Preparation of Two-Dimensional Pd@Ir Nanosheets and Application in Bacterial Infection Treatment by the Generation of Reactive Oxygen Species

Multifunctional nanozymatic biosensors: Awareness, regulation and pathogenic bacteria detection

It is estimated that approximately 700,000 fatalities occur annually due to infections attributed to various pathogens, which are capable of dissemination via multiple environmental vectors, including air, water, and soil. Consequently, there is an urgent need to enhance and refine rapid detection technologies for pathogens to prevent and control the spread of associated diseases. This review focuses on applying nanozymes in constructing biosensors, particularly their advancement in detecting pathogenic bacteria. Nanozymes, which are nanomaterials exhibiting enzyme-like activity, combine unique magnetic, optical, and electronic properties with structural diversity. This blend of characteristics makes them highly appealing for use in biocatalytic applications. Moreover, their nanoscale dimensions facilitate effective contact with pathogenic bacteria, leading to efficient detection and antibacterial effects. This article briefly summarizes the development, classification, and strategies for regulating the catalytic activity of nanozymes. It primarily focuses on recent advancements in constructing biosensors that utilize nanozymes as probes for sensitively detecting pathogenic bacteria. The discussion covers the development of various optical and electrochemical biosensors, including colorimetric, fluorescence, surface-enhanced Raman scattering (SERS), and electrochemical methods. These approaches provide a reliable solution for the sensitive detection of pathogenic bacteria. Finally, the challenges and future development directions of nanozymes in pathogen detection are discussed.

Iron-based nanozymes induced ferroptosis for tumor therapy

Iron-based nanozymes are an emerging class of nanomaterials demonstrating significant potential in tumor therapy by inducing ferroptosis-a regulated form of cell death marked by iron-mediated lipid peroxidation (LPO). These nanozymes exhibit unique enzymatic activities, including peroxidase, oxidase, and glutathione oxidase-like functions, enabling them to generate reactive oxygen species (ROS) and disrupt tumor microenvironment homeostasis. Leveraging Fenton chemistry, iron-based nanozymes amplify oxidative stress within tumor cells, thereby overcoming therapeutic challenges such as drug resistance and nonspecific toxicity. Despite significant advancements, the precise mechanisms by which iron-based nanozymes influence ferroptosis and their therapeutic efficacy remain underexplored. This review systematically categorizes these iron-based nanozymes, including iron oxides, single-atom enzymes, and metal-organic frameworks. We further elucidate their mechanisms in enhancing ferroptosis, focusing on their structural attributes, ROS generation pathways, and their enzymatic activities. Additionally, we summarized their biochemical applications alongside challenges in biosafety, nanozyme specificity, and advanced design and analysis approaches essential for maximizing their therapeutic efficacy.

Fabrication of a hierarchical PtIr@Rh hollow trimetallic nanozyme with a higher specific activity than that of HRP for sensitive colorimetric detection

Nanozymes have emerged as promising alternatives to natural enzymes in various fields, owing to their advantages in terms of stability, cost-effectiveness, and multifunctionality. However, their relatively low catalytic activity compared to natural enzymes remains a major challenge for practical applications. Here, we developed hierarchical PtIr@Rh hollow trimetallic nanorods, where Rh served as the substrate and the surface was decorated with numerous Pt nanoparticles doped with a small amount of Ir. The resulting nanorods exhibited remarkable peroxidase-like activity, with a specific activity of 2287 U mg-1, surpassing that of horseradish peroxidase (HRP). Additionally, the maximum reaction velocity (Vmax) was 1.024 × 10-6 M s-1, and the Michaelis-Menten constant (Km) was 1.706 mM. The enhanced catalytic performance was attributed to the unique hierarchical structure and the small amount of Ir doping, as supported by density functional theory (DFT) calculations. The PtIr@Rh nanozyme was successfully applied for the colorimetric detection of L-ascorbic acid, achieving a rapid detection with a limit of detection (LOD) of 0.12 μM. This study introduces a novel nanozyme with superior specific activity compared to natural enzymes, highlighting its potential for colorimetric sensing applications.

