Nanoceria as a DNase I mimicking nanozyme

Gadolinium Doping Modulates the Enzyme-like Activity and Radical-Scavenging Properties of CeO2 Nanoparticles

Their unique physicochemical properties and multi-enzymatic activity make CeO2 nanoparticles (CeO2 NPs) the most promising active component of the next generation of theranostic drugs. When doped with gadolinium ions, CeO2 NPs constitute a new type of contrast agent for magnetic resonance imaging, possessing improved biocatalytic properties and a high level of biocompatibility. The present study is focused on an in-depth analysis of the enzyme-like properties of gadolinium-doped CeO2 NPs (CeO2:Gd NPs) and their antioxidant activity against superoxide anion radicals, hydrogen peroxide, and alkylperoxyl radicals. Using an anion-exchange method, CeO2:Gd NPs (~5 nm) with various Gd-doping levels (10 mol.% or 20 mol.%) were synthesized. The radical-scavenging properties and biomimetic activities (namely SOD- and peroxidase-like activities) of CeO2:Gd NPs were assessed using a chemiluminescent method with selective chemical probes: luminol, lucigenin, and L-012 (a highly sensitive luminol analogue). In particular, gadolinium doping has been shown to enhance the radical-scavenging properties of CeO2 NPs. Unexpectedly, both bare CeO2 NPs and CeO2:Gd NPs did not exhibit SOD-like activity, acting as pro-oxidants and contributing to the generation of reactive oxygen species. Gadolinium doping caused an increase in the pro-oxidant properties of nanoscale CeO2. At the same time, CeO2:Gd NPs did not significantly inhibit the intrinsic activity of the natural enzyme superoxide dismutase, and CeO2:Gd NPs conjugated with SOD demonstrated SOD-like activity. In contrast to SOD-like properties, peroxidase-like activity was observed for both bare CeO2 NPs and CeO2:Gd NPs. This type of enzyme-like activity was found to be pH-dependent. In a neutral medium (pH = 7.4), nanoscale CeO2 acted as a prooxidant enzyme (peroxidase), while in an alkaline medium (pH = 8.6), it lost its catalytic properties; thus, it cannot be regarded as a nanozyme. Both gadolinium doping and conjugation with a natural enzyme were shown to modulate the interaction of CeO2 NPs with the key components of redox homeostasis.

Strategies to Promote the Journey of Nanoparticles Against Biofilm-Associated Infections

Biofilm-associated infections are one of the most challenging healthcare threats for humans, accounting for 80% of bacterial infections, leading to persistent and chronic infections. The conventional antibiotics still face their dilemma of poor therapeutic effects due to the high tolerance and resistance led by bacterial biofilm barriers. Nanotechnology-based antimicrobials, nanoparticles (NPs), are paid attention extensively and considered as promising alternative. This review focuses on the whole journey of NPs against biofilm-associated infections, and to clarify it clearly, the journey is divided into four processes in sequence as 1) Targeting biofilms, 2) Penetrating biofilm barrier, 3) Attaching to bacterial cells, and 4) Translocating through bacterial cell envelope. Through outlining the compositions and properties of biofilms and bacteria cells, recent advances and present the strategies of each process are comprehensively discussed to combat biofilm-associated infections, as well as the combined strategies against these infections with drug resistance, aiming to guide the rational design and facilitate wide application of NPs in biofilm-associated infections.

Surface Chemistry of Biologically Active Reducible Oxide Nanozymes

Reducible metal oxide nanozymes (rNZs) are a subject of intense recent interest due to their catalytic nature, ease of synthesis, and complex surface character. Such materials contain surface sites which facilitate enzyme-mimetic reactions via substrate coordination and redox cycling. Further, these surface reactive sites are shown to be highly sensitive to stresses within the nanomaterial lattice, the physicochemical environment, and to processing conditions occurring as part of their syntheses. When administered in vivo, a complex protein corona binds to the surface, redefining its biological identity and subsequent interactions within the biological system. Catalytic activities of rNZs each deliver a differing impact on protein corona formation, its composition, and in turn, their recognition, and internalization by host cells. Improving the understanding of the precise principles that dominate rNZ surface-biomolecule adsorption raises the question of whether designer rNZs can be engineered to prevent corona formation, or indeed to produce "custom" protein coronas applied either in vitro, and preadministration, or formed immediately upon their exposure to body fluids. Here, fundamental surface chemistry processes and their implications in rNZ material performance are considered. In particular, material structures which inform component adsorption from the application environment, including substrates for enzyme-mimetic reactions are discussed.

