Glucose-oxidase like catalytic mechanism of noble metal nanozymes

Au nanozyme-based colorimetric sensor array integrates machine learning to identify and discriminate monosaccharides

As different monosaccharides exhibit different redox characteristics, this paper presented a novel colorimetric sensor array based on the glucose oxidase-like (GOx-like) activity of Au nanoparticles (NPs) for monosaccharides identification. AuNPs can use O2, ABTS+•, or [Ag(NH3)2]+ as an electron acceptor to catalyze the oxidation of monosaccharides in different velocity, resulting in cross-responsive signals. The current sensor array can distinguish between different monosaccharides or their mixtures through linear discriminant analysis (LDA) and hierarchical clustering analysis (HCA). Moreover, the glucose and fructose concentrations can be estimated simultaneously using a neural network regression model based on the sensor array. This method shows potential for monosaccharide detection in industrial, medical, and biological applications.

Multifunctional nanomaterials for smart wearable diabetic healthcare devices

Wearable diabetic healthcare devices have attracted great attention for real-time continuous glucose monitoring (CGM) using biofluids such as tears, sweat, saliva, and interstitial fluid via noninvasive ways. In response to the escalating global demand for CGM, these devices enable proactive management and intervention of diabetic patients with incorporated drug delivery systems (DDSs). In this context, multifunctional nanomaterials can trigger the development of innovative sensing and management platforms to facilitate real-time selective glucose monitoring with remarkable sensitivity, on-demand drug delivery, and wireless power and data transmission. The seamless integration into wearable devices ensures patient's compliance. This comprehensive review evaluates the multifaceted roles of these materials in wearable diabetic healthcare devices, comparing their glucose sensing capabilities with conventionally available glucometers and CGM devices, and finally outlines the merits, limitations, and prospects of these devices. This review would serve as a valuable resource, elucidating the intricate functions of nanomaterials for the successful development of advanced wearable devices in diabetes management.

Glutathione-mediated copper sulfide nanoplatforms with morphological and vacancy-dependent photothermal catalytic activity for multi-model tannic acid assays

Interface engineering and vacancy engineering play an important role in the surface and electronic structure of nanomaterials. The combination of the two provides a feasible way for the development of efficient photocatalytic materials. Here, we use glutathione (GSH) as a coordination molecule to design a series of CuxS nanomaterials (CuxS-GSH) rich in sulfur vacancies using a simple ultrasonic-assisted method. Interface engineering can induce amorphous structure in the crystal while controlling the formation of porous surfaces of nanomaterials, and the formation of a large number of random orientation bonds further increases the concentration of sulfur vacancies in the crystal structure. This study shows that interface engineering and vacancy engineering can enhance the light absorption ability of CuxS-GSH nanomaterials from the visible to the near-infrared region, improve the efficiency of charge transfer between CuxS groups, and promote the separation and transfer of optoelectronic electron-hole pairs. In addition, a higher specific surface area can produce a large number of active sites, and the synergistic and efficient photothermal conversion efficiency (58.01%) can jointly promote the better photocatalytic performance of CuxS-GSH nanomaterials. Based on the excellent hot carrier generation and photothermal conversion performance of CuxS-GSH under illumination, it exhibits an excellent ability to mediate the production of reactive oxygen species (ROS) through peroxide cleavage and has excellent peroxidase activity. Therefore, CuxS-GSH has been successfully developed as a nanoenzyme platform for detecting tannic acid (TA) content in tea, and convenient and rapid detection of tannic acid is achieved through the construction of a multi-model strategy. This work not only provides a new way to enhance the enzyme-like activity of nanomaterials but also provides a new prospect for the application of interface engineering and vacancy engineering in the field of photochemistry.

