Rationally Modulate the Oxidase-like Activity of Nanoceria for Self-Regulated Bioassays

Unusual oxidase-mimetic catalytic performance surpassing peroxidase in amorphous CoOx: underlying mechanism and toward a novel H2O2-related detection paradigm

Different from crystalline cobalt oxides (Co3O4 and CoO) and most reported nanozymes, amorphous CoOx was found to exhibit better oxidase-like catalytic performance than the peroxidase one. Mechanistic investigations revealed that the introduction of H2O2 could decompose CoOx into inactive Co2+ under acidic conditions, leading to the loss of catalytic activity. With the unusual phenomenon, a proof-of-concept "turn-off" cascade system was fabricated to detect glucose colorimetrically via combining CoOx with glucose oxidase.

Interactions of metal-based nanozymes with aptamers, from the design of nanozyme to its application in aptasensor: Advances and perspectives

Nanozymes, characterized by enzyme-like activity, have been extensively used in quantitative analysis and rapid detection due to their small size, batch fabrication, and ease of modification. Researchers have combined aptamers, an emerging molecular probe, with nanozymes for biosensing to address the limited reaction specificity of nanozymes. Nanozyme aptasensors are currently experiencing significant growth, offering a promising solution to the lack of rapid detection methods across various fields. Unlike traditional nanozyme research, the development of nanozyme aptasensors is challenging as it requires the design of highly active nanozymes as well as the establishment of efficient and agile interactions between aptamers and nanozymes. Therefore, this review summarizes the active species and catalytic mechanisms of various nanozymes along with classical design options, discussing the future development of nanozyme aptasensors. It is anticipated that this review will inspire researchers in this domain, leading to the design of more enzymatically active nanozymes and advanced nanozyme aptasensors.

Self-cascade reaction triggered colorimetric detection of choline in triple-negative breast cancer

Achieving a simple process, detailed information, and visual response for cancer diagnosis and treatment is desirable but challenging. Herein, we develop a self-cascade system-triggered colorimetric array for the sensitive detection of choline, a promising biomarker in triple-negative breast cancer (TNBC). The system utilizes a ChOx-Ce3+ probe, where ChOx catalyzes the oxidation of target choline to betaine, generating H2O2, which then in situ reacts with Ce3+ to form a CeO2 nanozyme. This nanozyme exhibits robust oxidase (OXD)-like activity, oxidizing tetramethylbenzidine (TMB) to oxTMB, resulting in a visible color change that correlates with choline concentration. The self-triggered cascade mechanism significantly simplifies the detection process by eliminating the need for expensive materials and complex equipment. Additionally, it enhances the selectivity, resistance to protein interference, and long-term stability of the probe. The system demonstrated high accuracy in measuring choline concentrations in MDA-MB-231 cells and real samples, with recovery rates ranging from 97.4 % to 101 %. These results illustrate the potential of the self-cascade system-triggered colorimetric array for early TNBC detection and therapeutic monitoring, offering a cost-effective, user-friendly diagnostic tool for clinical applications.

Fe-N-C oxidase-mimicking nanozymes for discrimination of antioxidants and detection of Hg2

Single-atom nanozymes (SAzymes) with high atom utilization efficiency and well-defined coordination structures have been extensively studied. However, research on the use of the enzyme-like activity of SAzymes for the detection and discrimination of antioxidants remains relatively limited. Herein, synthesized Fe-N-C SAzymes (FeN4) display excellent oxidase-like activity with a maximum reaction rate of 1.083 × 10-7 M s-1, which is 40.85 times higher than that for NC nanozymes. Experimental studies and density functional theory (DFT) calculations revealed that the high catalytic performance arises from the efficient absorption and activation of O2 at highly exposed Fe sites. Based on the different inhibitory effects of ascorbic acid (AA), glutathione (GSH), and cysteine (Cys), a colorimetric sensor array for identifying antioxidants was developed. AA, GSH, and Cys were effectively distinguished through linear discriminant analysis (LDA). Moreover, a colorimetric platform for the rapid detection of trace Hg2+ was successfully presented, taking advantage of the strong binding ability between -SH of Cys and Hg2+, and achieving an impressive limit of detection (LOD) of 9.29 nM. This work not only provides a novel concept for distinguishing antioxidants but also expands the application of nanozymes in heavy metal ion detection.

Signal "Off-On Model'' for Colorimetric Sensing Proanthocyanidin B2 Achieved by the Organic Solvent-Processed Amorphous BiVO4 Nanozyme

Here, we report a "off-on model"-based colorimetric sensor without the assistance of H2O2, achieved by organic solvent-processed amorphous BiVO4 nanoparticles favorable for large-scale manufacturing. The amorphous material beyond traditional crystalline nanozymes has both vanadium vacancy (Vv) and oxygen vacancy (Ov), as well as single oxidase-like activity with both hydroxyl radical (•OH) and superoxide anion (O2•-) as electron acceptors. Despite the high enzymatic performance, the dual-defect-rich amorphous BiVO4 preserves good long-term activity in either buffer solution or the solid state. The specially designed BiVO4 is capable of accelerating TMB oxidation in the presence of polyphenols, thus leading to an interesting signal-intensified colorimetric response. This is probably due to the coordination of the ortho dihydroxyl group in polyphenols with the catalyst by replacing the surface-adsorbed NO3-, which results in faster charge transfer between BiVO4 and substrate and, thus, more rapid depletion of radicals for TMB oxidation. Based on these findings, a sensor platform for proanthocyanidin (PAC) B2 is established with a limit of detection (LOD) as low as 65 nM and good specificity. The sensor shows higher sensitivity than the standard Porter method (LOD: 0.29 μM) and comparable accuracy when analyzing PAC B2 in commercially available grape seed capsules, with quantitative recoveries varying from 104.0 to 108.3% and relative standard deviations ranging from 1.7 to 5.7%. To date, this is the only nanozyme-based chemical sensor that is active for the signal "off-on model" for the detection of reducing polyphenols. Also, this method seems quite general, and it can be used for sensing of a series of specific polyphenols in addition to PAC B2.

