A colorimetric sensor for rapid discrimination of tea polyphenols and tea authentication based on Rh-decorated Pd nanocubes with high peroxidase-like activity

The rapid development of nanozymes has offered substantial opportunities for the fields of biomedicine, chemical sensing, and food safety. Among these applications, multichannel sensors, with the capability of simultaneously detecting multiple target analytes, hold promise for the practical application of nanozymes in chemical sensing with high detection efficiency. In this study, Rh-decorated Pd nanocubes (Pd-Rh nanocubes) with significantly enhanced peroxidase-like activity are synthesized through the mediation of underpotential deposition (UPD) and subsequently employed to develop a multichannel colorimetric sensor for discriminating tea polyphenols (TPs) and tea authentication. Based on a single reactive unit of efficient catalytic oxidation of 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB), the nanozyme-based multichannel colorimetric sensor responds to each analyte in as short as 1 min. With the aid of principal component analysis (PCA) and hierarchical cluster analysis (HCA), various TPs and types of tea can be accurately identified. This work not only provides a new type of simply structured and highly active nanozymes but also develops a concise and rapid multichannel sensor for practical application in tea authentication and quality inspection.

Carbon-based nanozymes: design, catalytic mechanisms, and environmental applications

Carbon-based nanozymes are synthetic nanomaterials that are predominantly constituted of carbon-based materials, which mimic the catalytic properties of natural enzymes, boasting features such as tunable catalytic activity, robust regenerative capacity, and exceptional stability. Due to the impressive enzymatic performance similar to various enzymes such as peroxidase, superoxide dismutase, and oxidase, they are widely used for detecting and degrading pollutants in the environment. This paper presents an exhaustive review of the fundamental design principles, catalytic mechanisms, and prospective applications of carbon-based nanozymes in the environmental field. These studies not only serve to augment the comprehension on the intricate operational mechanism inherent in these synthetic nanostructures, but also provide essential guidelines and illuminating perspectives for advancing their development and practical applications. Future studies that are imperative to delve into the untapped potential of carbon-based nanozymes within the environmental domain was needed to be explored to fully harness their ability to deliver broader and more impactful environmental preservation and management outcomes.

Multiplexed Detection Strategies for Biosensors Based on the CRISPR-Cas System

A growing number of applications require simultaneous detection of multiplexed nucleic acid targets in a single reaction, which enables higher information density in combination with reduced assay time and cost. Clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR-Cas system have broad applications for the detection of nucleic acids due to their strong specificity, high sensitivity, and excellent programmability. However, realizing multiplexed detection is still challenging for the CRISPR-Cas system due to the nonspecific collateral cleavage activity, limited signal reporting strategies, and possible cross-reactions. In this review, we summarize the principles, strategies, and features of multiplexed detection based on the CRISPR-Cas system and further discuss the challenges and perspective.

Atomically dispersed bimetallic active sites as H2O2 self-supplied nanozyme for effective chemodynamic therapy, chemotherapy and starvation therapy

Tumor microenvironment (TME)-responsive chemodynamic therapy (CDT) is severely hindered by insufficient intracellular H2O2 level that seriously deteriorates antitumor efficacy, albeit with its extensively experimental and theoretical research. Herein, we designed atomically dispersed FeCo dual active sites anchored in porous carbon polyhedra (termed FeCo/PCP), followed by loading with glucose oxidase (GOx) and anticancer doxorubicin (DOX), named FeCo/PCP-GOx-DOX, which converted glucose into toxic hydroxyl radicals. The loaded GOx can either decompose glucose to self-supply H2O2 or provide fewer nutrients to feed the tumor cells. The as-prepared nanozyme exhibited the enhanced in vitro cytotoxicity at high glucose by contrast with those at less or even free of glucose, suggesting sufficient accumulation of H2O2 and continual transformation to OH for CDT. Besides, the FeCo/PCP-GOx-DOX can subtly integrate starvation therapy, the FeCo/PCP-initiated CDT, and DOX-inducible chemotherapy (CT), greatly enhancing the therapeutic efficacy than each monotherapy.

Macromolecule-Nanoparticle-Based Hybrid Materials for Biosensor Applications

Biosensors function as sophisticated devices, converting biochemical reactions into electrical signals. Contemporary emphasis on developing biosensor devices with refined sensitivity and selectivity is critical due to their extensive functional capabilities. However, a significant challenge lies in the binding affinity of biosensors to biomolecules, requiring adept conversion and amplification of interactions into various signal modalities like electrical, optical, gravimetric, and electrochemical outputs. Overcoming challenges associated with sensitivity, detection limits, response time, reproducibility, and stability is essential for efficient biosensor creation. The central aspect of the fabrication of any biosensor is focused towards forming an effective interface between the analyte electrode which significantly influences the overall biosensor quality. Polymers and macromolecular systems are favored for their distinct properties and versatile applications. Enhancing the properties and conductivity of these systems can be achieved through incorporating nanoparticles or carbonaceous moieties. Hybrid composite materials, possessing a unique combination of attributes like advanced sensitivity, selectivity, thermal stability, mechanical flexibility, biocompatibility, and tunable electrical properties, emerge as promising candidates for biosensor applications. In addition, this approach enhances the electrochemical response, signal amplification, and stability of fabricated biosensors, contributing to their effectiveness. This review predominantly explores recent advancements in utilizing macrocyclic and macromolecular conjugated systems, such as phthalocyanines, porphyrins, polymers, etc. and their hybrids, with a specific focus on signal amplification in biosensors. It comprehensively covers synthetic strategies, properties, working mechanisms, and the potential of these systems for detecting biomolecules like glucose, hydrogen peroxide, uric acid, ascorbic acid, dopamine, cholesterol, amino acids, and cancer cells. Furthermore, this review delves into the progress made, elucidating the mechanisms responsible for signal amplification. The Conclusion addresses the challenges and future directions of macromolecule-based hybrids in biosensor applications, providing a concise overview of this evolving field. The narrative emphasizes the importance of biosensor technology advancement, illustrating the role of smart design and material enhancement in improving performance across various domains.

Photo-Switchable Peroxidase/Catalase-Like Activity of Carbon Quantum Dots

Nanozymes possess multi-enzyme activities over the natural enzymes, which produce multi-pathway synergistic effects for varies of biomedical applications. Unfortunately, their multi-enzyme activities are in fighting, significantly reducing the synergistic effects. Dynamic regulation of their multi-enzyme activities is the bottleneck for intelligent therapies. Herein, we construct a novel oxygen-nitrogen functionalized carbon quantum dots (O/N-CQDs) with peroxidase-like (Reactive oxygen species (ROS) producer) activity. Interestingly, the peroxidase-like activity can be reversibly converted to catalase-like (ROS scavenger) activity under visible light irradiation. It is found that both the peroxidase/catalase-like activity of O/N-CQDs can be precisely manipulated by the light intensity. The mechanism of switchable enzyme activities is attributed to the polarization of quinoid nitrogen in polyaniline (PANI) precursor retained on O/N-CQDs under visible light, which consumes the ROS to produce O2 and H2O. As a proof-of-concept demonstration, we are able to non-intrusively up and down regulate the ROS level in cells successfully by simply switching off and on the light respectively, potentially facilitating the precise medicine based on the development of the disease. Indeed, the photo-switchable peroxidase/catalase-like activity of O/N-CQDs opens a non-invasive strategy for better manipulations of the multi-activity of nanozymes, promising their wider and more intelligent biomedical applications.

