidant substances and localized input of mechanical and electromagnetic waves (such as ultrasound, near infrared light, microwaves, and X-rays). The applications of these ROS-upregulating nanosystems in enhancing and synergizing cancer therapies including chemotherapy, chemodynamic therapy, phototherapy, and immunotherapy are surveyed. In addition, we discuss the challenges of ROS-upregulating systems and the prospects for future studies.

Smart Biomimetic Nanozymes for Precise Molecular Imaging: Application and Challenges

New nanotechnologies for imaging molecules are widely being applied to visualize the expression of specific molecules (e.g., ions, biomarkers) for disease diagnosis. Among various nanoplatforms, nanozymes, which exhibit enzyme-like catalytic activities in vivo, have gained tremendously increasing attention in molecular imaging due to their unique properties such as diverse enzyme-mimicking activities, excellent biocompatibility, ease of surface tenability, and low cost. In addition, by integrating different nanoparticles with superparamagnetic, photoacoustic, fluorescence, and photothermal properties, the nanoenzymes are able to increase the imaging sensitivity and accuracy for better understanding the complexity and the biological process of disease. Moreover, these functions encourage the utilization of nanozymes as therapeutic agents to assist in treatment. In this review, we focus on the applications of nanozymes in molecular imaging and discuss the use of peroxidase (POD), oxidase (OXD), catalase (CAT), and superoxide dismutase (SOD) with different imaging modalities. Further, the applications of nanozymes for cancer treatment, bacterial infection, and inflammation image-guided therapy are discussed. Overall, this review aims to provide a complete reference for research in the interdisciplinary fields of nanotechnology and molecular imaging to promote the advancement and clinical translation of novel biomimetic nanozymes.

The Integration of Nanomedicine with Traditional Chinese Medicine: Drug Delivery of Natural Products and Other Opportunities

The integration of progressive technologies such as nanomedicine with the use of natural products from traditional medicine (TM) provides a unique opportunity for the longed-for harmonization between traditional and modern medicine. Although several actions have been initiated decades ago, a disparity of reasons including some misunderstandings between each other limits the possibilities of a truly complementation. Herein, we analyze some common challenges between nanomedicine and traditional Chinese medicine (TCM). These challenges, if solved in a consensual way, can give a boost to such harmonization. Nanomedicine is a recently born technology, while TCM has been used by the Chinese people for thousands of years. However, for these disciplines, the regulation and standardization of many of the protocols, especially related to the toxicity and safety, regulatory aspects, and manufacturing procedures, are under discussion. Besides, both TCM and nanomedicine still need to achieve a wider social acceptance. Herein, we first briefly discuss the strengths and weaknesses of TCM. This analysis serves to focus afterward on the aspects where TCM and nanomedicine can mutually help to bridge the existing gaps between TCM and Western modern medicine. As discussed, many of these challenges can be applied to TM in general. Finally, recent successful cases in scientific literature that merge TCM and nanomedicine are reviewed as examples of the benefits of this harmonization.

Switchable ROS Scavenger/Generator for MRI-Guided Anti-Inflammation and Anti-Tumor Therapy with Enhanced Therapeutic Efficacy and Reduced Side Effects

Photosensitizer in photodynamic therapy (PDT)  accumulates in both tumor and adjacent normal tissue due to low selective biodistribution, results in undesirable side effect with limited clinic application. Herein, an intelligent nanoplatform is reported that selectively acts as reactive oxygen species (ROS) scavenger in normal tissue but as ROS generator in tumor microenvironment (TME) to differentially control ROS level in tumor and surrounding normal tissue during PDT. By down-regulating the produced ROS with dampened cytokine wave in normal tissue after PDT, the nanoplatform reduces the inflammatory response of normal tissue in PDT, minimizing the side effect and tumor metastasis in PDT. Alternatively, the nanoplatform switches from ROS scavenger to generator through the glutathione (GSH) responsive degradation in TME, which effectively improves the PDT efficacy with reduced GSH level and amplified oxidative stress in tumor. Simultaneously, the released Mn ions provide real-time and in situ signal change of magnetic resonance imaging (MRI) to monitor the reversal process of catalysis activity and achieve accurate tumor diagnosis. This TME-responsive ROS scavenger/generator with activable MRI contrast may provide a new dimension for design of next-generation PDT agents with precise diagnosis, high therapeutic efficacy, and low side effect.

Biomimetic Prussian blue nanozymes with enhanced bone marrow-targeting for treatment of radiation-induced hematopoietic injury

There is an urgent medical need to develop effective therapies that can ameliorate damage to the radiation-exposed hematopoietic system. Nanozymes with robust antioxidant properties have a therapeutic potential for mitigating radiation-induced hematopoietic injury. However, enhancing nanozyme recruitment to injured tissues in vivo while maintaining their catalytic activity remains a great challenge. Herein, we present the design and preparation of a biomimetic nanoparticle, a mesenchymal stem cell membrane camouflaged Prussian blue nanozyme (PB@MSCM), which exhibits biocompatible surface properties and demonstrates enhanced injury site-targeting towards the irradiated murine bone marrow niche. Notably, the constructed PB@MSCM possessed redox enzyme-mimic catalytic activity and could scavenge overproduced reactive oxygen species in the irradiated bone marrow cells, both in vitro and ex vivo. More importantly, the administration of PB@MSCM significantly mitigated hematopoietic cell apoptosis and accelerated the regeneration of hematopoietic stem and progenitor cells. Our findings provide a new targeted strategy to improve nanozyme therapy in vivo and mitigate radiation-induced hematopoietic injury.