DNA flexible chain modified MOFs as a versatile platform for chemoenzymatic cascade reactions in glucose catalysis

Glucose oxidase (GOD) is widely used in the pharmaceutical industry, fermentation products and glucose biosensors for its essential role in catalyzing the conversion of glucose to gluconic acid and hydrogen peroxide (H2O2). As H2O2 is the by-product and will have a toxic effect on glucose oxidase, so introducing another enzyme that could consume H2O2 to form an enzymatic cascade reaction is a practical solution. However, this decision will lead to extra expenses and complex condition optimization such as the specific mass ratio, temperature and pH to improve the activity, stability and recyclability. Herein, we describe a mild and versatile strategy by anchoring GOD on carboxyl-activated MOF (Cu-TCPP(Fe)) through DNA-directed immobilization (DDI) technology. Robust MOF nanosheets were utilized as not only the carrier for the immobilization of GOD, but also a peroxidase-like catalyst for the decomposition of H2O2 to reduce its harmful impacts. In this work, the immobilized GOD retained 55.78% of its initial activity after being used for 7 times. More than 60% of the immobilized enzyme's catalytic activity was still maintained after 96 h of being stored at 50 ℃. This study provides a new idea for preparing immobilized enzymes with enhanced stability, fast diffusion and high activity, which can be used in fields such as biocatalysis and biotechnology.

Hydrolytic nanozymes: Preparation, properties, and applications

Hydrolytic nanozymes, as promising alternatives to hydrolytic enzymes, can efficiently catalyze the hydrolysis reactions and overcome the operating window limitations of natural enzymes. Moreover, they exhibit several merits such as relatively low cost, easier recovery and reuse, improved operating stability, and adjustable catalytic properties. Consequently, they have found relevance in practical applications such as organic synthesis, chemical weapon degradation, and biosensing. In this review, we highlight recent works addressing the broad topic of the development of hydrolytic nanozymes. We review the preparation, properties, and applications of six types of hydrolytic nanozymes, including AuNP-based nanozymes, polymeric nanozymes, surfactant assemblies, peptide assemblies, metal and metal oxide nanoparticles, and MOFs. Last, we discuss the remaining challenges and future directions. This review will stimulate the development and application of hydrolytic nanozymes.

Albumin Retains Its Transport Function after Interaction with Cerium Dioxide Nanoparticles

The interaction of inorganic nanomaterials with biological fluids containing proteins can lead not only to the formation of a protein corona and thereby to a change in the biological activity of nanoparticles but also to a significant effect on the structural and functional properties of the biomolecules themselves. This work studied the interaction of nanoscale CeO2, the most versatile nanozyme, with human serum albumin (HSA). Fourier transform infrared spectroscopy, MALDI-TOF mass spectrometry, UV-vis spectroscopy, and fluorescence spectroscopy confirmed the formation of HSA-CeO2 nanoparticle conjugates. Changes in protein conformation, which depend on the concentration of both citrate-stabilized CeO2 nanoparticles and pristine CeO2 nanoparticles, did not affect albumin drug-binding sites and, accordingly, did not impair the HSA transport function. The results obtained shed light on the biological consequences of the CeO2 nanoparticles' entrance into the body, which should be taken into account when engineering nanobiomaterials to increase their efficiency and reduce the side effects.

Ce-based solid-phase catalysts for phosphate hydrolysis as new tools for next-generation nanoarchitectonics

This review comprehensively covers synthetic catalysts for the hydrolysis of biorelevant phosphates and pyrophosphates, which bridge between nanoarchitectonics and biology to construct their interdisciplinary hybrids. In the early 1980s, remarkable catalytic activity of Ce4+ ion for phosphate hydrolysis was found. More recently, this finding has been extended to Ce-based solid catalysts (CeO2 and Ce-based metal-organic frameworks (MOFs)), which are directly compatible with nanoarchitectonics. Monoesters and triesters of phosphates, as well as pyrophosphates, were effectively cleaved by these catalysts. With the use of either CeO2 nanoparticles or elegantly designed Ce-based MOF, highly stable phosphodiester linkages were also hydrolyzed. On the surfaces of all these solid catalysts, Ce4+ and Ce3+ coexist and cooperate for the catalysis. The Ce4+ activates phosphate substrates as a strong acid, whereas the Ce3+ provides metal-bound hydroxide as an eminent nucleophile. Applications of these Ce-based catalysts to practical purposes are also discussed.

Transition Metal-Based Therapies for Inflammatory Diseases

Inflammatory disease (ID) is a general term that covers all diseases in which chronic inflammation performs as the major manifestation of pathogenesis. Traditional therapies based on the anti-inflammatory and immunosuppressive drugs are palliative with the short-term remission. The emergence of nanodrugs has been reported to solve the potential causes and prevent recurrences, thus holding great potential for the treatment of IDs. Among various nanomaterial systems, transition metal-based smart nanosystems (TMSNs) with unique electronic structures possess therapeutic advantages owing to their large surface area to volume ratio, high photothermal conversion efficiency, X-ray absorption capacity, and multiple catalytic enzyme activities. In this review, the rationale, design principle, and therapeutic mechanisms of TMSNs for treatments of various IDs are summarized. Specifically, TMSNs can not only be designed to scavenge danger signals, such as reactive oxygen and nitrogen species and cell-free DNA, but also can be engineered to block the mechanism of initiating inflammatory responses. In addition, TMSNs can be further applied as nanocarriers to deliver anti-inflammatory drugs. Finally, the opportunities and challenges of TMSNs are discussed, and the future directions of TMSN-based ID treatment for clinical applications are emphasized.