Rational Design of Nanozymes for Engineered Cascade Catalytic Cancer Therapy

Nanozymes have shown significant potential in cancer catalytic therapy by strategically catalyzing tumor-associated substances and metabolites into toxic reactive oxygen species (ROS) in situ, thereby inducing oxidative stress and promoting cancer cell death. However, within the complex tumor microenvironment (TME), the rational design of nanozymes and factors like activity, reaction substrates, and the TME itself significantly influence the efficiency of ROS generation. To address these limitations, recent research has focused on exploring the factors that affect activity and developing nanozyme-based cascade catalytic systems, which can trigger two or more cascade catalytic processes within tumors, thereby producing more therapeutic substances and achieving efficient and stable cancer therapy with minimal side effects. This area has shown remarkable progress. This Perspective provides a comprehensive overview of nanozymes, covering their classification and fundamentals. The regulation of nanozyme activity and efficient strategies of rational design are discussed in detail. Furthermore, representative paradigms for the successful construction of cascade catalytic systems for cancer treatment are summarized with a focus on revealing the underlying catalytic mechanisms. Finally, we address the current challenges and future prospects for the development of nanozyme-based cascade catalytic systems in biomedical applications.

Exploration of uricase-like activity in Pd@Ir nanosheets and their application in relieving acute gout using self-cascade reaction

Gout, marked by the deposition of sodium urate crystals in joints and peripheral tissues, presents a considerable health challenge. Recent research has shown a growing interest in nanozyme-based treatments for gout. However, literature on nanozymes that combine uricase-like (UOX) activity for uric acid (UA) degradation with catalase (CAT)-like activity for H2O2 elimination through a self-cascade reaction is limited. Herein, we discovered that two-dimensional Pd@Ir nanosheets (NSs) exhibit UOX and CAT activities effectively. Notably, we observed a size-dependent effect of Pd@Ir on activation energy during UA degradation, with the larger Pd@Ir NSs demonstrating a lower energy barrier. The 46-nm Pd@Ir had activation energy as low as 35.9 kJ/mol, surpassing the efficiency of natural bacterial uricase and most reported nanozymes. Through a tandem self-cascade reaction of Pd@Ir, UA was effectively degraded via UOX activity, while the byproduct H2O2 was simultaneously eliminated by CAT-like activity. Cell experiments revealed that Pd@Ir protect normal cells from oxidative stress and promote cell proliferation, demonstrating an excellent self-cascade effect. Additionally, Pd@Ir substantially alleviated gout symptoms in monosodium urate-induced acute gout mice without causing toxic effects on biological organs and tissues. This study opens new avenues for using nanozyme-based cascade reaction systems in the treatment of metabolic diseases.

Electronic structure modulation of ultrathin PtRuMoCoNi high-entropy alloy nanowires for boosting peroxidase-like activity and sensitive colorimetric determination of isoniazid and hydrazine

Self-supported ultrathin PtRuMoCoNi high-entropy alloy nanowires (HEANWs) were synthesized by a one-pot co-reduction method, whose peroxidase (POD)-like activity and catalytic mechanism were elaborated in detail. As expected, the PtRuMoCoNi HEANWs showed excellent POD-like activity. It can quickly catalyze the oxidization of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue OXTMB through decomposition of H2O2 to superoxide radicals. Notably, isoniazid and hydrazine effectively scavenge the as-produced superoxide radicals and reduce the blue OXTMB, showing high reduction ability and antioxidant property. Thus, the PtRuMoCoNi HEANW-derived colorimetric method was developed for determination of isoniazid and hydrazine, which exhibited the linear ranges of 1.5 to 50 μM and 25 to 200 μM coupled with the lower detection limits of 2.3 and 12.6 μM for isoniazid and hydrazine, respectively. The excellent analytical performance mainly results from the synergistic catalytic effect of the multiple metals and distinctive ultra-thin nanowires. This work provides a simple and rapid colorimetric method for the determination of isoniazid and hydrazine in actual samples.

