Emerging Multifunctional Single-Atom Catalysts/Nanozymes

Ru single-atom nanozymes targeting ROS-ferroptosis pathways for enhanced endometrial regeneration in intrauterine adhesion therapy

Intrauterine adhesion (IUA) presents a significant challenge in gynecology, characterized by excessive fibrosis and compromised reproductive function, leading to severe infertility. Although biocompatible hydrogels integrated with stem cells offer a promising approach for IUA therapy, clinical applications remain limited. Recent studies have highlighted the role of ferroptosis and reactive oxygen species (ROS) in IUA pathogenesis, yet strategies targeting ferroptosis through antioxidant stress are underexplored. This study investigates the therapeutic effects and mechanisms of a Ru-Single-Atom Nanozyme (Ru-SAN) incorporated into chitosan hydrogel for treating IUA. Ru-SAN, which mimics the enzyme activities of catalase, superoxide dismutase, and glutathione peroxidase, effectively clears excess ROS and shows promise in treating oxidative stress-induced diseases. The results demonstrate the superior antioxidative capabilities of Ru-SAN, significantly suppressing the ROS-ferroptosis cycle at the injury site. This creates a favorable microenvironment for post-injury repair by inhibiting inflammation, enhancing mesenchymal-to-epithelial transformation, promoting angiogenesis, and polarizing M2 macrophages. Importantly, it mitigates adverse repair outcomes from inflammation and excessive collagen fiber deposition, ultimately restoring uterine glandular structures and thickness, thereby achieving the ultimate goal of restoring fertility and live birth rates. In conclusion, our study delineates a pioneering therapeutic approach leveraging the antioxidant properties of Ru-SAN to target ferroptosis, thereby offering an efficacious treatment for IUA.

Smartphone-assisted colorimetric sensor arrays based on nanozymes for high throughput identification of heavy metal ions in salmon

The rapid, precise, and high-throughput identification of multiple heavy metals ions holds immense importance in ensuring food safety and promoting public health. This study presents a novel smartphone-assisted colorimetric sensor array for the rapid and precise detection of multiple heavy metals ions. The sensor array is based on three signal recognition elements (AuPt@Fe-N-C, AuPt@N-C, and Fe-N-C) and the presence of different heavy metal ions affects the nanozymes-chromogenic substrate (TMB) catalytic color production, enabling the differentiation and quantification of various heavy metal ions. Combined with a smartphone-based RGB mode, the colorimetric sensor array can successfully identify five different heavy metal ions (Hg2+, Pb2+, Co2+, Cr6+, and Fe3+) as low as 0.5 μM and different ratios of binary and ternary mixed heavy metal ions in just 5 min. The sensor array successfully tested seawater and salmon samples with a total heavy metal content of 10 μM in the South China Sea (Haikou and Wenchang). Overall, this study highlights the potential of smartphone-assisted colorimetric sensor arrays for the rapid and precise detection of multiple heavy metal ions, which could significantly contribute to food safety and public health monitoring.

Multi-mechanism antitumor/antibacterial effects of Cu-EGCG self-assembling nanocomposite in tumor nanotherapy and drug-resistant bacterial wound infections

Chemotherapy and surgery stand as primary cancer treatments, yet the unique traits of the tumor microenvironment hinder their effectiveness. The natural compound epigallocatechin gallate (EGCG) possesses potent anti-tumor and antibacterial traits. However, the tumor's adaptability to chemotherapy due to its acidic pH and elevated glutathione (GSH) levels, coupled with the challenges posed by drug-resistant bacterial infections post-surgery, impede treatment outcomes. To address these challenges, researchers strive to explore innovative treatment strategies, such as multimodal combination therapy. This study successfully synthesized Cu-EGCG, a metal-polyphenol network, and detailly characterized it by using synchrotron radiation and high-resolution mass spectrometry (HRMS). Through chemodynamic therapy (CDT), photothermal therapy (PTT), and photodynamic therapy (PDT), Cu-EGCG showed robust antitumor and antibacterial effects. Cu+ in Cu-EGCG actively participates in a Fenton-like reaction, generating hydroxyl radicals (·OH) upon exposure to hydrogen peroxide (H2O2) and converting to Cu2+. This Cu2+ interacts with GSH, weakening the oxidative stress response of bacteria and tumor cells. Density functional theory (DFT) calculations verified Cu-EGCG's efficient GSH consumption during its reaction with GSH. Additionally, Cu-EGCG exhibited outstanding photothermal conversion when exposed to 808 nm near-infrared (NIR) radiation and produced singlet oxygen (1O2) upon laser irradiation. In both mouse tumor and wound models, Cu-EGCG showcased remarkable antitumor and antibacterial properties.

Bimetallic Single-Atom Catalysts for Water Splitting

Green hydrogen from water splitting has emerged as a critical energy vector with the potential to spearhead the global transition to a fossil fuel-independent society. The field of catalysis has been revolutionized by single-atom catalysts (SACs), which exhibit unique and intricate interactions between atomically dispersed metal atoms and their supports. Recently, bimetallic SACs (bimSACs) have garnered significant attention for leveraging the synergistic functions of two metal ions coordinated on appropriately designed supports. BimSACs offer an avenue for rich metal-metal and metal-support cooperativity, potentially addressing current limitations of SACs in effectively furnishing transformations which involve synchronous proton-electron exchanges, substrate activation with reversible redox cycles, simultaneous multi-electron transfer, regulation of spin states, tuning of electronic properties, and cyclic transition states with low activation energies. This review aims to encapsulate the growing advancements in bimSACs, with an emphasis on their pivotal role in hydrogen generation via water splitting. We subsequently delve into advanced experimental methodologies for the elaborate characterization of SACs, elucidate their electronic properties, and discuss their local coordination environment. Overall, we present comprehensive discussion on the deployment of bimSACs in both hydrogen evolution reaction and oxygen evolution reaction, the two half-reactions of the water electrolysis process.

Atomically Engineered Chlorine Coordination of Iron in Active Centers for Selectively Catalytic H2O2 Decomposition Toward Efficient Antitumor-Specific Therapy

The intervention of endogenous H2O2 via nanozymes provides a potential antitumor-specific therapy; however, the role of the nanozyme structure in relation to the selective decomposition of H2O2 to hydroxyl radicals (•OH) is yet to be fully understood, which limits the development of this therapeutic approaches. Herein, an iron single-atom nanozyme (Fe─N2Cl2─C SAzyme) is reported, which is prepared through precise Fe─Cl coordination based on the construction of a characteristic Fe-containing molecule. Fe─N2Cl2─C exhibits efficient catalytic H2O2 decomposition (2.19 × 106 mm-1 s-1), which is the highest among reported SAzymes. More importantly, it is found that H2O2 selectively decomposed into •OH on the Fe─N2Cl2─C surface, which is attributable to the d orbitals of the Fe active center matching the O-2p electrons of the adsorbed hydroxide (*OH) intermediate. Fe─N2Cl2─C is strongly cytotoxic toward a variety of cancer-cell lines in vitro but not to normal cells. Furthermore, Fe─N2Cl2─C shows an outstanding specific therapeutic effect in vivo; it efficiently destroys solid malignant tumors without injuring normal tissue. Altogether, these findings highlight the selective catalytic decomposition of H2O2 to •OH, which is achieved by engineering the active center on the atomic level, thereby providing an avenue for the development of specific nanomedicines with efficient antitumor activities.

