Accelerating peroxidase mimicking nanozymes using DNA

Advances in nanozymes with peroxidase-like activity for biosensing and disease therapy applications

Natural enzymes are crucial in biological systems and widely used in biomedicine, but their disadvantages, such as insufficient stability and high cost, have limited their widespread application. Since discovering the enzyme-like activity of Fe3O4 nanoparticles, extensive research progress in diverse nanozymes has been made with their in-depth investigation, resulting in rapid development of related nanotechnologies. Nanozymes can compensate for the defects of natural enzymes and show higher stability with lower costs. Among them, peroxidase (POD)-like nanozymes have attracted extensive attention in biomedical applications owing to their efficient catalytic performance and diverse structures. This review explores different types of nanozymes with POD-like activity and discusses their activity regulation, particularly emphasizing their latest development trends and advances in biosensing and disease treatment. Finally, the challenges and prospects for the development of POD-like nanozymes and their potential future applications in the biomedical field are also provided.

DNA Catalysis: Design, Function, and Optimization

Catalytic DNA has gained significant attention in recent decades as a highly efficient and tunable catalyst, thanks to its flexible structures, exceptional specificity, and ease of optimization. Despite being composed of just four monomers, DNA's complex conformational intricacies enable a wide range of nuanced functions, including scaffolding, electrocatalysis, enantioselectivity, and mechano-electro spin coupling. DNA catalysts, ranging from traditional DNAzymes to innovative DNAzyme hybrids, highlight the remarkable potential of DNA in catalysis. Recent advancements in spectroscopic techniques have deepened our mechanistic understanding of catalytic DNA, paving the way for rational structural optimization. This review will summarize the latest studies on the performance and optimization of traditional DNAzymes and provide an in-depth analysis of DNAzyme hybrid catalysts and their unique and promising properties.

Controlled Spread of a Ag Layer from the Core to the Tip along the Branches of AuAg Nanostars for Improved SERS Detection of Okadaic Acid in Shellfish

Plasmonic Au-Ag nanostars are excellent surface-enhanced Raman scattering (SERS) probes due to bimetallic coupling and the tip effect. However, the existing preparation methods of AuAg nanostars cannot achieve controlled growth of the Ag layer on the branches of nanostars and so cannot display their SERS to the maximum extent, thus limiting its sensitivity in biosensing. Herein, a novel strategy "PEI (polyethylenimine)-guided Ag deposition method" is proposed for synthesizing AuAg core-shell nanostars (AuAg@Ag NS) with a tunable distribution of the Ag layer from the core to the tip, which offers an avenue for investigating the correlation between SERS efficiency and the extent of spread of the Ag layer. It is found that AuAg@Ag NS with a Ag layer coated the whole branch has the strongest SERS performance because the coupling between the tips and Ag layer is maximized. Meanwhile, as a completely closed core-shell structure, AuAg@Ag NS can confine and anchor 4-ATP inside the Ag layer to avoid an unstable SERS signal. By connecting the aptamer, a reliable internal standard nanoprobe with a SERS enhancement factor (EF) up to 1.86 × 108 is prepared. Okada acid is detected through competitive adsorption of this SERS probes, and the detection limit is 36.6 pM. The results gain fundamental insights into tailoring the nanoparticle morphologies and preparation of internal standard nanoprobes and also provide a promising avenue for marine toxin detection in food safety.

Using the High-Entropy Approach to Obtain Multimetal Oxide Nanozymes: Library Synthesis, In Silico Structure-Activity, and Immunoassay Performance

High-entropy nanomaterials exhibit exceptional mechanical, physical, and chemical properties, finding applications in many industries. Peroxidases are metalloenzymes that accelerate the decomposition of hydrogen peroxide. This study uses the high-entropy approach to generate multimetal oxide-based nanozymes with peroxidase-like activity and explores their application as sensors in ex vivo bioassays. A library of 81 materials was produced using a coprecipitation method for rapid synthesis of up to 100 variants in a single plate. The A and B sites of the magnetite structure, (AA')(BB'B'')2O4, were substituted with up to six different cations (Cu/Fe/Zn/Mg/Mn/Cr). Increasing the compositional complexity improved the catalytic performance; however, substitutions of single elements also caused drastic reductions in the peroxidase-like activity. A generalized linear model was developed describing the relationship between material composition and catalytic activity. Binary interactions between elements that acted synergistically or antagonistically were identified, and a single parameter, the mean interaction effect, was observed to correlate highly with catalytic activity, providing a valuable tool for the design of high-entropy-inspired nanozymes.

A stable colorimetric biosensor for highly selective detection of malathion residue in food based on aptamer-regulated laccase-mimic activity

Malathion causes a serious threat to human health due to its widespread use in the environment. Herein, a novel and stable smartphone-integrated colorimetric biosensor for malathion detection is firstly established based on aptamer-enhanced laccase-mimicking activity. The results indicate that the M17-F aptamer can increase the affinity of Ag2O nanoparticles to the substrate 2,4-dichlorophenol and enhance their laccase-mimicking activity. Thus, abundant semiquinone radicals are produced in the catalytic system, which are combined with chromogenic agent to generate dark red products. The corresponding RGB values for the colour change of the solution can be easily obtained using smartphones, which is used for the rapid detection of malathion. The established biosensor for malathion has a limit of detection as low as 5.85 nmol·L-1, and displays good selectivity for other competitive pesticides. Moreover, further studies have verified the applicability of the biosensor in actual samples, indicating that it may have the potential for application in malathion detection in food.