A review on Pd-M bimetallic electrochemical sensors: Techniques, performance, and applications

Environmental pollution, food safety, and medical diagnostics pose severe threats to human health, making the development of effective detection technologies crucial. Electrochemical sensors, as an efficient detection method, are extensively employed in detecting environmental pollutants, food additives, and biomolecules. Pd-M bimetallic materials, known for their excellent electrocatalytic performance, are extensively utilized as electrode modification materials. Although earlier reviews have covered the sensing applications of bimetallic materials, they have not targeted discussed Pd-based bimetallic materials. This paper systematically summarizes the preparation methods of Pd-M bimetallic materials, explores their structural and morphological regulation, and elaborates on their recent applications in pesticide detection, environmental pollutant detection, food additive detection, drug detection, and biosensing. It enumerates the detection performance of various Pd-M bimetallic material-modified electrochemical sensors for the aforementioned analytes in detail, including specific modification materials, linear range, detection limits, and sensitivity parameters.

Cerium oxide-modified Pd nanosheets encapsulated by red blood cell membranes for high-efficiency RONS scavenging in depression treatment

Depression, a common and high-morbidity mental illness, can cause severe physical and psychiatric disorder. Recently, elevated levels of reactive oxygen and nitrogen species (RONS) have been recognized as a potential pathogenesis of depression. Unfortunately, available therapies provide limited outcomes in treating RONS-related depression symptoms. In addition, the low blood-brain barrier (BBB) penetration efficiency of some drugs is another major barrier to depression treatment. This study developed cerium oxide-modified Pd (Pd-CeO2) nanosheets with outstanding antioxidant activities for depression therapy. Under physiological conditions, Pd-CeO2 exhibited significant O2˙- and H2O2 clearance through their superoxide dismutase (SOD) and catalase (CAT) activities. Meanwhile, Pd-CeO2 also displayed the ability to scavenge ˙OH and reactive nitrogen radicals (RNS). What's more, when incorporated with biocompatible red blood cell (RBC) membranes, Pd-CeO2@RBC could overcome the BBB and protect brain tissues from oxidative damage caused by RONS. As a result, Pd-CeO2@RBC therapy reduced the proliferation of microglia and astrocytes and alleviated neuroinflammation and depression-like behaviors. This research not only provides a novel strategy for the effective treatment of depression, but also paves the way for new therapeutic options of nanozymes in neurological disorders.

Ultrasmall gold-encapsulated mesoporous platinum to promote photodynamic/catalytic therapy through cascade enzyme-like reactions

Mesoporous platinum (mPt) nanozyme possessed enzyme-like property of catalase (CAT) and peroxidase (POD), but the insufficient hydrogen peroxide (H2O2) concentration severely restricted its application in photodynamic therapy (PDT) and catalytic therapy. Herein, by depositing ultrasmall gold nanoparticles (AuNPs) and modifying photosensitizer IR808, a multifunctional nanozyme (mPt@Au-IR808) was designed to promote PDT/catalytic therapy through cascade enzyme-like reactions of glucose oxidase (GOx) and CAT/POD. In tumor microenvironment, the CAT-like oxygen (O2) generation improved the PDT efficacy, and the POD-like hydroxyl radical (·OH) generation achieved endogenous catalytic therapy. Using the GOx/CAT-like activities and endogenous H2O2, the yields of singlet oxygen and ·OH were significantly promoted. Furthermore, mPt@Au-IR808 showed higher photothermal conversion efficiency (41.2%) than mPt (36.1%). By combining the photothermal therapy and enhanced PDT/catalytic therapy, the developed mPt@Au-IR808 nanozyme showed excellent anti-tumor efficacy, which will be promising as cascade nanozyme to promote photo/catalytic therapy.