Multi-omics analysis of Au@Pt nanozyme for the modulation of glucose and lipid metabolism

Au@Pt nanozyme, a bimetallic core-shell structure Au and Pt nanoparticle, has attracted significant attention due to its excellent catalytic activity and stability. Here, we propose that Au@Pt improves glucose tolerance and reduces TG after four weeks administration. The transcriptomic analysis of mouse liver tissues treated with Au@Pt nanozyme showed changes in genes related to glucose and lipid metabolism signaling pathways, including glycolysis/gluconeogenesis, pyruvate metabolism, PPAR signaling, and insulin signaling. Moreover, analysis of fecal samples from mice treated with Au@Pt nanozyme showed significant changes in the abundance of beneficial gut microbiota such as Dubosiella, Parvibacter, Enterorhabdus, Monoglobus, Lachnospiraceae_UCG-008, Lachnospiraceae_UCG-006, Lachnospiraceae_UCG-001, and Christensenellaceae_R-7_group. Combined multi-omics correlation analyses revealed that the modulation of glucose and lipid metabolism by Au@Pt was strongly correlated with changes in hepatic gene expression profiles as well as changes in gut microbial profiles. Overall, our integrated multi-omics analysis demonstrated that Au@Pt nanozyme could modulate glucose and lipid metabolism by regulating the expression of key genes in the liver and altering the composition of gut microbiota, providing new insights into the potential applications of Au@Pt nanozyme in the treatment of metabolic disorder.

Arginine-Rich Peptide-Rhodium Nanocluster@Reduced Graphene Oxide Composite as a Highly Selective and Active Uricase-like Nanozyme for the Degradation of Uric Acid and Inhibition of Urate Crystal

Metal nanozymes have offered attractive opportunities for biocatalysis and biomedicine. However, fabricating nanozymes simultaneously possessing highly catalytic selectivity and activity remains a great challenge due to the lack of three-dimensional (3D) architecture of the catalytic pocket in natural enzymes. Here, we integrate rhodium nanocluster (RhNC), reduced graphene oxide (rGO), and protamine (PRTM, a typical arginine-rich peptide) into a composite facilely based on the single peptide. Remarkably, the PRTM-RhNC@rGO composite displays outstanding selectivity, activity, and stability for the catalytic degradation of uric acid. The reaction rate constant of the uric acid oxidation catalyzed by the PRTM-RhNC@rGO composite is about 1.88 × 10-3 s-1 (4 μg/mL), which is 37.6 times higher than that of reported RhNP (k = 5 × 10-5 s-1, 20 μg/mL). Enzyme kinetic studies reveal that the PRTM-RhNC@rGO composite exhibits a similar affinity for uric acid as natural uricase. Furthermore, the uricase-like activity of PRTM-RhNC@rGO nanozymes remains in the presence of sulfur substances and halide ions, displaying incredibly well antipoisoning abilities. The analysis of the structure-function relationship indicates the PRTM-RhNC@rGO composite features the substrate binding site near the catalytic site in a confined space contributed by 2D rGO and PRTM, resulting in the high-performance of the composite nanozyme. Based on the outstanding uricase-like activity and the interaction of PRTM and uric acid, the PRTM-RhNC@rGO composite can retard the urate crystallization significantly. The present work provides new insights into the design of metal nanozymes with suitable binding sites near catalytic sites by mimicking pocket-like structures in natural enzymes based on simple peptides, conducing to broadening the practical application of high-performance nanozymes in biomedical fields.

Linking atomic to mesoscopic scales in multilevel structural tailoring of single-atom catalysts for peroxide activation

A key challenge in designing single-atom catalysts (SACs) with multiple and synergistic functions is to optimize their structure across different scales, as each scale determines specific material properties. We advance the concept of a comprehensive optimization of SACs across different levels of scale, from atomic, microscopic to mesoscopic scales, based on interfacial kinetics control on the coupled metal-dissolution/polymer-growth process in SAC synthesis. This approach enables us to manipulate the multilevel interior morphologies of SACs, such as highly porous, hollow, and double-shelled structures, as well as the exterior morphologies inherited from the metal oxide precursors. The atomic environment around the metal centers can be flexibly adjusted during the dynamic metal-oxide consumption and metal-polymer formation. We show the versatility of this approach using mono- or bi-metallic oxides to access SACs with rich microporosity, tunable mesoscopic structures and atomic coordinating compositions of oxygen and nitrogen in the first coordination-shell. The structures at each level collectively optimize the electronic and geometric structure of the exposed single-atom sites and lower the surface *O formation barriers for efficient and selective peroxidase-type reaction. The unique spatial geometric configuration of the edge-hosted active centers further improves substrate accessibility and substrate-to-catalyst hydrogen overflow due to tunable structural heterogeneity at mesoscopic scales. This strategy opens up new possibilities for engineering more multilevel structures and offers a unique and comprehensive perspective on the design principles of SACs.

Green synthesis of iron-doped graphene quantum dots: an efficient nanozyme for glucose sensing

Single-atom nanozymes with well-defined atomic structures and electronic coordination environments can effectively mimic the functions of natural enzymes. However, the costly and intricate preparation processes have hindered further exploration and application of these single-atom nanozymes. In this study, we presented a synthesis technique for creating Fe-N central single-atom doped graphene quantum dot (FeN/GQDs) nanozymes using a one-step solvothermal process, where individual iron atoms form strong bonds with graphene quantum dots through nitrogen coordination. Unlike previous studies, this method significantly simplifies the synthesis conditions for single-atom nanozymes, eliminating the need for high temperatures and employing environmentally friendly precursors derived from pineapple (ananas comosus) leaves. The resulting FeN/GQDs exhibited peroxidase-like catalytic activity and kinetics comparable to that of natural enzymes, efficiently converting H2O2 into hydroxyl radical species. Leveraging their excellent peroxide-like activity, FeN/GQDs nanozymes have been successfully applied to construct a colorimetric biosensor system characterized by remarkably high sensitivity for glucose detection. This achievement demonstrated a promising approach to designing single-atom nanozymes with both facile synthesis procedures and high catalytic activity, offering potential applications in wearable sensors and personalized health monitoring.