Maneuvering the Peroxidase-Like Activity of Palladium-Based Nanozymes by Alloying with Oxophilic Bismuth for Biosensing

Engineering the catalytic performance of nanozymes is of vital importance for their broad applications in biological analysis, cancer treatment, and environmental management. Herein, a strategy to boost the peroxidase-like activity of Pd-based nanozymes with oxophilic metallic bismuth (Bi) is demonstrated, which is based on the incorporation of oxophilic Bi in the Pd-based alloy nanocrystals (NCs). To synthesize PdBi alloy NCs, a seed-mediated method is employed with the assistance of underpotential deposition (UPD) of Bi on Pd. The strong interaction of Bi atoms with Pd surfaces favors the formation of alloy structures with controllable shapes and excellent monodispersity. More importantly, the PdBi NCs show excellent peroxidase-like activities compared with pristine Pd NCs. The structure-function correlations for the PdBi nanozymes are elucidated, and an indirect colorimetric method based on cascade reactions to determine alkaline phosphatase (ALP) is established. This method has good linear range, low detection limit, excellent selectivity, and anti-interference. Collectively, this work not only provides new insights for the design of high-efficiency nanozymes, expands the colorimetric sensing platform based on enzyme cascade reactions, but also represents a new example for UPD-directed synthesis of alloy NCs.

Dual-Enzyme Cascade Composed of Chitosan Coated FeS2 Nanozyme and Glucose Oxidase for Sensitive Glucose Detection

Immobilizing enzymes with nanozymes to catalyze cascade reactions overcomes many of the shortcomings of biological enzymes in industrial manufacturing. In the study, glucose oxidases were covalently bound to FeS₂ nanozymes as immobilization carriers while chitosan encapsulation increased the activity and stability of the immobilized enzymes. The immobilized enzymes exhibited a 10% greater increase in catalytic efficiency than the free enzymes while also being more stable and catalytically active in environments with an alkaline pH of 9.0 and a high temperature of 100 °C. Additionally, the FeS₂ nanozyme-driven double-enzyme cascade reaction showed high glucose selectivity, even in the presence of lactose, dopamine, and uric acid, with a limit of detection (LOD) (S/N = 3) as low as 1.9 × 10^-6 M. This research demonstrates that nanozymes may be employed as ideal carriers for biological enzymes and that the nanozymes can catalyze cascade reactions together with natural enzymes, offering new insights into interactions between natural and synthetic biosystems.

In situ synthesized nanozyme for photoacoustic-imaging-guided photothermal therapy and tumor hypoxia relief

Nanozymes have attracted extensive research interest due to their ideal enzymatic catalytic performance; however, uncontrollable activities and nonspecific accumulation limit their further clinical application. To overcome these obstacles, we proposed in situ synthesized nanozyme, and realized the concept through an intelligent nanosystem (ISSzyme) based on Prussian blue (PB) precursor. PB nanozyme was synthesized at the tumor sites through the interaction of ISSzyme with glutathione, which was demonstrated by comparing with conventional PB nanozyme. ISSzyme is capable of tumor-specific photoacoustic imaging (PAI) and photothermal therapy (PTT), reducing the false-positive signals of PAI and the treatment side effects of PTT. ISSzyme has catalase-like activities, resulting in tumor hypoxia relief and metastasis inhibition. More importantly, the in situ synthesized PB nanozyme has the favorable property of minimal liver accumulation. Considering the above advantages, ISSzyme is expected to shed light on the design of the next-generation artificial enzymes, with many new biomedical applications.

Magnetic RuCo aerogels with enhanced peroxidase-like activity by regulation of boron and oxygen vacancies for colorimetric biosensing applications

Metallic aerogels (MAs) are self-supported porous nanomaterials with excellent catalytic activity, which could be a promising candidate for high-performance nanozymes. The interface regulation by heteroatom and vacancies is an effective strategy for boosting the enzyme-mimicking activity. Herein, magnetic RuCo aerogels with doping of boron and oxygen vacancies were prepared by a one-pot spontaneous NaBH₄ gelation method under a low temperature. The three-dimensional network structure with high specific surface area and interlinked pores of RuCo aerogels afford abundant active sites to facilitate the interaction with substrates. Moreover, the monolithic structure avoided conventional aggregation, thus enhancing stability during catalysis. Introducing elemtal boron and oxygen vacancies adjusted the electronic structure of RuCo aerogels to achieve enhanced enzyme-like performances. It is found that the RuCo aerogel nanozyme can mimic nature peroxidase, demonstrating their viable applications in the bioassay of H₂O₂ and glucose. The constructed glucose sensor possesses acceptable sensitivity and stability with a linear range of 0.002 ~ 5 mM and a low detection limit (1.66 μM). This work provides insights into the rational design of advanced nanozymes and paves the avenue for the applications of metallic aerogels in the bioassay field. A boron-doped RuCo bimetallic aerogel with rich oxygen vacancies was prepared by a facile self-assembly method under an ice bath. The unique physical and electronic structure of RuCo aerogel results in the improvement of the intrinsic peroxidaselike activity, and thus, a sensitive and robust colorimetric glucose sensor could be developed.