Development of nanozyme based sensors as diagnostic tools in clinic applications: a review

Since 1970, many artificial enzymes that imitate the activity and structure of natural enzymes have been discovered. Nanozymes are a group of nanomaterials with enzyme-mimetic properties capable of catalyzing natural enzyme processes. Nanozymes have attracted great interest in biomedicine due to their excellent stability, rapid reactivity, and affordable cost. The enzyme-mimetic activities of nanozymes may be modulated by numerous parameters, including the oxidative state of metal ions, pH, hydrogen peroxide (H2O2) level, and glutathione (GSH) concentration, indicating the tremendous potential for biological applications. This article delivers a comprehensive overview of the advances in the knowledge of nanozymes and the creation of unique and multifunctional nanozymes, and their biological applications. In addition, a future perspective of employing the as-designed nanozymes in biomedical and diagnostic applications is provided, and we also discuss the barriers and constraints for their further therapeutic use.

Antimicrobial activity and cytotoxicity study of cerium oxide nanoparticles with two different sizes

The control over bacterial diseases requires the development of novel antibacterial agents. The use of antibacterial nanomedicines is one of the strategies to tackle antibiotic resistance. The study was designed to assess the antimicrobial activity of cerium oxide (CeO₂ ) nanoparticles (NP) of two different sizes (CeO₂ NP1 [1-2 nm] and CeO₂ NP2 [10-12 nm]) and their cytotoxicity towards eukaryotic cells. The antimicrobial activity, effects of nanoparticles on DNA cleavage, microbial cell viability, and biofilm formation inhibition were analyzed. The impact of cerium oxide nanoparticles on eryptosis of erythrocytes was estimated using annexin V staining by flow cytometry. The newly synthesized CeO₂ NP1 and CeO₂ NP2 displayed moderate antimicrobial activities. CeO₂ NP1 and CeO₂ NP2 exhibited single-strand DNA cleavage ability. CeO₂ NPs were found to show 100% microbial cell viability inhibition at a concentration of 500 mg/L. In addition, CeO₂ NP1 and CeO₂ NP2 inhibited the biofilm formation of S. aureus and P. aeruginosa. Larger cerium oxide nanoparticles were found to be less toxic against erythrocytes compared with the smaller ones. CeO₂ nanoparticles demonstrate moderate antimicrobial activity and low cytotoxicity towards erythrocytes, which make them promising antibacterial agents.

Orthogonal light-triggered multiple effects based on photochromic nanoparticles for DNA cleavage and beyond

Efficient and spatiotemporally controllable cleavage of deoxyribonucleic acid (DNA) is of great significance for both disease treatment (e.g. tumour, bacterial infection, etc) and molecular biology applications (e.g. gene editing). The recently developed light-induced cleavage strategy based on catalytic nanoparticles has been regarded as a promising strategy for DNA controllable cleavage. Although the regulation based on orthogonal light in biomedical applications holds more significant advantages than that based on single light, nanoparticle-mediated DNA cleavage based on orthogonal light has yet to be reported. In this article, for the first time, we demonstrated an orthogonal light-regulated nanosystem for efficient and spatiotemporal DNA cleavage. In this strategy, tungsten oxide (WO₃) nanoparticles with photochromic properties were used as nano-antennae to convert the photoenergy from the orthogonal visible light (405 nm) and near-infrared light (808 nm) into chemical energy for DNA cleavage. We verified that only the orthogonal light can trigger high cleavage efficiency on different types of DNA. Moreover, such an orthogonal light-response nano-system can not only induce significant apoptosis of tumour cells, but also effectively eliminate bacterial biofilms.

Nanozyme's catalytic activity at neutral pH: reaction substrates and application in sensing

Nanozymes exhibit their great potential as alternatives to natural enzymes. In addition to catalytic activity, nanozymes also need to have biologically relevant catalytic reactions at physiological pH to fit in the definition of an enzyme and to achieve efficient analytical applications. Previous reviews in the nanozyme field mainly focused on the catalytic mechanisms, activity regulation, and types of catalytic reactions. In this paper, we discuss efforts made on the substrate-dependent catalytic activity of nanozymes at neutral pH. First, the discrepant catalytic activities for different substrates are compared, where the key differences are the characteristics of substrates and the adsorption of substrates by nanozymes at different pH. We then reviewed efforts to enhance reaction activity for model chromogenic substrates and strategies to engineer nanomaterials to accelerate reaction rates for other substrates at physiological pH. Finally, we also discussed methods to achieve efficient sensing applications at neutral pH using nanozymes. We believe that the nanozyme is catching up with enzymes rapidly in terms of reaction rates and reaction conditions. Designing nanozymes with specific catalysis for efficient sensing remains a challenge.