A low iridium content greatly improves the peroxidase-like activity of noble metal nanozymes for sensitive colorimetric detection

The enzyme-like activity of noble metal nanomaterials has been widely demonstrated. However, as an important noble metal, iridium (Ir) and its alloy nanomaterials have been less studied, particularly regarding the effect of Ir content on enzyme-like activity. Here, we demonstrated for the first time that a low Ir content can greatly improve the peroxidase-like activity of Pt-based nanozymes. When the weight percentage of Ir was 3.45% in trimetallic PtAuIr hollow nanorods (HNRs) and 2.86% in bimetallic PtIr HNRs, their specific activity increased by approximately 70% compared to their PtAu and Pt counterparts, respectively. However, a slightly higher percentage of Ir significantly diminished the enhancement effect on their specific activity. Density functional theory (DFT) calculations show that the rate-determining step (RDS) energy barrier of the nanozyme with low Ir content is lower than that of the nanozyme with slightly higher Ir content. Furthermore, we studied the kinetic properties of the PtAuIr nanozyme using TMB as the substrate. Its Michaelis-Menten constant (Km) and Vmax were 1.756 mM and 2.152 × 10-6 M s-1, respectively. Additionally, a colorimetric detection platform based on the PtAuIr nanozyme was established and applied to detect o-phenylenediamine (OPD), with a detection limit as low as 0.076 μM. This study highlights the important role of the Ir content in Pt-based nanozymes and demonstrates that PtAuIr nanozymes have potential applications in environmental detection.

Breaking the pH Limitation of Nanozymes: Mechanisms, Methods, and Applications

Although nanozymes have drawn great attention over the past decade, the activities of peroxidase-like, oxidase-like, and catalase-like nanozymes are often pH dependent with elusive mechanism, which largely restricts their application. Therefore, a systematical discussion on the pH-related catalytic mechanisms of nanozymes together with the methods to overcome this limitation is in need. In this review, various nanozymes exhibiting pH-dependent catalytic activities are collected and the root causes for their pH dependence are comprehensively analyzed. Subsequently, regulatory concepts including catalytic environment reconstruction and direct catalytic activity improvement to break this pH restriction are summarized. Moreover, applications of pH-independent nanozymes in sensing, disease therapy, and pollutant degradation are overviewed. Finally, current challenges and future opportunities on the development of pH-independent nanozymes are suggested. It is anticipated that this review will promote the further design of pH-independent nanozymes and broaden their application range with higher efficiency.

Structural engineering of Pt-on-Rh hollow nanorods with high-performance peroxidase-like specific activity for colorimetric detection

The preparation of nanozymes with high specific activity is highly important for various applications. However, only a few nanozymes have specific activities comparable to natural enzymes. Herein, novel Pt-on-Rh hollow nanorods (PtRh HNRs) were developed, in which surface Pt exhibited adjustable dispersity and interior Rh served as the support. The optimized PtRh HNRs demonstrated high-performance peroxidase (POD)-like activity, with a specific activity as high as 1352 U mg-1, which was 3.86 times that of their monometallic Pt counterparts. Density functional theory (DFT) calculations illustrated that the presence of Rh decreased the energy barrier of the rate-determining step. When PtRh HNRs were used as nanozymes in the colorimetric detection of hydrogen peroxide (H2O2) and ascorbic acid (AA), the limits of detection (LODs) were as low as 9.97 μM and 0.039 μM, respectively. The current work highlights a facile and powerful strategy for manufacturing nanozymes with high specific activity and demonstrates that the prepared PtRh HNRs have the potential for analysis and determination.

Sequential Regulation of Local Reactive Oxygen Species by Ir@Cu/Zn-MOF Nanoparticles for Promoting Infected Wound Healing

Most antimicrobials treat wound infections by an oxidation effect, which is induced by the generation of reactive oxygen species (ROS). However, the potential harm of the prolonged high level of ROS should not be ignored. In this study, we presented a novel cascade-reaction nanoparticle, Ir@Cu/Zn-MOF, to effectively regulate the ROS level throughout the healing progress of the infected wound. The nanoparticles consisted of a copper/zinc-modified metal-organic framework (Cu/Zn-MOF) serving as the external structure and an inner core composed of Ir-PVP NPs, which were achieved through a process known as "bionic mineralization". The released Cu2+ and Zn2+ from the shell structure contributed to the production of ROS, which acted as antimicrobial agents during the initial stage. With the disintegration of the shell, the Ir-PVP NP core was gradually released, exhibiting the property of multiple antioxidant enzyme activities, thereby playing an important role in clearing excessive ROS and alleviating oxidative stress. In a full-layer infected rat wound model, Ir@Cu/Zn-MOF nanoparticles presented exciting performance in promoting wound healing by clearing the bacteria and accelerating neovascularization as well as collagen deposition. This study provided a promising alternative for the repair of infected wounds.

