Computer-aided nanodrug discovery: recent progress and future prospects

Nanodrugs, which utilise nanomaterials in disease prevention and therapy, have attracted considerable interest since their initial conceptualisation in the 1990s. Substantial efforts have been made to develop nanodrugs for overcoming the limitations of conventional drugs, such as low targeting efficacy, high dosage and toxicity, and potential drug resistance. Despite the significant progress that has been made in nanodrug discovery, the precise design or screening of nanomaterials with desired biomedical functions prior to experimentation remains a significant challenge. This is particularly the case with regard to personalised precision nanodrugs, which require the simultaneous optimisation of the structures, compositions, and surface functionalities of nanodrugs. The development of powerful computer clusters and algorithms has made it possible to overcome this challenge through in silico methods, which provide a comprehensive understanding of the medical functions of nanodrugs in relation to their physicochemical properties. In addition, machine learning techniques have been widely employed in nanodrug research, significantly accelerating the understanding of bio-nano interactions and the development of nanodrugs. This review will present a summary of the computational advances in nanodrug discovery, focusing on the understanding of how the key interfacial interactions, namely, surface adsorption, supramolecular recognition, surface catalysis, and chemical conversion, affect the therapeutic efficacy of nanodrugs. Furthermore, this review will discuss the challenges and opportunities in computer-aided nanodrug discovery, with particular emphasis on the integrated "computation + machine learning + experimentation" strategy that can potentially accelerate the discovery of precision nanodrugs.

Sensitive colorimetric detection of glutathione in human serum based on peroxidase-like activity of chitosan-stabilized gold nanoparticles

A colorimetric sensor for the rapid and sensitive detection of GSH was developed. The hydrothermal method was utilized to synthesize chitosan-stabilized gold nanoparticles (CS-AuNPs). The synthesized CS-AuNPs were characterized by UV-vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray diffractograms (XRD), and Fourier transform infrared spectroscopy (FTIR). The CS-AuNPs are well-dispersed and possess a spherical shape with an average particle size of 10.05 ± 2.26 nm in aqueous solution. They show an intrinsic peroxidase-like activity, which could efficiently catalyze the decomposition of H2O2 to produce •OH radicals. These radicals then oxidized 3, 3´, 5, 5´-tetramethylbenzidine (TMB), resulting in the formation of the blue oxidized product oxTMB, observed a visible color change (from colorless to blue), and oxTMB had an obvious absorption peak at 652 nm. The presence of GSH could inhibit the peroxidase-like activity of CS-AuNPs, thereby reducing the formation of oxTMB. The solution's blue hue underwent a reduction in absorption intensity. Based on this fact, a novel and sensitive colorimetric sensor for detection of GSH was constructed. Under optimal conditions, the results of detection had an excellent linear relationship between the concentration of GSH and ∆A within the range 0.5 ~ 50.0 × 10-6 mol/L. The limit of detection (LOD) for GSH was 2.10 × 10-7 mol/L, which was much lower than those in most previous works. Furthermore, for detection in real human serum samples, the recoveries of GSH and the relative standard deviations (RSD) in the serum were in the range 98.40 ~ 103.32% and 1.85 ~ 3.54%, respectively. Thus, this visual colorimetric method has good precision and can be used for GSH detection in practical applications, promising in the fields of bioanalysis and illness diagnostics.

Smart Nanozymes for Diagnosis of Bacterial Infection: The Next Frontier from Laboratory to Bedside Testing

The global spread of infectious diseases caused by pathogenic bacteria significantly poses public health concerns, and methods for sensitive, selective, and facile diagnosis of bacteria can efficiently prevent deterioration and further spreading of the infections. The advent of nanozymes has broadened the spectrum of alternatives for diagnosing bacterial infections. Compared to natural enzymes, nanozymes exhibit the same enzymatic characteristics but offer greater economic efficiency, enhanced durability, and adjustable dimensions. The importance of early diagnosis of bacterial infection and conventional diagnostic approaches is introduced. Subsequently, the review elucidates the definition, properties, and catalytic mechanism of nanozymes. Eventually, the detailed application of nanozymes in detecting bacteria is explored, highlighting their utilization as biosensors that allow for accelerated and highly sensitive identification of bacterial infections and reflecting on the potential of nanozyme-based bacterial detection as a point-of-care testing (POCT) tool. A brief summary of obstacles and future perspectives in this field is presented at the conclusion of this review.

Nanoenzymes: A Radiant Hope for the Early Diagnosis and Effective Treatment of Breast and Ovarian Cancers

Breast and ovarian cancers, despite having chemotherapy and surgical treatment, still have the lowest survival rate. Experimental stages using nanoenzymes/nanozymes for ovarian cancer diagnosis and treatment are being carried out, and correspondingly the current treatment approaches to treat breast cancer have a lot of adverse side effects, which is the reason why researchers and scientists are looking for new strategies with less side effects. Nanoenzymes have intrinsic enzyme-like activities and can reduce the shortcomings of naturally occurring enzymes due to the ease of storage, high stability, less expensive, and enhanced efficiency. In this review, we have discussed various ways in which nanoenzymes are being used to diagnose and treat breast and ovarian cancer. For breast cancer, nanoenzymes and their multi-enzymatic properties can control the level of reactive oxygen species (ROS) in cells or tissues, for example, oxidase (OXD) and peroxidase (POD) activity can be used to generate ROS, while catalase (CAT) or superoxide dismutase (SOD) activity can scavenge ROS. In the case of ovarian cancer, most commonly nanoceria is being investigated, and also when folic acid is combined with nanoceria there are additional advantages like inhibition of beta galactosidase. Nanocarriers are also used to deliver small interfering RNA that are effective in cancer treatment. Studies have shown that iron oxide nanoparticles are actively being used for drug delivery, similarly ferritin carriers are used for the delivery of nanozymes. Hypoxia is a major factor in ovarian cancer, therefore MnO2-based nanozymes are being used as a therapy. For cancer diagnosis and screening, nanozymes are being used in sonodynamic cancer therapy for cancer diagnosis and screening, whereas biomedical imaging and folic acid gold particles are also being used for image guided treatments. Nanozyme biosensors have been developed to detect ovarian cancer. This review article summarizes a detailed insight into breast and ovarian cancers in light of nanozymes-based diagnostic and therapeutic approaches.