Modulating Electron Transfer between Pt and MOF Support through Pd Doping Promotes Nanozyme Catalytic Efficiency

Electron transfer is considered to be a typical parameter that affects the catalytic activity of nanozymes. However, there is still controversy regarding whether higher or lower electron transfer numbers are beneficial for improving the catalytic activity of nanozymes. To address this issue, we propose the introduction of Pd doping as an important electron regulation strategy to tune electron transfer between Pt and ZIF-8 carriers (PtxPd1@ZIF-8). We observe a volcano-shaped relationship between the electron transfer number and catalytic activity, reaching its peak at Pt4Pd1@ZIF-8. Mechanism studies indicate that as the electron transfer number from Pt to ZIF-8 carriers increases, the d-band center of the active site Pt increases, reducing the occupancy of antibonding states and enhancing the adsorption capacity of the key intermediate (*O). However, a further increase in the adsorption of *O energy makes it difficult to desorb and participate in the next reaction, thus exhibiting volcanic activity. The optimized Pt4Pd1@ZIF-8 nanozyme is applied to develop an immunoassay for the detection of zearalenone, achieving a detection limit of 0.01 μg/L, which is 6 times higher than that of the traditional enzyme-linked immunosorbent assay. This work not only reveals the potential regulatory mechanism of electron transfer on the catalytic activity of nanozymes but also improves the performance of nanozyme-based biosensors.

Selective Organ-Targeting Hafnium Oxide Nanoparticles with Multienzyme-Mimetic Activities Attenuate Radiation-Induced Tissue Damage

Radioprotective agents hold clinical promises to counteract off-target adverse effects of radiation and benefit radiotherapeutic outcomes, yet the inability to control drug transport in human organs poses a leading limitation. Based upon a validated rank-based multigene signature model, radiosensitivity indices are evaluated of diverse normal organs as a genomic predictor of radiation susceptibility. Selective ORgan-Targeting (SORT) hafnium oxide nanoparticles (HfO2 NPs) are rationally designed via modulated synthesis by α-lactalbumin, homing to top vulnerable organs. HfO2 NPs like Hensify are commonly radioenhancers, but SORT HfO2 NPs exhibit surprising radioprotective effects dictated by unfolded ligands and Hf(0)/Hf(IV) redox couples. Still, the X-ray attenuation patterns allow radiological confirmation in target organs by dual-beam spectral computed tomography. SORT HfO2 NPs present potent antioxidant activities, catalytically scavenge reactive oxygen species, and mimic multienzyme catalytic activities. Consequently, SORT NPs rescue radiation-induced DNA damage in mouse and rabbit models and provide survival benefits upon lethal exposures. In addition to inhibiting radiation-induced mitochondrial apoptosis, SORT NPs impede DNA damage and inflammation by attenuating activated FoxO, Hippo, TNF, and MAPK interactive cascades. A universal methodology is proposed to reverse radioenhancers into radioprotectors. SORT radioprotective agents with image guidance are envisioned as compelling in personalized shielding from radiation deposition.

Nanozymes with biomimetically designed properties for cancer treatment

Nanozymes, as a type of nanomaterials with enzymatic catalytic activity, have demonstrated tremendous potential in cancer treatment owing to their unique biomedical properties. However, the heterogeneity of tumors and the complex tumor microenvironment pose significant challenges to the in vivo catalytic efficacy of traditional nanozymes. Drawing inspiration from natural enzymes, scientists are now using biomimetic design to build nanozymes from the ground up. This approach aims to replicate the key characteristics of natural enzymes, including active structures, catalytic processes, and the ability to adapt to the tumor environment. This achieves selective optimization of nanozyme catalytic performance and therapeutic effects. This review takes a deep dive into the use of these biomimetically designed nanozymes in cancer treatment. It explores a range of biomimetic design strategies, from structural and process mimicry to advanced functional biomimicry. A significant focus is on tweaking the nanozyme structures to boost their catalytic performance, integrating them into complex enzyme networks similar to those in biological systems, and adjusting functions like altering tumor metabolism, reshaping the tumor environment, and enhancing drug delivery. The review also covers the applications of specially designed nanozymes in pan-cancer treatment, from catalytic therapy to improved traditional methods like chemotherapy, radiotherapy, and sonodynamic therapy, specifically analyzing the anti-tumor mechanisms of different therapeutic combination systems. Through rational design, these biomimetically designed nanozymes not only deepen the understanding of the regulatory mechanisms of nanozyme structure and performance but also adapt profoundly to tumor physiology, optimizing therapeutic effects and paving new pathways for innovative cancer treatment.

Simple and rapid determination of tartrazine in fake saffron using the metal organic framework (Fe SA MOF@CNF) by HPLC/PDA

The present study of a novel metal-organic framework containing Fe single atoms doped on electrospun carbon nanofibers (Fe SA-MOF@CNF) based on dispersive micro solid phase extraction (D-μ-SPE) using HPLC-PDA for detection tartrazine in fake saffron samples was designed. The Fe SA-MOF@CNF sorbent was extensively characterized through various techniques including N2 adsorption-desorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The specific area of surface of the sorbent was 577.384 m2/g. The study variables were optimized via the central composite design (CCD), which included a sorbent mass of 15 mg, a contact time of 6 min, a pH of 7.56, and a tartrazine concentration of 300 ng/ml. Under the optimum condition, the calibration curve of this method was linear in the range of 5-1000 ng/mL, with a correlation coefficient of 0.992. The LOD and LOQ values were ranged 0.38-0.74 and 1.34-2.42 ng/ml, respectively. This approach revealed significant improvements, including high extraction recovery (98.64), recovery rates (98.43-102.72%), and accuracy (RSDs < 0.75 to 3.6%). the enrichment factors were obtained in the range of 80.6-86.4 with preconcentration factor of 22.3. Consequently, the D-μ-SPE method based on synthesized Fe SA-MOF@CNF could be recommended as a sustainable sorbent for detecting tartrazine in saffron samples.

Building Feedback-Regulation System Through Atomic Design for Highly Active SO2 Sensing

Reasonably constructing an atomic interface is pronouncedly essential for surface-related gas-sensing reaction. Herein, we present an ingenious feedback-regulation system by changing the interactional mode between single Pt atoms and adjacent S species for high-efficiency SO2 sensing. We found that the single Pt sites on the MoS2 surface can induce easier volatilization of adjacent S species to activate the whole inert S plane. Reversely, the activated S species can provide a feedback role in tailoring the antibonding-orbital electronic occupancy state of Pt atoms, thus creating a combined system involving S vacancy-assisted single Pt sites (Pt-Vs) to synergistically improve the adsorption ability of SO2 gas molecules. Furthermore, in situ Raman, ex situ X-ray photoelectron spectroscopy testing and density functional theory analysis demonstrate the intact feedback-regulation system can expand the electron transfer path from single Pt sites to whole Pt-MoS2 supports in SO2 gas atmosphere. Equipped with wireless-sensing modules, the final Pt1-MoS2-def sensors array can further realize real-time monitoring of SO2 levels and cloud-data storage for plant growth. Such a fundamental understanding of the intrinsic link between atomic interface and sensing mechanism is thus expected to broaden the rational design of highly effective gas sensors.