Elucidating the catalytic mechanism of Prussian blue nanozymes with self-increasing catalytic activity

Although Prussian blue nanozymes (PBNZ) are widely applied in various fields, their catalytic mechanisms remain elusive. Here, we investigate the long-term catalytic performance of PBNZ as peroxidase (POD) and catalase (CAT) mimetics to elucidate their lifespan and underlying mechanisms. Unlike our previously reported Fe3O4 nanozymes, which exhibit depletable POD-like activity, the POD and CAT-like activities of PBNZ not only persist but slightly enhance over prolonged catalysis. We demonstrate that the irreversible oxidation of PBNZ significantly promotes catalysis, leading to self-increasing catalytic activities. The catalytic process of the pre-oxidized PBNZ can be initiated through either the conduction band pathway or the valence band pathway. In summary, we reveal that PBNZ follows a dual-path electron transfer mechanism during the POD and CAT-like catalysis, offering the advantage of a long service life.

Gold Nanodots-Anchored Cobalt Ferrite Nanoflowers as Versatile Tumor Microenvironment Modulators for Reinforced Redox Dyshomeostasis

Given that tumor microenvironment (TME) exerts adverse impact on the therapeutic response and clinical outcome, robust TME modulators may significantly improve the curative effect and increase survival benefits of cancer patients. Here, Au nanodots-anchored CoFe2O4 nanoflowers with PEGylation (CFAP) are developed to respond to TME cues, aiming to exacerbate redox dyshomeostasis for efficacious antineoplastic therapy under ultrasound (US) irradiation. After uptake by tumor cells, CFAP with glucose oxidase (GOx)-like activity can facilitate glucose depletion and promote the production of H2O2. Multivalent elements of Co(II)/Co(III) and Fe(II)/Fe(III) in CFAP display strong Fenton-like activity for·OH production from H2O2. On the other hand, energy band structure CFAP is superior for US-actuated 1O2 generation, relying on the enhanced separation and retarded recombination of e-/h+ pairs. In addition, catalase-mimic CFAP can react with cytosolic H2O2 to generate molecular oxygen, which may increase the product yields from O2-consuming reactions, such as glucose oxidation and sonosensitization processes. Besides the massive production of reactive oxygen species, CFAP is also capable of exhausting glutathione to devastate intracellular redox balance. Severe immunogenic cell death and effective inhibition of solid tumor by CFAP demonstrates the clinical potency of such heterogeneous structure and may inspire more relevant designs for disease therapy.

Nanozymes for the Therapeutic Treatment of Diabetic Foot Ulcers

Diabetic foot ulcers (DFU) are chronic, refractory wounds caused by diabetic neuropathy, vascular disease, and bacterial infection, and have become one of the most serious and persistent complications of diabetes mellitus because of their high incidence and difficulty in healing. Its malignancy results from a complex microenvironment that includes a series of unfriendly physiological states secondary to hyperglycemia, such as recurrent infections, excessive oxidative stress, persistent inflammation, and ischemia and hypoxia. However, current common clinical treatments, such as antibiotic therapy, insulin therapy, surgical debridement, and conventional wound dressings all have drawbacks, and suboptimal outcomes exacerbate the financial and physical burdens of diabetic patients. Therefore, development of new, effective and affordable treatments for DFU represents a top priority to improve the quality of life of diabetic patients. In recent years, nanozymes-based diabetic wound therapy systems have been attracting extensive interest by integrating the unique advantages of nanomaterials and natural enzymes. Compared with natural enzymes, nanozymes possess more stable catalytic activity, lower production cost and greater maneuverability. Remarkably, many nanozymes possess multienzyme activities that can cascade multiple enzyme-catalyzed reactions simultaneously throughout the recovery process of DFU. Additionally, their favorable photothermal-acoustic properties can be exploited for further enhancement of the therapeutic effects. In this review we first describe the characteristic pathological microenvironment of DFU, then discuss the therapeutic mechanisms and applications of nanozymes in DFU healing, and finally, highlight the challenges and perspectives of nanozyme development for DFU treatment.