Reaction Mechanisms and Kinetics of Nanozymes: Insights from Theory and Computation

"Nanozymes" usually refers to inorganic nanomaterials with enzyme-like catalytic activities. The research into nanozymes is one of the hot topics on the horizon of interdisciplinary science involving materials, chemistry, and biology. Although great progress has been made in the design, synthesis, characterization, and application of nanozymes, the study of the underlying microscopic mechanisms and kinetics is still not straightforward. Density functional theory (DFT) calculations compute the potential energy surfaces along the reaction coordinates for chemical reactions, which can give atomistic-level insights into the micro-mechanisms and kinetics for nanozymes. Therefore, DFT calculations have been playing an increasingly important role in exploring the mechanisms and kinetics for nanozymes in the past years. The calculations either predict the microscopic details for the catalytic processes to complement the experiments or further develop theoretical models to depict the physicochemical rules. In this review, the corresponding research progress is summarized. Particularly, the review focuses on the computational studies that closely interplay with the experiments. The relevant experimental results without DFT calculations will be also briefly discussed to offer a historic overview of how the computations promote the understanding of the microscopic mechanisms and kinetics of nanozymes.

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

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

Ultrasmall Cu2O@His Nanozymes with RONS Scavenging Capability for Anti-inflammatory Therapy

High concentrations of reactive oxygen and nitrogen species (RONS) are key characteristics of inflammatory sites. Scavenging RONS at the site of inflammation is an effective therapeutic strategy. This study introduces ultrasmall Cu2O@His nanoparticles with RONS-scavenging ability for the treatment of inflammatory bowel disease (IBD) in mice. The strong coordination between the nitrogen atom in histidine (His) and copper enhances the dispersion and stability of Cu2O@His. Due to their small size and large surface area, Cu2O@His exhibits outstanding RONS-clearing ability. Importantly, Cu2O@His can target mitochondrial sites and repair damaged mitochondria. With excellent dispersion and scavenging RONS ability, Cu2O@His demonstrates good efficacy in treating mouse IBD. This work provides a new paradigm for developing nanozymes with an ultrasmall size and multiple scavenging RONS abilities.

Nanozymes: A comprehensive review on emerging applications in cancer diagnosis and therapeutics

Nanozymes, a new class of nanomaterials-based artificial enzymes, have gained huge attraction due to their high operational stability, working efficiency in extreme conditions, and resistance towards protease digestion. Nowadays, they are effectively substituted for natural enzymes for catalysis by closely resembling the active sites found in natural enzymes. Nanozymes can compensate for natural enzymes' drawbacks, such as high cost, poor stability, low yield, and storage challenges. Due to their transforming nature, nanozymes are of utmost importance in the detection and treatment of cancer. They enable precise cancer detection, tailored drug delivery, and catalytic therapy. Through enhanced diagnosis, personalized therapies, and reduced side effects, their adaptability and biocompatibility can transform the management of cancer. The review focuses on metal and metal oxide-based nanozymes, highlighting their catalytic processes, and their applications in the prevention and treatment of cancer. It emphasizes their potential to alter diagnosis and therapy, particularly when it comes to controlling reactive oxygen species (ROS). The article reveals the game-changing importance of nanozymes in the future of cancer care and describes future research objectives, making it a useful resource for researchers, and scientists. Lastly, outlooks for future perspective areas in this rapidly emerging field have been provided in detail.

Single-atom nanozymes: classification, regulation strategy, and safety concerns

Nanozymes, nanomaterials possessing enzymatic activity, have been studied extensively by researchers. However, their complex composition, low density of active sites, and inadequate substrate selectivity have hindered the maturation and widespread acceptance of nanozymes. Single-atom nanozymes (SAzymes) with atomically dispersed active sites are leading the field of catalysis due to their exceptional performance. The maximum utilization rate of atoms, low cost, well-defined coordination structure, and active sites are the most prominent advantages of SAzymes that researchers favor. This review systematically categorizes SAzymes based on their support type and describes their specific applications. Additionally, we discuss regulation strategies for SAzyme activity and provide a comprehensive summary of biosafety challenges associated with these enzymes.