Recent Trends in Bio-nanomaterials and Non-invasive Combinatorial Approaches of Photothermal Therapy against Cancer

In 2020, approximately 10 million deaths worldwide were attributed to cancer, making it the primary cause of death globally. Photothermal therapy (PTT) is one of the novel ways to treat and abolish cancer. PTT significantly impacts cancer theranostics compared to other therapies like surgery, chemotherapy, and radiotherapy due to its remarkable binding capability to tumor sites and lower invasiveness into normal healthy tissues. PTT relies on photothermal agents (PTAs), which generate heat by absorbing the near-infrared (NIR) light and destroying cancer cells. Several PTT agents remain longer in the reticuloendothelial system (RES) and induce toxicity, restricting their use in the biomedical field. To overcome this problem, the usage of biodegradable nano-photothermal agents is required. This review has discussed the PTT mechanism of action and different types of novel bio-nanomaterials used for PTT. We also focussed on the combinatorial effects of PTT with other cancer therapies and their effect on human health. The role of LED lights and mild hypothermia in PTT has been discussed briefly in this review.

Nanozyme-Engineered Hydrogels for Anti-Inflammation and Skin Regeneration

Inflammatory skin disorders can cause chronic scarring and functional impairments, posing a significant burden on patients and the healthcare system. Conventional therapies, such as corticosteroids and nonsteroidal anti-inflammatory drugs, are limited in efficacy and associated with adverse effects. Recently, nanozyme (NZ)-based hydrogels have shown great promise in addressing these challenges. NZ-based hydrogels possess unique therapeutic abilities by combining the therapeutic benefits of redox nanomaterials with enzymatic activity and the water-retaining capacity of hydrogels. The multifaceted therapeutic effects of these hydrogels include scavenging reactive oxygen species and other inflammatory mediators modulating immune responses toward a pro-regenerative environment and enhancing regenerative potential by triggering cell migration and differentiation. This review highlights the current state of the art in NZ-engineered hydrogels (NZ@hydrogels) for anti-inflammatory and skin regeneration applications. It also discusses the underlying chemo-mechano-biological mechanisms behind their effectiveness. Additionally, the challenges and future directions in this ground, particularly their clinical translation, are addressed. The insights provided in this review can aid in the design and engineering of novel NZ-based hydrogels, offering new possibilities for targeted and personalized skin-care therapies.

Perspectives for the Role of Single-Atom Nanozymes in Assisting Food Safety Inspection and Food Nutrition Evaluation

Single-atom nanozymes (SAzymes) have been greatly developed for rapid detection, owing to their rich active sites and excellent catalytic activity. Although several excellent reviews concentrating on SAzymes have been reported, they mainly focused on advanced synthesis, sensing mechanisms, and biomedical applications. To date, few reviews elaborate on the promising applications of SAzymes in food safety inspection and food nutrition evaluation. In this paper, we systematically reviewed the enzyme-like activity of SAzymes and the catalytic mechanism, in addition to recent research advances of SAzymes in the domain of food safety inspection and food nutrition evaluation in the past few years. Furthermore, current challenges hampering practical applications of SAzymes in food assay are summarized and analyzed, and possible research areas focusing on SAzyme-based sensors in rapid food testing are also proposed.

Nanocarriers in topical photodynamic therapy

INTRODUCTION

Photodynamic therapy (PDT) has gained significant attention due to its superiority over conventional treatments. In the context of skin cancers and nonmalignant skin diseases, topical application of photosensitizer formulations onto affected skin, followed by illumination, offers distinct advantages. Topical PDT simplifies therapy by providing easy access to the skin, increasing drug concentration within the target area, and confining residual photosensitivity to the treated skin. However, the effectiveness of topical PDT is often hindered by challenges such as limited skin penetration or photosensitizer instability. Additionally, the hypoxic tumor environment poses further limitations. Nanocarriers present a promising solution to address these challenges.

AREAS COVERED

The objective of this review is to comprehensively explore and highlight the role of various nanocarriers in advancing topical PDT for the treatment of skin diseases. The primary focus is to address the challenges associated with conventional topical PDT approaches and demonstrate how nanotechnology-based strategies can overcome these challenges, thereby improving the overall efficiency and efficacy of PDT.

EXPERT OPINION

Nanotechnology has revolutionized the field of PDT, offering innovative tools to combat the unfavorable features of photosensitizers and hurdles in PDT. Nanocarriers enhance skin penetration and stability of photosensitizers, provide controlled drug release, reduce needed dose, increase production of reactive oxygen species, while reducing side effects, thereby improving PDT effectiveness.

Single-atom nanozymes with peroxidase-like activity: A review

Single-atom nanozymes (SANs) are nanomaterials-based nanozymes with atomically dispersed enzyme-like active sites. SANs offer improved as well as tunable catalytic activity. The creation of extremely effective SANs and their potential uses have piqued researchers' curiosity due to their advantages of cheap cost, variable catalytic activity, high stability, and large-scale production. Furthermore, SANs with uniformly distributed active centers and definite coordination structures offer a distinctive opportunity to investigate the structure-activity correlation and control the geometric and electrical features of metal centers. SANs have been extensively explored in photo-, thermal-, and electro-catalysis. However, SANs suffer from the following disadvantages, such as efficiency, non-mimicking of the 3-D complexity of natural enzymes, limited and narrow range of artificial SANs, and biosafety aspects. Among a quite limited range of artificial SANs, the peroxidase action of SANs has attracted significant research attention in the last five years with the aim of producing reactive oxygen species for use in cancer therapy, and water treatment among many other applications. In this review, we explore the recent progress of different SANs as peroxidase mimics, the role of the metal center in enzymatic activity, possible prospects, and underlying limitations in real-time applications.

Engineering FeCo Dual Sites on Tube-on-Plate Hollow Structure for Efficient Oxygen Electroreduction

Atomically dispersed single-atom catalysts are intriguing catalysts in the field of electrocatalysis for nearly 100% exploitation of metal atoms. However, they are still far from practical usage due to the scaling relationship limit and metal loading limit. Generation of a diatomic complex would offer superior catalytic performance through the cooperation of two neighboring atoms as active sites. Herein, Fe/Co dual atomic sites embedded in a tube-on-plate hollow structure are designed and fabricated for an efficient electrochemical oxygen reduction reaction (ORR). The unique structure composed of ultrathin nanotube building blocks dramatically maximizes the surface area for copious active site exposure. Thanks to the synergetic interaction between Fe/Co pairs, the obtained FeCo/NC exhibits outstanding ORR activity and stability in alkaline media. Furthermore, density functional theory calculations have revealed that the remarkable activity is attributed to the electron-deficient Fe sites in FeCoN6. This work may pave the way for the innovative design of highly dispersed dual-site catalysts for broader applications in the realm of electrochemical catalysis.

