Defect-Engineered Nanozyme-Linked Receptors

Characterisation of a SapYZU11@ZnFe2O4 biosensor reveals its mechanism for the rapid and sensitive colourimetric detection of viable Staphylococcus aureus in food matrices

Although bacteriophage-based biosensors hold promise for detecting Staphylococcus aureus in food products in a timely, simple, and sensitive manner, the associated targeting mechanism of the biosensors remains unclear. Herein, a colourimetric biosensor SapYZU11@ZnFe2O4, based on a broad-spectrum S. aureus lytic phage SapYZU11 and a ZnFe2O4 nanozyme, was constructed, and its capacity to detect viable S. aureus in food was evaluated. Characterisation of SapYZU11@ZnFe2O4 revealed its effective immobilisation, outstanding biological activity, and peroxidase-like capability. The peroxidase activity of SapYZU11@ZnFe2O4 significantly decreased after the addition of S. aureus, potentially due to blockage of the nanozyme active sites. Moreover, SapYZU11@ZnFe2O4 can detect S. aureus from various sources and S. aureus isolates that phage SapYZU11 could not lyse. This may be facilitated by the adsorption of the special receptor-binding proteins on the phage tail fibre and wall teichoic acid receptors of S. aureus. Besides, SapYZU11@ZnFe2O4 exhibited remarkable sensitivity and specificity when employing colourimetric techniques to rapidly determine viable S. aureus counts in food samples, with a detection limit of 0.87 × 102 CFU/mL. Thus, SapYZU11@ZnFe2O4 has broad application prospects for the detection of viable S. aureus cells on food substrates.

Recent advances in metal oxide nanozyme-based optical biosensors for food safety assays

Metal oxide nanozymes are emerging as promising materials for food safety detection, offering several advantages over natural enzymes, including superior stability, cost-effectiveness, large-scale production capability, customisable functionality, design options, and ease of modification. Optical biosensors based on metal oxide nanozymes have significantly accelerated the advancement of analytical research, facilitating the rapid, effortless, efficient, and precise detection and characterisation of contaminants in food. However, few reviews have focused on the application of optical biosensors based on metal oxide nanozymes for food safety detection. In this review, the catalytic mechanisms of the catalase, oxidase, peroxidase, and superoxide dismutase activities of metal oxide nanozymes are characterized. Research developments in optical biosensors based on metal oxide nanozymes, including colorimetric, fluorescent, chemiluminescent, and surface-enhanced Raman scattering biosensors, are comprehensively summarized. The application of metal oxide nanozyme-based biosensors for the detection of nitrites, sulphites, metal ions, pesticides, antibiotics, antioxidants, foodborne pathogens, toxins, and other food contaminants has been highlighted. Furthermore, the challenges and future development prospects of metal oxide nanozymes for sensing applications are discussed. This review offers insights and inspiration for further investigations on optical biosensors based on metal oxide nanozymes for food safety detection.

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

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

Rational Biomimetic Construction of Lignin-based Carbon Nanozyme for Identification of Uric Acid in Human Urine

Nanozymes have made remarkable progress in the field of sensing assays by replacing native enzyme functions. However, it is still a challenge to rationally design active centers from molecular structure to enhance the catalytic performance and develop low-cost nanozymes. In this work, guided by the catalytic site of horseradish peroxidase (HRP), iron source and histidine were coupled to the main chain of aminated sodium lignosulfonate (SL) through the self-assembly biomimetic strategy to construct His-SL-Fe with peroxidase activity. The inherent functional groups and basic framework of aminated SL provide a robust environment and promote the formation of active sites. His-SL-Fe shows excellent robustness over multiple test cycles and has a strong affinity for the substrate compared to HRP. His-SL-Fe had been effectively integrated in the sensing system for catalytic detection of uric acid (UA) to achieve accurate recognition of UA in the range of 0.5-100 μM with the limit of detection as low as 0.18 μM. The recovery of human urine samples is in the range of 96.8%-106.1 % and the error is within 4 %. This work not only provides a new approach for the directed design of high-performance nanozymes, but also demonstrates promising ideas for the refined application of biomass resources.