Smart Nanozymes for Cancer Therapy: The Next Frontier in Oncology

Nanomaterials that mimic the catalytic activity of natural enzymes in the complex biological environment of the human body are called nanozymes. Recently, nanozyme systems have been reported with diagnostic, imaging, and/or therapeutic capabilities. Smart nanozymes strategically exploit the tumor microenvironment (TME) by the in situ generation of reactive species or by the modulation of the TME itself to result in effective cancer therapy. This topical review focuses on such smart nanozymes for cancer diagnosis, and therapy modalities with enhanced therapeutic effects. The dominant factors that guide the rational design and synthesis of nanozymes for cancer therapy include an understanding of the dynamic TME, structure-activity relationships, surface chemistry for imparting selectivity, and site-specific therapy, and stimulus-responsive modulation of nanozyme activity. This article presents a comprehensive analysis of the subject including the diverse catalytic mechanisms of different types of nanozyme systems, an overview of the TME, cancer diagnosis, and synergistic cancer therapies. The strategic application of nanozymes in cancer treatment can well be a game changer in future oncology. Moreover, recent developments may pave the way for the deployment of nanozyme therapy into other complex healthcare challenges, such as genetic diseases, immune disorders, and ageing.

Myocardial-Targeting Tannic Cerium Nanocatalyst Attenuates Ischemia/Reperfusion Injury

Ischemic heart disease (IHD) is one of the leading causes of death worldwide. Medications or surgery have been considered as effective protocols to treat IHD for decades. Yet the reperfusion of the blood flow frequently leads to the generation of excessive reactive oxygen species (ROS), causing prominent and irreversible damage to the cardiomyocytes. In the present work, tannic acid-assembled tetravalent cerium (TA-Ce) nanocatalysts with appealing cardiomyocyte-targeting and antioxidation capability have been synthesized and applied for the effective and biocompatible ischemia/reperfusion injury therapeutics. TA-Ce nanocatalysts could effectively rescue the cardiomyocytes from oxidative stress induced by H2 O2 challenge as well as oxygen-glucose deprivation in vitro. In the murine ischemia/reperfusion model, cardiac accumulation and intracellular ROS scavenging could be achieved against the pathology, substantially reducing the myocardial infarct area and recovering heart functionality. This work illuminates the design of nanocatalytic metal complexes and their therapeutic prospects in ischemic heart diseases with high effectiveness and biocompatibility, paving the way for the clinical translation from bench to bedside.

Engineering 2D Multienzyme-Mimicking Pyroptosis Inducers for Ultrasound-Augmented Catalytic Tumor Nanotherapy

Overcoming apoptosis resistance is necessary to ensure an effective cancer treatment; however, it is currently very difficult to achieve. A desirable alternative for cancer treatment is the targeted activation of pyroptosis, a unique type of programmed cell death. However, the pyroptosis inducers that are efficient for cancer therapy are limited. This work reports the engineering of 2D NiCoOx nanosheets as inducers of the production of harmful reactive oxygen species (ROS), which promote intense cell pyroptosis, and that can be applied to ultrasound (US)-augmented catalytic tumor nanotherapy. The main therapeutic task is carried out by the 2D NiCoOx nanosheets, which have four multienzyme-mimicking activities: peroxidase- (POD), oxidase- (OXD), glutathione peroxidase- (GPx), and catalase- (CAT) mimicking activities. These activities induce the reversal of the hypoxic microenvironment, endogenous glutathione depletion, and a continuous ROS output. The ROS-induced pyroptosis process is carried out via the ROS-NLRP3-GSDMD pathway, and the exogenous US activation boosts the multienzyme-mimicking activities and favors the incremental ROS generation, thus inducing mitochondrial dysfunction. The anti-cancer experimental results support the dominance of NiCoOx nanosheet-induced pyroptosis. This work expands on the biomedical applications of engineering 2D materials for US-augmented catalytic breast cancer nanotherapy and deepens the understanding of the multienzyme activities of nanomaterials.

Beyond antioxidation: Harnessing the CeO2 nanoparticles as a renoprotective contrast agent for in vivo spectral CT angiography

It is a challenging task to develop a contrast agent that not only provides excellent image contrast but also protects impaired kidneys from oxidative-related stress during angiography. Clinically approved iodinated CT contrast media are associated with potential renal toxicity, making it necessary to develop a renoprotective contrast agent. Here, we develop a CeO2 nanoparticles (NPs)-mediated three-in-one renoprotective imaging strategy, namely, i) renal clearable CeO2 NPs serve as a one-stone-two-birds antioxidative contrast agent, ii) low contrast media dose, and iii) spectral CT, for in vivo CT angiography (CTA). Benefiting from the merits of advanced sensitivity of spectral CT and K-edge energy of Cerium (Ce, 40.4 keV), an improved image quality of in vivo CTA is successfully achieved with a 10 times reduction of contrast agent dosage. In parallel, the sizes of CeO2 NPs and broad catalytic activities are suitable to be filtered via glomerulus thus directly alleviating the oxidative stress and the accompanying inflammatory injury of the kidney tubules. In addition, the low dosage of CeO2 NPs reduces the hypoperfusion stress of renal tubules induced by concentrated contrast agents used in angiography. This three-in-one renoprotective imaging strategy helps prevent kidney injury from being worsened during the CTA examination.