Latest advances in biomimetic nanomaterials for diagnosis and treatment of cardiovascular disease

Cardiovascular disease remains one of the leading causes of death in China, with increasingly serious negative effects on people and society. Despite significant advances in preventing and treating cardiovascular diseases, such as atrial fibrillation/flutter and heart failure over the last few years, much more remains to be done. Therefore, developing innovative methods for identifying and managing cardiovascular disorders is critical. Nanomaterials provide multiple benefits in biomedicine, primarily better catalytic activity, drug loading, targeting, and imaging. Biomimetic materials and nanoparticles are specially combined to synthesize biomimetic nanoparticles that successfully reduce the nanoparticles' toxicity and immunogenicity while enhancing histocompatibility. Additionally, the biological targeting capability of nanoparticles facilitates the diagnosis and therapy of cardiovascular disease. Nowadays, nanomedicine still faces numerous challenges, which necessitates creating nanoparticles that are highly selective, toxic-free, and better clinically applicable. This study reviews the scientific accomplishments in this field over the past few years covering the classification, applications, and prospects of noble metal biomimetic nanozymes and biomimetic nanocarriers.

Aptamer-Functionalized Ce4+-Ion-Modified C-Dots: Peroxidase Mimicking Aptananozymes for the Oxidation of Dopamine and Cytotoxic Effects toward Cancer Cells

Aptamer-functionalized Ce⁴⁺-ion-modified C-dots act as catalytic hybrid systems, aptananozymes, catalyzing the H₂O₂ oxidation of dopamine. A series of aptananozymes functionalized with different configurations of the dopamine binding aptamer, DBA, are introduced. All aptananozymes reveal substantially enhanced catalytic activities as compared to the separated Ce⁴⁺-ion-modified C-dots and aptamer constituents, and structure-catalytic functions between the structure and binding modes of the aptamers linked to the C-dots are demonstrated. The enhanced catalytic functions of the aptananozymes are attributed to the aptamer-induced concentration of the reaction substrates in spatial proximity to the Ce⁴⁺-ion-modified C-dots catalytic sites. The oxidation processes driven by the Ce⁴⁺-ion-modified C-dots involve the formation of reactive oxygen species (^•OH radicals). Accordingly, Ce⁴⁺-ion-modified C-dots with the AS1411 aptamer or MUC1 aptamer, recognizing specific biomarkers associated with cancer cells, are employed as targeted catalytic agents for chemodynamic treatment of cancer cells. Treatment of MDA-MB-231 breast cancer cells and MCF-10A epithelial breast cells, as control, with the AS1411 aptamer- or MUC1 aptamer-modified Ce⁴⁺-ion-modified C-dots reveals selective cytotoxicity toward the cancer cells. In vivo experiments reveal that the aptamer-functionalized nanoparticles inhibit MDA-MB-231 tumor growth.

Zwitterionic Sulfhydryl Sulfobetaine Stabilized Platinum Nanoparticles for Enhanced Dopamine Detection and Antitumor Ability

Herein, three kinds of molecules were used to modify the surface of platinum nanoparticles (Pt NPs) to tune their surface charge. Zwitterionic thiol-functionalized sulfobetaine (SH-SB) stabilized Pt NPs (SH-SB/Pt NPs) had the highest oxidase activity and peroxidase activity in the prepared platinum nanozymes due to the generation of reactive oxygen species. In addition, a colorimetric dopamine detection method was established based on the peroxidase activity of SH-SB/Pt NPs. This method had a wide range (0-120 μM), a low detection limit (0.244 μM), and high specificity. More importantly, SH-SB/Pt NPs displayed little hemolysis and good stability in the presence of proteins. SH-SB/Pt NPs demonstrated high cytotoxicity in vitro and good antitumor ability in vivo, which was attributed to the photothermal conversion ability of SH-SB/Pt NPs and the generation of reactive oxygen species in the acidic environment. The surface modification of nanozymes using zwitterionic molecules opens a new method to improve the catalytic activity and antitumor ability of nanozymes.

Introducing Nanozymes: New Horizons in Periodontal and Dental Implant Care

The prevalence of periodontal and peri-implant diseases has been increasing worldwide and has gained a lot of attention. As multifunctional nanomaterials with enzyme-like activity, nanozymes have earned a place in the biomedical field. In periodontics and implantology, nanozymes have contributed greatly to research on maintaining periodontal health and improving implant success rates. To highlight this progress, we review nanozymes for antimicrobial therapy, anti-inflammatory therapy, tissue regeneration promotion, and synergistic effects in periodontal and peri-implant diseases. The future prospects of nanozymes in periodontology and implantology are also discussed along with challenges.

Glucose Oxidase-Integrated Metal-Polyphenolic Network as a Microenvironment-Activated Cascade Nanozyme for Hyperglycemic Wound Disinfection

The high systemic blood glucose concentration of hyperglycemic wound microenvironment (WME) severely impedes the disinfection and healing of infected skin wounds. Herein, a WME-activated smart natural product, integrated GOx-GA-Fe nanozyme (GGFzyme), is engineered, which combines a nanozyme and natural enzyme to promote reactive oxygen species (ROS) generation in situ for hyperglycemic wound disinfection. GGFzyme can consume a high concentration of glucose in hyperglycemia wounds and generate H₂O₂. The conversion of glucose into gluconic acid not avails starvation treatment but reduces the pH of WME to elevate the catalytic activities of both the nanozyme (GA-Fe) and natural enzyme (GOx). And H₂O₂ is then high efficiently catalyzed into ^•OH and O₂^•- in situ to combat pathogenic bacteria and promote wound disinfection. The high catalytic antibacterial capacity and superior biosafety, combined with beneficial WME modulation, demonstrate that GGFzyme is a promising therapeutic agent for hyperglycemic wounds.