Pre-Folded G-Quadruplex as a Tunable Reporter to Facilitate CRISPR/Cas12a-Based Visual Nucleic Acid Diagnosis

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a-based detection strategies with a fluorophore quencher-labeled ssDNA reporter or gold nanoparticle ssDNA reporter have been widely used in point-of-care (POC) molecular diagnostics. However, the potential of these CRISPR/Cas12a strategies for POC molecular diagnostics is often compromised due to the complex labeling, high cost, and low signal-to-noise ratio. Herein, we show a pre-folded G-quadruplex (G4) structure with tunable tolerance to CRISPR/Cas12a trans-cleavage and explore its mechanism. Two G4 structures (i.e., Tel22-10 and G16C) sensitive or tolerant to CRISPR/Cas12a trans-cleavage are designed and used as signal elements to fabricate a label-free visible fluorescent strategy or "signal-on" colorimetric strategy, respectively. These two strategies facilitate an ultrasensitive visual nucleic acid determination of Group B Streptococci with a naked-eye limit of detection of 1 aM. The feasibility of the developed G4-assisted CRISPR/Cas12a strategies for real-world applications is demonstrated in clinical vaginal/anal specimens and further verified by a commercial qPCR assay. This work suggests that the proposed G4 structures with tunable tolerance can act as promising signal reporters in the CRISPR/Cas12a system to enable ultrasensitive visible nucleic acid detection.

Emerging nanozyme-based multimodal synergistic therapies in combating bacterial infections

Pathogenic infections have emerged as major threats to global public health. Multidrug resistance induced by the abuse of antibiotics makes the anti-infection therapies to be a global challenge. Thus, it is urgent to develop novel, efficient and biosafe antibiotic alternatives for future antibacterial therapy. Recently, nanozymes have emerged as promising antibiotic alternatives for combating bacterial infections. More significantly, the multimodal synergistic nanozyme-based antibacterial systems open novel disinfection pathways. In this review, we are mainly focusing on the recent research progress of nanozyme-based multimodal synergistic therapies to eliminate bacterial infections. Their antibacterial mechanism, the synergistic antibacterial systems are systematically summarized and discussed according to the combination of mechanisms and the purpose to improve their antibacterial efficiency, biosafety and specificity. Finanly, the current challenges and prospects of the multimodal synergistic antibacterial systems are proposed.

Central Nervous System Injury Meets Nanoceria: Opportunities and Challenges

Central nervous system (CNS) injury, induced by ischemic/hemorrhagic or traumatic damage, is one of the most common causes of death and long-term disability worldwide. Reactive oxygen and nitrogen species (RONS) resulting in oxidative/nitrosative stress play a critical role in the pathological cascade of molecular events after CNS injury. Therefore, by targeting RONS, antioxidant therapies have been intensively explored in previous studies. However, traditional antioxidants have achieved limited success thus far, and the development of new antioxidants to achieve highly effective RONS modulation in CNS injury still remains a great challenge. With the rapid development of nanotechnology, novel nanomaterials provided promising opportunities to address this challenge. Within these, nanoceria has gained much attention due to its regenerative and excellent RONS elimination capability. To promote its practical application, it is important to know what has been done and what has yet to be done. This review aims to present the opportunities and challenges of nanoceria in treating CNS injury. The physicochemical properties of nanoceria and its interaction with RONS are described. The applications of nanoceria for stroke and neurotrauma treatment are summarized. The possible directions for future application of nanoceria in CNS injury treatment are proposed.

Nanozymes-recent development and biomedical applications

Nanozyme is a series of nanomaterials with enzyme-mimetic activities that can proceed with the catalytic reactions of natural enzymes. In the field of biomedicine, nanozymes are capturing tremendous attention due to their high stability and low cost. Enzyme-mimetic activities of nanozymes can be regulated by multiple factors, such as the chemical state of metal ion, pH, hydrogen peroxide (H₂O₂), and glutathione (GSH) level, presenting great promise for biomedical applications. Over the past decade, multi-functional nanozymes have been developed for various biomedical applications. To promote the understandings of nanozymes and the development of novel and multifunctional nanozymes, we herein provide a comprehensive review of the nanozymes and their applications in the biomedical field. Nanozymes with versatile enzyme-like properties are briefly overviewed, and their mechanism and application are discussed to provide understandings for future research. Finally, underlying challenges and prospects of nanozymes in the biomedical frontier are discussed in this review.

Insights on catalytic mechanism of CeO2 as multiple nanozymes

CeO₂ with the reversible Ce³⁺/Ce⁴⁺ redox pair exhibits multiple enzyme-like catalytic performance, which has been recognized as a promising nanozyme with potentials for disease diagnosis and treatments. Tailorable surface physicochemical properties of various CeO₂ catalysts with controllable sizes, morphologies, and surface states enable a rich surface chemistry for their interactions with various molecules and species, thus delivering a wide variety of catalytic behaviors under different conditions. Despite the significant progress made in developing CeO₂-based nanozymes and their explorations for practical applications, their catalytic activity and specificity are still uncompetitive to their counterparts of natural enzymes under physiological environments. With the attempt to provide the insights on the rational design of highly performed CeO₂ nanozymes, this review focuses on the recent explorations on the catalytic mechanisms of CeO₂ with multiple enzyme-like performance. Given the detailed discussion and proposed perspectives, we hope this review can raise more interest and stimulate more efforts on this multi-disciplinary field.