Nanozyme-based visual diagnosis and therapeutics for myocardial infarction: The application and strategy

BACKGROUND

Myocardial infarction (MI) is a heart injury caused by ischemia and low oxygen conditions. The occurrence of MI lead to the activation of a large number of neutrophils and macrophages, inducing severe inflammatory injury. Meanwhile, the inflammatory response produces much more free radicals, further exacerbating the inflammatory response and tissue damage. Efforts are being dedicated to developing antioxidants and enzymes, as well as small molecule drugs, for treating myocardial ischemia. However, poor pharmacokinetics and potential side effects limit the clinical application of these drugs. Recent advances in nanotechnology have paved new pathways in biomedical and healthcare environments. Nanozymes exhibit the advantages of biological enzymes and nanomaterials, including with higher catalytic activity and stability than natural enzymes. Thus, nanozymes provide new possibilities for the diagnosis and treatment of oxidative stress and inflammation-related diseases.

AIM OF REVIEW

We describe the application of nanozymes in the diagnosis and therapy of MI, aiming to bridge the gap between the diagnostic and therapeutic needs of MI.

KEY SCIENTIFIC CONCEPTS OF REVIEW

We describe the application of nanozymes in the diagnosis and therapy of MI, and discuss the new strategies for improving the diagnosis and treatment of MI. We review in detail the applications of nanozymes to achieve highly sensitive detection of biomarkers of MI. Due to their unique enzyme catalytic capabilities, nanozymes have the ability to sensitively detect biomolecules through colorimetric, fluorescent, and electrochemical assays. In addition, nanozymes exhibit excellent antioxidase-mimicking activity to treat MI by modulating reduction/oxidation (REDOX) homeostasis. Nanozymes can also passively or actively target MI tissue sites, thereby protecting ischemic myocardial tissue and reducing the infarct area. These innovative applications of nanozymes in the field of biomedicine have shown promising results in the diagnosis and treatment of MI, offering a novel therapeutic strategy.

Enhanced "Electronic Tongue" for Dental Bacterial Discrimination and Elimination Based on a DNA-Encoded Nanozyme Sensor Array

Bacterial infections are the second leading cause of death around the world, especially those caused by delayed treatment and misdiagnosis. Therefore, rapid discrimination and effective elimination of multiple bacteria are of great importance for improving the survival rate in clinic. Herein, a novel colorimetric sensor array for bacterial discrimination and elimination is constructed using programmable DNA-encoded iron oxide nanoparticles (IONPs) as sensing elements. Utilizing differential interactions of bacteria on DNA-encoded IONPs, 11 kinds of dental bacteria and 6 kinds of proteins have been successfully identified by linear discriminant analysis (LDA). Moreover, the developed sensing system also performs well in the quantitative determination of individual bacteria and identification of bacterial mixtures. More importantly, the practicability of this sensing strategy is further verified by precise differentiation of blind and artificial saliva samples. Furthermore, the sensor array is used for efficiently killing multiple bacteria, demonstrating great potential in clinical prophylaxis and therapy.

Dual chemodynamic/photothermal therapeutic nanoplatform based on DNA-functionalized prussian blue

The combination of chemodynamic therapy and photothermal therapy has a promising application owing to its impressive anti-cancer effects. However, the degradability of the material and the lack of targeting severely limit its further clinical application. Herein, DNAs containing nucleolin aptamer (AS1411) and different bases sequences were used to functionalize PB NPs for the targeted treatment. Compared to prussian blue, DNA-functionalized prussian blue does not reduce the photothermal properties of prussian blue. Moreover, DNA confers DNA-functionalized prussian blue targeting and higher enzymatic activity, thereby achieving a more effective combination of chemodynamic and photothermal treatment. The therapeutic efficacy of this nanoplatform was evaluated in vivo and in vitro experiments, exhibiting that DNA-functionalized prussian blue nanozyme can maximize the precise control of the therapeutic effect, reduce the toxic and side effects caused by non-specific accumulation on other normal cells, and effectively achieve targeted killing of cancer cells. This work demonstrates that DNA-functionalized prussian blue can improve the efficiency of combined tumor treatment and enhance the application value of prussian blue in tumor treatment, which is expected to provide theoretical support for clinical application.

A dual-mode sensing platform based on metal-organic framework for colorimetric and ratiometric fluorescent detection of organophosphorus pesticide

Pesticide residues have raised considerable concern about environmental health and food safety. Despite a great advance in enzymatic sensors for pesticide detection, the intrinsic fragility of native enzyme and possible fake results due to single mode signal have hindered its wide application. Here, a novel dual-mode sensor is reported for organophosphorus pesticide detection by using metal-organic framework (MOF) nanozyme NH2-CuBDC as sensing element. The intrinsic peroxidase-mimicking activity and fluorescence property of NH2-CuBDC enable both colorimetric and fluorescent detection of chlorpyrifos. Compared with previously reported chlorpyrifos sensors, our sensor exhibits outstanding sensitivity, and the limits of detection (LOD, S/N = 3) in colorimetric and fluorescent modes are 1.57 ng/mL and 2.33 ng/mL, respectively. No obvious interferences from other substances were measured and chlorpyrifos analysis in real samples presented good reliability, showing practical potential. This work is anticipated to provide new insights to develop multifunctional nanozymes and integrated multi-mode sensing platforms.