Regulating Second Coordination Shell of Ce Atom Site and Reshaping of Carrier Enable Single-Atom Nanozyme to Efficiently Express Oxidase-like Activity

Single-atom nanozymes (SANs) are considered to be ideal substitutes for natural enzymes due to their high atom utilization. This work reported a strategy to manipulate the second coordination shell of the Ce atom and reshape the carbon carrier to improve the oxidase-like activity of SANs. Internally, S atoms were symmetrically embedded into the second coordination layer to form a Ce-N4S2-C structure, which reduced the energy barrier for O2 reduction, promoted the electron transfer from the Ce atom to O atoms, and enhanced the interaction between the d orbital of the Ce atom and p orbital of O atoms. Externally, in situ polymerization of mussel-inspired polydopamine on the precursor helps capture metal sources and protects the 3D structure of the carrier during pyrolysis. On the other hand, polyethylene glycol (PEG) modulated the interface of the material to enhance water dispersion and mass transfer efficiency. As a proof of concept, the constructed PEG@P@Ce-N/S-C was applied to the multimodal assay of butyrylcholinesterase activity.

Progress in the Computer-Aided Analysis in Multiple Aspects of Nanocatalysis Research

Making the utmost of the differences and advantages of multiple disciplines, interdisciplinary integration breaks the science boundaries and accelerates the progress in mutual quests. As an organic connection of material science, enzymology, and biomedicine, nanozyme-related research is further supported by computer technology, which injects in new vitality, and contributes to in-depth understanding, unprecedented insights, and broadened application possibilities. Utilizing computer-aided first-principles method, high-speed and high-throughput mathematic, physic, and chemic models are introduced to perform atomic-level kinetic analysis for nanocatalytic reaction process, and theoretically illustrate the underlying nanozymetic mechanism and structure-function relationship. On this basis, nanozymes with desirable properties can be designed and demand-oriented synthesized without repeated trial-and-error experiments. Besides that, computational analysis and device also play an indispensable role in nanozyme-based detecting methods to realize automatic readouts with improved accuracy and reproducibility. Here, this work focuses on the crossing of nanocatalysis research and computational technology, to inspire the research in computer-aided analysis in nanozyme field to a greater extent.

Construct a Magnetic Pt/Ru Alloy Peroxidase Mimic As a Reusable and Cost-Effective "Signal-Off" Sensing Platform for Sensitive and Wide-Linear-Range Assay

"Signal-off" nanozyme sensing platforms are usually employed to detect analytes (e.g., ascorbic acid (AA) and alkaline phosphatase (ALP)), which are mostly based on oxidase (OXD) nanozymes. However, their drawbacks, like dissolved oxygen-dependent catalysis capability, relatively low enzyme activity, limited amount, and kind, may not favor sensing platforms' optimization. Meanwhile, with the need for sustainable development, a reusable "signal-off" sensing platform is essential for cutting down the cost of the assay, but it is rarely developed in previous studies. Magnetic peroxidase (POD) nanozymes potentially make up the deficiencies and become reusable and better "signal-off" sensing platforms. As a proof of concept, we first construct Fe3O4@polydopamine-supported Pt/Ru alloy nanoparticles (IOP@Pt/Ru) without stabilizers. IOP@Pt/Ru shows high POD activity with Vmax of 83.24 × 10-8 M·s-1 for 3,3',5,5'-Tetramethylbenzidine (TMB) oxidation. Meanwhile, its oxidation rate for TMB is slower than the reduction of oxidized TMB by reducers, favorable for a more significant detection signal. On the other hand, IOP@Pt/Ru possesses great magnet-responsive capability, making itself be recycled and reused for at least 15-round catalysis. When applying IOP@Pt/Ru for AA (ALP) detection, it performs better detectable adaptability, with a linear range of 0.01-0.2 mM (0.1-100 U/L) and a limit of detection of 0.01 mM (0.05 U/L), superior to most of OXD nanozyme-based ALP sensing platform. Finally, IOP@Pt/Ru's reusable assay was demonstrated in real blood samples for ALP assay, which has never been explored in previous studies. Overall, this study develops a reusable "signal-off" nanozyme sensing platform with superior assay capabilities than traditional OXD nanozymes, paves a new way to optimize nanozyme-based "signal-off" sensing platforms, and provides an idea for constructing inexpensive and sustainable sensing platforms.