Hierarchically mesoporous Ce-based MOFs with enhanced alkaline phosphatase-like activity for phosphorylated biomarker sensing

We developed a hierarchically mesoporous metal–organic framework nanozyme with enhanced alkaline phosphatase-mimicking activity for rapid and sensitive sensing of phosphorylated biomarkers.

New facets of nanozyme activity of ceria: lipo- and phospholipoperoxidase-like behaviour of CeO2 nanoparticles

Cerium dioxide nanoparticles have a special place among engineered nanomaterials due to the wide range of their enzyme-like activities. They possess SOD-, catalase- and peroxidase-like properties, as well as recently discovered phosphatase-, photolyase-, phospholipase- and nuclease-like properties. Advancing biomedical applications of CeO₂-based nanozymes requires an understanding of the features and mechanisms of the redox activity of CeO₂ nanoparticles when entering the vascular bed, especially when interacting with lipid-protein supramolecular complexes (biomembranes and lipoproteins). In this paper, CeO₂ nanoparticles are shown to possess two further types of nanozyme activity, namely lipo- and phospholipoperoxidase-like activities. Compared to a strong blood prooxidant, hemoglobin, CeO₂ nanoparticles act as a mild oxidising agent, since they exhibit a 10⁶ times lower, and 20 times lower, prooxidant capacity towards linoleic acid and phosphatidylcholine hydroperoxides, respectively. Compared to the widespread pharmacological preparation of iron, Fe(iii) carboxymaltose (antianemic preparation Ferinject®), the prooxidant capacity of CeO₂ nanoparticles towards lipid and phospholipid substrates has been shown to be 10² times lower, and 4 times higher, respectively. The data obtained on the mechanism of the interaction of nanodisperse CeO₂ with the main components of biological membranes, lipids and phospholipids enable the substantial expansion of the scope of biomedical applications of CeO₂ nanozymes.

CeO₂ nanoparticles were shown to possess two novel types of enzyme-like activity, namely lipoperoxidase and phospholipoperoxidase activity.

In Situ Fabrication of Nanoceria with Oxidase-like Activity at Neutral pH: Mechanism and Boosted Bio-Nanozyme Cascades

Catalytic cascades have drawn much attention by avoiding the isolation of intermediates and due to high atom economy. Yet, developing an efficient, one-pot biocatalytic cascade remains challenging. Combined with the selectivity of biological enzymes and tunable activity of nanozymes, we herein demonstrate an effective bio-nanozyme cascade formed by glucose oxidase (GOx) and in situ-generated nanoceria. The prepared H₂O₂-nanoceria complex shows strong oxidative activity for common chromogenic substrates under physiological conditions, which are the optimal reaction conditions for most biological enzymes. Interestingly, GOx not only provides H₂O₂ for the second step reaction but also simultaneously leads to 7.4-fold enhancement of activity. We characterized the process of in situ generation of nanoceria at pH 7.0 and how proteins boost the activity by enhancing product desorption. In addition, the proposed one-pot bio-nanozyme cascade shows high stability and analytical performance for serum glucose with a detection limit of 5 μM.

Nanozyme Catalytic Turnover and Self-Limited Reactions

Enzymes have catalytic turnovers. The field of nanozyme endeavors to engineer nanomaterials as enzyme mimics. However, a discrepancy in the definition of "nanozyme concentration" has led to an unrealistic calculation of nanozyme catalytic turnovers. To date, most of the reported works have considered either the atomic concentration or nanoparticle (NP) concentration as nanozyme concentration. These assumptions can lead to a significant under- or overestimation of the catalytic activity of nanozymes. In this article, we review some classic nanozymes including Fe₃O₄, CeO₂, and gold nanoparticles (AuNPs) with a focus on the reported catalytic activities. We argue that only the surface atoms should be considered as nanozyme active sites, and then the turnover numbers and rates were recalculated based on the surface atoms. According to the calculations, the catalytic turnover of peroxidase Fe₃O₄ NPs is validated. AuNPs are self-limited when performing glucose-oxidase like activity, but they are also true catalysts. For CeO₂ NPs, a self-limited behavior is observed for both oxidase- and phosphatase-like activities due to the adsorption of reaction products. Moreover, the catalytic activity of single-atom nanozymes is discussed. Finally, a few suggestions for future research are proposed.