Microbe-mediated synthesis of defect-rich CeO2 nanoparticles with oxidase-like activity for colorimetric detection of L-penicillamine and glutathione

To enhance production efficiency, curtail costs, and minimize environmental impact, developing simple and sustainable nanozyme synthesis methods has been the focus of relevant research. In this report, graphite-coated CeO2 nanoparticles (CeO2 NPs) with multiple defects (Ce3+ defects, oxygen vacancies and carbon defects) were synthesized via the culture filtrate of the extremely radioresistant bacterium Deinococcus wulumuqiensis R12 (D. wulumuqiensis R12). The as-prepared CeO2 NPs exhibit remarkable oxidase (OXD)-like activity, efficiently catalyzing the oxidation of the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) to form oxTMB, even in the absence of H2O2. The electron-rich bioactive substances in the supernatant were demonstrated to modulate the electronic state of the Ce atom and played a key role in the formation of multiple defects, thereby enhancing the OXD-like activity of CeO2 NPs. Based on the inhibitory effect of sulphydryl groups (-SH) on the TMB-CeO2 system, a colorimetric strategy for the detection of both L-penicillamine (L-PA) and glutathione (GSH) was devised and successfully applied in real sample analysis. The linear ranges of L-PA and GSH detection were found to be 10-500 μM and 9-200 μM with the limits of detection (LODs) at 8.53 and 5.19 μM, respectively. This work provides a straightforward, eco-friendly and nontoxic method for the synthesis and defect construction of CeO2 NPs with OXD-like activity.

MOF-Based Biomimetic Enzyme Microrobots for Efficient Detection of Total Antioxidant Capacity of Fruits and Vegetables

Green and efficient total antioxidant capacity (TAC) detection is significant for healthy diet and disease prevention. This work first proposed the concept of TAC colorimetric detection based on microrobots. A novel metal-organic framework (MOF)-based biomimetic enzyme microrobot (MIL-88A@Fe3O4) is developed that can efficiently and accurately detect the TAC of real fruits and vegetables. Unlike the previous colorimetric detection method to measure TAC which often requires the addition of toxic hydrogen peroxide (H2O2) or light, the microrobots strategy can realize efficient TAC detection without any additional chemicals or stimuli. This is attributed to the oxidase-like activity from MIL-88A, which is discovered and confirmed for the first time by experiments and theoretical calculations. In addition, the microrobots can significantly accelerate the color reaction, resulting in a significant improvement in the detection efficiency of TAC in the motion state owing to their self-stirring effect. More importantly, the results of the MOF-based biomimetic enzyme microrobots strategy for detecting TAC in real fruits and vegetables are comparable to those tested by commonly used quantitative detection kits, in addition to low cost, excellent stability, and anti-interference ability. This attractive MOF-based biomimetic enzyme microrobot holds great prospects for future applications in catalytic sensing and promoting a healthy diet.

Based on Fe and Ni prepared organic colloidal materials as efficient oxide nanozymes for chemiluminescence detection of GSH and Hg(II) ions

Metal-organic gels (MOGs) are a type of metal-organic colloid material with a large specific surface area, loose porous structure, and open metal active sites. In this work, FeNi-MOGs were synthesized by the simple one-step static method, using Fe(III) and Ni(II) as the central metal ions and terephthalic acid as the organic ligand. The prepared FeNi-MOGs could effectively catalyze the chemiluminescence of luminol without the involvement of H2O2, which exhibited good catalytic activity. Then, the multifunctional detected platform was constructed for the detection of GSH and Hg2+, based on the antioxidant capacity of GSH, and the strong affinity between mercury ion (Hg2+) and GSH which inactivated the antioxidant capacity of GSH. The experimental limits of detection (LOD) for GSH and Hg2+ were 76 nM and 210 nM, and the detection ranges were 2-100 μM and 8-4000 μM, respectively. The as-proposed sensor had good performance in both detection limit and detection range of GSH and Hg2+, which fully met the needs of daily life. Surprisingly, the sensor had low detection limits and an extremely wide detection range for Hg2+, spanning five orders of magnitude. Furthermore, the detection of mercury ions in actual lake water and GSH in human serum showed good results, with recovery rates ranging from 90.10 % to 105.37 %, which proved that the method was accurate and reliable. The as-proposed sensor had great potential as the platform for GSH and Hg2+ detection applications.

A high oxidase-like activity, bimetallic single-atom nanozyme FeCe/NC prepared by FeCe-ZIF-8 approach for sensing tannic acid in tea

To improve the activity of single-atom nanozymes (SAzymes) for applications in food analysis, a new bimetal SAzyme FeCe/NC was developed. Its oxidase-like activity is 40% higher than that of single metal SAzyme Fe/NC. Based on a series of characterization investigations, the catalytic mechanism is that it directly catalyzed O2 to generate •OH, O2 •-and 1O2. It could directly catalyze oxidation 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxTMB, thereunder, a FeCe/NC SAzyme-TMB colorimetric method for the detection of tannic acid (TA) was constructed after the optimization of catalytic conditions. The method has a high R2 of 0.995, a low limit of detection (LOD) of 0.26 μmol/L, and high stability. The detection performance was validated by the real samples (tea). Therefore, the prepared bimetallic SAzyme FeCe/NC can be applied for TA detection without the addition of H2O2, and will have broad applications in the areas of food, feed, and life science.

Computer-aided nanodrug discovery: recent progress and future prospects

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

Temperature-resilient and sustainable Mn-MOF oxidase-like nanozyme (UoZ-4) for total antioxidant capacity sensing in some citrus fruits: Breaking the temperature barrier

Current nanozyme applications rely heavily on peroxidase-like nanozymes and are limited to a specific temperature range, despite notable advancements in nanozyme development. In this work, we designed novel Mn-based metal organic frameworks (UoZ-4), with excellent oxidase mimic activity towards common substrates. UoZ-4 showed excellent oxidase-like activity (with Km 0.072 mM) in a wide range of temperature, from 10 °C to 100 °C with almost no activity loss, making it a very strong candidate for psychrophilic and thermophilic applications. Ascorbic acid, cysteine, and glutathione could quench the appearance of the blue color of oxTMB, led us to design a visual-based sensing platform for detection of total antioxidant capacity (TAC) in cold, mild and hot conditions. The visual mode successfully assessed TAC in citrus fruits with satisfactory recovery and precisions. Cold/hot adapted and magnetic property will broaden the horizon of nanozyme applications and breaks the notion of the temperature limitation of enzymes.

Breaking the pH Limitation of Nanozymes: Mechanisms, Methods, and Applications

Although nanozymes have drawn great attention over the past decade, the activities of peroxidase-like, oxidase-like, and catalase-like nanozymes are often pH dependent with elusive mechanism, which largely restricts their application. Therefore, a systematical discussion on the pH-related catalytic mechanisms of nanozymes together with the methods to overcome this limitation is in need. In this review, various nanozymes exhibiting pH-dependent catalytic activities are collected and the root causes for their pH dependence are comprehensively analyzed. Subsequently, regulatory concepts including catalytic environment reconstruction and direct catalytic activity improvement to break this pH restriction are summarized. Moreover, applications of pH-independent nanozymes in sensing, disease therapy, and pollutant degradation are overviewed. Finally, current challenges and future opportunities on the development of pH-independent nanozymes are suggested. It is anticipated that this review will promote the further design of pH-independent nanozymes and broaden their application range with higher efficiency.