Advances in colorimetric biosensors of exosomes: novel approaches based on natural enzymes and nanozymes

Exosomes are 30-150 nm vesicles derived from diverse cell types, serving as one of the most important biomarkers for early diagnosis and prognosis of diseases. However, the conventional detection method for exosomes faces significant challenges, such as unsatisfactory sensitivity, complicated operation, and the requirement of complicated devices. In recent years, colorimetric exosome biosensors with a visual readout underwent rapid development due to the advances in natural enzyme-based assays and the integration of various types of nanozymes. These synthetic nanomaterials show unique physiochemical properties and catalytic abilities, enabling the construction of exosome colorimetric biosensors with novel principles. This review will illustrate the reaction mechanisms and properties of natural enzymes and nanozymes, followed by a detailed introduction of the recent advances in both types of enzyme-based colorimetric biosensors. A comparison between natural enzymes and nanozymes is made to provide insights into the research that improves the sensitivity and convenience of assays. Finally, the advantages, challenges, and future directions of enzymes as well as exosome colorimetric biosensors are highlighted, aiming at improving the overall performance from different approaches.

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

In recent years, there has been a notable increase in interest surrounding nanozymes due to their ability to imitate the functions and address the limitations of natural enzymes. The scientific community has been greatly intrigued by the study of nanoceria, primarily because of their distinctive physicochemical characteristics, which include a variety of enzyme-like activities, affordability, exceptional stability, and the ability to easily modify their surfaces. Consequently, nanoceria have found extensive use in various biosensing applications. However, the impact of its redox activity on the enzymatic catalytic mechanism remains a subject of debate, as conflicting findings in the literature have presented both pro-oxidant and antioxidant effects. Herein, we creatively propose a seesaw model to clarify the regulatory mechanism on redox balance and survey possible mechanisms of multienzyme mimetic properties of nanoceria. In addition, this review aims to showcase the latest advancements in this field by systematically discussing over 180 research articles elucidating the significance of ceria-based nanozymes in enhancing, downsizing, and enhancing the efficacy of point-of-care (POC) diagnostics. These advancements align with the ASSURED criteria established by the World Health Organization (WHO). Furthermore, this review also examines potential constraints in order to offer readers a concise overview of the emerging role of nanoceria in the advancement of POC diagnostic systems for future biosensing applications.

Label-free colorimetric sensor for Pb2+ determination using catalytic activity of MnO2 nanoflowers and elongated aptamer

In this study, a label-free aptasensor utilizing colorimetric properties was developed to detect Pb2+ with high sensitivity. The approach involved applying modified aptamer which enhanced the oxidase-mimicking activity of MnO2 nanoflowers. This innovative method provides an efficient means for monitoring Pb2+ ions without requiring any labeling techniques. The fundamental principle of this aptasensor is based on the adsorption of a modified aptamer onto MnO2 nanoflowers' surface, which in turn increases their affinity for chromogenic substrates and enhances their catalytic activity. The proposed aptasensor exploits the high sensitivity due to the extension of the aptamer sequence length by terminal deoxynucleotidyl transferase (TdT). Under optimum experimental conditions, the developed colorimetric aptasensor indicated a linear detection range from 4 to 80 nM with a limit of detection (LOD) of 1.4 nM. Moreover, the aptasensor successfully monitored Pb2+ in the drinking water, milk and human serum samples. Henceforth, the colorimetric aptasensor exhibited in this study possesses several benefits such as uncomplicated operation, cost-effectiveness, label-free detection and remarkable sensitivity. Thus rendering it a suitable option for analyzing intricate samples.

Recent Advancements in the Formulation of Nanomaterials-Based Nanozymes, Their Catalytic Activity, and Biomedical Applications

Nanozymes are nanoparticles with intrinsic enzyme-mimicking properties that have become more prevalent because of their ability to outperform conventional enzymes by overcoming their drawbacks related to stability, cost, and storage. Nanozymes have the potential to manipulate active sites of natural enzymes, which is why they are considered promising candidates to function as enzyme mimetics. Several microscopy- and spectroscopy-based techniques have been used for the characterization of nanozymes. To date, a wide range of nanozymes, including catalase, oxidase, peroxidase, and superoxide dismutase, have been designed to effectively mimic natural enzymes. The activity of nanozymes can be controlled by regulating the structural and morphological aspects of the nanozymes. Nanozymes have multifaceted benefits, which is why they are exploited on a large scale for their application in the biomedical sector. The versatility of nanozymes aids in monitoring and treating cancer, other neurodegenerative diseases, and metabolic disorders. Due to the compelling advantages of nanozymes, significant research advancements have been made in this area. Although a wide range of nanozymes act as potent mimetics of natural enzymes, their activity and specificities are suboptimal, and there is still room for their diversification for analytical purposes. Designing diverse nanozyme systems that are sensitive to one or more substrates through specialized techniques has been the subject of an in-depth study. Hence, we believe that stimuli-responsive nanozymes may open avenues for diagnosis and treatment by fusing the catalytic activity and intrinsic nanomaterial properties of nanozyme systems.

