Extensive efforts are devoted to refining metal sites for optimizing the catalytic performance of single‐atom nanozymes (SANzymes), while the contribution of the defect environment of neighboring metal sites lacks attention. Herein, an iron‐based SANzyme (Fe‐SANzyme) is rationally designed by edge‐site engineering, which intensively exposes edge‐hosted defective Fe–N4 atomic sites anchored in hierarchical mesoporous structures. The Fe‐SANzyme exhibits excellent catalase‐like activity capable of efficiently catalyzing the decomposition of H2O2 into O2 and H2O, with a catalytic kinetic KM value superior to that of natural catalase and reported nanozymes. The mechanistic studies depict that the defects introduce notable charge transfer from the Fe atom to the carbon matrix, making the central Fe more activated to strengthen the interaction with H2O2 and weaken the OO bond. By performing catalase‐like catalysis, the Fe‐SANzyme significantly scavenges reactive oxygen species (ROS) and alleviates oxidative stress, thus eliminating the pathological angiogenesis in animal models of retinal vasculopathies without affecting the repair of normal vessels. This work provides a new way to refine SANzymes by engineering the defect environment and geometric structure around metal sites, and demonstrates the potential therapeutic effects of the nanozyme on retinal vasculopathies.

Edge‐Site Engineering of Defective Fe–N4 Nanozymes with Boosted Catalase‐Like Performance for Retinal Vasculopathies

Carbon-based nanozymes: Design, catalytic mechanism, and bioapplication

Nanozymes are nanomaterials with similar catalytic activities to natural enzymes. Compared with natural enzymes, they have numerous advantages, including higher physiochemical stability, versatility, and suitability for mass production. In the past decade, the synthesis of nanozymes and their catalytic mechanisms have advanced beyond the simple replacement of natural enzymes, allowing for fascinating applications in various fields such as biosensing and disease treatment. In particular, the exploration of nanozymes as powerful toolkits in diagnostic viral testing and antiviral therapy has attracted growing attention. It can address the great challenges faced by current natural enzyme-based viral testing technologies, such as high cost and storage difficulties. Therefore, nanozyme can provide a novel nanozyme-based antiviral therapeutic regime with broader availability and generalizability that are keys to fighting a pandemic such as COVID-19. Herein, we provide a timely review of the state-of-the-art nanozymes regarding their catalytic activities, as well as a focused discussion on recent research into the use of nanozymes in viral testing and therapy. The remaining challenges and future perspectives will also be outlined. Ultimately, this review will inform readers of the current knowledge of nanozymes and inspire more innovative studies to push forward the frontier of this field. 

Exploration of nanozymes in viral diagnosis and therapy

Clinical immunotherapy of solid tumors elicits durable responses only in a minority of patients, largely due to the highly immunosuppressive tumor microenvironment (TME). Although rational combinations of vaccine adjuvants with inflammatory cytokines or immune agonists that relieve immunosuppression represent an appealing therapeutic strategy against solid tumors, there are unavoidable nonspecific toxicities due to the pleiotropy of cytokines and undesired activation of off‐target cells. Herein, a Zn2+ doped layered double hydroxide (Zn‐LDH) based immunomodulating adjuvant, which not only relieves immunosuppression but also elicits robust antitumor immunity, is reported. Peritumorally injected Zn‐LDH sustainably neutralizes acidic TME and releases abundant Zn2+, promoting a pro‐inflammatory network composed of M1‐tumor‐associated macrophages, cytotoxic T cells, and natural‐killer cells. Moreover, the Zn‐LDH internalized by tumor cells effectively disrupts endo‐/lysosomes to block autophagy and induces mitochondrial damage, and the released Zn2+ activates the cGas‐STING signaling pathway to induce immunogenic cell death, which further promotes the release of tumor‐associated antigens to induce antigen‐specific cytotoxic T lymphocytes. Unprecedentedly, merely injection of Zn‐LDH adjuvant, without using any cytotoxic inflammatory cytokines or immune agonists, significantly inhibits the growth, recurrence, and metastasis of solid tumors in mice. This study provides a rational bottom‐up design of potent adjuvant for cancer metalloimmunotherapy against solid tumors.

A Peritumorally Injected Immunomodulating Adjuvant Elicits Robust and Safe Metalloimmunotherapy against Solid Tumors

Ischemic stroke (IS) is one of the most common causes of disability and death. Thrombolysis and neuroprotection are two current major therapeutic strategies to overcome the ischemic and reperfusion damages. Here, we have designed a novel peptide-templated MnO2 nanozyme (PNzyme/MnO2 ) that integrates the thrombolytic activity of the functional peptides with the ROS scavenging ability of the nanozyme. Through the self-assembled polypeptides that contains multiple functional motifs, the novel peptide-templated nanozyme is able to bind fibrin in the thrombus, cross blood brain barrier, and finally accumulate in the ischemic neuronal tissues, where the thrombolytic motif is "switch-on" by the action of thrombin. In mice and rat IS models, the PNzyme/MnO2 prolonged blood circulation time and exhibited strong thrombolytic action, and reduced the ischemic damages in brain tissues. Moreover, this peptide-templated nanozyme also effectively inhibited the activation of astrocytes and the secretion of pro-inflammatory cytokines. These data indicated that rationally designed PNzyme/MnO2 nanozyme exerts both thrombolytic and neuroprotective actions. Giving its long half-life in the blood and ability to target brain thrombi, the biocompatible nanozyme may serve as a novel therapeutic agent to improve the efficacy and prevent secondary thrombosis during the treatment of IS. This article is protected by copyright. All rights reserved.

A Thrombin-Activated Peptide-Templated Nanozyme for Remedying Ischemic Stroke Via Thrombolytic and Neuroprotective Actions.

Early diagnosis of acute liver failure (ALF) is critical for curable treatment of patients, because most existing ALF therapies have narrow therapeutic time windows after disease onset. Reactive oxygen species (ROS), which lead to the sequential occurrences of hepatocyte necrosis and the leakage of alanine aminotransferase (ALT), represent early biomarkers of ALF. Photoacoustic imaging is emerging as a powerful tool for in vivo imaging of ROS. However, high-performance imaging probes that can boost the photoacoustic signals of the short-lived ROS of ALF are yet to be developed, and there remains a great challenge for ROS-based imaging of ALF. Herein, a ROS-sensitive nanozyme-augmented photoacoustic nanoprobe for successful in vivo imaging of ALF is presented. The deep-penetrating photoacoustic signals of the nanoprobe can be activated by the overexpressed ROS in ALF due to the synergy between nanocatalytic bubbles generation and thermoelastic expansion. Impressively, the nanozyme-augmented ROS imaging enables earlier diagnosis of ALF than the clinical ALT method, and the ROS-activated catalytic activity of nanoprobe permits timely nanocatalytic therapy of ALF. 

A ROS‐Sensitive Nanozyme‐Augmented Photoacoustic Nanoprobe for Early Diagnosis and Therapy of Acute Liver Failure

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Exploration of nanozymes in viral diagnosis and therapy

A ROS‐Sensitive Nanozyme‐Augmented Photoacoustic Nanoprobe for Early Diagnosis and Therapy of Acute Liver Failure