Catalytic Nanoparticles in Biomedical Applications: Exploiting Advanced Nanozymes for Therapeutics and Diagnostics

Catalytic nanoparticles (CNPs) as heterogeneous catalyst reveals superior activity due to their physio-chemical features, such as high surface-to-volume ratio and unique optical, electric, and magnetic properties. The CNPs, based on their physio-chemical nature, can either increase the reactive oxygen species (ROS) level for tumor and antibacterial therapy or eliminate the ROS for cytoprotection, anti-inflammation, and anti-aging. In addition, the catalytic activity of nanozymes can specifically trigger a specific reaction accompanied by the optical feature change, presenting the feasibility of biosensor and bioimaging applications. Undoubtedly, CNPs play a pivotal role in pushing the evolution of technologies in medical and clinical fields, and advanced strategies and nanomaterials rely on the input of chemical experts to develop. Herein, a systematic and comprehensive review of the challenges and recent development of CNPs for biomedical applications is presented from the viewpoint of advanced nanomaterial with unique catalytic activity and additional functions. Furthermore, the biosafety issue of applying biodegradable and non-biodegradable nanozymes and future perspectives are critically discussed to guide a promising direction in developing span-new nanozymes and more intelligent strategies for overcoming the current clinical limitations.

Preparation and Application of Carbon Dots Nanozymes

Carbon dot (CD) nanozymes have enzyme-like activity. Compared with natural enzymes, CD nanozymes offer several advantages, including simple preparation, easy preservation, good stability and recycling, which has made them a popular research topic in various fields. In recent years, researchers have prepared a variety of CD nanozymes for biosensing detection, medicine and tumor therapy, and many of them are based on oxidative stress regulation and reactive oxygen species clearance. Particularly to expand their potential applications, elemental doping has been utilized to enhance the catalytic capabilities and other properties of CD nanozymes. This review discusses the prevalent techniques utilized in the synthesis of CD nanozymes and presents the diverse applications of CD nanozymes based on their doping characteristics. Finally, the challenges encountered in the current utilization of CD nanozymes are presented. The latest research progress of synthesis, application and the challenges outlined in the review can help and encourage the researchers for the future research on preparation, application and other related researches of CD nanozymes.

Phenylglycine amphiphile-metal ion chiral supramolecular nanozymes for enantioselective catalysis

L/D-Phenylglycine amphiphiles and metal ions with peroxidase-like activity self-assembled into chiral nanoribbons, which act as efficient chiral supramolecular nanozymes for catalyzing the 3,4-dihydroxy-L/D-phenylalanine (L/D-DOPA) oxidation reactions. The catalytic efficiency and enantioselectivity are dominated by the chirality transfer and the synergistic effect between the metal ions and chiral nanoribbons.

Enantioselective and Band-Gap Modulation in Photocatalysis of Metal-Free Chiral Carbon Dots

Photodriven chiral catalysis is the combination of photocatalysis and chiral catalysis and is considered one of the cleanest and most efficient methods for the synthesis of chiral compounds or drugs. Furthermore, due to the potential metal contamination associated with most metal-based catalysts, metal-free chiral photocatalysts are ideal candidates. In this work, we demonstrate that metal-free chiral carbon dots (CDs) exhibit size-dependent enantioselective photocatalytic activity. Using serine as the raw material, chiral CDs with well-defined structures and average sizes of 2.22, 3.01, 3.70, 4.77, and 7.21 nm were synthesized using the electrochemical method. These chiral CDs possess size-dependent band gaps and exhibit photoresponsive enantioselective catalytic activity toward the oxidation of dihydroxyphenylalanine (DOPA). Under light-assisted conditions, chiral CDs (L72, 500 μg/mL) exhibit high selectivity (selectivity factor: 2.07) and maintain a certain level of catalytic activity (1.34 μM/min) even at a low temperature of 5 °C. The high catalytic activity of the chiral CDs arises from their photoelectrons reducing O2 to generate O2-, as the active oxygen species for DOPA oxidation. The high enantioselectivity of the chiral CDs is attributed to their differential adsorption capabilities toward DOPA enantiomers. This study provides a new approach for designing metal-free chiral photocatalysts with high enantioselectivity.

Enhanced the intrinsic oxidase-like activity of chiral carbon dots via manganese doping for selective catalytic oxidation

It is highly desirable to design and construct chemical catalysts with high activity and specificity as the alternatives of natural enzymes for industrial application. Chiral carbon dots (CDs), possessing both the intrinsic enzyme-like activity and specific recognition ability, are one of good candidates for enzyme-like catalysts. However, their catalytic activity is far from that of natural enzymes and needs to be enhanced. In this work, the modulation of the chiral structure and catalytic activity of chiral CDs with intrinsic oxidase-like activity was implemented by manganese (Mn) doping. Under the light condition, chiral CDs (l-Ser-CDs and d-Ser-CDs) derived from chiral serine (Ser) show weak catalytic activity and low selectivity toward the oxidation of L type of dopamine (l-DOPA), whereas the Mn functionalized chiral CDs (l-Mn-CDs or d-Mn-CDs) exhibit 6.9 times higher in catalytic activity and 2.9 times in selectivity ratio (SR) than Ser-CDs. Mn-CDs involve two-path catalytic process, in which the photogenerated electrons could reduce O2 to O2- as the active species and the holes would oxidize DOPA directly. Moreover, doping of Mn enables the CDs to generate more O2-. Besides, l-Mn-CDs have higher catalytic activity than that of d-Mn-CDs (+54.2 %), and the chiral Mn-CDs have stronger selective adsorption capacity towards chiral DOPA than Ser-CDs. Our work provides a new method for designing and preparing novel chiral artificial enzymes.

Development of Optical Differential Sensing Based on Nanomaterials for Biological Analysis

The discrimination and recognition of biological targets, such as proteins, cells, and bacteria, are of utmost importance in various fields of biological research and production. These include areas like biological medicine, clinical diagnosis, and microbiology analysis. In order to efficiently and cost-effectively identify a specific target from a wide range of possibilities, researchers have developed a technique called differential sensing. Unlike traditional "lock-and-key" sensors that rely on specific interactions between receptors and analytes, differential sensing makes use of cross-reactive receptors. These sensors offer less specificity but can cross-react with a wide range of analytes to produce a large amount of data. Many pattern recognition strategies have been developed and have shown promising results in identifying complex analytes. To create advanced sensor arrays for higher analysis efficiency and larger recognizing range, various nanomaterials have been utilized as sensing probes. These nanomaterials possess distinct molecular affinities, optical/electrical properties, and biological compatibility, and are conveniently functionalized. In this review, our focus is on recently reported optical sensor arrays that utilize nanomaterials to discriminate bioanalytes, including proteins, cells, and bacteria.

Development of a flow injection chemiluminescence immunoassay based on DES-mediated CuCo2O4 nanoenzyme for ultrasensitive detection of zearalenone in foods

Nanoenzymes have been widely used to construct biosensors because of their cost-effectiveness, high stability, and easy modification. At the same time, the discovery of deep eutectic solvents (DES) was a great breakthrough in green chemistry, and their combination with different materials can improve the sensing performance of biosensors. In this work, we report an immunosensor using CuCo2O4 nanoenzyme combined with flow injection chemiluminescence immunoassay for the automated detection of zearalenone (ZEN). The immunosensor exhibited excellent sensing performance. Under the optimal conditions, the detection range of ZEN was 0.0001-100 ng mL-1, and the limit of detection (LOD) was 0.076 pg mL-1 (S/N = 3). In addition, the immunosensor showed excellent stability with a relative standard deviation (RSD) of 2.65% for  15 repetitive  injections. The method has been successfully applied to the analysis of real samples with satisfactory recovery results, and can hence provide a reference for the detection of small molecules in food and feed.