Histidine modified Fe3O4 nanoparticles improving the ethanol yield and tolerance of Saccharomyces cerevisiae

Saccharomyces cerevisiae, the primary microorganism involved in ethanol production, is hindered by the accumulation of ethanol, leading to reduced ethanol production. In this study, we employed histidine-modified Fe3O4 nanoparticles (His-Fe3O4) for the first time, to the best of our knowledge, as a method to enhance ethanol yield during the S. cerevisiae fermentation process. The results demonstrated that exposing S. cerevisiae cells to Fe3O4 nanoparticles (Fe3O4 NPs) led to increased cell proliferation and glucose consumption. Moreover, the introduction of His-Fe3O4 significantly boosted ethanol content by 17.3% (p < 0.05) during fermentation. Subsequent findings indicated that the increase in ethanol content was associated with enhanced ethanol tolerance and improved electron transport efficiency. This study provided evidence for the positive effects of His-Fe3O4 on S. cerevisiae cells and proposed a straightforward approach to enhance ethanol production in S. cerevisiae fermentation. The mediation of improved ethanol tolerance offers significant potential in the fermentation and bioenergy sectors.

An Encyclopedic Compendium on Chemosensing Supramolecular Metal-Organic Gels

Chemosensing, an interdisciplinary scientific domain, plays a pivotal role ranging from environmental monitoring to healthcare diagnostics and (inter)national security. Metal-organic gels (MOGs) are recognized for their stability, selectivity, and responsiveness, making them valuable for chemosensing applications. Researchers have explored the development of MOGs based on different metal ions and ligands, allowing for tailored properties and sensitivities, and have even demonstrated their applications as portable sensors such as paper-based test strips for practical use. Herein, several studies related to MOGs development and their applications in the chemosensing field via UV-visible or luminance along with electrochemical approach are presented. These papers explored MOGs as versatile materials with their use in sensing bio or environmental analytes. This review provides a foundational understanding of key concepts, methodologies, and recent advancements in this field, fostering the scientific community.

Gold Nanoparticle Delivery of Glut1 SiRNA Facilitates Glucose Starvation Therapy in Lung Cancer

Glucose transporter protein-1 (Glut1), is highly expressed in many cancer types and plays a crucial role in cancer progression through enhanced glucose transport. Its overexpression is associated with aggressive tumor behavior and poor prognosis. Herein, the nucleic acids modified gold nanoparticles (AuNPs) was synthesized to deliver small interfering RNA (siRNA) against Glut1 by microRNA 21 (miR-21) triggers toehold-mediated strand displacement reaction for lung cancer starvation therapy. Overexpression of miR-21 triggers toehold-mediated strand displacement, releasing the siRNA to knockdown of Glut1 in cancer cell instead of normal cell. Furthermore, the glucose oxidase-like activity of the AuNPs accelerates intracellular glucose consumption, promoting cancer cell starvation. The engineered AuNPs@anti-miR-21/siGlut1 complex inhibits cancer cell proliferation, xenograft tumor growth and promotes apoptosis through glucose starvation and ROS cascade signaling, underscoring its potential as an effective therapeutic strategy for lung cancer.

Heterogeneous Oxidase-Type Catalysis for H2 Generation at Low Temperatures

The long-term objective in the field of heterogeneous catalysis is to develop an enzyme-like catalytic pathway that can achieve exceptional catalytic performance even at low temperatures. Herein, we have demonstrated a heterogeneous oxidase-type catalysis on the ZnO-supported Ru clusters (Ru/ZnO) for efficient H2 generation from an aqueous solution of formaldehyde (HCHO) at low temperatures. Due to its unique reaction pathway, the Ru/ZnO catalysts exhibited a temperature-insensitive activity for H2 generation at the temperature of 15 to 45 °C. Remarkably, even at a low temperature of 5 °C, the Ru/ZnO catalysts still enabled an H2 generation rate of 13.8 mmol gcat-1 h-1 with a turnover frequency (TOF) of 1678 h-1. Additionally, instead of producing a CO2/CO molecule, the HCHO molecule underwent a transformation into formic acid and/or formate as the byproduct. This finding presents a novel class of heterogeneous catalysts to expand the potential application scenarios of liquid hydrogen storage and transportation systems.