Nucleic acid-functionalized nanozymes and their applications

Nanozymes are inorganic, organic and metal-organic framework nanoparticles that reveal catalytic functions by emulating native enzyme activities. Recently, these nanozymes have attracted growing scientific interest, finding diverse analytical and medical applications. However, the catalytic activities and functions of nanozymes are limited, due to the lack of substrate binding sites that concentrate on the substrate at the catalytic site (molarity effect), introduce substrate specificity and allow functional complexity of the catalysts (cascaded, switchable and cooperative catalysis). The modification of nanozymes with functional nucleic acids provides means to overcome these limitations and engineer nucleic acid/nanozyme hybrids for diverse applications. This is exemplified with the synthesis of aptananozymes, which are supramolecular aptamer-modified nanozymes. Aptananozymes exhibit combined specific binding and catalytic properties that drive diverse chemical transformations, revealing enhanced catalytic activities, as compared to the separated nanozyme/aptamer constituents. Relationships of structure-catalytic functions in the aptananozyme constructs are demonstrated. In addition, modification of nanozymes exhibiting multimodal catalytic functions with aptamers allows the engineering of nanozyme-based bioreactors for cascaded catalysis. Also, the functionalization of reactive oxygen species (ROS)-generating nanozymes with cancer cell-recognizing aptamers yields aptananozymes for targeted chemodynamic treatment of cancer cells and cancer tumors elicited in mice. Finally, nucleic acid-modified enzyme (glucose oxidase)-loaded metal-organic framework nanoparticles yield switchable biocatalytic nanozymes that drive the ON/OFF biocatalyzed oxidation of Amplex Red, dopamine or the generation of chemiluminescence. Herein, future challenges of the topic are addressed.

Research Progress in Iron-Based Nanozymes: Catalytic Mechanisms, Classification, and Biomedical Applications

Natural enzymes are crucial in biological systems and widely used in biology and medicine, but their disadvantages, such as insufficient stability and high-cost, have limited their wide application. Since Fe₃O₄ nanoparticles were found to show peroxidase-like activity, researchers have designed and developed a growing number of nanozymes that mimic the activity of natural enzymes. Nanozymes can compensate for the defects of natural enzymes and show higher stability with lower cost. Iron, a nontoxic and low-cost transition metal, has been used to synthesize a variety of iron-based nanozymes with unique structural and physicochemical properties to obtain different enzymes mimicking catalytic properties. In this perspective, catalytic mechanisms, activity modulation, and their recent research progress in sensing, tumor therapy, and antibacterial and anti-inflammatory applications are systematically presented. The challenges and perspectives on the development of iron-based nanozymes are also analyzed and discussed.

Single-stranded DNA binding protein coupled aptasensor with carbon-gold nanoparticle amplification for marine toxins detection assisted by a miniaturized absorbance reader

Okadaic acid (OA), one of the most widely distributed marine toxins worldwide poses a severe threat to human health. Previous sensing methods for OA detection are usually based on antigen-antibody binding mechanism. However, the drawbacks of antibodies especially the enzyme-labeled antibodies, such as the harsh storage condition and high cost, lead to significant challenges to OA detection in biological samples. To overcome these limitations, a single-stranded DNA binding protein (SSB) coupled aptasensor was developed for OA detection. SSB was incubated on the microplate as a substitute for conventional OA-protein conjugations. Carbon-gold nanoparticles were synthesized and labeled with horseradish peroxidase and thiol-modified aptamers to obtain a capture probe (CGNs@HRP-Apt) instead of the enzyme-labeled antibody for signal amplification. OA and SSB competed to bind with limited aptamers on CGNs@HRP-Apt probes followed by colorimetric assay to obtain the optical signals correlated to OA concentration. To achieve on-site detection, a miniaturized and multichannel absorbance reader (Smart-plate reader) was self-designed with full automation for OA detection. Utilizing the SSB coupled aptasensor and the Smart-plate reader, our approach enables cost-effective and on-site OA sensing with a detection range of 2.5-80 ppb and an ultra-low limit of detection of 0.68 ppb. Moreover, novel OA detection kits based on the SSB coupled aptasensor were prepared which can effectively reduce the cost by 15 times lower than that of commercial ELISA kits. Therefore, the developed platform provides a favorable and promising avenue for marine toxin detection in aquaculture and food safety.

A novel label-free dual-mode aptasensor based on the mutual regulation of silver nanoclusters and MoSe2 nanosheets for reliable detection of ampicillin

Current methods for the rapid detection of trace antibiotics in the environment remains problems of low accuracy and false negative or false positive, making the development of fast, and accurate, and reliable methods for antibiotic testing a major challenge that needs to be addressed. Herein, we developed a novel label-free colorimetric and fluorescent dual-mode aptasensor assembled by the strong interaction of layered MoSe₂ nanosheets (MoSe₂ NSs) with ampicillin (AMP) aptamer functionalized silver nanoclusters (Apt-AgNCs) that specifically bind AMP to allow the sensitive and selective detection of AMP. Apt-AgNCs could be adsorbed on the surface of MoSe₂ NSs via van der Waals force to form a nanocomposite, Apt-AgNCs/MoSe₂ NSs. Interestingly, Apt-AgNCs/MoSe₂ NSs act together to construct dual mode aptasensor through modulation of the intrinsic peroxidase activity of MoSe₂ NSs and the fluorescence of Apt-AgNCs. In the presence of AMP, Apt-AgNCs could specifically bind AMP, triggering desorption from the MoSe₂ NSs surface, leading to a decrease in the peroxidase activity of the system with the recovery in Apt-AgNCs fluorescence. The dual-signal aptasensor exhibited good linear colorimetric and fluorescence responses in the AMP concentration ranges of 0.115-2.00 μM and 6-100 nM, respectively. Furthermore, the aptasensor was successfully measured AMP levels in commercially-bought milk and lake water with satisfactory results. Unlike single-signal aptasensors, the constructed dual-signal aptasensor could not only improve the detection precision, but also reduce the false positive or false negative results. These promising results suggest that the dual-readout strategy as demonstrated is general mode for the detection of other antibiotics or compounds using various aptamers functionalized AgNCs in concert with MoSe₂ NSs.