Enhanced oxidase mimic activity of raspberry-like N-doped Mn3O4 with oxygen vacancies for efficient colorimetric detection of gallic acid coupled with smartphone

The content of gallic acid (GA) is positively correlated with the quality grade of tea. Here, we developed a colorimetric method based on raspberry-like N-doped Mn3O4 nanospheres (N-Mn3O4 NSs) with oxidase-like activity for GA assay. Modulating the electronic structure of Mn3O4 by N doping could promote the catalysis ability, and the produced oxygen vacancies (OVs) can provide high surface energy and abundant active sites. The N-Mn3O4 NSs presented low Michaelis-Menten constant (Km) of 0.142 mM and maximum initial velocity (Vmax) of 9.8 × 10-6 M s-1. The sensor exhibited excellent analytical performance towards GA detection, including low LOD (0.028 μM) and promising linear range (5 ∼ 30 μM). It is attributed that OVs and O2- participated in TMB oxidation. Based on the reaction color changes, a visualized semi-quantitative GA detection could be realized via a smartphone-based system. It could be applied for evaluating GA quality in market-purchased black tea and green tea.

Direct detection of acetylcholinesterase by Fe(HCOO)2.6(OH)0.3. H2O nanosheets with oxidase-like activity on a smartphone platform

Monitoring acetylcholinesterase (AChE) is crucial in clinical diagnosis and drug screening. Traditional methods for detecting AChE usually require the addition of intermediates like acetylthiocholine, which complicates the detection process and introduces interference risks. Herein, we develop a direct colorimetric assay based on alkaline iron formate nanosheets (Fe(HCOO)2.6(OH)0.3·H2O NSs, Fef NSs) for the detection of AChE without any intermediates. The as-prepared Fef NSs exhibit oxidase-like activity, catalyzing the generation of O2·-, 1O2 and ·OH, which leads to a color change from colorless to blue when exposed to 3,3',5,5'-tetramethylbenzidine. AChE directly inhibits the oxidase-like activity of Fef NSs, resulting in a hindered color reaction, enabling the detection of AChE. The biosensor has a linear detection range of 0.1-30 mU/mL, with a minimum detection limit of 0.0083 mU/mL (S/N = 3), representing a 100-fold improvement in detection sensitivity over the traditional Ellman's method. Satisfactory results were obtained when analyzing real AChE samples. Attractively, a method for the quantitative detection of AChE by a smartphone is established based on the Fef NSs. This method enables instant acquisition of AChE concentrations, achieving real-time visualized detection.

Self-sacrificing-induced defect enhances the oxidase-like activity of MnOOH for total antioxidant capacity evaluation

Nanozymes is a kind of nanomaterials with enzyme catalytic properties. Compared with natural enzymes, nanozymes merge the advantages of both nanomaterials and natural enzymes, which is highly important in applications such as biosensing, clinical diagnosis, and food inspection. In this study, we prepared β-MnOOH hexagonal nanoflakes with a high oxygen vacancy ratio by utilizing SeO2 as a sacrificial agent. The defect-rich MnOOH hexagonal nanoflakes demonstrated excellent oxidase-like activity, catalyzing the oxidation substrate in the presence of O2, thereby rapidly triggering a color reaction. Consequently, a colorimetric sensing platform was constructed to assess the total antioxidant capacity in commercial beverages. The strategy of introducing defects in situ holds great significance for the synthesis of a series of high-performance metal oxide nanozymes, driving the development of faster and more efficient biosensing and analysis methods.

Bifunctional mesoporous glasses for bone tissue engineering: Biological effects of doping with cerium and polyphenols in 2D and 3D in vitro models

This study evaluates the cytocompatibility of cerium-doped mesoporous bioactive glasses (Ce-MBGs) loaded with polyphenols (Ce-MBGs-Poly) for possible application in bone tissue engineering after tumour resection. We tested MBGs powders and pellets on 2D and 3D in vitro models using human bone marrow-derived mesenchymal stem cells (hMSCs), osteosarcoma cells (U2OS), and endothelial cells (EA.hy926). Promisingly, at a low concentration in culture medium, Poly-loaded MBGs powders containing 1.2 mol% of cerium inhibited U2OS metabolic activity, preserved hMSCs viability, and had no adverse effects on EA.hy926 migration. Moreover, the study discussed the possible interaction between cerium and Poly, influencing anti-cancer effects. In summary, this research provides insights into the complex interactions between Ce-MBGs, Poly, and various cell types in distinct 2D and 3D in vitro models, highlighting the potential of loaded Ce-MBGs for post-resection bone tissue engineering with a balance between pro-regenerative and anti-tumorigenic activities.

A photoelectrochemical aptasensor for omethoate determination based on a photocatalysis of CeO2@MnO2 heterojunction for glucose oxidation

In the present work, we developed a photoelectrochemical aptasensor to determine omethoate (OMT) based on the dual signal amplification of CeO2@MnO2 photocatalysis for glucose oxidation and exonuclease I-assisted cyclic catalytic hydrolysis. CeO2@MnO2 heterojunction material prepared by hydrothermal method was linked with captured DNA (cDNA) and then assembled on the ITO conductive glass to form ITO/CeO2@MnO2-cDNA, which exhibited significant photocurrent response and good photocatalytic performance for glucose oxidation under visible light irradiation, providing the feasibility for sensitive determining OMT. After binding with the aptamer of OMT (apt), the formation of rigid double stranded cDNA/apt kept CeO2@MnO2 away from ITO surface, which ensured a low photocurrent background for the constructed ITO/CeO2@MnO2-cDNA/apt aptasensor. In the presence of target OMT, the restoration of the cDNA hairpin structure and the exonuclease I-assisted cyclic catalytic hydrolysis led to the generation and amplification of measurement photocurrent signals, and allowed the aptasensor to have an ideal quantitative range of 0.01-10.0 nM and low detection limit of 0.0027 nM. Moreover, the aptasensor has been applied for selective determination of OMT in real samples with good precision of the relative standard deviation less than 6.2 % and good accuracy of the recoveries from 93 % to 108 %. What's more, the aptasensor can be used for other target determination only by replacing the captured DNA and corresponding aptamer.