Targeting starvation therapy for diabetic bacterial infections with endogenous enzyme-triggered hyaluronan-modified nanozymes in the infection microenvironment

The high-glycemic microenvironment of diabetic wounds promotes bacterial proliferation, leading to persistent infections and delayed wound healing. This poses a significant threat to human health, necessitating the development of new nanodrug visualization platforms. In this study, we designed and synthesized cascade nano-systems modified with targeted peptide and hyaluronic acid for diabetic infection therapy. The nano-systems were able to target the site of infection using LL-37, and in the microenvironment of wound infection, the hyaluronic acid shell of the nano-systems was degraded by endogenous hyaluronidase. This precise degradation released a cascade of nano-enzymes on the surface of the bacteria, effectively destroying their cytoskeleton. Additionally, the metals in the nano-enzymes provided a photo-thermal effect, accelerating wound healing. The cascade nano-visualization platform demonstrated excellent bactericidal efficacy in both in vitro antimicrobial assays and in vivo diabetic infection models. In conclusion, this nano-system employs multiple approaches including targeting, enzyme-catalyzed therapy, photothermal therapy, and chemodynamic therapy to kill bacteria and promote healing. The Ag@Pt-Au-LYZ/HA-LL-37 formulation shows great potential for the treatment of diabetic wounds.

Glucose Oxidase Energized Osmium with Dual-Active Centers and Triple Enzyme Activities for Infected Diabetic Wound Management

Diabetic wounds are susceptible to bacterial infections, largely linked to high blood glucose levels (hyperglycemia). To treat such wounds, enzymes like glucose oxidase (GOx) can be combined with nanozymes (nanomaterials mimic enzymes) to use glucose effectively for purposes. However, there is still room for improvement in these systems, particularly in terms of process simplification, enzyme activity regulation, and treatment effects. Herein, the approach utilizes GOx to directly facilitate the biomineralized growth of osmium (Os) nanozyme (GOx-OsNCs), leading to dual-active centers and remarkable triple enzyme activities. Initially, GOx-OsNCs use vicinal dual-active centers, enabling a self-cascaded mechanism that significantly enhances glucose sensing performance compared to step-by-step reactions, surpassing the capabilities of other metal sources such as gold and platinum. In addition, GOx-OsNCs are integrated into a glucose-sensing gel, enabling instantaneous visual feedback. In the treatment of infected diabetic wounds, GOx-OsNCs exhibit multifaceted benefits by lowering blood glucose levels and exhibiting antibacterial properties through the generation of hydroxyl free radicals, thereby expediting healing by fostering a favorable microenvironment. Furthermore, the catalase-like activity of GOx-OsNCs aids in reducing oxidative stress, inflammation, and hypoxia, culminating in improved healing outcomes. Overall, this synergistic enzyme-nanozyme blend is user-friendly and holds considerable promise for diverse applications.

Modulating Electron Transfer between Pt and MOF Support through Pd Doping Promotes Nanozyme Catalytic Efficiency

Electron transfer is considered to be a typical parameter that affects the catalytic activity of nanozymes. However, there is still controversy regarding whether higher or lower electron transfer numbers are beneficial for improving the catalytic activity of nanozymes. To address this issue, we propose the introduction of Pd doping as an important electron regulation strategy to tune electron transfer between Pt and ZIF-8 carriers (PtxPd1@ZIF-8). We observe a volcano-shaped relationship between the electron transfer number and catalytic activity, reaching its peak at Pt4Pd1@ZIF-8. Mechanism studies indicate that as the electron transfer number from Pt to ZIF-8 carriers increases, the d-band center of the active site Pt increases, reducing the occupancy of antibonding states and enhancing the adsorption capacity of the key intermediate (*O). However, a further increase in the adsorption of *O energy makes it difficult to desorb and participate in the next reaction, thus exhibiting volcanic activity. The optimized Pt4Pd1@ZIF-8 nanozyme is applied to develop an immunoassay for the detection of zearalenone, achieving a detection limit of 0.01 μg/L, which is 6 times higher than that of the traditional enzyme-linked immunosorbent assay. This work not only reveals the potential regulatory mechanism of electron transfer on the catalytic activity of nanozymes but also improves the performance of nanozyme-based biosensors.