p-d Orbital Hybridization-Engineered PdSn Nanozymes for a Sensitive Immunoassay

Nanozymes with peroxidase-like activity have been extensively studied for colorimetric biosensing. However, their catalytic activity and specificity still lag far behind those of natural enzymes, which significantly affects the accuracy and sensitivity of colorimetric biosensing. To address this issue, we design PdSn nanozymes with selectively enhanced peroxidase-like activity, which improves the sensitivity and accuracy of a colorimetric immunoassay. The peroxidase-like activity of PdSn nanozymes is significantly higher than that of Pd nanozymes. Theoretical calculations reveal that the p-d orbital hybridization of Pd and Sn not only results in an upward shift of the d-band center to enhance hydrogen peroxide (H2O2) adsorption but also regulates the O-O bonding strength of H2O2 to achieve selective H2O2 activation. Ultimately, the nanozyme-linked immunosorbent assay has been successfully developed to sensitively and accurately detect the prostate-specific antigen (PSA), achieving a low detection limit of 1.696 pg mL-1. This work demonstrates a promising approach for detecting PSA in a clinical diagnosis.

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.

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

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

Photothermal-Switched Single-Atom Nanozyme Specificity for Pretreatment and Sensing

Various applications lead to the requirement of nanozymes with either specific activity or multiple enzyme-like activities. To this end, intelligent nanozymes with freely switching specificity abilities hold great promise to adapt to complicated and changeable practical conditions. Herein, a nitrogen-doped carbon-supported copper single-atom nanozyme (named Cu SA/NC) with switchable specificity is reported. Atomically dispersed active sites endow Cu SA/NC with specific peroxidase-like activity at room temperature. Furthermore, the intrinsic photothermal conversion ability of Cu SA/NC enables the specificity switch by additional laser irradiation, where photothermal-induced temperature elevation triggers the expression of oxidase-like and catalase-like activity of Cu SA/NC. For further applications in practice, a pretreatment-and-sensing integration kit (PSIK) is constructed, where Cu SA/NC can successively achieve sample pretreatment and sensitive detection by switching from multi-activity mode to specific-activity mode. This study sets the foundation for nanozymes with switchable specificity and broadens the application scope in point-of-care testing.

Defect Engineering in Biomedical Sciences

With the promotion of nanochemistry research, large numbers of nanomaterials have been applied in vivo to produce desirable cytotoxic substances in response to endogenous or exogenous stimuli for achieving disease-specific therapy. However, the performance of nanomaterials is a critical issue that is difficult to improve and optimize under biological conditions. Defect-engineered nanoparticles have become the most researched hot materials in biomedical applications recently due to their excellent physicochemical properties, such as optical properties and redox reaction capabilities. Importantly, the properties of nanomaterials can be easily adjusted by regulating the type and concentration of defects in the nanoparticles without requiring other complex designs. Therefore, this tutorial review focuses on biomedical defect engineering and briefly discusses defect classification, introduction strategies, and characterization techniques. Several representative defective nanomaterials are especially discussed in order to reveal the relationship between defects and properties. A series of disease treatment strategies based on defective engineered nanomaterials are summarized. By summarizing the design and application of defective engineered nanomaterials, a simple but effective methodology is provided for researchers to design and improve the therapeutic effects of nanomaterial-based therapeutic platforms from a materials science perspective.