Copper Nanodots-Based Hybrid Hydrogels with Multiple Enzyme Activities for Acute and Infected Wound Repair

Effectively controlling bacterial infection, reducing the inflammation and promoting vascular regeneration are all essential strategies for wound repair. Nanozyme technology has potential applications in the treatment of infections because its non-antibiotic dependent, topical and noninvasive nature. In wound management, copper-based nanozymes have emerged as viable alternatives to antibiotics. In this study, an ultrasmall cupric enzyme with high enzymatic activity is synthesized and added to a nontoxic, self-healing, injectable cationic guar gum (CG) hydrogel network. The nanozyme exhibits remarkable antioxidant properties under neutral conditions, effectively scavenging reactive nitrogen and oxygen species (RNOS). Under acidic conditions, Cu NDs have peroxide (POD) enzyme-like activity, which allows them to eliminate hydrogen peroxides and produce free radicals locally. Antibacterial experiments show that they can kill bacteria and remove biofilms. It reveals that low concentrations of Cu ND/CG decrease the expression of the inflammatory factors in cells and tissues, effectively controlling inflammatory responses. Cu ND/CG hydrogels also inhibit HIF-1α and promote VEGF expression in the wound with the ability to promote vascular regeneration. In vivo safety assessments reveal a favorable biosafety profile. Cu ND/CG hydrogels offer a promising solution for treating acute and infected wounds, highlighting the potential of innovative nanomaterials in wound healing.

Biosystem-Inspired Engineering of Nanozymes for Biomedical Applications

Nanozymes with intrinsic enzyme-mimicking activities have shown great potential to become surrogates of natural enzymes in many fields by virtue of their advantages of high catalytic stability, ease of functionalization, and low cost. However, due to the lack of predictable descriptors, most of the nanozymes reported in the past have been obtained mainly through trial-and-error strategies, and the catalytic efficacy, substrate specificity, as well as practical application effect under physiological conditions, are far inferior to that of natural enzymes. To optimize the catalytic efficacies and functions of nanozymes in biomedical settings, recent studies have introduced biosystem-inspired strategies into nanozyme design. In this review, recent advances in the engineering of biosystem-inspired nanozymes by leveraging the refined catalytic structure of natural enzymes, simulating the behavior changes of natural enzymes in the catalytic process, and mimicking the specific biological processes or living organisms, are introduced. Furthermore, the currently involved biomedical applications of biosystem-inspired nanozymes are summarized. More importantly, the current opportunities and challenges of the design and application of biosystem-inspired nanozymes are discussed. It is hoped that the studies of nanozymes based on bioinspired strategies will be beneficial for constructing the new generation of nanozymes and broadening their biomedical applications.

Colorimetric assay for α-amanitin based on inhibition of carbon dots/AuNPs nanoenzyme activity

Accidental ingestion of poisonous mushrooms leading to poisoning is a global issue. The most important and lethal toxin causing mushroom poisoning is α-amanitin, with a lethal dose of about 0.1 mg kg-1. Rapid detection of wild mushrooms before consumption or rapid identification of toxins after poisoning can effectively reduce the occurrence of fatalities. This study established a method for detecting α-amanitin using carbon dots/AuNPs nanoenzymes (D-Glu-CDs/AuNPs) with robust peroxidase-like activity. This nanoenzyme was prepared employing glucose carbon dots and sodium citrate as reducing and stabilizing agents, respectively. It could oxidize the substrate TMB (tetramethylbenzidine) to produce blue o-TMB. When α-amanitin specifically bound to the active site of the nanoenzyme, a resultant decrease was observed in catalytic activity and the absorbance value at 652 nm. The regression equation Y = -0.06083x + 0.9643, with an R2 value of 0.996, was obtained. The limit of detection was determined to be 48.03 ng mL-1, and the recoveries in urine ranged from 91.2% to 97.6%. This method enabled the visualization of α-amanitin, and the whole detection process was completed within 20 min. The approach holds promise for the quantitative and qualitative determination of α-amanitin in urine samples.

Fe-codoped carbon dots serving as a peroxidase mimic to generate in situ hydrogen peroxide for the visual detection of glucose

Nanozyme technology has gained significant regard and been successfully implemented in various applications including chemical sensing, bio-medicine, and environmental monitoring. Fe-CDs were synthesized and characterized well in this study. As compared to HRP (3.7 mM), the Fe-CDs exhibited a higher affinity towards H2O2 (0.2 mM) using the steady-state kinetic assay and stronger catalytic capability by changing the color of TMB to the blue color of the oxidized state, oxTMB. Additionally, an efficient peroxidase mimic, Fe-CDs/GOx, based on the hybrid cascade system to produce in situ H2O2 for the visual detection of glucose (color change: colorless to blue, and then to green), has been developed in detail, with limits of detection (LODs) for H2O2 and glucose of 0.33 μM and 1.17 μM, respectively. The changes further demonstrate a linear relationship between absorbance and H2O2 concentration, ranging from 10 to 60 μM, and for glucose (1 to 60 μM). To assess the accuracy and detection capability of the Fe-CDs/GOx system, we evaluated a real human serum sample obtained from adult males in a local hospital. In conclusion, Fe-CDs serving as a peroxidase mimic have the potential for various applications in the fields of biomedicine and nanozymes.

Nanozyme-Engineered Hydrogels for Anti-Inflammation and Skin Regeneration

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

Hydrous ruthenium oxide triggers template-free and spontaneous growth of metal nanostructures

Intrinsically conductive ruthenium oxide is an excellent material for energy storage and conversion. Herein, we present hydrous RuO2 (H-RuO2) as a potent reducing agent to achieve spontaneous growth of multiple noble metals at room temperature. Self-assembled gold and platinum, comprising small-sized nanoparticles, are generated on the surface of H-RuO2 without the need for additional templates. Structural analysis reveals that the disordered structure and the presence of oxygen vacancies trigger interfacial redox reactions between H-RuO2 and oxidative metal salts. The resulting integrated nanostructures, consisting of a metal oxide and different metals (H-RuO2@metal), are subsequently used to treat inflammatory bowel diseases. In addition to biomedical applications, our developed synthetic strategy, using reactive oxides to spontaneously generate multicomponent nanostructures, also holds great significance for other catalysis-based applications.

Recent Progress and Prospect of Metal-Organic Framework-Based Nanozymes in Biomedical Application

A nanozyme is a nanoscale material having enzyme-like properties. It exhibits several superior properties, including low preparation cost, robust catalytic activity, and long-term storage at ambient temperatures. Moreover, high stability enables repetitive use in multiple catalytic reactions. Hence, it is considered a potential replacement for natural enzymes. Enormous research interest in nanozymes in the past two decades has made it imperative to look for better enzyme-mimicking materials for biomedical applications. Given this, research on metal-organic frameworks (MOFs) as a potential nanozyme material has gained momentum. MOFs are advanced hybrid materials made of inorganic metal ions and organic ligands. Their distinct composition, adaptable pore size, structural diversity, and ease in the tunability of physicochemical properties enable MOFs to mimic enzyme-like activities and act as promising nanozyme candidates. This review aims to discuss recent advances in the development of MOF-based nanozymes (MOF-NZs) and highlight their applications in the field of biomedicine. Firstly, different enzyme-mimetic activities exhibited by MOFs are discussed, and insights are given into various strategies to achieve them. Modification and functionalization strategies are deliberated to obtain MOF-NZs with enhanced catalytic activity. Subsequently, applications of MOF-NZs in the biosensing and therapeutics domain are discussed. Finally, the review is concluded by giving insights into the challenges encountered with MOF-NZs and possible directions to overcome them in the future. With this review, we aim to encourage consolidated efforts across enzyme engineering, nanotechnology, materials science, and biomedicine disciplines to inspire exciting innovations in this emerging yet promising field.