Nanoceria, the versatile nanoparticles: Promising biomedical applications

Nanotechnology has been a boon for the biomedical field due to the freedom it provides for tailoring of pharmacokinetic properties of different drug molecules. Nanomedicine is the medical application of nanotechnology for the diagnosis, treatment and/or management of the diseases. Cerium oxide nanoparticles (CNPs) are metal oxide-based nanoparticles (NPs) which possess outstanding reactive oxygen species (ROS) scavenging activities primarily due to the availability of "oxidation switch" on their surface. These NP have been found to protect from a number of disorders with a background of oxidative stress such as cancer, diabetes etc. In fact, the CNPs have been found to possess the environment-dependent ROS modulating properties. In addition, the inherent catalase, SOD, oxidase, peroxidase and phosphatase mimetic properties of CNPs provide them superiority over a number of NPs. Further, chemical reactivity of CNPs seems to be a function of their surface chemistry which can be precisely tuned by defect engineering. However, the contradictory reports make it necessary to critically evaluate the potential of CNPs, in the light of available literature. The review is aimed at probing the feasibility of CNPs to push towards the clinical studies. Further, we have also covered and censoriously discussed the suspected negative impacts of CNPs before making our way to a consensus. This review aims to be a comprehensive, authoritative, critical, and accessible review of general interest to the scientific community.

Biocatalytic Nanomaterials: A New Pathway for Bacterial Disinfection

Clinical treatment of pathogenic infection has emerged as a growing challenge in global public health. Such treatment is currently limited to antibiotics, but abuse of antibiotics have induced multidrug resistance and high fatality rates in anti-infection therapies. Thus, it is vital to develop alternative bactericidal agents to open novel disinfection pathways. Drawing inspiration from elements of the human immune system that show great potential for controlling pathogens or regulating cell apoptosis, the design of biocatalytic nanomaterials (BCNs) have provided unrivaled opportunities for future antibacterial therapies. More significantly, BCNs exhibit various superior properties to immune cells and natural enzymes, such as higher biocatalytic performance, extraordinary stability against harsh conditions, and scalable production. In this review, the most recent efforts toward developing BCN-based biomedical applications in combating bacterial infections are focused upon. BCNs' antibacterial mechanisms, the classification of BCNs, antibacterial activities that can be triggered or augmented by energy conversion, and the eradication of biofilms with BCNs are systematically introduced and discussed. The current challenges and prospects of BCNs for biocatalytic disinfection are also summarized. It is anticipated this review will provide new therapeutic insights into combating bacteria and biofilms and offer significant new inspiration for designing future biocatalytic nanomaterials.

Ceria Nanozyme and Phosphate Prodrugs: Drug Synthesis through Enzyme Mimicry

Nanozymes can mimic the activities of diverse enzymes, and this ability finds applications in analytical sciences and industrial chemistry, as well as in biomedical applications. Among the latter, prodrug conversion mediated by nanozymes is investigated as a step toward site-specific drug synthesis, to achieve localized therapeutic effects. In this work, we investigated a ceria nanozyme as a mimic to phosphatase, to mediate conversion of phosphate prodrugs into corresponding therapeutics. To this end, the substrate scope of ceria as a phosphatase mimic was analyzed using a broad range of natural phosphor(di)esters and pyrophosphates. Knowledge of this scope guided the selection of existing phosphate prodrugs that can be converted by ceria into the corresponding therapeutics. "Extended scaffold phosphates" were engineered using self-immolative linkers to accommodate a prodrug design for amine-containing drugs, such as monomethyl auristatin E. Phosphate prodrugs masked activity of the toxin, whereas prodrug conversion mediated by the nanozyme restored drug toxicity, which was validated in mammalian cell culture. The main novelty of this work lies in the rational pairing of the ceria nanozyme with the existing and the de novo designed "extended scaffold" phosphate prodrugs toward their use in nanozyme-prodrug therapy based on the defined nanozyme substrate scope.

Multifaceted Therapy of Nanocatalysts in Neurological Diseases

With the development of enzymes immobilization technology and the discover of nanozymes, catalytic therapy exhibited tremendous potential for neurological diseases therapy. In especial, since the discovery of Fe₃O₄ nanoparticles possessing intrinsic peroxidase-like activity, various nanozymes have been developed and recently started to explore for neurological diseases therapy, such as Alzheimer's disease, Parkinson's disease and stroke. By combining the catalytic activities with other properties (such as optical, thermal, electrical, and magnetic properties) of nanomaterials, the multifunctional nanozymes would not only alleviate oxidative and nitrosative stress on the basis of multienzymes-mimicking activity, but also exert positive effects on immunization, inflammation, autophagy, protein aggregation, which provides the foundation for multifaceted treatments. This review will summarize various types of nanocatalysts and further provides a valuable discussion on multifaceted treatment by nanozymes for neurological diseases, which is anticipated to provide an easily accessible guide to the key opportunities and current challenges of the nanozymes-mediated treatments for neurological diseases.

The phosphatase-like activity of zirconium oxide nanoparticles and their application in near-infrared intracellular imaging

In this study, the phosphatase mimetic activity of zirconium oxide nanoparticles (ZrO2 NPs) has been demonstrated. They can effectively catalyze the dephosphorylation of a series of commercial fluorogenic and chromogenic substrates of natural phosphatases. Compared with natural phosphatases, ZrO2 NPs possess several advantages such as low cost, facile preparation procedures, and high stability in a broader pH range or at high temperatures. In addition, the activity of ZrO2 NPs toward some important biomolecules was investigated. The ZrO2 NPs can catalyze the dephosphorylation of ATP and o-phospho-l-tyrosine, but they cannot react with DNA strands. These data are important for the further bio-related applications of ZrO2 NPs. Finally, the potential application of ZrO2 NPs in intracellular imaging is also demonstrated by using a near-infrared fluorescent substrate of alkaline phosphatase.