Reversed Regulation Effects of ssDNA on the Mimetic Oxidase and Peroxidase Activities of Covalent Organic Frameworks

Nanomaterials with enzyme mimetic activity have attracted extensive attention, especially in the regulation of their catalytic activities by biomolecules or other polymers. Here, a covalent organic framework (Tph-BT COF) with excellent photocatalytic activity is constructed by Schiff base reaction, and its mimetic oxidase activity and peroxidase activity is inversely regulated via single-stranded DNA (ssDNA). Under light-emitting diode (LED) light irradiation, Tph-BT exhibited outstanding oxidase activity, which efficiently catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue oxTMB, and ssDNA, especially those with poly-thymidine (T) sequences, can significantly inhibit its oxidase activity. On the contrary, Tph-BT showed weak peroxidase activity, and the presence of ssDNA, particularly poly-cytosine (C) sequences, can remarkably enhance the peroxidase activity. The influence of base type, base length, and other factors on the activities of two enzymes is also studied, and the results reveal that the adsorption of ssDNA on the surface of Tph-BT prevented intersystem crossing (ISC) and energy transfer processes to reduce ¹ O₂ generation, while the electrostatic interaction between ssDNA and TMB enhanced Tph-BT's affinity for TMB to facilitate the electron transfer from TMB to ^• OH. This study investigates multitype mimetic enzyme activities of nonmetallic D-A conjugated COFs and demonstrates their feasibility of regulation by ssDNA.

Insight into the Sensing Behavior of DNA Probes Based on MOF-Nucleic Acid Interaction for Bioanalysis

Adsorption of DNA probes onto nanomaterials is a promising strategy for bioassay establishment typically using fluorescence or catalytic activities to generate signals. Albeit important, there is currently a lack of systematic understanding of the sensing behaviors building on nanomaterial-DNA interactions, which greatly limits the rational method design and their subsequent applications. Herein, the issue was investigated by employing multifunctional metal-organic frameworks (MOFs) (FeTCPP⊂UiO-66) as a model that was synthesized via integrating heme-like ligand FeTCPP into commonly used MOFs (UiO-66). Our results demonstrated that the fluorescently labeled DNA adsorbed onto FeTCPP⊂UiO-66 was quenched through photoinduced electron transfer, fluorescence resonance energy transfer, and the internal filtration effect. Among different DNA structures, double-stranded DNA and hybridization chain reaction products largely retained their fluorescence due to desorption and conformational variation, respectively. In addition, ssDNA could maximally inhibit the peroxidase activity of FeTCPP⊂UiO-66, and this inhibition was strongly dependent on the strand length but independent of base composition. On the basis of these discoveries, a fluorescence/colorimetric dual-modal detection was designed against aflatoxin B1 with satisfactory performances obtained to further verify our results. This study provided some new insights into the sensing behaviors based on MOF-DNA interactions, indicating promising applications for rational bioassay design and its performance improvement.

Amalgamation of DNAzymes and Nanozymes in a Coronazyme

Artificial enzymes such as nanozymes and DNAzymes are economical and stable alternatives to natural enzymes. By coating Au nanoparticles (AuNPs) with a DNA corona (AuNP@DNA), we amalgamated nanozymes and DNAzymes into a new artificial enzyme with catalytic efficiency 5 times higher than AuNP nanozymes, 10 times higher than other nanozymes, and significantly greater than most of the DNAzymes on the same oxidation reaction. The AuNP@DNA demonstrates excellent specificity as its reactivity on a reduction reaction does not change with respect to pristine AuNP. Single-molecule fluorescence and force spectroscopies and density functional theory (DFT) simulations indicate a long-range oxidation reaction initiated by radical production on the AuNP surface, followed by radical transport to the DNA corona, where the binding and turnover of substrates take place. The AuNP@DNA is named coronazyme because of its natural enzyme mimicking capability through the well-orchestrated structures and synergetic functions. By incorporating different nanocores and corona materials beyond DNAs, we anticipate that the coronazymes represent generic enzyme mimics to carry out versatile reactions in harsh environments.

A guide to mass spectrometric analysis of extracellular vesicle proteins for biomarker discovery

Exosomes (small extracellular vesicles) in living organisms play an important role in processes such as cell proliferation or intercellular communication. Recently, exosomes have been extensively investigated for biomarker discoveries for various diseases. An important aspect of exosome analysis involves the development of enrichment methods that have been introduced for successful isolation of exosomes. These methods include ultracentrifugation, size exclusion chromatography, polyethylene glycol-based precipitation, immunoaffinity-based enrichment, ultrafiltration, and asymmetric flow field-flow fractionation among others. To confirm the presence of exosomes, various characterization methods have been utilized such as Western blot analysis, atomic force microscopy, electron microscopy, optical methods, zeta potential, visual inspection, and mass spectrometry. Recent advances in high-resolution separations, high-performance mass spectrometry and comprehensive proteome databases have all contributed to the successful analysis of exosomes from patient samples. Herein we review various exosome enrichment methods, characterization methods, and recent trends of exosome investigations using mass spectrometry-based approaches for biomarker discovery.