Specializing Carbon Nanozyme Active Sites for Sensitive Alkaline Phosphatase Activity Metal-Free Detection

As biological enzymes regulate metabolic processes, alkaline phosphatase (ALP) is a critical diagnostic indicator associated with many diseases. To accurately measure the enzyme activity, nanozymactic materials can offer sensitive strategies for ALP detection. However, nanozymes often lack specific target binding sites, and the presence of common co-components, e. g., metal ions, may cause false-positive or false-negative results in enzyme activity determination. Herein, we developed a colorimetric assay for ALP detection using metal-free nanozymatic carbon dots (CDs). The ALP hydrolysis of pyrophosphate ions (PPi) to phosphate ions (Pi) induces a "turn-on" response based on the nanozyme activity. This PPi-induced inhibition mechanism is extensively studied via the Michaelis-Menten model, revealing that PPi acts as a noncompetitive inhibitor for CDs at a binding site distinct from the common nanozyme active site. With superior responses to ALP substrates, a highly sensitive and selective method is established for sensing ALP activity with a linear range of 0.010-0.200 U/L and a detection limit of 0.009 U/L. This finding explores the recognition and binding behavior of nanozymes, allowing for precise and reliable measurements even in complex samples, and represents a significant breakthrough for nanozyme-based assays in biological analysis.

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

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

Polyoxometalates as Potential Artificial Enzymes toward Biological Applications

Artificial enzymes, as alternatives to natural enzymes, have attracted enormous attention in the fields of catalysis, biosensing, diagnostics, and therapeutics because of their high stability and low cost. Polyoxometalates (POMs), a class of inorganic metal oxides, have recently shown great potential in mimicking enzyme activity due to their well-defined structure, tunable composition, high catalytic efficiency, and easy storage properties. This review focuses on the recent advances in POM-based artificial enzymes. Different types of POMs and their derivatives-based mimetic enzyme functions are covered, as well as the corresponding catalytic mechanisms (where available). An overview of the broad applications of representative POM-based artificial enzymes from biosensing to theragnostic is provided. Insight into the current challenges and the future directions for POMs-based artificial enzymes is discussed.

Ultrasmall calcium-enriched Prussian blue nanozymes promote chronic wound healing by remodeling the wound microenvironment

Chronic wound healing remains challenging due to the oxidative microenvironment. Prussian blue (PB) nanoparticles exhibiting multiple antioxidant enzyme-like activities have attracted widespread attention, while their antioxidant efficacy remains unsatisfied. Herein, ultrasmall calcium-enriched Prussian blue nanoparticles (CaPB NPs) are simply constructed with high yields for the wound repair application. Owing to the ultrasmall size and synergistic effect of the generated dual active sites, the CaPB NPs exhibit prominent antioxidase-like activities, protecting cells from oxidative stress-induced damage. In addition to the effect of Ca on regulating keratinocyte and fibroblast growth, it has been demonstrated that the administration of CaPB NPs obviously promoted wound closure as well as collagen deposition and neovascularization in the full-thickness wound defect model in mice. Importantly, the CaPB NP treatment can effectively up-regulate the expression levels of anti-inflammatory cytokines and vascular endothelial growth factors to remodel the wound microenvironment, thereby accelerating the wound healing process. Overall, this work reveals that metal atom substitution is an effective strategy to construct ultrasmall and high-catalytic-performance PB-based nanozymes and further potentiate their effectiveness for chronic wound management.

Utilising the Nanozymatic Activity of Copper-Functionalised Mesoporous C3 N5 for Sensing Biomolecules

Designing unique nanomaterials for the selective sensing of biomolecules is of significant interest in the field of nanobiotechnology. In this work, we demonstrated the synthesis of ordered Cu nanoparticle-functionalised mesoporous C3 N5 that has unique peroxidase-like nanozymatic activity for the ultrasensitive and selective detection of glucose and glutathione. A nano hard-templating technique together with the in-situ polymerisation and self-assembly of Cu and high N-containing CN precursor was adopted to introduce mesoporosity as well as high N and Cu content in mesoporous C3 N5 . Due to the ordered structure and highly dispersed Cu in the mesoporous C3 N5 , a large enhancement of the peroxidase mimetic activity in the oxidation of a redox dye in the presence of hydrogen peroxide could be obtained. Additionally, the optimised Cu-functionalised mesoporous C3 N5 exhibited excellent sensitivity to glutathione with a low detection limit of 2.0 ppm. The strong peroxidase activity of the Cu-functionalised mesoporous C3 N5 was also effectively used for the sensing of glucose with a detection limit of 0.4 mM through glucose oxidation with glucose oxidase. This unique Cu-functionalised mesoporous C3 N5 has the potential for detecting various molecules in the environment as well as for next-generation glucose and glutathione diagnostic devices.

Deep Insight of Design, Mechanism, and Cancer Theranostic Strategy of Nanozymes

Since the discovery of enzyme-like activity of Fe3O4 nanoparticles in 2007, nanozymes are becoming the promising substitutes for natural enzymes due to their advantages of high catalytic activity, low cost, mild reaction conditions, good stability, and suitable for large-scale production. Recently, with the cross fusion of nanomedicine and nanocatalysis, nanozyme-based theranostic strategies attract great attention, since the enzymatic reactions can be triggered in the tumor microenvironment to achieve good curative effect with substrate specificity and low side effects. Thus, various nanozymes have been developed and used for tumor therapy. In this review, more than 270 research articles are discussed systematically to present progress in the past five years. First, the discovery and development of nanozymes are summarized. Second, classification and catalytic mechanism of nanozymes are discussed. Third, activity prediction and rational design of nanozymes are focused by highlighting the methods of density functional theory, machine learning, biomimetic and chemical design. Then, synergistic theranostic strategy of nanozymes are introduced. Finally, current challenges and future prospects of nanozymes used for tumor theranostic are outlined, including selectivity, biosafety, repeatability and stability, in-depth catalytic mechanism, predicting and evaluating activities.

Coal waste-derived synthesis of yellow oxidized graphene quantum dots with highly specific superoxide dismutase activity: characterization, kinetics, and biological studies

The disintegration of coal-based precursors for the scalable production of nanozymes relies on the fate of solvothermal pyrolysis. Herein, we report a novel economic and scalable strategy to fabricate yellow luminescent graphene quantum dots (YGQDs) by remediating unburnt coal waste (CW). The YGQDs (size: 7-8 nm; M.W: 3157.9 Da) were produced using in situ "anion-radical" assisted bond cleavage in water (within 8 h; at 121 °C) with yields of ∼87%. The presence of exposed surface and edge groups, such as COOH, C-O-C, and O-H, as structural defects accounted for its high fluorescence with εmax ∼530 nm at pH 7. Besides, these defects also acted as radical stabilizers, demonstrating prominent anti-oxidative activity of ∼4.5-fold higher than standard ascorbic acid (AA). In addition, the YGQDs showed high biocompatibility towards mammalian cells, with 500 μM of treatment dose showing <15% cell death. The YGQDs demonstrated specific superoxide dismutase (SOD) activity wherein 15 μM YGQDs equalled the activity of 1-unit biological SOD (bSOD), measured using the pyrogallol assay. The Km for YGQDs was ∼10-fold higher than that for bSOD. However, the YGQDs retained their SOD activity in harsh conditions like high temperatures or denaturing reactions, where the activity of bSOD is completely lost. The binding affinity of YGQDs for superoxide ions, measured from isothermal calorimetry (ITC) studies, was only 10-fold lower than that of bSOD (Kd of 586 nM vs. 57.3 nM). Further, the pre-treatment of YGQDs (∼10-25 μM) increased the cell survivability to >75-90% in three cell lines during ROS-mediated cell death, with the highest survivability being shown for C6-cells. Next, the ROS-induced apoptosis in C6-cells (model for neurodegenerative diseases study), wherein YGQDs uptake was confirmed by confocal microscopy, showed ∼5-fold apoptosis alleviation with only 5 μM pretreatment. The YGQDs also restored the expression of pro-inflammatory Th1 cytokines (TNF-α, IFN-γ, IL-6) and anti-inflammatory Th2 cytokines (IL-10) to their basal levels, with a net >3-fold change observed. This further explains the molecular mechanism for the antioxidant property of YGQDs. The high specific SOD activity associated with YGQDs may provide the cheapest alternative source for producing large-scale SOD-based nanozymes that can treat various oxidative stress-linked disorders/diseases.