Multienzyme-Mimicking Au@Cu2O with Complete Antioxidant Capacity for Reactive Oxygen Species Scavenging

Most enzyme catalysts are unable to achieve effective oxidation resistance because of the monotonous mimicking function or production of secondary reactive oxygen species (ROS). Herein, the Au@Cu₂O heterostructure with multienzyme-like activities is deigned, which has significantly improved antioxidant capacity compared with pure Cu₂O for the scavenging of highly cell-damaging secondary ROS, i.e.,·OH. Experiments and theoretical calculations show that the heterostructure exhibits a built-in electric field and lattice mismatch at the metal-semiconductor interface, which facilitate to generate abundant oxygen vacancies, redox couples, and surface electron deficiency. On the one hand, the presence of rich oxygen vacancies and redox couple can enhance the adsorption and activation of oxygen-containing ROS (including O₂^·- and H₂O₂). On the other hand, the electron transfer between the electron-deficient Au@Cu₂O surface and electron donor would promote peroxide-like activity and avoid producing ·OH. Importantly, endogenous ·OH could be eliminated in both acidic and neutral conditions, which is no longer limited by the volatile physiological environment. Therefore, Au@Cu₂O can simulate superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione peroxidase (GPx) to form a complete antioxidant system. The deigned nanoenzyme is explored in the real sample world such as A549 cells and zebrafish. This work provides theoretical and practical strategies for the construction of a complete antioxidant enzyme system.

Machine Learning Guided Discovery of Superoxide Dismutase Nanozymes for Androgenetic Alopecia

Androgenetic alopecia (AGA) is a common form of hair loss, which is mainly caused by oxidative stress induced dysregulation of hair follicles (HF). Herein, a highly efficient manganese thiophosphite (MnPS₃) based superoxide dismutase (SOD) mimic was discovered using machine learning (ML) tools. Remarkably, the IC₅₀ of MnPS₃ is 3.61 μg·mL^-1, up to 12-fold lower than most reported SOD-like nanozymes. Moreover, a MnPS₃ microneedle patch (MnMNP) was constructed to treat AGA that could diffuse into the deep skin where HFs exist and remove excess reactive oxygen species. Compared with the widely used minoxidil, MnMNP exhibits higher ability on hair regeneration, even at a reduced frequency of application. This study not only provides a general guideline for the accelerated discovery of SOD-like nanozymes by ML techniques, but also shows a great potential as a next generation approach for rational design of nanozymes.

Application and prospect of ROS-related nanomaterials for orthopaedic related diseases treatment

The importance of reactive oxygen species (ROS) in the occurrence and development of orthopaedic related diseases is becoming increasingly prominent. ROS regulation has become a new method to treat orthopaedic related diseases. In recent years, the application of nanomaterials has become a new hope for precision and efficient treatment. However, there is a lack of reviews on ROS-regulated nanomaterials for orthopaedic related diseases. Based on the key significance of nanomaterials for the treatment of orthopaedic related diseases, we searched the latest related studies and reviewed the nanomaterials that regulate ROS in the treatment of orthopaedic related diseases. According to the function of nanomaterials, we describe the scavenging of ROS related nanomaterials and the generation of ROS related nanomaterials. In this review, we closely integrated nanomaterials with the treatment of orthopaedic related diseases such as arthritis, osteoporosis, wound infection and osteosarcoma, etc., and highlighted the advantages and disadvantages of existing nanomaterials. We also looked forward to the design of ROS-regulated nanomaterials for the treatment of orthopaedic related diseases in the future.

Nanozymes: Versatile Platforms for Cancer Diagnosis and Therapy

Natural enzymes usually suffer from high production cost, ease of denaturation and inactivation, and low yield, making them difficult to be broadly applicable. As an emerging type of artificial enzyme, nanozymes that combine the characteristics of nanomaterials and enzymes are promising alternatives. On the one hand, nanozymes have high enzyme-like catalytic activities to regulate biochemical reactions. On the other hand, nanozymes also inherit the properties of nanomaterials, which can ameliorate the shortcomings of natural enzymes and serve as versatile platforms for diverse applications. In this review, various nanozymes that mimic the catalytic activity of different enzymes are introduced. The achievements of nanozymes in different cancer diagnosis and treatment technologies are summarized by highlighting the advantages of nanozymes in these applications. Finally, future research directions in this rapidly developing field are outlooked.

Exploration of nanozymes in viral diagnosis and therapy

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.

Perspective for Single Atom Nanozymes Based Sensors: Advanced Materials, Sensing Mechanism, Selectivity Regulation, and Applications

Nanozymes are a kind of nanomaterial mimicking enzyme catalytic activity, which has aroused extensive interest in the fields of biosensors, biomedicine, and climate and ecosystems management. However, due to the complexity of structures and composition of nanozymes, atomic scale active centers have been extensively investigated, which helps with in-depth understanding of the nature of the biocatalysis. Single atom nanozymes (SANs) cannot only significantly enhance the activity of nanozymes but also effectively improve the selectivity of nanozymes owing to the characteristics of simple and adjustable coordination environment and have been becoming the brightest star in the nanozyme spectrum. The SANs based sensors have also been widely investigated due to their definite structural features, which can be helpful to study the catalytic mechanism and provide ways to improve catalytic activity. This perspective presents a comprehensive understanding on the advances and challenges on SANs based sensors. The catalytic mechanisms of SANs and then the sensing application from the perspectives of sensing technology and sensor construction are thoroughly analyzed. Finally, the major challenges, potential future research directions, and prospects for further research on SANs based sensors are also proposed.