Switchable Nanozyme Activity of Porphyrins Intercalated in Layered Gadolinium Hydroxide

In this study, organo-inorganic nanohybrids LHGd-MTSPP with enzyme-like activity were prepared by in situ intercalation of anionic 5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin and its complexes with Zn(II) and Pd(II) (MTSPP, M = 2H, Zn(II) and Pd(II)) into gadolinium layered hydroxide (LHGd). The combination of powder XRD, CHNS analysis, FT-IR, EDX, and TG confirmed the layered structure of the reaction products. The basal interplanar distances in LHGd-MTSPP samples were 22.3-22.6 Å, corresponding to the size of an intercalated tetrapyrrole molecule. According to SEM data, LHGd-MTSPP hybrids consisted of individual lamellar nanoparticles 20-50 nm in thickness. The enzyme-like activity of individual constituents, LHGd-Cl and sulfoporphyrins TSPP, ZnTSPP and PdTSPP, and hybrid LHGd-MTSPP materials, was studied by chemiluminescence analysis using the ABAP/luminol system in phosphate buffer solution. All the individual porphyrins exhibited dose-dependent antioxidant properties with respect to alkylperoxyl radicals at pH 7.4. The intercalation of free base TSPP porphyrin into the LHGd preserved the radical scavenging properties of the product. Conversely, in LHGd-MTSPP samples containing Zn(II) and Pd(II) complexes, the antioxidant properties of the porphyrins changed to dose-dependent prooxidant activity. Thus, an efficient approach to the design and synthesis of advanced LHGd-MTSPP materials with switchable enzyme-like activity was developed.

Recent Advances in Nanomaterial-Based Sensing for Food Safety Analysis

The increasing public attention on unceasing food safety incidents prompts the requirements of analytical techniques with high sensitivity, reliability, and reproducibility to timely prevent food safety incidents occurring. Food analysis is critically important for the health of both animals and human beings. Due to their unique physical and chemical properties, nanomaterials provide more opportunities for food quality and safety control. To date, nanomaterials have been widely used in the construction of sensors and biosensors to achieve more accurate, fast, and selective food safety detection. Here, various nanomaterial-based sensors for food analysis are outlined, including optical and electrochemical sensors. The discussion mainly involves the basic sensing principles, current strategies, and novel designs. Additionally, given the trend towards portable devices, various smartphone sensor-based point-of-care (POC) devices for home care testing are discussed.

2D Co3O4 modified by IrO2 nanozyme for convenient detection of aqueous Fe2+ and intercellular H2O2

A portable sensor for visual monitoring of Fe²⁺ and H₂O₂, two-dimensional Co₃O₄ modified by nano-IrO₂ (IrO₂@2D Co₃O₄) was prepared in this work, for the first time, with the help of microwave radiation at 140 °C, which was further stabilized onto common test strips. The present IrO₂@2D Co₃O₄ possessed superior dual-function enzyme-like activity with low toxicity and excellent biocompatibility. Especially, trace Fe²⁺ and H₂O₂ could exclusively alter their enzyme-like catalytic activity with discriminating hyperchromic or hypochromic effect, i.e., from blue to colorless or to dark blue for both IrO₂@2D Co₃O₄ dispersion and its functionalized test strips. The linear regression equations were A₆₅₂ = 0.5940 - 0.00041 c_Fe²⁺ (10^-8 M, R² = 0.9927) for Fe²⁺ and ∆A₆₅₂ = 0.0023 c_H2O2 + 0.00025 (10^-7 M, R² = 0.9982) for H₂O₂, respectively. When applied to visual monitoring of aqueous Fe²⁺ and intercellular H₂O₂, the recoveries were 101.2 ~ 102.5% and 95.8 ~ 103.7% with detection limits of 1.25 × 10^-8 mol/L and 1.02 × 10^-7 mol/L, respectively, far below the permitted values in drinking water set by the World Health Organization. The mechanisms for the enhancing enzyme-mimetic activity of IrO₂@2D Co₃O₄ and its selective responses to Fe²⁺ and H₂O₂ were investigated in detail.

Progress and prospects of nanozymes for enhanced antitumor therapy

Nanozymes are nanomaterials with mimicked enzymatic activity, whose catalytic activity can be designed by changing their physical parameters and chemical composition. With the development of biomedical and material science, artificially created nanozymes have high biocompatibility and can catalyze specific biochemical reactions under biological conditions, thus playing a vital role in regulating physiological activities. Under pathological conditions, natural enzymes are limited in their catalytic capacity by the varying reaction conditions. In contrast, compared to natural enzymes, nanozymes have advantages such as high stability, simplicity of modification, targeting ability, and versatility. As a result, the novel role of nanozymes in medicine, especially in tumor therapy, is gaining increasing attention. In this review, function and application of various nanozymes in the treatment of cancer are summarized. Future exploration paths of nanozymes in cancer therapies based on new insights arising from recent research are outlined.

Penetration and translocation of functional inorganic nanomaterials into biological barriers

With excellent physicochemical properties, inorganic nanomaterials (INMs) have exhibited a series of attractive applications in biomedical fields. Biological barriers prevent successful delivery of nanomedicine in living systems that limits the development of nanomedicine especially for sufficient delivery of drugs and effective therapy. Numerous researches have focused on overcoming these biological barriers and homogeneity of organisms to enhance therapeutic efficacy, however, most of these strategies fail to resolve these challenges. In this review, we present the latest progress about how INMs interact with biological barriers and penetrate these barriers. We also summarize that both native structure and components of biological barriers and physicochemical properties of INMs contributed to the penetration capacity. Knowledge about the relationship between INMs structure and penetration capacity will guide the design and application of functional and efficient nanomedicine in the future.