Metal-Free Peroxidase-Mimetic Nanocatalysts for Chemodynamic Vascular-Disrupting Cancer Therapy

Metal ion-facilitated chemodynamic therapy (CDT) is an emerging method for treating cancer. However, its potential is hindered by its low catalytic performance in weakly acidic tumor microenvironments (TMEs) and the severe toxicity of free metal ions. A new approach to tumor therapy, chemodynamic vascular disruption (CVD), is introduced using metal-free, peroxidase (POD)-mimetic multihydroxylated [70] fullerene (MHF) nanocatalysts. The research shows that MHF contains C···O active sites, as demonstrated by density functional theory (DFT) calculations, and converts H2 O2 into ∙OH across a pH range of 6.0-10.0. The generation of ∙OH and the dismantling of tumor blood vessels are observed in real-time using mouse dorsal skin-fold chamber (DSFC) models. Applying proteomics, it is discovered that the CVD mechanism involves the nanocatalytic MHF enhancing H2 O2 decomposition in the TME, producing ∙OH. This damages tumor vascular endothelial junction proteins, causing vascular leakage and subsequently cutting off the vascular supply to the tumor cells. This method deviates from the traditional CDT that targets tumor cells. Instead, the proficient MHF nanocatalysts aim to directly disrupt the tumor vasculature, enhancing anti-tumor efficiency without triggering harmful toxicity. The proposed CVD therapeutic strategy enhances the application of gentle carbon nanocatalysts in cancer therapy, offering new perspectives on nanocatalytic medicine.

Emerging enzyme-based nanocomposites for catalytic biomedicine

With the promising advances in nanomedicine, numerous strategies have emerged for the diagnosis and treatment of diseases. Among them, enzyme-based multifunctional nanocomposites have attracted a great deal of attention in the field of catalytic biomedicine. These nanocomposites with high catalytic activity are capable of converting low/non-toxic substances into therapeutic ones, thus realizing highly efficient, site-specific therapy with minimal side effects. Enzyme-based nanocomposites for catalytic biomedicine are mainly divided into three types: (i) natural-enzyme based nanocomposites; (ii) artificial-nanozyme based nanocomposites; and (iii) nanocomposites of natural-enzymes and nanozymes. In this review, we discuss key aspects of enzyme-based catalytic biomedicine, including the construction of enzyme-based nanocomposites, their unique properties and applications in catalytic biomedicine. We also highlight the main challenges faced in this field, and provide relevant guidelines for the rational design and extensive application of enzyme-based nanocomposites from our point of view.

Nanozyme-Based Biofuel Cell Ingeniously Coupled with Luminol Chemiluminescence System through In Situ Co-Reactant Generation for Dual-Signal Biosensing

Classical luminol-based chemiluminescence (CL) is the process of emitting light enhanced by the addition of coreactant hydrogen peroxide (H2O2). To address the instability issue of H2O2 decomposition, herein, we proposed a nanozyme-based biofuel cell (BFC) ingeniously coupled with a luminol CL system via in situ generation of H2O2. Specifically, the gold nanoparticle (AuNP) nanozyme with glucose oxidase-like activity can act as the anodic enzyme of BFC to catalyze the oxidation of glucose to produce H2O2 and electrons. In this case, H2O2 as a coreactant enhanced the CL intensity and the cathode of the BFC obtained electrons to generate the open circuit voltage (EOCV) signals. As a result, a dual-signal biosensing platform was successfully constructed. Interestingly, the AuNPs-catalyzed system operates in an alkaline medium, which precisely meets the pH requirement for luminol luminescence. Such a BFC-CL system not only greatly lessens the effect of unstable exogenous H2O2 on the signal stability but also enhances the CL of luminol. Furthermore, both CL and EOCV signals present a positive correlation with the glucose concentration. Therefore, this novel BFC-CL system shows good performance for dual-signal biosensing, which would serve as a valuable guideline for the design and application of BFC-based self-powered or CL biosensors.

Review of paper-based microfluidic analytical devices for in-field testing of pathogens

Pathogens cause various infectious diseases and high morbidity and mortality which is a global public health threat. The highly sensitive and specific detection is of significant importance for the effective treatment and intervention to minimise the impact. However, conventional detection methods including culture and molecular method gravely depend on expensive equipment and well-trained skilled personnel, limiting in the laboratory. It remains challenging to adapt in resource-limiting areas, e.g., low and middle-income countries (LMICs). To this end, low-cost, rapid, and sensitive detection tools with the capability of field testing e.g., a portable device for identification and quantification of pathogens, has attracted increasing attentions. Recently, paper-based microfluidic analytical devices (μPADs) have shown a promising tool for rapid and on-site diagnosis, providing a cost-effective and sensitive analytical approach for pathogens detection. The fast turn-round data collection may also contribute to better understanding of the risks and insights on mitigation method. In this paper, critical developments of μPADs for in-field detection of pathogens both for clinical diagnostics and environmental surveillance are reviewed. The future development, and challenges of μPADs for rapid and onsite detection of pathogens are discussed, including using the cross-disciplinary development with, emerging techniques such as deep learning and Internet of Things (IoT).

Reactive oxygen nanobiocatalysts: activity-mechanism disclosures, catalytic center evolutions, and changing states

Benefiting from low costs, structural diversities, tunable catalytic activities, feasible modifications, and high stability compared to the natural enzymes, reactive oxygen nanobiocatalysts (RONBCs) have become dominant materials in catalyzing and mediating reactive oxygen species (ROS) for diverse biomedical and biological applications. Decoding the catalytic mechanism and structure-reactivity relationship of RONBCs is critical to guide their future developments. Here, this timely review comprehensively summarizes the recent breakthroughs and future trends in creating and decoding RONBCs. First, the fundamental classification, activity, detection method, and reaction mechanism for biocatalytic ROS generation and elimination have been systematically disclosed. Then, the merits, modulation strategies, structure evolutions, and state-of-art characterisation techniques for designing RONBCs have been briefly outlined. Thereafter, we thoroughly discuss different RONBCs based on the reported major material species, including metal compounds, carbon nanostructures, and organic networks. In particular, we offer particular insights into the coordination microenvironments, bond interactions, reaction pathways, and performance comparisons to disclose the structure-reactivity relationships and mechanisms. In the end, the future challenge and perspectives for RONBCs are also carefully summarised. We envision that this review will provide a comprehensive understanding and guidance for designing ROS-catalytic materials and stimulate the wide utilisation of RONBCs in diverse biomedical and biological applications.