Transition-Metal-Based Nanozymes: Synthesis, Mechanisms of Therapeutic Action, and Applications in Cancer Treatment

Cancer, as one of the leading causes of death worldwide, drives the advancement of cutting-edge technologies for cancer treatment. Transition-metal-based nanozymes emerge as promising therapeutic nanodrugs that provide a reference for cancer therapy. In this review, we present recent breakthrough nanozymes for cancer treatment. First, we comprehensively outline the preparation strategies involved in creating transition-metal-based nanozymes, including hydrothermal method, solvothermal method, chemical reduction method, biomimetic mineralization method, and sol-gel method. Subsequently, we elucidate the catalytic mechanisms (catalase (CAT)-like activities), peroxidase (POD)-like activities), oxidase (OXD)-like activities) and superoxide dismutase (SOD)-like activities) of transition-metal-based nanozymes along with their activity regulation strategies such as morphology control, size manipulation, modulation, composition adjustment and surface modification under environmental stimulation. Furthermore, we elaborate on the diverse applications of transition-metal-based nanozymes in anticancer therapies encompassing radiotherapy (RT), chemodynamic therapy (CDT), photodynamic therapy (PDT), photothermal therapy (PTT), sonodynamic therapy (SDT), immunotherapy, and synergistic therapy. Finally, the challenges faced by transition-metal-based nanozymes are discussed alongside future research directions. The purpose of this review is to offer scientific guidance that will enhance the clinical applications of nanozymes based on transition metals.

Advancing piezoelectric 2D nanomaterials for applications in drug delivery systems and therapeutic approaches

Precision drug delivery and multimodal synergistic therapy are crucial in treating diverse ailments, such as cancer, tissue damage, and degenerative diseases. Electrodes that emit electric pulses have proven effective in enhancing molecule release and permeability in drug delivery systems. Moreover, the physiological electrical microenvironment plays a vital role in regulating biological functions and triggering action potentials in neural and muscular tissues. Due to their unique noncentrosymmetric structures, many 2D materials exhibit outstanding piezoelectric performance, generating positive and negative charges under mechanical forces. This ability facilitates precise drug targeting and ensures high stimulus responsiveness, thereby controlling cellular destinies. Additionally, the abundant active sites within piezoelectric 2D materials facilitate efficient catalysis through piezochemical coupling, offering multimodal synergistic therapeutic strategies. However, the full potential of piezoelectric 2D nanomaterials in drug delivery system design remains underexplored due to research gaps. In this context, the current applications of piezoelectric 2D materials in disease management are summarized in this review, and the development of drug delivery systems influenced by these materials is forecast.

Core-Shell Au@Pd Bimetallic Nanozyme Mediated Mild Photothermal Therapy through Reactive Oxygen Species-Regulating Tumor Thermoresistance

Mild photothermal therapy (mPTT), which circumvents the limitations of conventional photothermal therapy, is emerging and exhibits remarkable potential in clinical applications. Nevertheless, mPTT is not able to efficiently eradicate tumors because its therapeutic efficacy is dramatically diminished by stress-induced heat shock proteins (HSP). Herein, a core-shell structured Au@Pd (AP) bimetallic nanozyme was fabricated for reactive oxygen species (ROS) augmentation-induced mPTT. The nanocatalytic AP nanozymes with photothermal conversion performance harbor multienzymatic (catalase, oxidase, and peroxidase) activities to induce ROS storm formation. The generated ROS could suppress the heat-defense response of tumor cells by cleaving HSP. Overall, our work highlights a ROS-regulating strategy to counteract hyperthermia-associated resistance in mPTT.