Mo@ZIF-8 nanozyme preparation and its antibacterial property evaluation

Types of nanozymes can produce free radicals and/or reactive oxygen species (ROS) to serve as broad spectrum antibacterial materials. Developing nanozyme-based antibacterial materials with good biocompatibility exhibits promising application prospects. In this study, we doped Mo to ZIF-8 (both components have good biocompatibility) to prepare a new nanozyme, Mo@ZIF-8, which can produce hydroxyl radicals (•OH) triggered by a low dosage of hydrogen peroxide (H₂O₂), exhibiting effective antibacterial capability against both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). This work provides a reference for the design of antibacterial nanozymes with good biocompatibility.

Recent Progress in Nanotechnology-Based Approaches for Food Monitoring

Throughout the food supply chain, including production, storage, and distribution, food can be contaminated by harmful chemicals and microorganisms, resulting in a severe threat to human health. In recent years, the rapid advancement and development of nanotechnology proposed revolutionary solutions to solve several problems in scientific and industrial areas, including food monitoring. Nanotechnology can be incorporated into chemical and biological sensors to improve analytical performance, such as response time, sensitivity, selectivity, reliability, and accuracy. Based on the characteristics of the contaminants and the detection methods, nanotechnology can be applied in different ways in order to improve conventional techniques. Nanomaterials such as nanoparticles, nanorods, nanosheets, nanocomposites, nanotubes, and nanowires provide various functions for the immobilization and labeling of contaminants in electrochemical and optical detection. This review summarizes the recent advances in nanotechnology for detecting chemical and biological contaminations in the food supply chain.

Aptamer-Modified Au Nanoparticles: Functional Nanozyme Bioreactors for Cascaded Catalysis and Catalysts for Chemodynamic Treatment of Cancer Cells

Polyadenine-stabilized Au nanoparticles (pA-AuNPs) reveal dual nanozyme catalytic activities toward the H₂O₂-mediated oxidation of dopamine to aminochrome and toward the aerobic oxidation of glucose to gluconic acid and H₂O₂. The conjugation of a dopamine-binding aptamer (DBA) to the pA-AuNPs yields aptananozyme structures catalyzing simultaneously the H₂O₂-mediated oxidation of dopamine to aminochrome through the aerobic oxidation of glucose. A set of aptananozymes consisting of DBA conjugated through the 5'- or 3'-end directly or spacer bridges to pA-AuNPs were synthesized. The set of aptananozymes revealed enhanced catalytic activities toward the H₂O₂-catalyzed oxidation of dopamine to dopachrome, as compared to the separated pA-AuNPs and DBA constituents, and structure-function relationships within the series of aptananozymes were demonstrated. The enhanced catalytic function of the aptananozymes was attributed to the concentration of the dopamine at the catalytic interfaces by means of aptamer-dopamine complexes. The dual catalytic activities of aptananozymes were further applied to design bioreactors catalyzing the effective aerobic oxidation of dopamine in the presence of glucose. Mechanistic studies demonstrated that the aptananozymes generate reactive oxygen species. Accordingly, the AS1411 aptamer, recognizing the nucleolin receptor associated with cancer cells, was conjugated to the pA-AuNPs, yielding a nanozyme for the chemodynamic treatment of cancer cells. The AS1411 aptamer targets the aptananozyme to the cancer cells and facilitates the selective permeation of the nanozyme into the cells. Selective cytotoxicity toward MDA-MB-231 breast cancer cells (ca. 70% cell death) as compared to MCF-10A epithelial cells (ca. 2% cell death) is demonstrated.

Reductive damage induced autophagy inhibition for tumor therapy

Numerous therapeutic anti-tumor strategies have been developed in recent decades. However, their therapeutic efficacy is reduced by the intrinsic protective autophagy of tumors. Autophagy plays a key role in tumorigenesis and tumor treatment, in which the overproduction of reactive oxygen species (ROS) is recognized as the direct cause of protective autophagy. Only a few molecules have been employed as autophagy inhibitors in tumor therapy to reduce protective autophagy. Among them, hydroxychloroquine is the most commonly used autophagy inhibitor in clinics, but it is severely limited by its high therapeutic dose, significant toxicity, poor reversal efficacy, and nonspecific action. Herein, we demonstrate a reductive-damage strategy to enable tumor therapy by the inhibition of protective autophagy via the catalytic scavenging of ROS using porous nanorods of ceria (PN-CeO2) nanozymes as autophagy inhibitor. The antineoplastic effects of PN-CeO2 were mediated by its high reductive activity for intratumoral ROS degradation, thereby inhibiting protective autophagy and activating apoptosis by suppressing the activities of phosphatidylinositide 3-kinase/protein kinase B and p38 mitogen-activated protein kinase pathways in human cutaneous squamous cell carcinoma. Further investigation highlighted PN-CeO2 as a safe and efficient anti-tumor autophagy inhibitor. Overall, this study presents a reductive-damage strategy as a promising anti-tumor approach that catalytically inhibits autophagy and activates the intrinsic antioxidant pathways of tumor cells and also shows its potential for the therapy of other autophagy-related diseases.