Accelerated discovery of superoxide-dismutase nanozymes via high-throughput computational screening

The activity of nanomaterials (NMs) in catalytically scavenging superoxide anions mimics that of superoxide dismutase (SOD). Although dozens of NMs have been demonstrated to possess such activity, the underlying principles are unclear, hindering the discovery of NMs as the novel SOD mimics. In this work, we use density functional theory calculations to study the thermodynamics and kinetics of the catalytic processes, and we develop two principles, namely, an energy level principle and an adsorption energy principle, for the activity. The first principle quantitatively describes the role of the intermediate frontier molecular orbital in transferring electrons for catalysis. The second one quantitatively describes the competition between the desired catalytic reaction and undesired side reactions. The ability of the principles to predict the SOD-like activities of metal-organic frameworks were verified by experiments. Both principles can be easily implemented in computer programs to computationally screen NMs with the intrinsic SOD-like activity.

Potentiality of Nanoenzymes for Cancer Treatment and Other Diseases: Current Status and Future Challenges

Studies from past years have observed various enzymes that are artificial, which are issued to mimic naturally occurring enzymes based on their function and structure. The nanozymes possess nanomaterials that resemble natural enzymes and are considered an innovative class. This innovative class has achieved a brilliant response from various developments and researchers owing to this unique property. In this regard, numerous nanomaterials are inspected as natural enzyme mimics for multiple types of applications, such as imaging, water treatment, therapeutics, and sensing. Nanozymes have nanomaterial properties occurring with an inheritance that provides a single substitute and multiple platforms. Nanozymes can be controlled remotely via stimuli including heat, light, magnetic field, and ultrasound. Collectively, these all can be used to increase the therapeutic as well as diagnostic efficacies. These nanozymes have major biomedical applications including cancer therapy and diagnosis, medical diagnostics, and bio sensing. We summarized and emphasized the latest progress of nanozymes, including their biomedical mechanisms and applications involving synergistic and remote control nanozymes. Finally, we cover the challenges and limitations of further improving therapeutic applications and provide a future direction for using engineered nanozymes with enhanced biomedical and diagnostic applications.

Nanozymes in Point-of-Care Diagnosis: An Emerging Futuristic Approach for Biosensing

Nanomaterial-based artificial enzymes (or nanozymes) have attracted great attention in the past few years owing to their capability not only to mimic functionality but also to overcome the inherent drawbacks of the natural enzymes. Numerous advantages of nanozymes such as diverse enzyme-mimicking activities, low cost, high stability, robustness, unique surface chemistry, and ease of surface tunability and biocompatibility have allowed their integration in a wide range of biosensing applications. Several metal, metal oxide, metal-organic framework-based nanozymes have been exploited for the development of biosensing systems, which present the potential for point-of-care analysis. To highlight recent progress in the field, in this review, more than 260 research articles are discussed systematically with suitable recent examples, elucidating the role of nanozymes to reinforce, miniaturize, and improve the performance of point-of-care diagnostics addressing the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to the end user) criteria formulated by World Health Organization. The review reveals that many biosensing strategies such as electrochemical, colorimetric, fluorescent, and immunological sensors required to achieve the ASSURED standards can be implemented by using enzyme-mimicking activities of nanomaterials as signal producing components. However, basic system functionality is still lacking. Since the enzyme-mimicking properties of the nanomaterials are dictated by their size, shape, composition, surface charge, surface chemistry as well as external parameters such as pH or temperature, these factors play a crucial role in the design and function of nanozyme-based point-of-care diagnostics. Therefore, it requires a deliberate exertion to integrate various parameters for truly ASSURED solutions to be realized. This review also discusses possible limitations and research gaps to provide readers a brief scenario of the emerging role of nanozymes in state-of-the-art POC diagnosis system development for futuristic biosensing applications.

Dynamic nanoassemblies for imaging and therapy of neurological disorders

The past decades have witnessed an increased incidence of neurological disorders (NDs) such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, ischemic stroke, and epilepsy, which significantly lower patients' life quality and increase the economic and social burden. Recently, nanomedicines composed of imaging and/or therapeutic agents have been explored to diagnose and/or treat NDs due to their enhanced bioavailability, blood-brain barrier (BBB) permeability, and targeting capacity. Intriguingly, dynamic nanoassemblies self-assembled from functional nanoparticles to simultaneously interfere with multiple pathogenic substances and pathological changes, have been regarded as one of the foremost candidates to improve the diagnostic and therapeutic efficacy of NDs. To help readers better understand this emerging field, in this review, the pathogenic mechanism of different types of NDs is briefly introduced, then the functional nanoparticles used as building blocks in the construction of dynamic nanoassemblies for NDs theranostics are summarized. Furthermore, dynamic nanoassemblies that can actively cross the BBB to target brain lesions, sensitively and efficiently diagnose or treat NDs, and effectively promote neuroregeneration are highlighted. Finally, we conclude with our perspectives on the future development in this field.

A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

Bioengineering CXCR4-overexpressing cell membrane functionalized ROS-responsive nanotherapeutics for targeting cerebral ischemia-reperfusion injury

Rationale: As a potentially life-threatening disorder, cerebral ischemia-reperfusion (I/R) injury is associated with significantly high mortality, especially the irreversible brain tissue damage associated with increased reactive oxygen radical production and excessive inflammation. Currently, the insufficiency of targeted drug delivery and “on-demand” drug release remain the greatest challenges for cerebral I/R injury therapy. Bioengineered cell membrane-based nanotherapeutics mimic and enhance natural membrane functions and represent a potentially promising approach, relying on selective interactions between receptors and chemokines and increase nanomedicine delivery efficiency into the target tissues.