Nanozyme Rich in Oxygen Vacancies Derived from Mn-Based Metal-Organic Gel for the Determination of Alkaline Phosphatase

Vacancy engineering as an effective strategy has been widely employed to regulate the enzyme-mimic activity of nanomaterials by adjusting the surface, electronic structure, and creating more active sites. Herein, we purposed a facile and simple method to acquire transition metal manganese oxide rich in oxygen vacancies (OVs-Mn2O3-400) by pyrolyzing the precursor of the Mn(II)-based metal-organic gel directly. The as-prepared OVs-Mn2O3-400 exhibited superior oxidase-like activity as oxygen vacancies participated in the generation of O2•-. Besides, steady state kinetic constant (Km) and catalytic kinetic constant (Ea) suggested that OVs-Mn2O3-400 had a stronger affinity toward 3,3',5,5'-tetramethylbenzidine and possessed prominent catalytic performance. By taking 2-phospho-l-ascorbic acid as the substrate, which can be converted into reducing substance ascorbic acid in the presence of alkaline phosphatase (ALP), OVs-Mn2O3-400 can be applied as an efficient nanozyme for ALP colorimetric analysis without the help of destructive H2O2. The colorimetric sensor established by OVs-Mn2O3-400 for ALP detection showed a good linearity from 0.1 to 12 U/L and a lower limit of detection of 0.054 U/L. Our work paves the way for designing enhanced enzyme-like activity nanozymes, which is of significance in biosensing.

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.

High-loading Cu single-atom nanozymes supported by carbon nitride with peroxidase-like activity for the colorimetric detection of tannic acid

The design of nanozymes with high metal atom loading is of great significance to improve enzyme activity and is also the key to furthering the construction of highly sensitive colorimetric sensors. In this work, a colorimetric sensor for the quantitative analysis of tannic acid (TA) was developed based on two-dimensional carbon nanosheet carbon nitride (CN)-supported Cu single-atom nanozymes (Cu/CN). Cu/CN was synthesized by supramolecular preorganization and calcination, with an ultrathin nanosheet structure and a high density of Cu active sites, with a Cu loading of up to 14.3 wt%. Benefiting from the above characteristics, Cu/CN exhibits peroxidase-mimicking activity and excellent catalytic performance. Therefore, a colorimetric sensor was constructed for the fast and sensitive quantitative analysis of TA with good linearity in the range of 0.09-3.2 μM and a low detection limit of 30 nM. Furthermore, the sensor was successfully applied to the analysis of TA in tea samples of different varieties. This work sheds new light on the design of nanozymes with a high density of active sites and the analysis of TA in real environments.

Activity Regulating Strategies of Nanozymes for Biomedical Applications

On accounts of the advantages of inherent high stability, ease of preparation and superior catalytic activities, nanozymes have attracted tremendous potential in diverse biomedical applications as alternatives to natural enzymes. Optimizing the activity of nanozymes is significant for widening and boosting the applications into practical level. As the research of the catalytic activity regulation strategies of nanozymes is boosting, it is essential to timely review, summarize, and analyze the advances in structure-activity relationships for further inspiring ingenious research into this prosperous area. Herein, the activity regulation methods of nanozymes in the recent 5 years are systematically summarized, including size and morphology, doping, vacancy, surface modification, and hybridization, followed by a discussion of the latest biomedical applications consisting of biosensing, antibacterial, and tumor therapy. Finally, the challenges and opportunities in this rapidly developing field is presented for inspiring more and more research into this infant yet promising area.

Amino-Ligand-Coordinated Dicopper Active Sites Enable Catechol Oxidase-Like Activity for Chiral Recognition and Catalysis

Developing highly active and selective advanced nanozymes for enzyme-mimicking catalysis remains a long-standing challenge for basic research and practical applications. Herein, we grafted a chiral histidine- (His-) coordinated copper core onto Zr-based metal-organic framework (MOF) basic backbones to structurally mirror the bimetal active site of natural catechol oxidase. Such a biomimetic fabricated process affords MOF-His-Cu with catechol oxidase-like activity, which can catalyze dehydrogenation and oxidation of o-diphenols and then transfer electrons to O₂ to generate H₂O₂ by the cyclic conversion of Cu(II) and Cu(I). Specifically, the elaborate incorporation of chiral His arms results in higher catalytic selectivity over the chiral catechol substrates than natural enzyme. Density functional theory calculations reveal that the binding energy and potential steric effect in active site-substrate interactions account for the high stereoselectivity. This work demonstrates efficient and selective enzyme-mimicking catalytic processes and deepens the understanding of the catalytic mechanism of nanozymes.