Bimetallic Ions Functionalized Metal-Organic-Framework Nanozyme for Tumor Microenvironment Regulating and Enhanced Photodynamic Therapy for Hypoxic Tumor

Photodynamic therapy (PDT), as a light irradiation inducing reactive oxygen species (ROS) generation for cancer treatment, offers facile and promising solutions with respect to spatiotemporal control of ROS generation, and minimizes the systemic toxicity and side effects for highly precise tumor therapy. However, the PDT efficiency is often severely compromised by the complex tumor microenvironment (TME), such as the hypoxic condition and overexpressed antioxidants. Here, for the first time, a bimetallic ion-modified metal-organic framework nanozyme (Zr4+ -MOF-Ru3+ /Pt4+ -Ce6@HA, ZMRPC@HA) is designed. ZMRPC@HA with catalase (CAT) and glutathione oxidase (GSHOx) mimetic activities, can efficiently regulate TME by generation of O2 and deplete the GSH synergistically for enhancing the long-term PDT efficacy toward the hypoxic tumor. The in vitro cell inhibition and in vivo on tumor xenograft evaluations demonstrate the PDT strategy by using ZMRPC@HA can successfully inhibit the differentiation and proliferation of tumor cells under a 660 nm laser irradiation in deep tissues. These findings open a new avenue for the design of multimetallic ions functionalized MOF-based nanozymes with multienzyme mimetic activities toward the antitumor and various other biological applications.

Pathogen-Targeting Bimetallic Nanozymes as Ultrasonic-Augmented ROS Generator against Multidrug Resistant Bacterial Infection

Clinical treatment of multidrug resistant (MDR) pathogens-induced infection is emerging as a growing challenge in global public health due to the limited selection of clinically available antibiotics. Nanozymes as artificial enzymes that mimicked natural enzyme-like activities, are received great attention for combating MDR pathogens. However, the relatively deficient catalytic activity in the infectious microenvironment and inability to precisely targeting pathogen restrains their clinical anti-MDR applications. Here, pathogen-targeting bimetallic BiPt nanozymes for nanocatalytic therapy against MDR pathogen are reported. Benefiting from electronic coordination effect, BiPt nanozymes exhibit dual-enzymatic activities, including peroxidase-mimic and oxidase-mimic activities. Moreover, the catalytic efficiency can be efficiently increased 300-fold by ultrasound under inflammatory microenvironment. Notably, BiPt nanozyme is further cloaked with a platelet-bacteria hybrid membrane (BiPt@HMVs), thus presenting excellent homing effect to infectious sites and precise homologous targeting to pathogen. By integrating accurate targeting with highly efficient catalytic, BiPt@HMVs can eliminate carbapenem-resistant Enterobacterales and methicillin-resistant Staphylococcus aureus in osteomyelitis rats model, muscle-infected mice model, and pneumonia mice model. The work provides an alternative strategy based on nanozymes for clinically addressing MDR bacteria-induced infections.

Specific detection of fungicide thiophanate-methyl: A smartphone colorimetric sensor based on target-regulated oxidase-like activity of copper-doped carbon nanozyme

Nanozyme-based colorimetric assays have shown great potential in the rapid and sensitive determination of pesticide residue in environment. However, the non-specific enzyme inhibition makes the assays generally lack of selectivity. In this study, we proposed a colorimetric sensing platform for the specific detection of the agricultural fungicide thiophanate-methyl (TM) based on its distinctive inhibitory effect on the nanozyme activity. Since TM contains the symmetric ethylenediamine- and bisthiourea-like groups, it displays strong affinity to the metal site, leading to a loss of the catalytic activity. Accordingly, a Cu-doped carbon nanozyme with excellent oxidase-like properties was designed, and the oxidation process of chromogenic substrate is promoted by Cu-induced generation of reactive oxygen species. Interestingly, the nanozyme activity can be directly and strongly restrained by TM, rather than other probably coexistent pesticides. Consequently, the as-proposed analytical method exhibits specific response toward TM and good linear relationship in the range of 0.2-15 μg mL-1 with a low limit of detection of 0.04 μg mL-1 (S/N = 3). Besides, a smartphone-assisted rapid detection was achieved through identifying the RGB value of the chromogenic system. This work provides a new nanozyme inhibition strategy for the specific detection of TM in environmental sample.

Recent Progresses in Optical Biosensors for Interleukin 6 Detection

Interleukin 6 (IL-6) is pleiotropic cytokine with pathological pro-inflammatory effects in various acute, chronic and infectious diseases. It is involved in a variety of biological processes including immune regulation, hematopoiesis, tissue repair, inflammation, oncogenesis, metabolic control, and sleep. Due to its important role as a biomarker of many types of diseases, its detection in small amounts and with high selectivity is of particular importance in medical and biological fields. Laboratory methods including enzyme-linked immunoassays (ELISAs) and chemiluminescent immunoassays (CLIAs) are the most common conventional methods for IL-6 detection. However, these techniques suffer from the complexity of the method, the expensiveness, and the time-consuming process of obtaining the results. In recent years, too many attempts have been conducted to provide simple, rapid, economical, and user-friendly analytical approaches to monitor IL-6. In this regard, biosensors are considered desirable tools for IL-6 detection because of their special features such as high sensitivity, rapid detection time, ease of use, and ease of miniaturization. In this review, current progresses in different types of optical biosensors as the most favorable types of biosensors for the detection of IL-6 are discussed, evaluated, and compared.

Biomimetic and bioorthogonal nanozymes for biomedical applications

Nanozymes mimic the function of enzymes, which drive essential intracellular chemical reactions that govern biological processes. They efficiently generate or degrade specific biomolecules that can initiate or inhibit biological processes, regulating cellular behaviors. Two approaches for utilizing nanozymes in intracellular chemistry have been reported. Biomimetic catalysis replicates the identical reactions of natural enzymes, and bioorthogonal catalysis enables chemistries inaccessible in cells. Various nanozymes based on nanomaterials and catalytic metals are employed to attain intended specific catalysis in cells either to mimic the enzymatic mechanism and kinetics or expand inaccessible chemistries. Each nanozyme approach has its own intrinsic advantages and limitations, making them complementary for diverse and specific applications. This review summarizes the strategies for intracellular catalysis and applications of biomimetic and bioorthogonal nanozymes, including a discussion of their limitations and future research directions.

Carbon-Based Enzyme Mimetics for Electrochemical Biosensing

Natural enzymes are used as special reagents for the preparation of electrochemical (bio)sensors due to their ability to catalyze processes, improving the selectivity of detection. However, some drawbacks, such as denaturation in harsh experimental conditions and their rapid de- gradation, as well as the high cost and difficulties in recycling them, restrict their practical applications. Nowadays, the use of artificial enzymes, mostly based on nanomaterials, mimicking the functions of natural products, has been growing. These so-called nanozymes present several advantages over natural enzymes, such as enhanced stability, low cost, easy production, and rapid activity. These outstanding features are responsible for their widespread use in areas such as catalysis, energy, imaging, sensing, or biomedicine. These materials can be divided into two main groups: metal and carbon-based nanozymes. The latter provides additional advantages compared to metal nanozymes, i.e., stable and tuneable activity and good biocompatibility, mimicking enzyme activities such as those of peroxidase, catalase, oxidase, superoxide dismutase, nuclease, or phosphatase. In this review article, we have focused on the use of carbon-based nanozymes for the preparation of electrochemical (bio)sensors. The main features of the most recent applications have been revised and illustrated with examples selected from the literature over the last four years (since 2020).