In vitro selection and application of lanthanide-dependent DNAzymes

Highly sensitive and selective detection of lanthanide ions is a major analytical challenge. In recent years, the use of DNA for this purpose has been pursued. For such highly charged cations, it is difficult to select their aptamers due to strong nonspecific binding. On the other hand, the use of catalytic DNA or DNAzymes has an advantage to overcome this problem, especially DNAzymes with RNA-cleaving activity. In this chapter, a few such DNAzymes are introduced and methods for in vitro selection of lanthanide-dependent RNA-cleaving DNAzymes are described in detail, including the selection protocols, the DNA sequences used, the characterization of selected DNAzymes and their conversion into biosensors. All of the experiments use only fluorophore-labeled DNA, and radioisotope labeling is completely avoided. The resulting DNAzymes can distinguish lanthanides from non-lanthanide metals, tell the difference between light and heavy lanthanides, and can be used together to discriminate individual lanthanides.

Chemiluminescence of the Ce(IV)/CDP-Star System Based on the Phosphatase-like Activity of Ce(IV) Ions

The phosphatase-like activity of Ce(IV) ions was applied for chemiluminescence (CL) analysis for the first time. Ce(IV) can catalyze the hydrolysis of CDP-star, which is a phosphatase substrate, to produce strong CL emission. The CL performance of the Ce(IV)/CDP-star system can be significantly improved by the addition of ionic liquids. In the presence of 1-butyl-3-methylimidazolium tetrafluoroborate, the selective and sensitive CL detection of Ce(IV) ions was achieved with a detection limit of 460 nM. The proposed CL system was also used for the detection of ascorbic acid and ClO-. It is based on the phenomenon that Ce(IV) can catalyze the hydrolysis of CDP-star, while Ce(III) cannot. The introduction of reductive ascorbic acid into the mixture of Ce(IV)/CDP-star can turn off the CL signal, while the addition of oxidative ClO- into the solution of Ce(III)/CDP-star can turn on the CL emission. Finally, Ce(IV)/CDP-star CL was successfully applied for evaluating the total antioxidant capacity in commercial fruit juice samples.

Nanozyme's catching up: activity, specificity, reaction conditions and reaction types

Nanozymes aim to mimic enzyme activities. In addition to catalytic activity, nanozymes also need to have specificity and catalyze biologically relevant reactions under physiological conditions to fit in the definition of enzyme and to set nanozymes apart from typical inorganic catalysts. Previous discussions in the nanozyme field mainly focused on the types of reactions or certain analytical, biomedical or environmental applications. In this article, we discuss efforts made to mimic enzymes. First, the catalytic cycles are compared, where a key difference is specific substrate binding by enzymes versus non-specific substrate adsorption by nanozymes. We then reviewed efforts to engineer and surface-modify nanomaterials to accelerate reaction rates, strategies to graft affinity ligands and molecularly imprinted polymers to achieve specific catalysis, and methods to bring nanozyme reactions to neutral pH and ambient temperature. Most of the current nanozyme reactions used a few model chromogenic substrates of no biological relevance. Therefore, we also reviewed efforts to catalyze the conversion of biomolecules and biopolymers using nanozymes. By the efforts to close the gaps between nanozymes and enzymes, we believe nanozymes are catching up rapidly. Still, challenges exist in materials design to further improve nanozymes as true enzyme mimics and achieve impactful applications.

R, Sissi C, Pecina A, Riccardi L, De Vivo M, Mancin F, Scrimin P. A Gold Nanoparticle Nanonuclease Relying on a Zn(II) Mononuclear Complex

Similarly to enzymes, functionalized gold nanoparticles efficiently catalyze chemical reactions, hence the term nanozymes. Herein, we present our results showing how surface-passivated gold nanoparticles behave as synthetic nanonucleases, able to cleave pBR322 plasmid DNA with the highest efficiency reported so far for catalysts based on a single metal ion mechanism. Experimental and computational data indicate that we have been successful in creating a catalytic site precisely mimicking that suggested for natural metallonucleases relying on a single metal ion for their activity. It comprises one Zn(II) ion to which a phosphate diester of DNA is coordinated. Importantly, as in nucleic acids-processing enzymes, a positively charged arginine plays a key role by assisting with transition state stabilization and by reducing the pKa of the nucleophilic alcohol of a serine. Our results also show how designing a catalyst for a model substrate (bis-p-nitrophenylphosphate) may provide wrong indications as for its efficiency when it is tested against the real target (plasmid DNA).