Application of Nanozymes in Environmental Monitoring, Management, and Protection

Nanozymes are nanomaterials with enzyme-like activity, possessing the unique properties of nanomaterials and natural enzyme-like catalytic functions. Nanozymes are catalytically active, stable, tunable, recyclable, and versatile. Therefore, increasing attention has been paid in the fields of environmental science and life sciences. In this review, we focused on the most recent applications of nanozymes for environmental monitoring, environmental management, and environmental protection. We firstly introduce the tuning catalytic activity of nanozymes according to some crucial factors such as size and shape, composition and doping, and surface coating. Then, the application of nanozymes in environmental fields are introduced in detail. Nanozymes can not only be used to detect inorganic ions, molecules, organics, and foodborne pathogenic bacteria but are also involved in the degradation of phenolic compounds, dyes, and antibiotics. The capability of nanozymes was also reported for assisting air purification, constructing biofuel cells, and application in marine antibacterial fouling removal. Finally, the current challenges and future trends of nanozymes toward environmental fields are proposed and discussed.

Enzyme-Free Colorimetric Method for Fast Detection of PIK3CA Gene Mutation by Praseodymia Nanorods

The frequently mutated phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) gene is associated with multiple tumors and endocytosis of viruses. Identification of muted nucleotides at the hotspot can help in finding the susceptible people who are vulnerable to cancers and viruses. Herein, a simple enzyme-free colorimetric method is developed for the quick detection of PIK3CA gene mutations. The main mechanism lies in the dissimilar interactions between praseodymia nanorods and different nucleotides, as well as the underlying oxidase-mimicking characteristics of praseodymia. With rational designs of probes and processes, this method has great potential for expanded applications in the screening of mutations in other genes of interest.

Colorimetric aptasensor for fumonisin B1 detection based on the DNA tetrahedra-functionalized magnetic beads and DNA hydrogel-coated bimetallic MOFzyme

The toxicity and incidence of fumonisin B₁ (FB₁) pose a major challenge to public health and the environment, prompting the development of alternative quantitative strategies for FB₁. Herein, a colorimetric aptasensor was constructed based on DNA tetrahedra-functionalized magnetic beads (MBs) and DNA hydrogel-coated Mn-Zr bimetallic metal-organic frameworks-based nanozyme (MOFzyme). Initially, MBs functionalized by DNA tetrahedra demonstrated excellent capturing capability for FB₁. Along with the capture of FB₁, catalyst DNA (C) was released into the supernatant. Aided by fuel DNA (F), C can trigger continuous cleavage of the main chains and cross-linking points of the DNA hydrogel through an entropy-driven DNA circuit integrated into the hydrogel coating. Subsequently, the bimetallic MOFzyme encapsulated inside the DNA hydrogel was exposed and exerted its superb peroxidase-like activity, producing a colorimetric signal whose intensity was positively dependent on the amount of FB₁. The developed aptasensor exhibited good linearity in the range of 5 × 10^-4 to 50 ng mL^-1 with a limit of detection (LOD) of 0.38 pg mL^-1, and reasonable specificity in different matrices. Furthermore, the aptasensor was successfully applied to quantify FB₁ in actual samples with recoveries fell within 92.25 %- 108.00 %, showing its great potential in environmental monitoring and food safety.

Recent advances in colorimetric sensors based on nanozymes with peroxidase-like activity

Nanozymes have been widely used to construct colorimetric sensors due to their advantages of cost-effectiveness, high stability, good biocompatibility, and ease of modification. The emergence of nanozymes greatly enhanced the detection sensitivity and stability of the colorimetric sensing platform. Recent significant research has focused on designing various sensors based on nanozymes with peroxidase-like activity for colorimetric analysis. However, with the deepening of research, nanozymes with peroxidase-like activity has also exposed some problems, such as weak affinity and low catalytic activity. In view of the above issues, existing investigations have shown that the catalytic properties of nanozymes can be improved by adding surface modification and changing the structure of nanomaterials. In this review, we summarize the recent trends and advances of colorimetric sensors based on several typical nanozymes with peroxidase-like activities, including noble metals, metal oxides, metal sulfides/metal selenides, and carbon and metal-organic frameworks (MOF). Finally, the current challenges and prospects of colorimetric sensors based on nanozymes with peroxidase-like activity are summarized and discussed to provide a reference for researchers in related fields.

Nucleotide Interaction with Nanocrystalline Ceria Surface

The adsorption of nucleotides on the surface of nanocrystalline cerium dioxide (pHpzc = 6.3) in NaCl solutions was investigated using multi-batch adsorption experiments over a wide range of pH. The obtained results were interpreted as a formation of outer and inner sphere surface complexes with the participation of phosphate moieties. The Basic Stern surface complexation model was applied to obtain quantitative equilibrium reaction constants.

DNA-based platform for efficient and precisely targeted bioorthogonal catalysis in living systems

As one of the typical bioorthogonal reactions, copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction holds great potential in organic synthesis, bioconjugation, and surface functionalization. However, the toxicity of Cu(I), inefficient catalytic activity, and the lack of cell specific targeting of the existing catalysts hampered their practical applications in living systems. Herein, we design and construct a DNA-based platform as a biocompatible, highly efficient, and precisely targeted bioorthogonal nanocatalyst. The nanocatalyst presents excellent catalytic efficiency in vitro, which is one order of magnitude higher than the commonly used catalyst CuSO₄/sodium ascorbate. The theoretical calculation further supports the contribution of DNA structure and its interaction with substrates to the superior catalytic activity. More importantly, the system can achieve efficient prodrug activation in cancer cells through cell type-specific recognition and produce a 40-fold enhancement of transformation compared to the non-targeting nanocatalyst, resulting in enhanced antitumor efficacy and reduced adverse effects. In vivo tumor therapy demonstrates the safety and efficacy of the system in mammals.