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

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

Self-Cascade Ce-MOF-818 Nanozyme for Sequential Hydrolysis and Oxidation

Mimicking efficient biocatalytic cascades using nanozymes has gained enormous attention in catalytic chemistry, but it remains challenging to develop a nanozyme-based cascade system to sequentially perform the desired reactions. Particularly, the integration of sequential hydrolysis and oxidation reactions into nanozyme-based cascade systems has not yet been achieved, despite their significant roles in various domains. Herein, a self-cascade Ce-MOF-818 nanozyme for sequential hydrolysis and oxidation reactions is developed. Ce-MOF-818 is the first Ce(IV)-based heterometallic metal-organic framework constructed through the coordination of Ce and Cu to distinct groups. It is successfully synthesized using an improved solvothermal method, overcoming the challenge posed by the significant difference in the binding speeds of Ce and Cu to ligands. With excellent organophosphate hydrolase-like (Km = 42.3 µM, Kcat = 0.0208 min-1 ) and catechol oxidase-like (Km = 2589 µM, Kcat = 1.25 s-1 ) activities attributed to its bimetallic active centers, Ce-MOF-818 serves as a promising self-cascade platform for sequential hydrolysis and oxidation. Notably, its catalytic efficiency surpasses that of physically mixed nanozymes by approximately fourfold, owning to the close integration of active sites. The developed hydrolysis-oxidation self-cascade nanozyme has promising potential applications in catalytic chemistry and provides valuable insights into the rational design of nanozyme-based cascade systems.

Surface Chemistry of Biologically Active Reducible Oxide Nanozymes

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

Iron-doped carbon nitride with enhanced peroxidase-like activity for smartphone-based colorimetric assay of total antioxidant capacity

The facile detection of total antioxidant capacity (TAC) is limited by in-situ analysis, because it usually requires complex laboratory equipments. Here, a colorimetric assay for TAC detection is developed based on the peroxidase-like activity of iron-doped carbon nitride (Fe/NC) and the smartphone platform. The peroxidase-like activity of carbon nitride is greatly improved by the introduction of Fe atoms, and the active sites turn to Fe-Nx coordination groups in the Fe/NC. The inhibition mechanism of the chromogenic reaction for different kinds of antioxidants is also studied. The colorimetric assay is fabricated by the relationship of absorbance-color-antioxidant content and applied successfully to the TAC detection of several fruit juicesand commercial beverages. This work not only provides a promising approach for convenient in-situ TAC assay without the use of large instruments, but also expands the application of nanozymes in nutritional value assessment of foods.

Polydopamine on Copper-Doped Cerium Dioxide Nanosheets as Peroxidase Mimics for the Intelligent Detection of Cholesterol

The catalytic ability of nanozymes has become an enzymology hotspot in the field of application. Most nanozymes were characterized to simultaneously have oxidase-like and peroxidase-like activities, but the practical application often focuses on certain activity; other complex activities may cause interference. The peroxidase-like activity (POD-like activity) of nanozymes have been widely used in the colorimetric detection of H2O2 or substances producing H2O2 as an intermediate, such as the detection of small biological molecules with the oxidative reaction of a chromogenic reagent in the presence of POD-like nanozymes. In this work, we used polydopamine (PDA) as the surface coating of Cu-CeO2 nanosheets (PDA@ Cu-CeO2), which enhanced peroxidase-like activity while inhibiting their oxidase-like activity, providing a feasible method for the sensitive determination of cholesterol by integrating visual colorimetric detection and a smartphone application as a readout. The absorbance intensity and RGB values displayed a linear range on cholesterol from 0.05 to 1.2 mM with the LOD (limit of detection) of 42.7 and 99.4 μM. In addition, the method is expected to apply in detecting cholesterol in human serum with acceptable accuracy.

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.

Multifunctional light-controllable nanozyme enabled bimodal fluorometric/colorimetric sensing of mercury ions at ambient pH

Nanomaterials with enzyme-like catalytic features (nanozymes) find wide use in analytical sensing. Apart from catalytic characteristics, some other interesting functions coexist in the materials. How to combine these properties to design multifunctional nanozymes for new sensing strategy development is challenging. Besides, in nanozymes it is still a challenge to conveniently control the catalytic process, which also hinders their further applications in advanced biochemical analysis. To remove the above barriers, here we design a light-controllable multifunctional nanozyme, namely manganese-inserted cadmium telluride (Mn-CdTe) particles, that integrates oxidase-like activity with luminescence together, to achieve the fluorometric/colorimetric dual-mode detection of toxic mercury ions (Hg2+) at ambient pH. The Mn-CdTe exhibits a light-triggered oxidase-mimicking catalytic behavior to induce chromogenic reactions, thus enabling one to start or stop the catalytic progress easily via applying or withdrawing light irradiation. Meanwhile, the quantum dot material can exhibit bright photoluminescence, which provides the fluorometric channel to sense targets. When Hg2+ is introduced, it rapidly leans toward Mn-CdTe through electrostatic interaction and Te-Hg bonding and induces the aggregation of the latter. As a result, the luminescence of Mn-CdTe is dynamically quenched, and the masking of active sites in aggregated Mn-CdTe leads to the decrease of light-initiated oxidase-mimetic activity. According to this principle, a new fluorometric/colorimetric bimodal method was established for Hg2+ determination with excellent performance. A 3D-printed portable platform combining paper-based test strips and an App-equipped smartphone was further fabricated, making it possible to achieve in-field sensing of the analyte in various matrices.

Infrared and Raman Diagnostic Modeling of Phosphate Adsorption on Ceria Nanoparticles

Cerium dioxide (CeO2; ceria) nanoparticles (CeNPs) are promising nanozymes that show a variety of biological activity. Effective nanozymes need to retain their activity in the face of surface speciation in biological environments, and characterizing surface speciation is therefore critical to understanding and controlling the therapeutic capabilities of CeNPs. In particular, adsorbed phosphates can impact the enzymatic activity exploited to convert phosphate prodrugs into therapeutics in vivo and also define the early stages of the phosphate-scavenging processes that lead to the transformation of active CeO2 into inactive CePO4. In this work, we utilize ab initio lattice-dynamics calculations to study the interaction of phosphates with the three major surfaces of ceria and to predict the infrared (IR) and Raman spectral signatures of adsorbed phosphate species. We find that phosphates adsorb strongly to CeO2 surfaces in a range of stable binding configurations, of which 5-fold coordinated P species in a trigonal bipyramidal coordination may represent a stable intermediate in the early stages of phosphate scavenging. We find that the phosphate species show characteristic spectral fingerprints between 500 and 1500 cm-1, whereas the bare CeO2 surfaces show no active modes above 600 cm-1, and the 5-fold coordinated P species in particular show potential diagnostic P-O stretching modes between 650 and 700 cm-1 in both IR and Raman spectra. This comprehensive exploration of different binding modes for phosphates on CeO2 and the set of reference spectra provides an important step toward the experimental characterization of phosphate speciation and, ultimately, control of its impact on the performance of ceria nanozymes.