Highly Active Single-Atom Nanozymes with High-Loading Iridium for Sensitive Detection of Pesticides

Single-atom nanozymes (SAzymes) are novel mimic-enzyme materials with atomically doped active sites. They play a pivotal role in the field of nanozymes because of their excellent catalytic activities, high utilization efficiency of the metal atoms, and simple model of active sites. Herein, the peroxidase (POD)-like SAzymes with high-loading iridium (Ir) (5.31%) on graphene oxide (GO) nanosheets [Ir(III)/GO] were prepared through a coordination reaction between the Ir(III) complex and the oxygen-containing groups in GO. The preparation strategy avoids nitrogen doping and pyrolysis procedures which are the usually used strategies to improve the GO-based enzyme mimic activity. Ascribed to the highly active Ir atoms, Ir(III)/GO SAzymes demonstrate outstanding POD-like activity without the oxidase-like activity. In advantage of the excellent POD-like activity, a simple and sensitive colorimetric pesticide detection platform is established. The developed sensing platform offers an excellent "switch-on" pirimicarb (PIB) detection in the linear range of 10-300 nM with a limit of detection (LOD) of 2.81 nM. Moreover, the detection platform was fabricated into a portable test kit, which is composed of a test swab and sample processing tube. In the aid of a color-reading APP, the test kit can detect PIB with the LOD of 3.31 nM. It is astonishing to get this excellent detection sensitivity just using the simple colorimetric strategy. This work not only provides a novel strategy to synthesize Ir-based SAzymes but also exhibits the super capability of Ir(III)/GO in the biosensing field.

Magnetic three-phase single-drop microextraction for highly sensitive detection of aflatoxin B1 in agricultural product samples based on peroxidase-like spatial network structure

In this work, a highly sensitive method for aflatoxin B₁ (AFB₁) detection was developed based on a peroxidase-like spatial network structure. The specific antibody and antigen of AFB₁ were coated on a histidine-modified Fe₃O₄ nanozyme to form the capture/detection probes. Based on the competition/affinity effect, the spatial network structure was constructed by the probes, which could be rapidly (8 s) separated by a magnetic three-phase single-drop microextraction process. In this single-drop microreactor, the network structure was applied to catalyze a colorimetric 3,3',5,5'-tetramethylbenzidine oxidation reaction for AFB₁ detection. The signal was amplified significantly due to the strong peroxidase-like ability of the spatial network structure and the enrichment effect of the microextraction. Thus, a low detection limit (0.034 pg/mL) was achieved. The matrix effect of real sample can be eliminated by the extraction approach, and the practicability of this method was proved by agricultural product samples analysis.

Metal-organic framework (MOF) hybridized gold nanoparticles as a bifunctional nanozyme for glucose sensing

Inspired by natural enzymes that possess multiple catalytic activities, here we develop a bifunctional metal-organic frame-work (MOF) for biosensing applications. Ultrasmall gold nano-particles (AuNPs) are grown in the internal cavities of an iron (Fe) porphyrin-based MOF to produce a hybridized nanozyme, AuNPs@PCN-224(Fe), in which AuNPs and PCN-224(Fe) exhibit the catalytic activity of glucose oxidase (GOx) and horseradish peroxidase (HRP), respectively. We established that the bifunctional nanozyme was capable of a cascade reaction to generate hydrogen peroxide in the presence of d-glucose and oxygen in situ, and subsequently activate a colorimetric or chemiluminescent substrate through HRP-mimicking catalytic activity. The nanozyme was selective over a range of other saccharides, and 93% of the catalytic activity was retained after being recycled five times.

Dual-mode colorimetric and homogeneous electrochemical detection of intracellular/extracellular H2O2 based on FeSx/SiO2 nanoparticles with high peroxidase-like activity

Abnormal expression of hydrogen peroxide (H₂O₂) elucidates cell dysfunctions and might induce the occurrence and deterioration of various diseases. However, limited by its ultralow level under pathophysiological conditions, intracellular and extracellular H₂O₂ was difficult to be detected accurately. Herein, a colorimetric and homogeneous electrochemical dual-mode biosensing platform was constructed for intracellular/extracellular H₂O₂ detection based on FeS_x/SiO₂ nanoparticles (FeS_x/SiO₂ NPs) with high peroxidase-like activity. In this design, FeS_x/SiO₂ NPs were synthesized with excellent catalytic activity and stability compared to natural enzymes, which improved the sensitivity and stability of sensing strategy. 3,3',5,5'-Tetramethylbenzidine (TMB), as a multifunctional indicator, was oxidized in the presence of H₂O₂, generated color changes and realized visual analysis. In this process, the characteristic peak current of TMB decreased, which could realize the ultrasensitive detection of H₂O₂ by homogeneous electrochemistry. Accordingly, by integrating visual analysis ability of colorimetry and the high sensitivity of homogeneous electrochemistry, the dual-mode biosensing platform exhibited high accuracy, sensitivity and reliability. The detection limits of H₂O₂ were 0.2 μM (S/N = 3) for the colorimetric method and 2.5 nM (S/N = 3) for the homogeneous electrochemistry assay. Therefore, the dual-mode biosensing platform provided a new opportunity for highly accurate and sensitive detection of intracellular/extracellular H₂O₂.

Facile Synthesis of MXene-Ti3C2/Co Nanosheet Hydrogel Sensor with the Assistance of a Smartphone for On-Site Monitoring of Glucose in Beverages

A one-step cobaltous chloride (CoCl₂) molten salt method was employed to prepare multilayer MXene-Ti₃C₂/Co materials with further ultrasonic treatment to acquire single-layer MXene-Ti₃C_2/Co nanosheets (NSs). MXene-Ti₃C₂/Co NSs were characterized, and their enzyme-like activities were investigated. Under the catalysis of MXene-Ti₃C₂/Co NSs, 3,3',5,5'-tetramethylbenzidine (TMB) could be oxidized by H₂O₂, with the color changing from colorless to blue. The affinity of MXene-Ti₃C₂/Co NSs to H₂O₂ and TMB was better than that of nanozymes reported in previous studies. The MXene-Ti₃C₂/Co NSs were used for the colorimetric determination of H₂O₂/glucose, with limits of detection (LODs) of 0.033 mM and 1.7 μM, respectively. MXene-Ti₃C₂/Co NSs embedded in sodium alginate (SA) hydrogel were used to construct a sensor platform. The digital pictures combined with a smartphone-installed app (color recognizer) could be used to analyze RGB values for colorimetric detection of glucose in beverages. This point-of-care testing platform has the advantages of cost-effectiveness and good transferability, with the potential to realize quick, intelligent and on-site detection.

"Three-in-one" platform based on Fe-CDs nanozyme for dual-mode/dual-target detection and NIR-assisted bacterial killing

As nanozymes, carbon dots (CDs) have attracted increasing attention due to their remarkable properties. Besides general enzyme activity, their photoluminescence and photothermal properties have been explored rarely, whereas their synergistic effects might produce CDs-based nanozymes of high performance. Here, iron-doped CDs (Fe-CDs) with tunable fluorescence and enhanced peroxidase-like activity were designed to develop a novel "three-in-one" multifunctional platform to provide dual-mode/dual-target detection and near infrared (NIR)-assisted antibacterial ability. This proposed strategy for a H₂O₂ test exhibited a wide linear relationship with a low limit of detection (LOD) of 0.16 μM (colorimetric) and 0.14 μM (ratiometric fluorescent). Furthermore, due to the nature of cholesterol being oxidized to H₂O₂ by cholesterol oxidase, sensitive and selective detection of cholesterol was realized, and the LOD was 0.42 μM (colorimetric) and 0.27 μM (ratiometric fluorescent), surpassing that reported previously. This result suggested that Fe-CDs could be used for dual-mode quantification of large family of H₂O₂-producing metabolites, thereby paving the way for developing multi-mode sensing strategies based on nanozymes. Moreover, this platform showed synergistic effects for antibacterial application, indicating great prospects for bacterial killing as well as wound disinfection and healing. Hence, this platform could contribute to the construction of multifunctional CDs with high performance.