Designing M13 Bacteriophage and Fe-Nanonest Self-Assembly System for Universal and Facile Preparation of Metal Single Atoms as Stable Mimicking Enzymes

Metal single-atom catalysts (MSACs) possess multiple advantages in chemical synthesis; their efficient fabrication routes, however, remain a challenge to date. Here, an interdisciplinary design using M13 bacteriophage virus as a biotemplate to carry Fe nanoclusters, which we figuratively call "Fe-nanonests", is proposed to enable facile and versatile synthesis of MSACs. The feasibility and generality of this self-assembly method was demonstrated by the observation of six different metal single atoms (MSAs) including Ag, Pt, Pd, Zn, Cu, and Ni. With Pd as a representative, key factors dominating the fabrication were determined. The Pd single atoms exhibited excellent horseradish peroxidase (HRP)-like activity, which was further improved by 50% via genetic editing of the M13 pVIII protein terminals. Excellent stability was also observed in the quantification of acid phosphatase, a cancer predictor. X-ray absorption near-edge structure spectroscopy has been applied to the analysis of Pd single atoms as well, and the Pd-N4 coordination explained the mechanism of high HRP-like catalytic activity. The MSAs synthesized by the M13 phage and Fe-nanonest self-assembly method show promising prospects in non-cold-chain medical detection applications.

Engineering Atomically Dispersed Cu-N1 S2 Sites via Chemical Vapor Deposition to Boost Enzyme-Like Activity for Efficient Tumor Therapy

Single-atom nanozymes (SAzymes), with well-defined and uniform atomic structures, are an emerging type of natural enzyme mimics. Currently, it is important but challenging to rationally design high-performance SAzymes and deeply reveal the interaction mechanism between SAzymes and substrate molecules. Herein, this work reports the controllable fabrication of a unique Cu-N1 S2 -centred SAzyme (Cu-N/S-C) via a chemical vapor deposition-based sulfur-engineering strategy. Benefiting from the optimized geometric and electronic structures of single-atom sites, Cu-N/S-C SAzyme shows boosted enzyme-like activity, especially in catalase-like activity, with a 13.8-fold increase in the affinity to hydrogen peroxide (H2 O2 ) substrate and a 65.2-fold increase in the catalytic efficiency when compared to Cu-N-C SAzyme with Cu-N3 sites. Further theoretical studies reveal that the increased electron density around single-atom Cu is achieved through electron redistribution, and the efficient charge transfer between Cu-N/S-C and H2 O2 is demonstrated to be more beneficial for the adsorption and activation of H2 O2 . The as-designed Cu-N/S-C SAzyme possesses an excellent antitumor effect through the synergy of catalytic therapy and oxygen-dependent phototherapy. This study provides a strategy for the rational design of SAzymes, and the proposed electron redistribution and charge transfer mechanism will help to understand the coordination environment effect of single-atom metal sites on H2 O2 -mediated enzyme-like catalytic processes.

Fe-Ni dual-single atoms nanozyme with high peroxidase-like activity for sensitive colorimetric and fluorometric dual-mode detection of cholesterol

Cholesterol is widely existed in nerve myelin sheath and various membrane structures, whose abnormal level would deteriorate human cells or even cause diseases. Herein, Fe-Ni dual-single-atom nanozyme was efficiently incorporated into N-doped carbon nanosheets (FeNi DSAs/N-CSs) by a simple calcination method. Its nanozyme activity and catalytic mechanism were investigated in details. The FeNi DSAs/N-CSs nanozyme showed superior peroxidase-like property, which was applied for the dual-mode determination of hydrogen peroxide (H2O2) and cholesterol. The colorimetric/fluorometric assays of H2O2 displayed the linear ranges of 1-50 mM and 5-40 mM with low limits of detection of 0.45 mM and 3.33 mM, respectively. In parallel, there exhibited the linear ranges of 0.5-5.0 mM and 0.25-5.0 mM for the colorimetric/fluorometric analysis of cholesterol, coupled with the limits of detection down to 0.19 mM and 0.044 mM, respectively. This work provided a rapid, cost-effectiveness and simple colorimetric/fluorometric method for sensitive dual-mode detection of cholesterol in human serum samples.

Single-Atom Nanoenzyme-Based Autoluminescence System for Cancer Cell Imaging and Mitochondrial-Targeted Therapy

The autoluminescence nanoplatform based on a single-atom catalyst has the potential to achieve accurate tumor diagnosis and treatment. Taking advantage of this, glycyrrhetinic acid (GA) and chitosan-modified single Fe-N-C atom catalysts (SAF NPs) loaded with luminol-curcumin (Cur) were fabricated (SAF-LCCG). Once delivered to the tumor, this autoluminescence SAF-LCCG could target the mitochondria to restrain tumor metastasis and promote the production of hydrogen peroxide (H2O2). Then, SAF NPs with Fenton-like properties could actively utilize intracellular H2O2 to produce ·OH for chemodynamic therapy. After that, excess ·OH and H2O2 were transmitted to luminol to emit blue-violet chemiluminescence (CL) for cancer cell imaging. Synchronously, light was transferred to Cur to produce reactive oxygen species (ROS) which realized photodynamic therapy. Besides, Cur could be served as a chemotherapeutic drug to enhance intracellular ROS for penetrating therapy. More importantly, the massive accumulation of ROS in cancer cells can promote the CL intensity of luminol, which realized the cyclic ROS amplification. This autoluminescence nanoplatform was developed for accurate cancer cell imaging, effective inhibition of tumor metastasis, and synergistic and penetrated treatment of tumors.

Cu single-atom catalyst-based flexible hydrogen peroxide electrochemical sensor with oxygen resistance for monitoring ROS bursts

The study of cellular responses linked to oxidative stress mechanisms is crucial in comprehending diverse physiological and pathological life processes, including mitochondrial dysfunction. Nonetheless, despite the interference of O2, the monitoring of ROS released from cells poses a challenging task. In this study, carbon-based copper single-atom catalysts (Cu SACs) were synthesized that exhibits excellent electrocatalytic performance for H2O2 reduction with an initial potential at 0.23 V and effectively avoids interference from O2. Based on this catalyst, a flexible and stretchable oxygen-tolerant sensor was constructed and applied to monitor the calcium ion-induced ROS burst in human umbilical vein endothelial cells (HUVECs) in a simulated physiological condition. This study effectively eradicates interference that may arise from the reduction of O2 and presents a dependable platform for real-time in situ monitoring of physiologically active molecules by utilizing H2O2 detection.

Synthesis of Two-Dimensional (Cu-S)n Metal-Organic Framework Nanosheets Applied as Peroxidase Mimics for Detection of Glutathione

Facilely synthesized peroxidase-like nanozymes with high catalytic activity and stability may serve as effective biocatalysts. The present study synthesizes peroxidase-like nanozymes with multinuclear active sites using two-dimensional (2D) metal-organic framework (MOF) nanosheets and evaluates them for their practical applications. A simple method involving a one-pot bottom-up reflux reaction is developed for the mass synthesis of (Cu-S)n MOF 2D nanosheets, significantly increasing production quantity and reducing reaction time compared to traditional autoclave methods. The (Cu-S)n MOF 2D nanosheets with the unique coordination of Cu(I) stabilized in Cu-based MOFs demonstrate impressive activity in mimicking natural peroxidase. The active sites of the peroxidase-like activity of (Cu-S)n MOF 2D nanosheets were predominantly verified as Cu(I) rather than Cu(II) of other Cu-based MOFs. The cost-effective and long-term stability of (Cu-S)n MOF 2D nanosheets make them suitable for practical applications. Furthermore, the inhibition of the peroxidase-like activity of (Cu-S)n MOF nanosheets by glutathione (GSH) could provide a simple strategy for colorimetric detection of GSH against other amino acids. This work remarkably extends the utilization of (Cu-S)n MOF 2D nanosheets in biosensing, revealing the potential for 2D (Cu-S)n MOFs.