N-Rich and Sulfur-Doped Nano Hollow Carbons with High Oxidase-like Activity Prepared Using a Green Template of CaCO3 for Bacteriostasis

Nanozymes, enzyme-mimicking nanomaterials, have attracted increasing attention due to their low cost, high stability, and catalytic ability compared with natural enzymes. However, the catalytic efficiency of the nanozymes is still relatively low, and catalytic reaction mechanisms remain unclear. To address these issues, herein we prepared nitrogen-riched and sulfur-codoped nano hollow carbons (N/S-HCS) using a green and useful template of CaCO3. N/S-HCS exhibits enhanced oxidase-like activity and catalytic kinetic performance. It could directly oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to the heavy blue colored ox-TMB without H2O2. The maximum reaction rate (Vmax) is 186.7 × 10-8 M·s-1, and Michaelis-Menten constant (Km) is 0.162 mM. DFT results show that N and S codoping could work synergistically to provide more active sites, resulting in the superior ability to adsorb oxygen and enhanced catalytic activity. Meantime, we develop a multispectral characterization strategy to unravel catalytic reaction mechanisms about N/S-HCS. It successfully induces the generation of superoxide (•O2-) and hydroxyl (•OH) during the colorimetric reaction which are the key intermediate products of the catalytic reaction. Furthermore, N/S-HCS increased the cellular reactive oxygen species level significantly and induced bacteriostasis to more than 95% of Escherichia coli.

Construction of Metal Organic Framework-Derived Fe-N-C Oxidase Nanozyme for Rapid and Sensitive Detection of Alkaline Phosphatase

Alkaline phosphatase (ALP) is a phosphomonoester hydrolase and serves as a biomarker in various diseases. However, current detection methods for ALP rely on bulky instruments, extended time, and complex operations, which are particularly challenging in resource-limited regions. Herein, we synthesized a MOF-derived Fe-N-C nanozyme to create biosensors for the coulometric and visual detection of ALP. Specifically, we found the Fe-N-C nanozyme can efficiently oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue-colored tetramethyl benzidine (TMBox) without the need for H2O2. To construct the biosensor, we incorporated the ALP enzymatic catalytic reaction to inhibit the oxidation of TMB by Fe-N-C oxidase nanozyme. This biosensor showed rapid and highly sensitive detection of ALP in both buffer and clinical samples. The limit of detection (LOD) of our approach could be achieved at 3.38 U L-1, and the linear range was from 5 to 60 U L-1. Moreover, we also developed a visual detection for ALP by using a smartphone-based assay and facilitated practical and accessible point-and-care testing (POCT) in resource-limited areas. The visual detection method also achieved a similar LOD of 2.12 U L-1 and a linear range of 5-60 U L-1. Our approach presents potential applications for other biomarker detections by using ALP-based ELISA methods.

Platinum-Nickel Nanoparticles with Enhanced Oxidase-like Activity for Total Antioxidant Capacity Bioassay

While great progress in nanozyme-enabled analytical chemistry has been made, most current nanozyme-based biosensing platforms are based on peroxidase-like nanozymes. However, peroxidase-like nanozymes with multienzymatic activities can influence the detection sensitivity and accuracy, while the use of unstable hydrogen peroxide (H₂O₂) in a peroxidase-like catalytic reaction may result in the reproducibility challenge of sensing signals. We envision that constructing biosensing systems by using oxidase-like nanozymes can address these limitations. Herein, we reported that platinum-nickel nanoparticles (Pt-Ni NPs) with Pt-rich shells and Ni-rich cores possessed high oxidase-like catalytic efficiency, exhibiting a 2.18-fold higher maximal reaction velocity (v_max) than initial pure Pt NPs. The oxidase-like Pt-Ni NPs were applied to develop a colorimetric assay for the determination of total antioxidant capacity (TAC). The antioxidant levels of four bioactive small molecules, two antioxidant nanomaterials, and three cells were successfully measured. Our work not only provides new insights for preparing highly active oxidase-like nanozymes but also manifests their applications for TAC analysis.

Metal-Based Nanozymes with Multienzyme-Like Activities as Therapeutic Candidates: Applications, Mechanisms, and Optimization Strategy

Most nanozymes in development for medical applications only exhibit single-enzyme-like activity, and are thus limited by insufficient catalytic activity and dysfunctionality in complex pathological microenvironments. To overcome the impediments of limited substrate availabilities and concentrations, some metal-based nanozymes may mimic two or more activities of natural enzymes to catalyze cascade reactions or to catalyze multiple substrates simultaneously, thereby amplifying catalysis. Metal-based nanozymes with multienzyme-like activities (MNMs) may adapt to dissimilar catalytic conditions to exert different enzyme-like effects. These multienzyme-like activities can synergize to realize "self-provision of the substrate," in which upstream catalysts produce substrates for downstream catalytic reactions to overcome the limitation of insufficient substrates in the microenvironment. Consequently, MNMs exert more potent antitumor, antibacterial, and anti-inflammatory effects in preclinical models. This review summarizes the cellular effects and underlying mechanisms of MNMs. Their potential medical utility and optimization strategy from the perspective of clinical requirements are also discussed, with the aim to provide a theoretical reference for the design, development, and therapeutic application of their catalytic effects.

Plasmon-Mediated Oxidase-like Activity on Ag@ZnS Heterostructured Hollow Nanowires for Rapid Visual Detection of Nitrite

Rational design of fast and sensitive determination of nitrite (NO₂^-) from a complicated actual sample overtakes a crucial role in constructing a high-efficiency sensing platform. Herein, a visual NO₂^- sensing platform with outstanding selectivity, sensitivity, and stability based on a surface plasmon resonance (SPR)-enhanced oxidase-like activity has been proposed. Benefiting from the intrinsic photocatalytic activity and limited light penetration of ZnS, the oxidase-like activity based on ZnS decorated on Ag nanowires (Ag@ZnS) is determined. It is demonstrated that the electrons are generated efficiently on the surface of ZnS and then transferred into the hot electrons of Ag with the help of localized SPR excitation, thus greatly oxidating the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to produce dark blue oxidized TMB (oxTMB). When nitrite is added into the reaction system, the oxTMB will selectively react with NO₂^- to generate diazotized oxTMB, leading to a visual color change from dark blue to light green and subsequently to dark yellow. Owing to the specific recognition between nitrite and oxTMB, the recovery of catalytic activity induced an enhanced colorimetric test with a wider linear range for NO₂^- determination, an ultralow detection limit of 0.1 μM, excellent selectivity, and practicability for application in real samples. This plasmon-enhanced oxidase-like activity not only provides a smart approach to realize a colorimetric assay with high sensitivity and simplicity but also modulates oxidase-like activities.