High-Indexed Intermetallic Pt3Sn Nanozymes with High Activity and Specificity for Sensitive Immunoassay

Great efforts have been made to expand the application fields of nanozymes, which puts forward requirements for nanozymes with both superior catalytic activity and specificity. Herein, we reported the high-indexed intermetallic Pt₃Sn (H-Pt₃Sn) with high peroxidase-like activity and specificity. The resultant H-Pt₃Sn exhibits a specific activity of 345.3 U/mg, which is 1.82 times higher than Pt. Moreover, H-Pt₃Sn possesses negligible oxidase-like and catalase-like activities, achieving superior catalytic specificity toward H₂O₂ activation. Experimental and theoretical calculations reveal both the splitting energy for adsorbed H₂O₂ and the energy barrier for the rate-determining step of H-Pt₃Sn are significantly decreased compared with Pt₃Sn and Pt. Finally, a nanozyme-linked immunosorbent assay is successfully developed, achieving the sensitive and accurate colorimetric detection for carcinoembryonic antigen with a low detection limit of 0.49 pg/mL and showing practical feasibility in serum sample detection.

Tuning iron spin states in single-atom nanozymes enables efficient peroxidase mimicking

The large-scale application of nanozymes remains a significant challenge owing to their unsatisfactory catalytic performances. Featuring a unique electronic structure and coordination environment, single-atom nanozymes provide great opportunities to vividly mimic the specific metal catalytic center of natural enzymes and achieve superior enzyme-like activity. In this study, the spin state engineering of Fe single-atom nanozymes (FeNC) is employed to enhance their peroxidase-like activity. Pd nanoclusters (PdNC) are introduced into FeNC, whose electron-withdrawing properties rearrange the spin electron occupation in Fe(ii) of FeNC-PdNC from low spin to medium spin, facilitating the heterolysis of H2O2 and timely desorption of H2O. The spin-rearranged FeNC-PdNC exhibits greater H2O2 activation activity and rapid reaction kinetics compared to those of FeNC. As a proof of concept, FeNC-PdNC is used in the immunosorbent assay for the colorimetric detection of prostate-specific antigen and achieves an ultralow detection limit of 0.38 pg mL-1. Our spin-state engineering strategy provides a fundamental understanding of the catalytic mechanism of nanozymes and facilitates the design of advanced enzyme mimics.

Nanozyme-encoded luminescent detection for food safety analysis: An overview of mechanisms and recent applications

With the rapid growth in global food production, delivery, and consumption, reformative food analytical techniques are required to satisfy the monitoring requirements of speed and high sensitivity. Nanozyme-encoded luminescent detections (NLDs) integrating nanozyme-based rapid detections with luminescent output signals have emerged as powerful methods for food safety monitoring, not only because of their preeminent performance in analysis, such as rapid, facile, low background signal, and ultrasensitive, but also due to their strong attractiveness for future sensing research. However, the lack of a full understanding of the fundamentals of NLDs for food safety detection technologies limits their further application. In this review, a systematic overview of the mechanisms of NLDs and their applications in the food industry is summarized, which covers the nanozyme-mimicking types and their luminescent signal generation mechanisms, as well as their applications in monitoring common foodborne contaminants. As demonstrated by previous studies, NLDs are bridging the gap to practical-oriented food analytical technologies and various opportunities to improve their food analytical performance to be considered in the future are proposed.