Transition Metal High-Entropy Nanozyme: Multi-Site Orbital Coupling Modulated High-Efficiency Peroxidase Mimics

Strong substrate affinity and high catalytic efficiency are persistently pursued to generate high-performance nanozymes. Herein, with unique surface atomic configurations and distinct d-orbital coupling features of different metal components, a class of highly efficient MnFeCoNiCu transition metal high-entropy nanozymes (HEzymes) is prepared for the first time. Density functional theory calculations demonstrate that improved d-orbital coupling between different metals increases the electron density near the Fermi energy level (EF ) and shifts the position of the overall d-band center with respect to EF , thereby boosting the efficiency of site-to-site electron transfer while also enhancing the adsorption of oxygen intermediates during catalysis. As such, the proposed HEzymes exhibit superior substrate affinities and catalytic efficiencies comparable to that of natural horseradish peroxidase (HRP). Finally, HEzymes with superb peroxidase (POD)-like activity are used in biosensing and antibacterial applications. These results suggest that HEzymes have great potential as new-generation nanozymes.

Tailoring the Surface and Composition of Nanozymes for Enhanced Bacterial Binding and Antibacterial Activity

With the advantages of diverse structures, tunable enzymatic activity, and high stability, nanozymes are widely used in medicine, chemistry, food, environment, and other fields. As an alternative to traditional antibiotics, nanozymes attract more and more attention from the scientific researchers in recent years. Developing nanozymes-based antibacterial materials opens up a new avenue for the bacterial disinfection and sterilization. In this review, the classification of nanozymes and their antibacterial mechanisms are discussed. The surface and composition of nanozymes are critical for the antibacterial efficacy, which can be tailored to enhance both the bacterial binding and the antibacterial activity. On the one hand, the surface modification of nanozymes enables binding and targeting of bacteria that improves the antibacterial performance of nanozymes including the biochemical recognition, the surface charge, and the surface topography. On the other hand, the composition of nanozymes can be modulated to achieve enhanced antibacterial performance including the single nanozyme-mediated synergistic and multiple nanozymes-mediated cascade catalytic antibacterial applications. In addition, the current challenges and future prospects of tailoring nanozymes for antibacterial applications are discussed. This review can provide insights into the design of future nanozymes-based materials for the antibacterial treatments.

Nanozyme-Mediated Catalytic Signal Amplification for Microfluidic Biosensing of Foodborne Bacteria

Early detection of foodborne bacteria is urgently needed to ensure food quality and to avoid the outbreak of foodborne bacterial diseases. Here, a kind of metal-organic framework (Zr-MOF) modified with Pt nanoparticles (Pt-PCN-224) was designed as a peroxidase-like signal amplifier for microfluidic biosensing of foodborne bacteria. Taking Escherichia coli (E. coli) O157:H7 as a model, a linear range from 2.93 × 102 to 2.93 × 108 CFU/mL and a limit of detection of 2 CFU/mL were obtained. The whole detection procedure was integrated into a single microfluidic chip. Water, milk, and cabbage samples were successfully detected, showing consistency with the results of the standard culture method. Recoveries were in the range from 90 to 110% in spiked testing. The proposed microfluidic biosensor realized the specific and sensitive detection of E. coli O157:H7 within 1 h, implying broad prospects of MOF with biomimetic enzyme activities for biosensing.

Metal-Based Nanozymes with Multienzyme-Like Activities as Therapeutic Candidates: Applications, Mechanisms, and Optimization Strategy

Most nanozymes in development for medical applications only exhibit single-enzyme-like activity, and are thus limited by insufficient catalytic activity and dysfunctionality in complex pathological microenvironments. To overcome the impediments of limited substrate availabilities and concentrations, some metal-based nanozymes may mimic two or more activities of natural enzymes to catalyze cascade reactions or to catalyze multiple substrates simultaneously, thereby amplifying catalysis. Metal-based nanozymes with multienzyme-like activities (MNMs) may adapt to dissimilar catalytic conditions to exert different enzyme-like effects. These multienzyme-like activities can synergize to realize "self-provision of the substrate," in which upstream catalysts produce substrates for downstream catalytic reactions to overcome the limitation of insufficient substrates in the microenvironment. Consequently, MNMs exert more potent antitumor, antibacterial, and anti-inflammatory effects in preclinical models. This review summarizes the cellular effects and underlying mechanisms of MNMs. Their potential medical utility and optimization strategy from the perspective of clinical requirements are also discussed, with the aim to provide a theoretical reference for the design, development, and therapeutic application of their catalytic effects.