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.

Transition Metal Single-Atom Catalysts for the Electrocatalytic Nitrate Reduction: Mechanism, Synthesis, Characterization, Application, and Prospects

Excessive accumulation of nitrate in the environment will affect human health. To combat nitrate pollution, chemical, biological, and physical technologies have been developed recently. The researcher favors electrocatalytic reduction nitrate reaction (NO3 RR) because of the low post-treatment cost and simple treatment conditions. Single-atom catalysts (SACs) offer great activity, exceptional selectivity, and enhanced stability in the field of NO3 RR because of their high atomic usage and distinctive structural characteristics. Recently, efficient transition metal-based SACs (TM-SACs) have emerged as promising candidates for NO3 RR. However, the real active sites of TM-SACs applied to NO3 RR and the key factors controlling catalytic performance in the reaction process remain ambiguous. Further understanding of the catalytic mechanism of TM-SACs applied to NO3 RR is of practical significance for exploring the design of stable and efficient SACs. In this review, from experimental and theoretical studies, the reaction mechanism, rate-determining steps, and essential variables affecting activity and selectivity are examined. The performance of SACs in terms of NO3 RR, characterization, and synthesis is then discussed. In order to promote and comprehend NO3 RR on TM-SACs, the design of TM-SACs is finally highlighted, together with the current problems, their remedies, and the way forward.

Recent advances in the synthesis and applications of single-atom nanozymes in food safety monitoring

Nanozymes are synthetic compounds with enzyme-like tunable catalytic properties. The success of nanozymes for catalytic applications can be attributed to their small dimensions, cost-effective synthesis, appreciable stability, and scalability to molecular dimensions. The emergence of single atom nanozymes (SANzymes) has opened up new possibilities in bioanalytical applications. In this regard, this review outlines enzyme-mimicking features of SANzymes for food safety applications in relation to the key variables controlling their catalytic performance. The discussion is extended further to cover the applications of SANzymes for the monitoring of various compounds/biomaterials of significance with respect to food safety (e.g., pesticides, veterinary drug residues, foodborne pathogenic bacteria, mycotoxins/bacterial endotoxin, antioxidant residues, hydrogen peroxide residues, and heavy metal ions). Furthermore, the performance of SANzymes is evaluated in terms of various performance metrics such as limit of detection (LOD), linear dynamic range, and figure of merit (FoM). The challenges and future road map for the applications of SANzymes are also addressed along with their upscaling in the area of food safety.

Emerging antibacterial nanozymes for wound healing

Wound infections continuously impose a huge economic and social burden on public healthcare. Despite the effective treatment of bacteria-infected wounds after using traditional antibiotics, the misuse of antibiotics usually causes the spread of bacterial resistance and decreases therapeutic outcomes. Therefore, the development of efficient antibacterial agents is urgently needed. Nanozymes, as a new generation of artificial enzymes, combine the intrinsic abilities of nanomaterials and natural enzymes. Recently, nanozymes has been widely developed to kill bacteria and treat wound infections by catalyzing the generation of various reactive oxygen species. Thus, this new concept of "antibacterial nanozymes" will promote the further advances of connecting nanozymes and bacterial elimination. To highlight these achievements, we summarize different types of antibacterial nanozymes for wound healing. It is believed that such a promising therapeutic strategy of developing antibacterial nanozymes will make a great contribution in the field of skin regeneration. We expect that antibacterial nanozymes will play the significant roles in both basic research and clinical applications.

Copper Single-Atom Jellyfish-like Nanomotors for Enhanced Tumor Penetration and Nanocatalytic Therapy

Single-atom catalysts with extraordinary catalytic activity have been receiving great attention in tumor therapy. However, most single-atom catalysts lack self-propulsion properties, restricting them from actively approaching cancer cells or penetrating the interior of tumors. Herein, we design N-doped jellyfish-like mesoporous carbon nanomotors coordinated with single-atom copper (Cu-JMCNs). It is a combination of single-atom nanocatalytic medicine and nanomotor self-propulsion for cancer therapy. The Cu single atom can catalyze H₂O₂ into toxic hydroxyl radical (^•OH) for chemodynamic therapy (CDT). Near-infrared light triggers Cu-JMCNs to achieve self-thermophoretic motion because of the jellyfish-like asymmetric structure and photothermal property of carbon, which significantly improves the cellular uptake and the penetration of three-dimensional tumors. In vivo experiments indicate that the combination of single-atom Cu for CDT and near-infrared light propulsion can achieve over 85% tumor inhibition rate. This work sheds light on the development of advanced nanomotors with single-atom catalysts for biomedical applications.

Occurrence, transport, and detection techniques of emerging pollutants in groundwater

Emerging pollutants (EPs) are a group of different contaminants, such as hormones, pesticides, heavy metals, and drugs, usually found in concentrations between the order of ng and µg per liter. The global population's daily city and agro-industrial activities release EPs into the environment.  Due to the chemical nature of EPs and deficient wastewater treatment and management, they are transported to superficial and groundwater through the natural water cycle, where they can potentially cause harmful effects on living organisms. Recent efforts have focused on developing technology that allows EPs quantification and monitoring in real-time and in situ. The newly developed technology aims to provide accessible groundwater management that detects and treats EPs while avoiding their contact with living beings and their toxic effects. This review presents some of the recently reported techniques that have been applied to advance the detection of EPs in groundwater and potential technologies that can be used for EP removal.

Single-atom nanozymes Co-N-C as an electrochemical sensor for detection of bioactive molecules

A properly designed sensing interface is crucial for the accurate and sensitive detection of biologically active molecules. Single-atom nanozymes from transition metal and nitrogen-doped carbon materials (M-N-C) have caught attention owing to their large surface area and strong bionic enzyme activity. Herein, a three-dimensional layered electrochemical electrode consisting of a Co-N-C nanoenzyme embedded in a reduced graphene oxide aerogel was prepared for the detection of hydrogen peroxide (H₂O₂), dopamine (DA) and uric acid (UA). Due to its unique three-dimensional layered structure, rGA has excellent electrical conductivity and high material loading and is used to enhance the electrocatalytic performance of Co-N-C. The combination of single-atom nanozymes and electrochemical detection shows unique advantages in catalytic activity and selectivity. The limit of detection and detection range are 0.74 μM and 3-2991 μM respectively for H₂O_2. Furthermore, it has been successfully implemented for the in-situ detection of H₂O₂ in living cells. In addition, their simultaneous detection is also realized by the sensors for DA and UA. And it can accurately capture the signal of UA and DA in the urine. Meanwhile, the electrode displays satisfactory stability and repeatability. Therefore, this paper provides a new detection strategy for a variety of bioactive molecules, showing great potential in cell biology, pathophysiology and diagnostics.