Copper-click reaction has been used for a wide range of bio-conjugations but does suffer from toxicity issues. Here, the authors report on the growth of copper nanoparticles on DNA with linked aptamer targeting and demonstrate high catalytic effect and improved application due to targeting and biocompatibility.

Regulation Mechanism of ssDNA Aptamer in Nanozymes and Application of Nanozyme-Based Aptasensors in Food Safety

Food safety issues are a worldwide concern. Pathogens, toxins, pesticides, veterinary drugs, heavy metals, and illegal additives are frequently reported to contaminate food and pose a serious threat to human health. Conventional detection methods have difficulties fulfilling the requirements for food development in a modern society. Therefore, novel rapid detection methods are urgently needed for on-site and rapid screening of massive food samples. Due to the extraordinary properties of nanozymes and aptamers, biosensors composed of both of them provide considerable advantages in analytical performances, including sensitivity, specificity, repeatability, and accuracy. They are considered a promising complementary detection method on top of conventional ones for the rapid and accurate detection of food contaminants. In recent years, we have witnessed a flourishing of analytical strategies based on aptamers and nanozymes for the detection of food contaminants, especially novel detection models based on the regulation by single-stranded DNA (ssDNA) of nanozyme activity. However, the applications of nanozyme-based aptasensors in food safety are seldom reviewed. Thus, this paper aims to provide a comprehensive review on nanozyme-based aptasensors in food safety, which are arranged according to the different interaction modes of ssDNA and nanozymes: aptasensors based on nanozyme activity either inhibited or enhanced by ssDNA, nanozymes as signal tags, and other methods. Before introducing the nanozyme-based aptasensors, the regulation by ssDNA of nanozyme activity via diverse factors is discussed systematically for precisely tailoring nanozyme activity in biosensors. Furthermore, current challenges are emphasized, and future perspectives are discussed.

Modulating the catalytic activity of gold nanoparticles using amine-terminated ligands

Nanozymes have broad applications in theranostics and point-of-care tests. To enhance the catalytic activity of nanozymes, the conventional strategy is doping metals to form highly active nanoalloys. However, high-quality and stable nanoalloys are hard to synthesize. Ligand modification is a powerful strategy to achieve chemoselectivity or bioactivity by changing the surface chemistry. Here, we explore different ligands to enhance the catalytic activity of nanozymes, e.g., gold nanoparticles (AuNPs). We systematically studied the impacts on the enzymatic activity of AuNPs by ligand engineering of surface chemistry (charge, group, and surface distance). Our work established critical guidelines for surface modification of nanozymes. The amine group favors higher activity of AuNPs than other groups. The flexible amine-rich ligand enhances the catalytic activity of AuNPs in contrast to other ligands and unmodified AuNPs. Using a proof-of-concept model, we screened many candidate ligands to obtain polyamine-AuNPs, which have strongly enhanced peroxidase-like activity and 100 times enhanced sensitivity compared to unmodified AuNPs. The strategy of enhancing the catalytic activity of AuNPs using ligands will facilitate the catalysis-related applications of nanozymes in biology and diagnostics.

Surface ligand engineering can precisely modulate the catalytic activity of nanozymes from inactive to highly active.

Self-Adaptive Single-Atom Catalyst Boosting Selective Ferroptosis in Tumor Cells

Ferroptosis, resulting from the catastrophic accumulation of lipid reactive oxygen species (ROS) and the inactivation of glutathione (GSH)-dependent peroxidase 4 (GPX4), has emerged as a form of regulated cell death for cancer therapy. Despite progress made with current ferroptosis inducers, efficient systems to trigger ferroptosis remain challenging, owing largely to their low activity, uncontrollable behavior, and even nonselective interactions. Here, we report a self-adaptive ferroptosis platform by engineering a DNA modulator onto the surface of single-atom nanozymes (SAzymes). The modulator could not only specifically intensify the ROS-generating activity but also endow the SAzymes with on-demand GSH-consuming ability in tumor cells, accelerating selective and safe ferroptosis. The self-adaptive antitumor response has been demonstrated in colon cancer and breast cancer, promoting the development of selective cancer therapy.

Coating Fe3O4 quantum dots with sodium alginate showing enhanced catalysis for capillary array-based rapid analysis of H2O2 in milk

A simple and high-throughput colorimetric analysis array has been constructed for quantifying H₂O₂ in milk using Fe₃O₄ quantum dots (QDs), which were coated with sodium alginate (SA) and chromogenic substrate onto the arrayed capillary tubes. It was discovered that the Fe₃O₄ QDs could present larger peroxidase-like catalysis than Fe₃O₄ nanoparticles (NPs). Particularly, dramatically enhanced catalysis activity could be achieved for Fe₃O₄ QDs if coated with SA films. Moreover, the use of SA could protect Fe₃O₄ QDs to expect the improved environmental stability. A capillary arrays-based high-throughput colorimetric platform was thereby developed for the detection of H₂O₂ in milk, with levels linearly ranging from 10 to 400 μM. Importantly, the developed colorimetric platform with the capillarity power for automatic fetching of multiple samples may promise the practical applications for extensive monitoring of multiple H₂O₂ samples for food safety.