Nanozyme-based pollutant sensing and environmental treatment: Trends, challenges, and perspectives

Nanozymes are defined as nanomaterials exhibiting enzyme-like properties, and they possess both catalytic functions and nanomaterial's unique physicochemical characteristics. Due to the excellent stability and improved catalytic activity in comparison to natural enzymes, nanozymes have established a wide base for applications in environmental pollutants monitoring and remediation. Nanozymes have been applied in the detection of heavy metal ions, molecules, and organic compounds, both quantitatively and qualitatively. Additionally, within the natural environment, nanozymes can be employed for the degradation of organic and persistent pollutants such as antibiotics, phenols, and textile dyes. Further, the potential sphere of applications for nanozymes traverses from indoor air purification to anti-biofouling agents, and even they show promise in combatting pathogenic bacteria. However, nanozymes may have inherent toxicity, which can restrict their widespread utility. Thus, it is important to evaluate and monitor the interaction and transformation of nanozymes towards biosphere damage when employed within the natural environment in a cradle-to-grave manner, to assure their utmost safety. In this context, various studies have concluded that the green synthesis of nanozymes can efficiently overcome the toxicity limitations in real life applications, and nanozymes can be well utilized in the sensing and degradation of several toxic pollutants including metal ions, pesticides, and chemical warfare agents. In this seminal review, we have explored the great potential of nanozymes, whilst addressing a range of concerns, which have often been overlooked and currently restrict widespread applications and commercialization of nanozymes.

Molecular, biochemical and micromorphological responses of cacao seedlings of the Parinari series, carrying the lethal gene Luteus-Pa, in the presence and absence of cotyledons

Investigations of the compatibility between cacao genotypes of the population of the Parinari series (Pa), resulting from the reciprocal crossing of Pa 30 × Pa 169 and Pa 121 × Pa 169, allowed the verification of the occurrence of the recessive lethal single character called Luteus-Pa. These genotypes have this gene in heterozygosity, which when intercross or self-fertilize, segregate in a 3:1 ratio. Normal (NS) and mutant (MS) seedlings grow normally and, after a period of approximately 30 days of age, MS leaves begin to show a metallic yellow color, followed by necrotic spots, and death of the entire seedling, approximately 40 days after the emergency. The work evaluate the molecular, biochemical and micromorphological responses in NS and MS, with and without cotyledons, resulting from the crossing of the Pa 30 × Pa 169 cacao genotypes, aiming to elucidate the possible lethal mechanisms of the homozygous recessive Luteus-Pa. The presence of the lethal gene Luteus-Pa in the seedlings of the cacao genotypes of the population of the Parinari (Pa), with and without cotyledons, resulting from the crossing of Pa 30 × Pa 169, in addition to regulating the synthesis of proteins related to the photosynthetic and stress defense processes, promoted an increase in the synthesis of proteins involved in the glycolic pathway, induced oxidative stress, altered the mobilization of cotyledonary reserves, the integrity of cell membranes, leaf micromorphology and induced the death of seedlings, soon after depletion of protein and carbohydrate reserves, especially in the absence of cotyledons.

Structure design mechanisms and inflammatory disease applications of nanozymes

Nanozymes are artificial enzymes with high catalytic activity, low cost, and good biocompatibility, and have received ever-increasing attention in recent years. Various inorganic and organic nanoparticles have been found to exhibit enzyme-like activities and are used as nanozymes for diverse biomedical applications ranging from tumor imaging and therapeutics to detection. However, their further clinical applications are hindered by the potential toxicity and long-term retention of nanomaterials in vivo. Clarifying the catalytic mechanism of nanozymes and identifying the key factors responsible for their behavior can guide the design of nanozyme structure, enlighten the ways to improve their enzyme-like activities, and minimize the dosage of nanozymes, leading to reduced toxicity to the human body for a real biomedical application prospect. In particular, inflammation occurring in numerous diseases is closely related to reactive oxygen species, and the active oxygen scavenging ability of nanozymes potentially exerts excellent therapeutic effects on inflammatory diseases. In this review, we systematically summarize the structure-activity relationship of nanozymes, including regulation strategies for size and morphology, surface structure, and composition. Based on the structure-activity mechanisms, a series of chemically designed nanozymes developed to target various inflammatory diseases are briefly summarized.

Fluoride-assisted detection of glutathione by surface Ce3+/Ce4+ engineered nanoceria

Nanoceria has evolved as a promising nanomaterial due to its unique enzyme-like properties, including excellent oxidase mimetic activity, which significantly increases in the presence of fluoride ions. However, this significant increase in oxidase activity has never been utilised as a signal enhancer for the detection of biological analytes partly because of the lack of understanding of the mechanism involved in this process. In this study, we show that the surface oxidation state of cerium ions plays a very crucial role in different enzymatic activities, especially the oxidase mimetic activity by engineering nanoceria with three different surface Ce⁴⁺/Ce³⁺ compositions. Using DFT calculations combined with Bader charge analysis, it is demonstrated that stoichiometric ceria registers a higher oxidase mimetic activity than oxygen-deficient ceria with a low Ce⁴⁺/Ce³⁺ ratio due to a higher charge transfer from a substrate, 3,3',5,5' tetramethylbenzidine (TMB), to the ceria surface. We also show that the fluoride ions can significantly increase the charge transfer from the TMB surface to ceria irrespective of the surface Ce⁴⁺/Ce³⁺ ratio. Using this knowledge, we first compare the fluoride sensing properties of nanoceria with high Ce⁴⁺ and mixed Ce⁴⁺/Ce³⁺ oxidation states and further demonstrate that the linear detection range of fluoride ions can be extended to 1-10 ppm for nanoceria with mixed oxidation states. Then, we also demonstrate an assay for fluoride assisted detection of glutathione, an antioxidant with elevated levels during cancer, using nanoceria with a high surface Ce⁴⁺/Ce³⁺ ratio. The addition of fluoride ions in this assay allows the detection of glutathione in the linear range of 2.5-50 ppm with a limit of detection (LOD) of 3.8 ppm. These studies not only underpin the role of the surface Ce⁴⁺/Ce³⁺ ratio in tuning the fluoride assisted boost in the oxidase mimetic activity of nanoceria but also its strategic application in designing better colourimetric assays.