Single Atom-Doped Nanosonosensitizers for Mutually Optimized Sono/Chemo-Nanodynamic Therapy of Triple Negative Breast Cancer

Sonodynamic therapy (SDT) represents a promising therapeutic modality for treating breast cancer, which relies on the generation of abundant reactive oxygen species (ROS) to induce oxidative stress damage. However, mutant breast cancers, especially triple-negative breast cancer (TNBC), have evolved to acquire specific antioxidant defense functions, significantly limiting the killing efficiency of SDT. Herein, the authors have engineered a distinct single copper atom-doped titanium dioxide (Cu/TiO2 ) nanosonosensitizer with highly catalytic and sonosensitive activities for synergistic chemodynamic and sonodynamic treatment of TNBC. The single-atom Cu is anchored on the most stable Ti vacancies of hollow TiO2 sonosensitizers, which not only substantially improved the catalytic activity of Cu-mediated Fenton-like reaction, but also considerably augmented the sonodynamic efficiency of TiO2 by facilitating the separation of electrons (e- ) and holes (h+ ). Both the in vitro and in vivo studies demonstrate that the engineered single atom-doped nanosonosensitizers effectively achieved the significantly inhibitory effect of TNBC, providing a therapeutic paradigm for non-invasive and safe tumor elimination through the mutual process of sono/chemo-nanodynamic therapy based on multifunctional single-atom nanosonosensitizers.

Synergy of Ultrathin CoOx Overlayer and Nickel Single Atoms on Hematite Nanorods for Efficient Photo-Electrochemical Water Splitting

To solve surface carrier recombination and sluggish water oxidation kinetics of hematite (α-Fe₂ O₃ ) photoanodes, herein, an attractive surface modification strategy is developed to successively deposit ultrathin CoO_x overlayer and Ni single atoms on titanium (Ti)-doped α-Fe₂ O₃ (Ti:Fe₂ O₃ ) nanorods through a two-step atomic layer deposition (ALD) and photodeposition process. The collaborative decoration of ultrathin CoO_x overlayer and Ni single atoms can trigger a big boost in photo-electrochemical (PEC) performance for water splitting over the obtained Ti:Fe₂ O₃ /CoO_x /Ni photoanode, with the photocurrent density reaching 1.05 mA cm^-2 at 1.23 V vs. reversible hydrogen electrode (RHE), more than three times that of Ti:Fe₂ O₃ (0.326 mA cm^-2 ). Electrochemical and electronic investigations reveal that the surface passivation effect of ultrathin CoO_x overlayer can reduce surface carrier recombination, while the catalysis effect of Ni single atoms can accelerate water oxidation kinetics. Moreover, theoretical calculations evidence that the synergy of ultrathin CoO_x overlayer and Ni single atoms can lower the adsorption free energy of OH* intermediates and relieve the potential-determining step (PDS) for oxygen evolution reaction (OER). This work provides an exemplary modification through rational engineering of surface electrochemical and electronic properties for the improved PEC performances, which can be applied in other metal oxide semiconductors as well.

Axial N Ligand-Modulated Ultrahigh Activity and Selectivity Hyperoxide Activation over Single-Atoms Nanozymes

Learning and studying the structure-activity relationship in the bio-enzymes is conducive to the design of nanozymes for energy and environmental application. Herein, Fe single-atom nanozymes (Fe-SANs) with Fe-N5 site, inspired by the structure of cytochromes P450 (CYPs), are developed and characterized. Similar to the CYPs, the hyperoxide can activate the Fe(III) center of Fe-SANs to generate Fe(IV)O intermediately, which can transfer oxygen to the substrate with ultrafast speed. Particularly, using the peroxymonosulfate (PMS)-activated Fe-SANs to oxidize sulfamethoxazole, a typical antibiotic contaminant, as the model hyperoxides activation reaction, the excellent activity within 284 min-1 g-1 (catalyst) mmol-1 (PMS) oxidation rate and 91.6% selectivity to the Fe(IV)O intermediate oxidation are demonstrated. More importantly, instead of promoting PMS adsorption, the axial N ligand modulates the electron structure of FeN5 SANs for the lower reaction energy barrier and promotes electron transfer to PMS to produce Fe(IV)O intermediate with high selectivity. The highlight of the axial N coordination in the nanozymes in this work provides deep insight to guide the design and development of nanozymes nearly to the bio-enzyme with excellent activity and selectivity.

Atomically dispersed golds on degradable zero-valent copper nanocubes augment oxygen driven Fenton-like reaction for effective orthotopic tumor therapy

Herein, we employ a galvanic replacement approach to create atomically dispersed Au on degradable zero-valent Cu nanocubes for tumor treatments on female mice. Controlling the addition of precursor HAuCl₄ allows for the fabrication of different atomic ratios of Au_xCu_y. X-ray absorption near edge spectra indicates that Au and Cu are the predominant oxidation states of zero valence. This suggests that the charges of Au and Cu remain unchanged after galvanic replacement. Specifically, Au_0.02Cu_0.98 composition reveals the enhanced •OH generation following O₂ → H₂O₂ → •OH. The degradable Au_0.02Cu_0.98 released Cu⁺ and Cu²⁺ resulting in oxygen reduction and Fenton-like reactions. Simulation studies indicate that Au single atoms boot zero-valent copper to reveal the catalytic capability of Au_0.02Cu_0.98 for O₂ → H₂O₂ → •OH as well. Instead of using endogenous H₂O₂, H₂O₂ can be sourced from the O₂ in the air through the use of nanocubes. Notably, the Au_0.02Cu_0.98 structure is degradable and renal-clearable.

The Local Coordination Effects on the Reactivity and Speciation of Active Sites in Graphene-Embedded Single-Atom Catalysts over Wide pH and Potential Range

Understanding the catalytic performance of different materials is of crucial importance for achieving further technological advancements. This especially relates to the behaviors of different classes of catalysts under operating conditions. Here, we analyzed the effects of local coordination of metal centers (Mn, Fe, Co) in graphene-embedded single-atom catalysts (SACs). We started with well-known M@N₄-graphene catalysts and systematically replaced nitrogen atoms with oxygen or sulfur atoms to obtain M@O_xN_y-graphene and M@S_xN_y-graphene SACs (x + y = 4). We show that local coordination strongly affects the electronic structure and reactivity towards hydrogen and oxygen species. However, stability is even more affected. Using the concept of Pourbaix plots, we show that the replacement of nitrogen atoms in metal coordinating centers with O or S destabilized the SACs towards dissolution, while the metal centers were easily covered by O and OH, acting as additional ligands at high anodic potentials and high pH values. Thus, not only should local coordination be considered in terms of the activity of SACs, but it is also necessary to consider its effects on the speciation of SAC active centers under different potentials and pH conditions.