Preparing Selective Nanozymes by Molecular Imprinting

Recently, many nanomaterials such as Fe₃O₄, CeO₂, and gold nanoparticles have been reported to have enzyme-like activities and they are called nanozymes. Although these nanozymes have oxidase or peroxidase-like activities, they can catalyze the oxidation of many substrates and thus lack the specificity expected for enzymes. The selectivity of nanozymes can be significantly enhanced up to 100-fold by coating them with a molecularly imprinted polymer (MIP) layer. Since MIP creates specific binding pockets for the imprinted substrate, the imprinted molecules can be enriched, selectively access the catalytic core, and be oxidized, while other substrates are blocked from accessing the nanozyme surface. In this chapter, the detailed protocol for the preparation of the MIP-coated Fe₃O₄ peroxidase-mimicking nanozymes is described. In addition, some procedures needing special attention are described in detail, which will facilitate the applications of MIP-coated nanozymes in analytical, biomedical, and environmental fields.

Porphyrin metalation catalyzed by DNAzymes and nanozymes

In this review, DNA and nanomaterial based catalysts for porphyrin metalation reactions are summarized, including the selection of DNAzymes, choice of nanomaterials, their catalytic mechanisms, and applications of the reactions.

Assessment of pulmonary toxicity of potential antioxidant drug PEGylated nanoceria after intratracheal instillation in rats

Cerium oxide (CeO₂ ) nanoparticles have unique redox properties and exert excellent antioxidant effects in the biological environment. In recent years, many researchers have focused on the CeO₂ nanoparticles as an effective antioxidant drug in the prevention and treatment of various diseases. However, the toxicity of CeO₂ nanoparticles in vivo remains controversial and still needs intensive research. Therefore, the objective of this study is to investigate the pulmonary and systemic toxicity in rats after 14 days of exposure to the PEGylated CeO₂ nanoparticles (abbreviated as CNPs; exposure dose of 2, 10, or 20 mg/kg) through a single intratracheal instillation (IT). We assessed the indicators of lung injury and the pathological damage degree of lung tissue. The bronchoalveolar lavage fluid (BALF) analysis and lung histopathology revealed the occurrence of slight pulmonary inflammation in the 20-mg/kg experimental group rats. However, the inflammation factors in the lung tissue of every group rats did not significantly increase, and the levels of superoxide dismutase (SOD) and glutathione (GSH) in lung tissue homogenate rose considerably in the experimental groups. Collectively, these results indicated that pulmonary exposure by the high dose of CNPs could induce mild pulmonary inflammation but did not cause severe systemic toxicity. Moreover, we speculate that the mechanism of pulmonary toxicity of CNPs in rats was due to the autophagic death of healthy lung epithelial cells mediated by endoplasmic reticulum stress. Our results implicate that CNPs can be safely used as an antioxidant drug for the oxidative stress pulmonary diseases.

Designing signal-on sensors by regulating nanozyme activity

Nanozymes are nanomaterials with enzyme-like activities. Compared to natural enzymes, nanozymes are more stable and cost-effective, and they have unique properties due to their nanoscale size and surface chemistry. In this review, we summarize 'signal-on' nanozyme-based sensors for detecting metal ions, anions, small molecules and proteins. Since protein-based enzymes are already highly active, they were used to detect their inhibitors, resulting in 'signal-off' sensors. On the other hand, for nanozymes, target molecules were detected either as a promotor of nanozyme activity or for its ability to selectively remove nanozyme inhibitors. In both cases, 'signal-on' detection was achieved. We classify the commonly used nanozymes based on their composition such as metal oxide, gold nanoparticles and other nanomaterials, most of which belong to the oxidase, peroxidase and catalase mimics. The nanozymes can catalyze the oxidation of colorless or non-fluorescent substrates to produce a visual or fluorescent signal. Based on this, this article presents some typical 'turn-on' and 'turn-off-on' sensors, and we critically review their design principles. At the end, further perspectives for the nanozyme-based sensors are outlined.

Cerium Oxide Nanoparticles: Recent Advances in Tissue Engineering

Submicron biomaterials have recently been found with a wide range of applications for biomedical purposes, mostly due to a considerable decrement in size and an increment in surface area. There have been several attempts to use innovative nanoscale biomaterials for tissue repair and tissue regeneration. One of the most significant metal oxide nanoparticles (NPs), with numerous potential uses in future medicine, is engineered cerium oxide (CeO2) nanoparticles (CeONPs), also known as nanoceria. Although many advancements have been reported so far, nanotoxicological studies suggest that the nanomaterial's characteristics lie behind its potential toxicity. Particularly, physicochemical properties can explain the positive and negative interactions between CeONPs and biosystems at molecular levels. This review represents recent advances of CeONPs in biomedical engineering, with a special focus on tissue engineering and regenerative medicine. In addition, a summary report of the toxicity evidence on CeONPs with a view toward their biomedical applications and physicochemical properties is presented. Considering the critical role of nanoengineering in the manipulation and optimization of CeONPs, it is expected that this class of nanoengineered biomaterials plays a promising role in the future of tissue engineering and regenerative medicine.

Cleaving DNA by nanozymes

Various nanomaterials can mimic the activities of nucleases for hydrolytic and oxidative DNA cleavage on different sites allowing interesting biomedical and bioanalytical applications.