Nanobiocatalysis: a materials science road to biocatalysis

With high activity and specificity to conduct catalysis under mild conditions, enzymes show great promise in many fields. However, they are not acclimatized to environments in practice after leaving the familiar biological conditions. Aiming at this issue, nanobiocatalysis, a fresh area integrating nanotechnology and enzymatic catalysis, is expected to design biocatalysis based on materials science. Specifically, nano-integrated biocatalysis and bio-inspired nanocatalysis are considered as two effective nanobiocatalytic systems to meet different design needs. Notably, both systems are not entirely separated, and the combination of both further sparks more possibilities. This review summarizes the type, construction, and function of nanobiocatalytic systems, analyzing the pros and cons of different strategies. Moreover, the corresponding applications in bioassay, biotherapy, and environmental remediation are highlighted. We hope that the advent of nanobiocatalysis will help in grasping the inherence of biocatalysis and propel biocatalytic applications.

Mild Hyperthermia Induced by Hollow Mesoporous Prussian Blue Nanoparticles in Alliance with a Low Concentration of Hydrogen Peroxide Shows Powerful Antibacterial Effect

The emergence of superbacteria as well as the drug resistance of the current bacteria gives rise to worry regarding a bacterial pandemic and also calls for the development of novel ways to combat the bacteria. Here in this article, we demonstrate that mild hyperthermia induced by hollow mesoporous Prussian blue nanoparticles (HMPBNPs) in alliance with a low concentration of hydrogen peroxide (H₂O₂) shows a powerful inhibition effect on bacteria. Our results demonstrate that this therapeutic regime could realize almost full growth inhibition of both Gram-positive (Staphylococcus aureus, S. aureus) and -negative bacteria (Escherichia coli, E. coli), as well as potent inhibition/elimination of the S. aureus biofilm. The wound healing results indicate that combination regime of the antibacterial system could be conveniently used for wound disinfection in vivo and could promote wound healing. To our limited knowledge, this is one of the few pioneer works to apply mild hyperthermia for the combat of bacteria, which provides a novel strategy to inspire future studies.

Ultrathin Ruthenium Nanosheets with Crystallinity-Modulated Peroxidase-like Activity for Protein Discrimination

Noble-metal-based nanozymes have attracted great interest as enzyme mimics because of their unique properties. To modulate the performance and meet the requirements of practical biosensing applications, phase engineering is promising for the design of novel noble-metal-based nanomaterials. Herein, a simple salt-assist strategy was employed for the synthesis of Ru nanosheets (NSs) with the controlled crystalline degree. The crystalline degree plays a significant role in tuning peroxidase-like activity by optimizing the affinity toward the catalytic substrate. Furthermore, the inhibition effect of mercapto molecules on the peroxidase-like activity of Ru NSs was investigated. As a proof-of-concept, the Ru NSs-based colorimetric sensing arrays were developed to distinguish mercapto molecules, and five model molecules were well classified according to the different inhibition effects. Given the complexity of practical conditions, the sensing array was further applied to discriminate proteins possessing rich mercapto groups. This work not only provides an effective strategy for the design of highly active nanozymes but also achieves promising sensing arrays for practical needs.

Fe-N-C Single-Atom Catalyst Coupling with Pt Clusters Boosts Peroxidase-like Activity for Cascade-Amplified Colorimetric Immunoassay

Although single-atom catalysts with high enzyme-like activities have been found, the rational design of highly active peroxidase (POD)-like nanozymes is still a formidable challenge. Herein, highly active POD-like nanozymes were synthesized through loading Pt clusters on the Fe single-atom (Fe_SA-Pt_C) nanozymes. The POD-like activity of Fe_SA-Pt_C nanozymes is enhanced 4.5-fold and 7-fold, in comparison to that of Fe_SA and Pt_C nanozymes, respectively, which is attributed to the unexpected synergistic effect between Fe single atoms and Pt clusters. Based on the outstanding POD-like activity of Fe_SA-Pt_C nanozymes, a cascade signal amplification strategy was constructed by combining glucose oxidase for the colorimetric biosensing of prostate-specific antigens, exhibiting satisfactory sensitivity, high selectivity, a low detection limit of 1.8 pg/mL, and practical feasibility in serum sample detection. This work may serve as a tough foundation to guide the design of superior POD-like nanozymes and expand the application in biosensing.