Electronic Supplementary Material

Supplementary material (cellular uptake of PN-CeO2, effects of PN-CeO2 on several common malignant tumor models, viability of HaCaT cells treated with PN-CeO2 at different concentrations, time-dependent body-weight curves of SCL-1 tumor-bearing nude mice, the biodistribution of Ce element in main tissues and tumors after injection of PN-CeO2, measurement of Ce element concentration in urine and feces samples, H&E-stained images of main organs, and measurement of liver and kidney function in mice after different treatment) is available in the online version of this article at 10.1007/s12274-022-5139-z.

Aligned electrospun fiber film loaded with multi-enzyme mimetic iridium nanozymes for wound healing

A film with elaborate microstructures that offers biomimetic properties and multi functionalities is highly desired in wound healing. Here, we develop an aligned hydrogel fiber film integrated with multi-active constituents to promote wound healing. Such fiber films are designed and constructed by photo-crosslinking the methacrylate gelatin (GelMA) doped with silver nanoparticles (Ag NPs) and iridium nanoparticles coated with polyvinylpyrrolidone (PVP-Ir NPs) in the precursor solution using electrospinning. The nature of GelMA hydrogel and the aligned arrangement of nanofibers endow the film with high-water content, self-degradability, improved bionic characteristics, oriented cell growth, and improved cell proliferation and migration. Moreover, the encapsulated nanozymes and Ag NPs offer the fiber film with superior reactive oxygen species (ROS) scavenging and antibacterial capability. The infected wound model shows that the multi-active hydrogel fiber film can reduce inflammation by killing bacteria and decomposing ROS, which accelerates the growth of new blood vessels and granulation tissue. Benefitting from these features, the versatile aligned GelMA fiber film demonstrates the clinically translational potential for wound healing.

Recent advances in near-infrared-II hollow nanoplatforms for photothermal-based cancer treatment

Near-infrared-II (NIR-II, 1000–1700 nm) light-triggered photothermal therapy (PTT) has been regarded as a promising candidate for cancer treatment, but PTT alone often fails to achieve satisfactory curative outcomes. Hollow nanoplatforms prove to be attractive in the biomedical field owing to the merits including good biocompatibility, intrinsic physical-chemical nature and unique hollow structures, etc. On one hand, hollow nanoplatforms themselves can be NIR-II photothermal agents (PTAs), the cavities of which are able to carry diverse therapeutic units to realize multi-modal therapies. On the other hand, NIR-II PTAs are capable of decorating on the surface to combine with the functions of components encapsulated inside the hollow nanoplatforms for synergistic cancer treatment. Notably, PTAs generally can serve as good photoacoustic imaging (PAI) contrast agents (CAs), which means such kind of hollow nanoplatforms are also expected to be multifunctional all-in-one nanotheranostics. In this review, the recent advances of NIR-II hollow nanoplatforms for single-modal PTT, dual-modal PTT/photodynamic therapy (PDT), PTT/chemotherapy, PTT/catalytic therapy and PTT/gas therapy as well as multi-modal PTT/chemodynamic therapy (CDT)/chemotherapy, PTT/chemo/gene therapy and PTT/PDT/CDT/starvation therapy (ST)/immunotherapy are summarized for the first time. Before these, the typical synthetic strategies for hollow structures are presented, and lastly, potential challenges and perspectives related to these novel paradigms for future research and clinical translation are discussed.

Nanozymes for Regenerative Medicine

Nanozymes refer to nanomaterials that catalyze enzyme substrates into products under relevant physiological conditions following enzyme kinetics. Compared to natural enzymes, nanozymes possess the characteristics of higher stability, easier preparation, and lower cost. Importantly, nanozymes possess the magnetic, fluorescent, and electrical properties of nanomaterials, making them promising replacements for natural enzymes in industrial, biological, and medical fields. On account of the rapid development of nanozymes recently, their application potentials in regeneration medicine are gradually being explored. To highlight the achievements in the regeneration medicine field, this review summarizes the catalytic mechanism of four types of representative nanozymes. Then, the strategies to improve the biocompatibility of nanozymes are discussed. Importantly, this review covers the recent advances in nanozymes in tissue regeneration medicine including wound healing, nerve defect repair, bone regeneration, and cardiovascular disease treatment. In addition, challenges and prospects of nanozyme researches in regeneration medicine are summarized.

Precise Regulation of Iron Spin States in Single FeN4 Sites for Efficient Peroxidase-Mimicking Catalysis

The catalytic activity and selectivity of single-atom sites catalysts is strongly dependent on the supports structure and central metal coordination environment. However, the further optimization of electronic configuration to improve the catalytic performance is usually hampered by the strong coordination effect between the support and metal atoms. Herein, it is discovered that enzyme-mimicking catalytic performance can be enhanced at the fixed coordination single-atom Fe sites by regulating the Fe spin states. The X-ray absorption fine structure, ⁵⁷ Fe Mössbauer spectrum, and temperature-dependent magnetization measurements reveal that the spin states of Fe in single FeN₄  sites can be well manipulated via changing the pyrolysis temperature. The intermediate-spin Fe sites catalyst (t_2g 4 e_g 1) demonstrates a much higher peroxidase-mimicking activity in comparison with high-spin structure (t_2g 3 e_g 2). More importantly, the based enzymes system realizes sensitive detection of H₂ O₂  and glucose by colorimetric sensors with high catalytic activity and selectivity. Furthermore, theoretical calculations unveil that the intermediate-spin FeN₄  promotes the OH* desorption process, thus greatly reducing the reaction energy barrier. These findings provide a route to design highly active enzyme-mimicking catalysts and an engineering approach for regulating spin states of metal sites to enhance their catalytic performance.