Emerging single-atom iron catalysts for advanced catalytic systems

Due to the elusive structure-function relationship, traditional nanocatalysts always yield limited catalytic activity and selectivity, making them practically difficult to replace natural enzymes in wide industrial and biomedical applications. Accordingly, single-atom catalysts (SACs), defined as catalysts containing atomically dispersed active sites on a support material, strikingly show the highest atomic utilization and drastically boosted catalytic performances to functionally mimic or even outperform natural enzymes. The molecular characteristics of SACs (e.g., unique metal-support interactions and precisely located metal sites), especially single-atom iron catalysts (Fe-SACs) that have a similar catalytic structure to the catalytically active center of metalloprotease, enable the accurate identification of active centers in catalytic reactions, which afford ample opportunity for unraveling the structure-function relationship of Fe-SACs. In this review, we present an overview of the recent advances of support materials for anchoring an atomic dispersion of Fe. Subsequently, we highlight the structural designability of support materials as two sides of the same coin. Moreover, the applications described herein illustrate the utility of Fe-SACs in a broad scope of industrially and biologically important reactions. Finally, we present an outlook of the major challenges and opportunities remaining for the successful combination of single Fe atoms and catalysts.

Applications of Single Atom Catalysts for Environmental Management

With the rapid development of industrialization, human beings have caused many negative effects on the environment that have endangered the survival and development of human beings, such as the greenhouse effect, water pollution, energy depletion, etc [...].

Cascade Processes with Micellar Reaction Media: Recent Advances and Future Directions

Reducing the use of solvents is an important aim of green chemistry. Using micelles self-assembled from amphiphilic molecules dispersed in water (considered a green solvent) has facilitated reactions of organic compounds. When performing reactions in micelles, the hydrophobic effect can considerably accelerate apparent reaction rates, as well as enhance selectivity. Here, we review micellar reaction media and their potential role in sustainable chemical production. The focus of this review is applications of engineered amphiphilic systems for reactions (surface-active ionic liquids, designer surfactants, and block copolymers) as reaction media. Micelles are a versatile platform for performing a large array of organic chemistries using water as the bulk solvent. Building on this foundation, synthetic sequences combining several reaction steps in one pot have been developed. Telescoping multiple reactions can reduce solvent waste by limiting the volume of solvents, as well as eliminating purification processes. Thus, in particular, we review recent advances in “one-pot” multistep reactions achieved using micellar reaction media with potential applications in medicinal chemistry and agrochemistry. Photocatalyzed reactions in micellar reaction media are also discussed. In addition to the use of micelles, we emphasize the process (steps to isolate the product and reuse the catalyst).

Mn-doped single atom nanozyme composited Au for enhancing enzymatic and photothermal therapy

As an emerging technology, nanocatalytic medicine attracts much attention, especially the ones according to the enzymatic reaction by using excess H₂O₂ in the tumor. Among various candidates, single-atom catalyst (SAC) revealed unique and outstanding redox reaction performance, since the active sites consisting of single metal atoms may achieve the maximum utilization of metal atoms and emerge obviously amplified reaction rate. Here we developed an M-N_x (M = Mn, Zn) center-based SAC with a hollow structure by calcination of Mn²⁺-doped zeolitic imidazolate frameworks (ZIF-8), and PEGylation was applied to improve the hydrophilicity. According to the enzymatic reaction, the M-N_x (M = Mn, Zn) centers have an inherent peroxidase-like activity to catalyze over-expressed H₂O₂ in the weak acidic tumor microenvironment and generate a large amount of toxic reactive oxygen species (ROS) like hydroxyl radicals for therapy. To keep efficient therapeutic output, we integrated the hollow SAC with Au which could expend the glucose in tumor and supply H₂O₂ as the substrate of peroxidase-like activity. Better yet, Au may boost the photothermal effect of SAC and offer another non-invasive photothermal therapy (PTT) to promote the effect of tumor removal. This platform provided a new idea for the construction of more efficient peroxidase-like activity in tumor therapy.

Single-Atom Catalysts (SACs) for Photocatalytic CO2 Reduction with H2 O: Activity, Product Selectivity, Stability, and Surface Chemistry

In recent years, single-atom catalysts (SACs) have attracted the interest of researchers owing to their suitability for various catalytic applications. For instance, their optoelectronic features, site-specific activity, and cost-effectiveness make SACs ideal for photocatalytic CO₂ reduction. The activity, product selectivity, and photostability of SACs depend on various factors such as the nature of the metal/support material, the interaction between the metal atoms and support, light-harvesting ability, charge separation behavior, CO₂ adsorption ability, active sites, and defects. Consequently, it is necessary to investigate these factors in depth to elucidate the working principle(s) of SACs for catalytic applications. Herein, the recent progress in the development of SACs for photocatalytic CO₂ reduction with H₂ O is reviewed. First, a brief overview of CO₂ photoreduction and SACs for CO₂ conversion is provided. Several synthesis strategies and useful techniques for characterizing SACs employed in heterogeneous catalysis are then described. Next, the challenges of SACs for photocatalytic CO₂ reduction and related optimization strategies, in terms of activity, product selectivity, and stability, are explored. The progress in the development of noble metal- and transition metal-based SACs and dual-SACs for photocatalytic CO₂ reduction is discussed. Finally, the prospects of SACs for CO₂ reduction are considered.

Single Atom Catalysts for Selective Methane Oxidation to Oxygenates

Direct conversion of methane (CH₄) to C_1-2 liquid oxygenates is a captivating approach to lock carbons in transportable value-added chemicals, while reducing global warming. Existing approaches utilizing the transformation of CH₄ to liquid fuel via tandemized steam methane reforming and the Fischer-Tropsch synthesis are energy and capital intensive. Chemocatalytic partial oxidation of methane remains challenging due to the negligible electron affinity, poor C-H bond polarizability, and high activation energy barrier. Transition-metal and stoichiometric catalysts utilizing harsh oxidants and reaction conditions perform poorly with randomized product distribution. Paradoxically, the catalysts which are active enough to break C-H also promote overoxidation, resulting in CO₂ generation and reduced carbon balance. Developing catalysts which can break C-H bonds of methane to selectively make useful chemicals at mild conditions is vital to commercialization. Single atom catalysts (SACs) with specifically coordinated metal centers on active support have displayed intrigued reactivity and selectivity for methane oxidation. SACs can significantly reduce the activation energy due to induced electrostatic polarization of the C-H bond to facilitate the accelerated reaction rate at the low reaction temperature. The distinct metal-support interaction can stabilize the intermediate and prevent the overoxidation of the reaction products. The present review accounts for recent progress in the field of SACs for the selective oxidation of CH₄ to C_1-2 oxygenates. The chemical nature of catalytic sites, effects of metal-support interaction, and stabilization of intermediate species on catalysts to minimize overoxidation are thoroughly discussed with a forward-looking perspective to improve the catalytic performance.