Nanoceria dissolution at acidic pH by breaking off the catalytic loop

This manuscript proves the reproducibility and robustness of cerium oxide nanoparticles, nanoceria, employed as a chemical reagent with oxidizing capacity (as an electron sink) at acidic pH. Unlike nanoceria multi-enzyme-mimetic capabilities at neutral or high pH, nanoceria can behave as a stoichiometric reagent at low pH where insoluble Ce4+ ions transform into soluble Ce3+ in the nanocrystal that finally dissolves. This behaviour can be interpreted as enzyme-like when nanoceria is in excess with respect to the substrate. Under these conditions, the Ce3+/Ce4+ ratio in the NPs can easily be estimated by titration with ferrocyanide. This procedure could become a rapid assessment tool for evaluating nanoceria capacity in liquid environments.

Oxidase-like ZnCoFe Three-Atom Nanozyme as a Colorimetric Platform for Ascorbic Acid Sensing

Great enthusiasm in single-atom catalysts for various catalytic reactions continues to heat up. However, the poor activity of the existing single/dual-metal-atom catalysts does not meet the actual requirement. In this scenario, the precise design of triple-metal-atom catalysts is vital but still challenging. Here, a triple-atom site catalyst of FeCoZn catalyst coordinated with S and N, which is doped in the carbon matrix (named FeCoZn-TAC/SNC), is designed. The FeCoZn catalyst can mimic the activity of oxidase by activating O₂ into ^•O₂^- radicals by virtue of its atomically dispersed metal active sites. Employing this characteristic, triple-atom catalysts can become a great driving force for the development of novel biosensors featuring adequate sensitivity. First, the property of FeCoZn catalyst as an oxidase-like nanozyme was explored. The obtained FeCoZn-TAC/SNC shows remarkably enhanced catalytic performance than that of FeCoZn-TAC/NC and single/dual-atom site catalysts (FeZn, CoZn, FeCo-DAC/NC and Fe, Zn, Co-SAC/NC) because of trimetallic sites, demonstrating the synergistic effect. Further, the utility of the oxidase-like FeCoZn-TAC/SNC in biosensor field is evaluated by the colorimetric sensing of ascorbic acid. The nanozyme sensor shows a wide concentration range from 0.01 to 90 μM and an excellent detection limit of 6.24 nM. The applicability of the nanozyme sensor in biologically relevant detection was further proved in serum. The implementation of TAC in colorimetric detection holds vast promise for further development of biomedical research and clinical diagnosis.

Preparation, Characterization and Multiple Biological Properties of Peptide-Modified Cerium Oxide Nanoparticles

Although cerium oxide nanoparticles are attracting much attention in the biomedical field due to their unique physicochemical and biological functions, the cerium oxide nanoparticles greatly suffer from several unmet physicochemical challenges, including loss of enzymatic activity during the storage, non-specific cellular uptake, off-target toxicities, etc. Herein, in order to improve the targeting property of cerium oxide nanoparticles, we first modified cerium oxide nanoparticles (CeO₂) with polyacrylic acid (PAA) and then conjugated with an endothelium-targeting peptide glycine-arginine-aspartic acid (cRGD) to construct CeO₂@PAA@RGD. The physiochemical characterization results showed that the surface modifications did not impact the intrinsic enzymatic properties of CeO₂, including catalase-like (CAT) and superoxide dismutase-like (SOD) activities. Moreover, the cellular assay data showed that CeO₂@PAA@RGD exhibited a good biocompatibility and a higher cellular uptake due to the presence of RGD targeting peptide on its surface. CeO₂@PAA@RGD effectively scavenged reactive oxygen species (ROS) to protect cells from oxidative-stress-induced damage. Additionally, it was found that the CeO₂@PAA@RGD converted the phenotype of macrophages from proinflammatory (M1) to anti-inflammatory (M2) phenotype, inhibiting the occurrence of inflammation. Furthermore, the CeO₂@PAA@RGD also promoted endothelial cell-mediated migration and angiogenesis. Collectively, our results successfully demonstrate the promising application of CeO₂@PAA@RGD in the future biomedical field.

A colorimetric smartphone-based platform for pesticides detection using Fe-N/C single-atom nanozyme as oxidase mimetics

In this study, a novel highly sensitive colorimetric platform has been designed for malathion assay based on Fe-N/C SAzyme. The as-synthesized SAzyme can directly oxidize 3,3´,5,5´-tetramethylbenzidine (TMB) to generate blue colored oxidized TMB. L-ascorbic acid-2-phosphate (AA2P), a substrate of acid phosphatase (ACP), could be hydrolyzed to AA, thereafter inhibit the oxidization reaction of TMB, leading to a conspicuous blue color fading. With the addition of malathion hindered the ACP activity and limited the AA production, resulting in the recovery of the catalytic activity of single-atom nanozyme. Under optimized operational conditions, a novel colorimetric assay has been designed for malathion detection with LOD of 0.42 nM. Besides, quantification of malathion in environmental and food samples was achieved based on the proposed strategy. In addition, the successfully integrated paper/smartphone sensor provided sensitive, and rapid, reliable detection of malathion with a LOD of 1 nM.

Colorimetric detection of total antioxidants in green tea with oxidase-mimetic CoOOH nanorings

Green tea is a popular beverage and is widely consumed due to its taste and antioxidative polyphenols. Herein, a smartphone-based colorimetric reader using cobalt oxyhydroxide (CoOOH) nanorings has been successfully applied to detect antioxidants in green tea with high reliability and robustness. By exploiting the oxidase-mimicking activity, the as-synthesized CoOOH nanorings replaces natural enzymes to directly catalyze oxidate colorless 3,3 ´ ,5,5 ´ -tetramethylbenzidine (TMB), while antioxidants can disintegrate CoOOH, leading to an antioxidant concentration-dependent color change. Benefiting from the CoOOH nanorings-based colorimetric strategy, a smartphone-assistant nanosensor was devised for portable and visual detection of antioxidants in green tea. The proposed method can be extended to visual detection of a diverse range of diseases by responding to their specific antioxidant, and thus provide a pivotal disease toolbox that is compatible for development at the point-of-care.