Methods: We employed a systematic method to synthesize biomimetic smart nanoparticles. The CXCR4-overexpressing primary mouse thoracic aorta endothelial cell (PMTAEC) membranes and RAPA@HOP were extruded through a 200 nm polycarbonate porous membrane using a mini-extruder to harvest the RAPA@BMHOP. The bioengineered CXCR4-overexpressing cell membrane-functionalized ROS-responsive nanotherapeutics, loaded with rapamycin (RAPA), were fabricated to enhance the targeted delivery to lesions with pathological overexpression of SDF-1.

Results: RAPA@BMHOP exhibited a three-fold higher rate of target delivery efficacy via the CXCR4/SDF-1 axis than its non-targeting counterpart in an in vivo model. Additionally, in response to the excessive pathological ROS, nanotherapeutics could be degraded to promote “on-demand” cargo release and balance the ROS level by p-hydroxy-benzyl alcohol degradation, thereby scavenging excessive ROS and suppressing the free radical-induced focal damage and local inflammation. Also, the stealth effect of cell membrane coating functionalization on the surface resulted in extended circulation time and high stability of nanoparticles.

Conclusion: The biomimetic smart nanotherapeutics with active targeting, developed in this study, significantly improved the therapeutic efficacy and biosafety profiles. Thus, these nanoparticles could be a candidate for efficient therapy of cerebral I/R injury.

Superoxide dismutase nanozymes: an emerging star for anti-oxidation

Superoxide dismutases (SODs) are a group of metalloenzymes that catalyze the dismutation of superoxide radicals (O2˙-) into hydrogen peroxide (H2O2) and oxygen (O2). As the first line of defense against reactive oxygen species (ROS)-mediated damage, SODs are expected to play an important role in the treatment of oxidative stress-related diseases. However, the clinical applications of SODs have been severely limited by their structural instability and high cost. Compared with natural enzymes, nanozymes, nanomaterials with enzyme-like activity, are more stable, and economical, can be easily modified and their activities can be adjusted. Due to their excellent characteristics, nanozymes have attracted widespread attention in recent years and are expected to become effective substitutes for natural enzymes in many application fields. Importantly, some nanozymes with SOD-like activity have been developed and proved to have a mitigating effect on diseases caused by oxidative stress. These studies on SOD-like nanozymes provide a feasible strategy for breaking through the dilemma of SOD clinical applications. However, at present, the specific catalytic mechanism of SOD-like nanozymes is still unclear, and many important issues need to be resolved. Although there are many comprehensive reviews to introduce the overall situation of the nanozyme field, the research on SOD-like nanozymes still lacks a systematic review. From the structure and mechanism of natural SOD enzymes to the structure and regulation of SOD-like nanozymes, and then to the measurement and application of nanozymes, this review systematically summarizes the recent progress in SOD-like nanozymes. The existing shortcomings and possible future research hotspots in the development of SOD-like nanozymes are summarized and prospected. We hope that this review would provide ideas and inspirations for further research on the catalytic mechanism and rational design of SOD-like nanozymes.

Reactive Oxygen Species-Regulating Strategies Based on Nanomaterials for Disease Treatment

Reactive oxygen species (ROS) play an essential role in physiological and pathological processes. Studies on the regulation of ROS for disease treatments have caused wide concern, mainly involving the topics in ROS-regulating therapy such as antioxidant therapy triggered by ROS scavengers and ROS-induced toxic therapy mediated by ROS-elevation agents. Benefiting from the remarkable advances of nanotechnology, a large number of nanomaterials with the ROS-regulating ability are developed to seek new and effective ROS-related nanotherapeutic modalities or nanomedicines. Although considerable achievements have been made in ROS-based nanomedicines for disease treatments, some fundamental but key questions such as the rational design principle for ROS-related nanomaterials are held in low regard. Here, the design principle can serve as the initial framework for scientists and technicians to design and optimize the ROS-regulating nanomedicines, thereby minimizing the gap of nanomedicines for biomedical application during the design stage. Herein, an overview of the current progress of ROS-associated nanomedicines in disease treatments is summarized. And then, by particularly addressing these known strategies in ROS-associated therapy, several fundamental and key principles for the design of ROS-associated nanomedicines are presented. Finally, future perspectives are also discussed in depth for the development of ROS-associated nanomedicines.

A review on metal nanozyme-based sensing of heavy metal ions: Challenges and future perspectives

Large scale mining, manufacturing industries, exploitation of underground water, depletion of groundwater level, and uncontrolled discharge of industrial wastes have caused severe heavy metal ion pollution to the environment throughout the world. Therefore, the rapid detection of such toxic metal ions is inevitable. However, conventional methods require sophisticated instruments and skilled manpower and are difficult to operate in on-field conditions. Recently, metal nanozyme-based assays have been found to have the potential as an alternative to conventional methods due to their portability, simplicity, and high sensitivity to detect metal ion concentration to as low as parts per trillion (ppt). Metal nanozyme-based systems for heavy metal ions enable rapid and cheap screening on the spot with a very simple instrument such as a UV-vis absorption spectrophotometer and therefore, are convenient for use in field operations, especially in remote parts of the world. The sensing mechanism of a nanozyme-based sensor is highly dependent on its surface properties and specific interactions with particular metal ion species. Such method often encounters selectivity issues, unlike natural enzyme-based assays. Therefore, in this review, we mainly focus our discussion on different types of target recognition and inhibition/enhancement mechanisms, and their responses toward the catalytic activity in the sensing of target metal ions, design strategies, challenges, and future perspectives.