Energy-Supporting Enzyme-Mimic Nanoscaffold Facilitates Tendon Regeneration Based on a Mitochondrial Protection and Microenvironment Remodeling Strategy

Tendon injury is a tricky and prevalent motor system disease, leading to compromised daily activity and disability. Insufficient regenerative capability and dysregulation of immune microenvironment are the leading causes of functional loss. First, this work identifies persistent oxidative stress and mitochondrial impairment in the regional tendon tissues postinjury. Therefore, a smart scaffold incorporating the enzyme mimicry nanoparticle-ceria nanozyme (CeNPs) into the nanofiber bundle scaffold (NBS@CeO) with porous, anisotropic, and enhanced mechanical properties is designed to innovatively explore a targeted energy-supporting repair strategy by rescuing mitochondrial function and remodeling the microenvironment favoring endogenous regeneration. The integrated CeNPs scavenge excessive reactive oxygen species (ROS), stabilize the mitochondria membrane potential (ΔΨm), and ATP synthesis of tendon-derived stem cells (TDSCs) under oxidative stress. In a rat Achilles tendon defect model, NBS@CeO reduces oxidative damage and accelerates structural regeneration of collagen fibers, manifesting as recovering mechanical properties and motor function. Furthermore, NBS@CeO mediates the rebalance of endogenous regenerative signaling and dysregulated immune microenvironment by alleviating senescence and apoptosis of TDSCs, downregulating the secretion of senescence-associated secretory phenotype (SASP), and inducing macrophage M2 polarization. This innovative strategy highlights the role of NBS@CeO in tendon repair and thus provides a potential therapeutic approach for promoting tendon regeneration.

Nanomedicine in the Face of Parkinson's Disease: From Drug Delivery Systems to Nanozymes

The complexity and overall burden of Parkinson's disease (PD) require new pharmacological approaches to counteract the symptomatology while reducing the progressive neurodegeneration of affected dopaminergic neurons. Since the pathophysiological signature of PD is characterized by the loss of physiological levels of dopamine (DA) and the misfolding and aggregation of the alpha-synuclein (α-syn) protein, new proposals seek to restore the lost DA and inhibit the progressive damage derived from pathological α-syn and its impact in terms of oxidative stress. In this line, nanomedicine (the medical application of nanotechnology) has achieved significant advances in the development of nanocarriers capable of transporting and delivering basal state DA in a controlled manner in the tissues of interest, as well as highly selective catalytic nanostructures with enzyme-like properties for the elimination of reactive oxygen species (responsible for oxidative stress) and the proteolysis of misfolded proteins. Although some of these proposals remain in their early stages, the deepening of our knowledge concerning the pathological processes of PD and the advances in nanomedicine could endow for the development of potential treatments for this still incurable condition. Therefore, in this paper, we offer: (i) a brief summary of the most recent findings concerning the physiology of motor regulation and (ii) the molecular neuropathological processes associated with PD, together with (iii) a recapitulation of the current progress in controlled DA release by nanocarriers and (iv) the design of nanozymes, catalytic nanostructures with oxidoreductase-, chaperon, and protease-like properties. Finally, we conclude by describing the prospects and knowledge gaps to overcome and consider as research into nanotherapies for PD continues, especially when clinical translations take place.

Ultrasmall Pt Nanozymes Immobilized on Spherical Polyelectrolyte Brushes with Robust Peroxidase-like Activity for Highly Sensitive Detection of Cysteine

Distinct platinum (Pt) nanozymes as peroxidase mimics have received extensive interest owing to their outstanding catalytic activity, high environmental tolerance, lower consumption, and great potential in replacing natural enzymes. However, easy agglomeration of Pt nanoparticles (Pt NPs) resulting from the high surface free energy significantly decrease their peroxidase-like activity. Herein, spherical polyelectrolyte brush (SPB)-stabilized ultrasmall Pt NPs (SPB@Pt NPs) were prepared by a novel synthetic strategy where the SPB not only performed as a nanoreactor for the synthesis of ultrasmall Pt NPs but also greatly stabilized Pt NPs against aggregation. The well-defined SPB@Pt NP nanozymes exhibited outstanding peroxidase-like activity for the catalytic oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB and were then used to establish a colorimetric sensor for rapid detection of cysteine, giving a limit of detection of 0.11 μM. Moreover, the colorimetric detection system was demonstrated with outstanding performance in sensitive and selective detection of cysteine in the presence of several interference molecules. From these results, SPB@Pt NPs have been regarded as promising peroxidase mimics for a large number of applications such as in biosensing, biomedicine, the food industry, and environmental chemistry.

A synergistic chemodynamic-photodynamic-photothermal therapy platform based on biodegradable Ce-doped MoOx nanoparticles

Near-infrared light-induced catalysts are considered to be potential nanoagents for tumor therapy. Cerium (Ce) is a non-biotoxic lanthanide element and exhibits variable valence states for catalytic reactions. In this work, we report a one-step hydrothermal synthesis for Ce-doped MoO_x (CMO) nanomaterials. The obtained CMO nanomaterials show high absorption in the NIR II regime and a high photothermal conversion efficiency of 67.7% (1064 nm). Moreover, due to the doping of Ce element, the consumption of hydrogen peroxide (H₂O₂) and glutathione (GSH) is boosted which enhances the chemodynamic and photodynamic therapy simultaneously. Under NIR II laser irradiation, the designed CMO nanocatalysts induce metabolism disruption and mitochondrial damage in the tumor cells. As-prepared CMO nanomaterials also show good biocompatibility and pH-responsive degradation behavior, which can be degraded rapidly under alkaline conditions (pH = 7.4) and remain stable in acidic solution (pH = 5.6). These properties make CMO nanomaterials ideal biodegradable nanotheranostic agents for synergistic chemodynamic-photodynamic-photothermal antitumor therapy.