Magnetic Nanozyme Based on Loading Nitrogen-Doped Carbon Dots on Mesoporous Fe3O4 Nanoparticles for the Colorimetric Detection of Glucose

The simple and accurate monitoring of blood glucose level is of great significance for the prevention and control of diabetes. In this work, a magnetic nanozyme was fabricated based on loading nitrogen-doped carbon dots (N-CDs) on mesoporous Fe₃O₄ nanoparticles for the colorimetric detection of glucose in human serum. Mesoporous Fe₃O₄ nanoparticles were easily synthesized using a solvothermal method, and N-CDs were then prepared in situ and loaded on the Fe₃O₄ nanoparticles, leading to a magnetic N-CDs/Fe₃O₄ nanocomposite. The N-CDs/Fe₃O₄ nanocomposite exhibited good peroxidase-like activity and could catalyze the oxidation of the colorless enzyme substrate 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMB oxide (ox-TMB) in the presence of hydrogen peroxide (H₂O₂). When the N-CDs/Fe₃O₄ nanozyme was combined with glucose oxidase (Gox), Gox catalyzed the oxidization of glucose, producing H₂O₂ and leading to the oxidation of TMB under the catalysis of the N-CDs/Fe₃O₄ nanozyme. Based on this mechanism, a colorimetric sensor was constructed for the sensitive detection of glucose. The linear range for glucose detection was from 1 to 180 μM, and the limit of detection (LOD) was 0.56 μM. The recovered nanozyme through magnetic separation showed good reusability. The visual detection of glucose was also realized by preparing an integrated agarose hydrogel containing the N-CDs/Fe₃O₄ nanozyme, glucose oxidase, and TMB. The colorimetric detection platform has an enormous potential for the convenient detection of metabolites.

Reactive Template-Engaged Synthesis of NiSx/MoS2 Nanosheets Decorated on Hollow and Porous Carbon Microtubes with Optimal Electronic Modulation toward High-Performance Enzyme-like Performance

As a promising cost-effective nanozyme, MoS₂ nanosheets (NSs) have been considered as a good candidate for the enzyme-like catalysis. However, their catalytic activity is still restricted by the insufficient active sites and poor conductivity, and thus, the comprehensive performances are still unsatisfactory. To address these issues, herein, we design and fabricate an intelligent tubular nanostructure of hierarchical hollow nanotubes, which are assembled by NiS_x/MoS₂ NSs encapsulated into N-doped carbon microtubes (NiS_x/MoS₂@NCMTs). The N-doped carbon microtubes (NCMTs) serve as a conductive skeleton, integrating with NiS_x/MoS₂ NSs and ensuring their well-distribution, thereby maximally exposing more active sites. Additionally, the tube-like structure is favorable for increasing the mass transfusion to ensure their excellent catalytic performance. Profiting from their component and structural advantages, the obtained NiS_x/MoS₂@NCMTs exhibit a surprisingly enhanced enzyme-like activity. Based on these, a facile colorimetric sensing platform to detect H₂O₂ and GSH has been developed. This proposed approach can be expected to synthesize a series of tubular heterostructured MoS₂-based composites, which will be widely applied in catalysis, energy storage, disease diagnosis, etc.

Electrochemical biomimetic enzyme cascade amplification combined with target-induced DNA walker for detection of thrombin

Fe-N-doped carbon nanomaterials (Fe-N/CMs) were designed as a novel biomimetic enzyme with excellent peroxidase-like activity to achieve high-efficient enzyme cascade catalytic amplification with the aid of glucose oxidase (GOx), which was further combined with target-induced DNA walker amplification to develop a sensitive electrochemical biosensor for thrombin detection. Impressively, massive output DNA was transformed from small amounts of target thrombin by highly effective DNA walker amplification as protein-converting strategy, which could then induce the immobilization of functionalized nanozyme on the electrode surface to achieve the high-efficient electrochemical biomimetic enzyme cascade amplification. As a result, an amplified enzyme cascade catalytic signal was measured for thrombin detection ranging from 0.01 pM to 1 nM with a low detection limit of 3 fM. Importantly, the new biomimetic enzyme cascade reaction coupled the advantages of natural enzyme and nanozyme, which paved an avenue to construct varied artificial multienzymes amplification systems for biosensing, bioanalysis, and disease diagnosis applications.

Single-Atom Fe Nanozyme with Enhanced Oxidase-like Activity for the Colorimetric Detection of Ascorbic Acid and Glutathione

Single-atom nanozymes (SAzymes) have drawn ever-increasing attention due to their maximum atom utilization efficiency and enhanced enzyme-like activity. Herein, a facile pyrolysis strategy is reported for the synthesis of the iron-nitrogen-carbon (Fe-N-C) SAzyme using ferrocene trapped within porous zeolitic imidazolate framework-8 (ZIF-8@Fc) as a precursor. The as-prepared Fe-N-C SAzyme exhibited exceptional oxidase-mimicking activity, catalytically oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) with high affinity (K_m) and fast reaction rate (V_max). Taking advantage of this property, we designed two colorimetric sensing assays based on different interaction modes between small molecules and Fe active sites. Firstly, utilizing the reduction activity of ascorbic acid (AA) toward oxidized TMB (TMBox), a colorimetric bioassay for AA detection was established, which exhibited a good linear range of detection from 0.1 to 2 μM and a detection limit as low as 0.1 μM. Additionally, based on the inhibition of nanozyme activity by the thiols of glutathione (GSH), a colorimetric biosensor for GSH detection was constructed, showing a linear response over a concentration range of 1-10 μM, with a detection limit of 1.3 μM. This work provides a promising strategy for rationally designing oxidase-like SAzymes and broadening their application in biosensing.

Nanozymes towards Personalized Diagnostics: A Recent Progress in Biosensing

This review highlights the recent advancements in the field of nanozymes and their applications in the development of point-of-care biosensors. The use of nanozymes as enzyme-mimicking components in biosensing systems has led to improved performance and miniaturization of these sensors. The unique properties of nanozymes, such as high stability, robustness, and surface tunability, make them an attractive alternative to traditional enzymes in biosensing applications. Researchers have explored a wide range of nanomaterials, including metals, metal oxides, and metal-organic frameworks, for the development of nanozyme-based biosensors. Different sensing strategies, such as colorimetric, fluorescent, electrochemical and SERS, have been implemented using nanozymes as signal-producing components. Despite the numerous advantages, there are also challenges associated with nanozyme-based biosensors, including stability and specificity, which need to be addressed for their wider applications. The future of nanozyme-based biosensors looks promising, with the potential to bring a paradigm shift in biomolecular sensing. The development of highly specific, multi-enzyme mimicking nanozymes could lead to the creation of highly sensitive and low-biofouling biosensors. Integration of nanozymes into point-of-care diagnostics promises to revolutionize healthcare by improving patient outcomes and reducing costs while enhancing the accuracy and sensitivity of diagnostic tools.

Nanodrugs with intrinsic radioprotective exertion: Turning the double-edged sword into a single-edged knife

Ionizing radiation (IR) poses a growing threat to human health, and thus ideal radioprotectors with high efficacy and low toxicity still receive widespread attention in radiation medicine. Despite significant progress made in conventional radioprotectants, high toxicity, and low bioavailability still discourage their application. Fortunately, the rapidly evolving nanomaterial technology furnishes reliable tools to address these bottlenecks, opening up the cutting-edge nano-radioprotective medicine, among which the intrinsic nano-radioprotectants characterized by high efficacy, low toxicity, and prolonged blood retention duration, represent the most extensively studied class in this area. Herein, we made the systematic review on this topic, and discussed more specific types of radioprotective nanomaterials and more general clusters of the extensive nano-radioprotectants. In this review, we mainly focused on the development, design innovations, applications, challenges, and prospects of the intrinsic antiradiation nanomedicines, and presented a comprehensive overview, in-depth analysis as well as an updated understanding of the latest advances in this topic. We hope that this review will promote the interdisciplinarity across radiation medicine and nanotechnology and stimulate further valuable studies in this promising field.