A Cerium Vanadate Nanozyme with Specific Superoxide Dismutase Activity Regulates Mitochondrial Function and ATP Synthesis in Neuronal Cells

Nanoparticles that functionally mimic the activity of metal-containing enzymes (metallo-nanozymes) are of therapeutic importance for treating various diseases. However, it is still not clear whether such nanozymes can completely substitute the function of natural enzymes in living cells. In this work, we show for the first time that a cerium vanadate (CeVO₄ ) nanozyme can substitute the function of superoxide dismutase 1 and 2 (SOD1 and SOD2) in the neuronal cells even when the natural enzyme is down-regulated by specific gene silencing. The nanozyme prevents the mitochondrial damage in SOD1- and SOD2-depleted cells by regulating the superoxide levels and restores the physiological levels of the anti-apoptotic Bcl-2 family proteins. Furthermore, the nanozyme effectively prevents the mitochondrial depolarization, leading to a significant improvement in the cellular levels of ATP under oxidative stress.

Application of magnetic nanomaterials in electroanalytical methods: A review

Magnetic nanomaterials (MNMs) have gained high attention in different fields of studies due to their ferromagnetic/superparamagnetic properties and their low toxicity and high biocompatibility. MNMs contain magnetic elements such as iron and nickel in metallic, bimetallic, metal oxide, and mixed metal oxide. In electroanalytical methods, MNMs have been applied as sorbents for sample preparation before the electrochemical detection (sorbent role), as the electrode modifier (catalytic role), and the integration of the above two roles (as both sorbent and catalytic agent). In this paper, the application of MNMs in electroanalytical methods have been classified based on the main role of the nanomaterial and discussed separately. Furthermore, catalytic activities of MNMs in electroanalytical methods such as redox electrocatalytic, nanozymes catalytic (peroxidase, catalase activity, oxidase activity, superoxide dismutase activity), catalyst gate, and nanocontainer have been discussed.

Antioxidant metal oxide nanozymes: role in cellular redox homeostasis and therapeutics

Nanomaterials with enzyme-like activity, generally referred to as ‘nanozymes’, find myriad potential in various biomedical fields. More importantly, the nanoparticles that can functionally mimic the activity of cellular antioxidant enzymes attract tremendous interest owing to their possible therapeutic candidature in oxidative stress-mediated disorders. Oxidative stress culminating due to excess reactive oxygen species (ROS) level and dysregulated cellular antioxidant machinery is implicated in the development and progression of various pathophysiological disorders such as cancer, diabetes, cardiovascular and neurodegenerative diseases. Moreover, the optimum essentiality of ROS due to its pivotal role in cell signaling evokes the requirement of novel artificial antioxidant enzymes that can circumvent the detrimental effects of enhanced ROS levels without perturbing the basal redox status of cells. In recent years, the fast emanating artificial enzymes, i.e. nanozymes with antioxidant enzyme-like activity, has made tremendous progress with their broad applications in therapeutics, diagnostic medicine, bio-sensing, and immunoassay. Among various antioxidant nanoparticles reported till-date, the metal oxide nanozymes have emerged as the most efficient and successful candidates in mimicking the activity of first-line defense antioxidant enzymes, i.e. superoxide dismutase, catalase, and glutathione peroxidase. This review intends to exclusively highlight the development of representative metal oxide-based antioxidant nanozymes capable of maintaining the cellular redox homeostasis and their potential therapeutic significance.

Intrinsic Enzyme-like Activities of Cerium Oxide Nanocomposite and Its Application for Extracellular H2O2 Detection Using an Electrochemical Microfluidic Device

Artificial enzyme mimics have gained considerable attention for use in sensing applications due to their high stability and outstanding catalytic activity. We show that cerium oxide nanosheets (NSs) exhibit triple-enzyme mimetic activity. The oxidase-, peroxidase-, and catalase-like activities of the proposed nanoparticles are demonstrated using both colorimetric and electron paramagnetic resonance (EPR) spectroscopy. On the basis of the excellent catalytic activity of cerium oxide NSs toward hydrogen peroxide, an electrochemical approach for the high-throughput detection of H₂O₂ in living cells was established. This report presents an analytical microfluidic chip integrated with a cerium oxide NS mimic enzyme for the fabrication of a simple, sensitive, and low-cost electrochemical sensor. Three Au microelectrodes were fabricated on a glass substrate using photolithography, and the working electrode was functionalized using cerium oxide NSs. The operation of this biosensor is based on cerium oxide NSs and presents a high sensitivity over a wide detection range, between 100 nM and 20 mM, with a low detection limit of 20 nM and a high sensitivity threshold of 226.4 μA·cm^-2·μM^-1. This microfluidic sensor shows a strong response to H₂O₂, suggesting potential applications in monitoring H₂O₂ directly secreted from living cells. This sensor chip provides a promising platform for applications in the field of diagnostics and sensing.