One-Pot Synthesis of MnOx-SiO2 Porous Composites as Nanozymes with ROS-Scavenging Properties

The development of nanomaterials that mimic the activity of enzymes is a topic of interest, for the decomposition of reactive oxygen species (ROS). We report the preparation of a novel nanocomposite of MnO_x needles covered with SiO₂ porous material. The material was prepared in one pot with a two-step procedure. The material was characterized by EDX, SEM, TEM, XRD, nitrogen adsorption-desorption isotherms, and XPS. The synthesis protocol took advantage of the atrane method, favoring the nucleation and initial growth of manganese oxide needles that remained embedded and homogeneously dispersed in a mesoporous silica matrix. The final composite had a high concentration of Mn (Si/Mn molar ratio of ca. 1). The nanozyme presented bimodal porosity: intraparticle and interparticle association with the surfactant micelles and the gaps between silica particles and MnO_x needles, respectively. The porosity favored the migration of the reagent to the surface of the catalytic MnO_x. The nanozyme showed very efficient SOD and catalase activities, thus improving other materials previously described. The kinetics were studied in detail, and the reaction mechanisms were proposed. It was shown that silica does not play an innocent role in the case of catalase activity, increasing the reaction rate.

Fe-Doped MoS2 Nanozyme for Antibacterial Activity and Detoxification of Mustard Gas Simulant

The peroxidase-like catalytic activity of various nanozymes was extensively applied in various fields. In this study, we have demonstrated the preparation of Fe-doped MoS₂ (Fe@MoS₂) nanomaterials with enhanced peroxidase-like activity of MoS₂ in a co-catalytic pathway. In view of Fenton reaction, the peroxidase-like Fe@MoS₂ nanozyme prompted the decomposition of hydrogen peroxide (H₂O₂) to a reactive hydroxyl radical (·OH). The efficient decomposition of H₂O₂ in the presence of Fe@MoS₂ has been employed toward the antibacterial activity and detoxification of mustard gas simulant. The combined effect of Fe@MoS₂ and H₂O₂ showed remarkable antibacterial activity against the drug-resistant bacterial strain methicillin-resistant Staphylococcus aureus and Escherichia coli with the use of minimal concentration of H₂O₂. Fe@MoS₂ was further applied for the detoxification of the chemical warfare agent sulfur mustard simulant, 2-chloroethyl ethyl sulfide, by selective conversion to the nontoxic sulfoxide. This work demonstrates the development of a hybrid nanozyme and its environmental remediation from harmful chemicals to microbes.

Catalase-Like Nanozymes: Classification, Catalytic Mechanisms, and Their Applications

The field of nanozymes has developed rapidly over the past decade. Among various oxidoreductases mimics, catalase (CAT)-like nanozyme, acting as an essential part of the regulation of reactive oxygen species (ROS), has attracted extensive research interest in recent years. However, CAT-like nanozymes are not as well discussed as other nanozymes such as peroxidase (POD)-like nanozymes, etc. Compared with natural catalase or artificial CAT enzymes, CAT-like nanozymes have unique properties of low cost, size-dependent properties, high catalytic activity and stability, and easy surface modification, etc., which make them widely used in various fields, especially in tumor therapy and disease treatment. Consequently, there is a great requirement to make a systematic discussion on CAT-like nanozymes. In this review, some key aspects of CAT-like nanozymes are deeply summarized as: 1) Typical CAT-like nanozymes classified by different nanomaterials; 2) The catalytic mechanisms proposed by experimental and theoretical studies; 3) Extensive applications in regard to tumor therapy, cytoprotection and sensing. Therefore, it is prospected that this review will contribute to the further design of CAT-like nanozymes and optimize their applications with much higher efficiency than before.

Protein-Mimicking Nanoparticles in Biosystems

Proteins are essential elements for almost all life activities. The emergence of nanotechnology offers innovative strategies to create a diversity of nanoparticles (NPs) with intrinsic capacities of mimicking the functions of proteins. These artificial mimics are produced in a cost-efficient and controllable manner, with their protein-mimicking performances comparable or superior to those of natural proteins. Moreover, they can be endowed with additional functionalities that are absent in natural proteins, such as cargo loading, active targeting, membrane penetrating, and multistimuli responding. Therefore, protein-mimicking NPs have been utilized more and more often in biosystems for a wide range of applications including detection, imaging, diagnosis, and therapy. To highlight recent progress in this broad field, herein, representative protein-mimicking NPs that fall into one of the four distinct categories are summarized: mimics of enzymes (nanozymes), mimics of fluorescent proteins, NPs with high affinity binding to specific proteins or DNA sequences, and mimics of protein scaffolds. This review covers their subclassifications, characteristic features, functioning mechanisms, as well as the extensive exploitation of their great potential for biological and biomedical purposes. Finally, the challenges and prospects in future development of protein-mimicking NPs are discussed.