Nucleoside-regulated catalytic activity of copper nanoclusters and their application for mercury ion detection

In this work, a novel method for the synthesis of copper nanoclusters is developed using nucleosides as templates and hydroxylamine hydrochloride as the reductant. Various nucleosides can regulate the catalytic activity of copper nanoclusters.

Pyrophosphate-Enhanced Oxidase Activity of Cerium Oxide Nanoparticles for Colorimetric Detection of Nucleic Acids

In recent years, cerium oxide (CeO₂) nanoparticles (NPs) have drawn significant attention owing to their intrinsic enzyme mimetic properties, which make them powerful tools for biomolecular detection. In this work, we evaluated the effect of pyrophosphate (PPi) on the oxidase activity of CeO₂ NPs. The presence of PPi was found to enhance the oxidase activity of CeO₂ NPs, with enhanced colorimetric signals. This particular effect was then used for the colorimetric detection of target nucleic acids. Overall, the PPi-enhanced colorimetric signals of CeO₂ NPs oxidase activity were suppressed by the presence of the target nucleic acids. Compared with previous studies using CeO₂ NPs only, our proposed system significantly improved the signal change (ca. 200%), leading to more sensitive and reproducible colorimetric analysis of target nucleic acids. As a proof-of-concept study, the proposed system was successfully applied to the highly selective and sensitive detection of polymerase chain reaction products derived from Klebsiella pneumoniae. Our findings will benefit the rapid detection of nucleic acid biomarkers (e.g., pathogenic bacterial DNA or RNA) in point-of-care settings.

Progress in Nanomaterials-Based Optical and Electrochemical Methods for the Assays of Exosomes

Exosomes with diameters of 30-150 nm are small membrane-bound vesicles secreted by a variety of cells. They play an important role in many biological processes, such as tumor-related immune response and intercellular signal transduction. Exosomes have been considered as emerging and noninvasive biomarkers for cancer diagnosis. Recently, a large number of optical and electrochemical biosensors have been proposed for sensitive detection of exosomes. To meet the increasing demands for ultrasensitive detection, nanomaterials have been integrated with various techniques as powerful components. Because of their intrinsic merits of biological compatibility, excellent physicochemical features and unique catalytic ability, nanomaterials have significantly improved the analytical performances of exosome biosensors. In this review, we summarized the recent progress in nanomaterials-based biosensors for the detection of cancer-derived exosomes, including fluorescence, colorimetry, surface plasmon resonance spectroscopy, surface enhanced Raman scattering spectroscopy, electrochemistry, electrochemiluminescence and so on.

Nanozyme-Participated Biosensing of Pesticides and Cholinesterases: A Critical Review

To improve the output and quality of agricultural products, pesticides are globally utilized as an efficient tool to protect crops from insects. However, given that most pesticides used are difficult to decompose, they inevitably remain in agricultural products and are further enriched into food chains and ecosystems, posing great threats to human health and the environment. Thus, developing efficient methods and tools to monitor pesticide residues and related biomarkers (acetylcholinesterase and butylcholinesterase) became quite significant. With the advantages of excellent stability, tailorable catalytic performance, low cost, and easy mass production, nanomaterials with enzyme-like properties (nanozymes) are extensively utilized in fields ranging from biomedicine to environmental remediation. Especially, with the catalytic nature to offer amplified signals for highly sensitive detection, nanozymes were finding potential applications in the sensing of various analytes, including pesticides and their biomarkers. To highlight the progress in this field, here the sensing principles of pesticides and cholinesterases based on nanozyme catalysis are definitively summarized, and emerging detection methods and technologies with the participation of nanozymes are critically discussed. Importantly, typical examples are introduced to reveal the promising use of nanozymes. Also, some challenges in the field and future trends are proposed, with the hope of inspiring more efforts to advance nanozyme-involved sensors for pesticides and cholinesterases.

Engineering DNA/Fe-N-C single-atom nanozymes interface for colorimetric biosensing of cancer cells

Single atom nanozymes (SAzymes) represent the state-of-the-art technology in nanomaterial-based catalysis, which have attracted attentions in catalysis, cancer treatment, disinfection and biosensing fields. However, numerous SAzymes suffered from low aqueous dispersion and without recognition capacity, which impeded their applications in bioanalysis. Herein, we engineered DNA onto SAzymes to obtain the DNA/SAzymes conjugates, which significantly improved the aqueous dispersion and recognition ability of SAzymes. We synthesized iron SAzymes (Fe-N-C SAzymes) as the catalytic nanomaterials, and investigated the interactions between Fe-N-C SAzymes and DNA. We compared A₁₅, T₁₅ and C₁₅ adsorption of Fe-N-C SAzymes in HEPES containing 2 mM MgCl₂. We found that 50 μg mL^-1 Fe-N-C SAzymes produced nearly 100% A₁₅ adsorption, 90% T₁₅ adsorption and only 69% C₁₅ adsorption, indicating that adenine and thymine had higher adsorption affinity on Fe-N-C SAzymes. More importantly, DNA modification did not affect the peroxidase-like activity of Fe-N-C SAzymes and the bioactivity of the adsorbed DNA. Taking the advantage of the diblock DNA with one DNA sequence (adenine) binding to Fe-N-C SAzymes and the other DNA sequence (i.e., aptamer) binding to cancer cells, we designed Apt/Fe-N-C SAzymes for colorimetric detection of cancer cells, which offered new insights for the use of SAzymes in biomedicine.