Fullerene-like MoS2 Nanoparticles as Cascade Catalysts Improving Lubricant and Antioxidant Abilities of Artificial Synovial Fluid

Intraarticular injection of hyaluronic acid (HA) for viscosupplementation is a nonsurgical therapy for osteoarthritis (OA). However, HA fails to lubricate under a significant load and tends to be depolymerized by the overproduction of reactive oxygen species (ROS) in inflammation. Here, we for the first time reported that fullerene-like MoS₂ (F-MoS₂) nanoparticles are efficient lubricants and antioxidants for artificial synovial fluid. A model of arthrosis was built, to evaluate the tribological behavior of F-MoS₂ nanoparticles. The tests showed that they significantly improve the antiwear and friction-reducing abilities of the artificial synovial fluid. More importantly, the F-MoS₂ nanoparticles possess intrinsic dual-enzyme-like activity, mimicking superoxide dismutases (SOD) and catalases (CAT) under physiological conditions (pH 7.4, 25 °C). By coupling of these unique properties, a self-organized cascade catalytic system was constructed, which includes the disproportionation of superoxide radicals (O₂^•-) to hydrogen peroxide (H₂O₂) and subsequently the disproportionation of H₂O₂ into oxygen (O₂). The effectiveness of the detox system was evaluated by human umbilical vein endothelial cells (HUVEC) models exposed to oxidative stress. After that, F-MoS₂ nanoparticles were used to regulate the ROS level in artificial synovial fluid containing HA. Relative viscosity measurements showed the excellent protective effect of F-MoS₂ nanoparticles against HA oxidative damage offered by O₂^•-. These results indicate that F-MoS₂ nanoparticles are promising candidates for treatment of OA and other diseases caused by lubrication deficiency or oxidative stress.

Ultrafine and monodispersed iridium nanoparticles supported on nitrogen-functionalized carbon: an efficient oxidase mimic for glutathione colorimetric detection

Ultrafine and monodispersed Ir NPs supported on nitrogen-functionalized carbon served as an efficient oxidase mimic for glutathione colorimetric detection.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Silver-gold-apoferritin nanozyme for suppressing oxidative stress during cryopreservation

Reactive oxygen species (ROS) cause oxidative stress, which involves in the pathogenesis of many serious diseases. Apoferittin containing gold-silver nanoparticles (Au-Ag-AFT) was designed and evaluated as a nanozyme for scavenging the ROS. The nanozyme consisting of silver-gold nanohybrid in apoferittin cage represents superoxide dismutase, catalase and peroxidase mimetic activities. The Au-Ag-AFT nanozyme was characterized by spectroscopy, FESEM, TEM and dynamic light scattering. The inhibition process for pyrogallol autoxidation was used for assaying the superoxide dismutase mimetic activity and measuring the kinetic parameters of Au-Ag-AFT nanozyme. Additionally, Aebi method and standard protocol was used for evaluating the catalase and peroxidase mimetic activity. The k_cat values for superoxide dismutase, catalase and peroxidase mimetics activity were 1.4 × 10⁶, 0.1 and 9 × 10³ s^-1 respectively. These values indicated that Au-Ag-AFT nanozyme could act as a suitable ROS scavenger. Additionally, Au-Ag-AFT nanozyme was examined as a protective agent for human sperm against oxidative stress induced during the cryopreservation process. Presence of the nanozyme in the sperm media significantly increased the motility and viability of the cells and also decreased the ROS, apoptosis and necrosis (P < 0.05) compare to the control group.

Exploring the activities of ruthenium nanomaterials as reactive oxygen species scavengers

Research on noble metal nanoparticles (NPs) able to scavenge reactive oxygen species (ROS) has undergone a tremendous growth recently. However, the interactions between ruthenium nanoparticles (Ru NPs) and ROS have never been systematically explored thus far. This research focused on the decomposition of hydrogen peroxide (H₂O₂), scavenging of hydroxyl radicals (^•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), 2,2'-azino-bis(3-ethylbenzenothiazoline- 6-sulfonic acid ion (ABTS^•+), and 1,1-diphenyl-2-picrylhydrazyl radical (^•DPPH) in the presence of commercial Ru NPs using the electron spin resonance technique. In vitro cell studies demonstrated that Ru NPs have excellent biocompatibility and exert a cytoprotective effect against oxidative stress. These findings may spark fresh enthusiasm for the applications of Ru NPs under relevant physiologically conditions.

Amplified Peroxidase-Like Activity in Iron Oxide Nanoparticles Using Adenosine Monophosphate: Application to Urinary Protein Sensing

Numerous compounds such as protein and double-stranded DNA have been shown to efficiently inhibit intrinsic peroxidase-mimic activity in Fe₃O₄ nanoparticles (NP) and other related nanomaterials. However, only a few studies have focused on finding new compounds for enhancing the catalytic activity of Fe₃O₄ NP-related nanomaterials. Herein, phosphate containing adenosine analogs are reported to enhance the oxidation reaction of hydrogen peroxide (H₂O₂) and amplex ultrared (AU) for improving the peroxidase-like activity in Fe₃O₄ NPs. This enhancement is suggested to be a result of the binding of adenosine analogs to Fe²⁺/Fe³⁺ sites on the NP surface and from adenosine 5'-monophosphate (AMP) acting as the distal histidine residue of horseradish peroxidase for activating H₂O₂. Phosphate containing adenosine analogs revealed the following trend for the enhanced activity of Fe₃O₄ NPs: AMP > adenosine 5'-diphosphate > adenosine 5'-triphosphate. The peroxidase-like activity in the Fe₃O₄ NPs progressively increased with increasing AMP concentration and polyadenosine length. The Michaelis constant for AMP attached Fe₃O₄ NPs is 5.3-fold lower and the maximum velocity is 2.7-fold higher than those of the bare Fe₃O₄ NPs. Furthermore, on the basis of AMP promoted peroxidase mimicking activity in the Fe₃O₄ NPs and the adsorption of protein on the NP surface, a selective fluorescent turn-off system for the detection of urinary protein is developed.