Nano-scale minerals in-situ supporting CeO2 nanoparticles for off-on colorimetric detection of L-penicillamine and Cu2+ ion

Realizing the high value-added utilization of cheap minerals in environmental catalysis has important practical significance. Herein, four nano-scale minerals, namely halloysite (Hal) nanotubes, palygorskite (Pal) nanorods, and montmorillonite (Mon) and hydrotalcite (LDH) nanosheets, were selected for in-situ supporting CeO₂ nanoparticles (NPs) by a facile one-pot hydrothermal method. Among various nanocomposites (NCs), CeO₂/Pal behaves the highest peroxidase-like activity, attributing to larger surface area for uniformly dispersing CeO₂ NPs and more exposed active oxygen vacancy (O_vac) defects. A novel off-on colorimetric strategy was constructed for detecting toxic L-penicillamine (LPA) and Cu²⁺ ion with limit of detections (LODs) of 8.37 and 9.80 μM, respectively. Density functional theory (DFT) calculations show that the O_vac defect on CeO₂(111) surface can catalyze the heterolytic cleavage of H₂O₂ into H₂O and oxygen radical (•O), instead of being two hydroxyl radicals (•OH) on clean surface. It can also act as trapping site for O₂ and H₂O adsorption, improving the oxygen affinity and hydrophilicity of CeO₂/Pal. This study provides a feasible strategy for designing mineral-based nanozymes and an insight into the possible catalytic mechanism.

Dual-Active Au@PNIPAm Nanozymes for Glucose Detection and Intracellular H2O2 Modulation

As a nanozyme, gold nanoparticles have some advantages compared with natural enzymes, such as stable structure, adjustable catalytic activity, multifunctionality, and recyclability. Due to their special dimension, they are easy to aggregate rapidly and lose their catalytic performance when exposed to normal saline or special pH environment. To avoid such a situation, Au@PNIPAm nanozymes with core-shell structure are constructed and their mimic peroxidase and glucose oxidase enzymatic activities are investigated. Kinetic examinations manifest that Au@PNIPAm nanozymes exhibited a high affinity for 3,3,5,5-tetramethylbenzidine (TMB), hydrogen peroxide (H₂O₂), and glucose. These predominant peroxidase-like and glucose-like oxidase Au@PNIPAm catalytic activities are successfully used in the detection of H₂O₂ or glucose (LOD is 2.43 mM or 5.07 mM). Otherwise, the potential Au@PNIPAm nanozymes are provided with a clear ability for decomposing the intracellular H₂O₂ in living cells. And it could protect cells from oxidative stress damage with inducing by H₂O₂. Therefore, it is easy to consider that Au@PNIPAm nanozymes show a certain possibility to retard cell senescence and increase the production of the hydroxyl radical which could prevent carcinogenesis of the cell.

Recent Trends in Composite Nanozymes and Their Pro-Oxidative Role in Therapeutics

Nanozymes are inorganic nanostructures whose enzyme mimic activities are increasingly explored in disease treatment, taking inspiration from natural enzymes. The catalytic ability of nanozymes to generate reactive oxygen species can be used for designing effective antimicrobials and antitumor therapeutics. In this context, composite nanozymes are advantageous, particularly because they integrate the properties of various nanomaterials to offer a single multifunctional platform combining photodynamic therapy (PDT), photothermal therapy (PTT), and chemodynamic therapy (CDT). Hence, recent years have witnessed great progress in engineering composite nanozymes for enhanced pro-oxidative activity that can be utilized in therapeutics. Therefore, the present review traverses over the newer strategies to design composite nanozymes as pro-oxidative therapeutics. It provides recent trends in the use of composite nanozymes as antibacterial, antibiofilm, and antitumor agents. This review also analyzes various challenges yet to be overcome by pro-oxidative composite nanozymes before being used in the field.

Modulating the Biomimetic and Fluorescence Quenching Activities of Metal-Organic Framework/Platinum Nanoparticle Composites and Their Applications in Molecular Biosensing

Nanoscale metal-organic frameworks (nMOFs) have gained considerable attention with significant potential applications. Although great efforts have been devoted to designing and fabricating nanoscaffold structures, approaches of deliberately regulating the intrinsic functionality of nMOFs have been poorly explored. Herein, we report a simple and novel strategy to regulate the catalytic and fluorescence quenching behaviors of nMOFs through coordination-driven self-assembly. As a proof-of-concept, we synthesized a synergistic and stable MOF-metal nanocomposite by loading platinum nanoparticles (PtNPs) on a commonly used Fe-MOF, i.e., MIL-88B-NH₂/Pt, as a MOF composite model for exploration. On one hand, the complexation with ATP effectively broke the pH limitation of the peroxidase-mimicking MIL-88B-NH₂/Pt nanozyme, bringing a 10-fold increased catalytic activity under alkaline condition. Based on the distinct catalytic enhancement between ATP and other nucleotides, real-time monitoring of apyrase activity as well as colorimetric detection of alkaline phosphatase (ALP) was performed. On the other hand, interactions of MIL-88B-NH₂/Pt with fluorescent DNA were tolerant of different nucleic acids and, more importantly, were further manipulated by inorganic molecules. As a result, H₂O₂ could only trigger the release of a G-rich sequence, while phosphates could readily induce desorption of various DNA molecules with varying lengths, sequences, and fluorescent dyes. Accordingly, fluorescent DNA and MIL-88B-NH₂/Pt as functional probe-quencher pairs were proposed, allowing the establishment of a fluorescence bioassay for ALP and PPase detection and Boolean logic calculations. This work offers a means to tune the intrinsic activities of nMOFs by surface engineering, benefiting design of functional nanomaterials and development of advanced biosensing systems.

An Unprecedented FeMo6 @Ce-Uio-66 Nanocomposite with Cascade Enzyme-Mimic Activity as Colorimetric Sensing Platform

Introducing the idea of integrated design and cascade activity into nanozyme, the novel integrated nanozymes (INAzymes), FeMo₆ @Ce-Uio-66 (FC-66(n)), were designed and synthesized by encapsulating iron-based polyoxometalates (FeMo₆ ) into the ceria-based metal-organic framework (Ce-Uio-66). Due to the oxygen-driven reversible Ce³⁺ /Ce⁴⁺ couple sites, the "Fenton-like" effect by iron centers, the "nanoscale proximity" effects by nanocages, and their synergistic effects, FC-66(n) as INAzymes exhibit elegant cascade enzyme-mimic activities (oxidase-, peroxidase-, and Fenton-like activity), which realizes INAzyme activities based on polyoxometalates based metal-organic framework (POMOFs). By employing dopamine (DA) detection as a model reaction, a high-efficient fluorescent "turning-on-enhanced" platform under near neutral conditions was established.