Nanozyme-Incorporated Microneedles for the Treatment of Chronic Wounds

Acute wounds are converted to chronic wounds due to advanced age and diabetic complications. Nanozymes catalyze ROS production to kill bacteria without causing drug resistance, while microneedles (MNs) can break through the skin barrier to deliver drugs effectively. Nanozymes can be intergrateded into MNs delivery systems to improve painless drug delivery. It can also reduce the effective dose of drug sterilization while increasing delivery efficiency and effectively killing wounded bacteria while preventing drug resistance. This paper describes various types of metal nanozymes from previous studies and compares their mutual enhancement with nanozymes. The pooled results show that the MNs, through material innovation, are able to both penetrate the scab and deliver nanozymes and exert additional anti-inflammatory and bactericidal effects. The catalytic effect of some of the nanozymes can also accelerate the lysis of the MNs or create a cascade reaction against inflammation and infection. However, the issue of increased toxicity associated with skin penetration and clinical translation remains a challenge. This study reviews the latest published results and corresponding challenges associated with the use of MNs combined with nanozymes for the treatment of wounds, providing further information for future research.

Transition-metal-based nanozymes for biosensing and catalytic tumor therapy

Nanozymes, as an emerging class of enzyme mimics, have attracted much attention due to their adjustable catalytic activity, low cost, easy modification, and good stability. Researchers have made great efforts in developing and applying high-performance nanozymes. Recently, transition-metal-based nanozymes have been designed and widely developed because they possess unique photoelectric properties and high enzyme-like catalytic activities. To highlight these achievements and help researchers to understand the research status of transition-metal-based nanozymes, the development of transition-metal-based nanozymes from material characteristics to biological applications is summarized. Herein, we focus on introducing six categories of transition-metal-based nanozymes and highlight their progress in biomarker sensing and catalytic therapy for tumors. We hope that this review can guide the further development of transition-metal-based nanozymes and promote their practical applications in cancer diagnosis and treatment.

Transition-Metal-Based Nanozymes: Synthesis, Mechanisms of Therapeutic Action, and Applications in Cancer Treatment

Cancer, as one of the leading causes of death worldwide, drives the advancement of cutting-edge technologies for cancer treatment. Transition-metal-based nanozymes emerge as promising therapeutic nanodrugs that provide a reference for cancer therapy. In this review, we present recent breakthrough nanozymes for cancer treatment. First, we comprehensively outline the preparation strategies involved in creating transition-metal-based nanozymes, including hydrothermal method, solvothermal method, chemical reduction method, biomimetic mineralization method, and sol-gel method. Subsequently, we elucidate the catalytic mechanisms (catalase (CAT)-like activities), peroxidase (POD)-like activities), oxidase (OXD)-like activities) and superoxide dismutase (SOD)-like activities) of transition-metal-based nanozymes along with their activity regulation strategies such as morphology control, size manipulation, modulation, composition adjustment and surface modification under environmental stimulation. Furthermore, we elaborate on the diverse applications of transition-metal-based nanozymes in anticancer therapies encompassing radiotherapy (RT), chemodynamic therapy (CDT), photodynamic therapy (PDT), photothermal therapy (PTT), sonodynamic therapy (SDT), immunotherapy, and synergistic therapy. Finally, the challenges faced by transition-metal-based nanozymes are discussed alongside future research directions. The purpose of this review is to offer scientific guidance that will enhance the clinical applications of nanozymes based on transition metals.

Single-site iron-anchored amyloid hydrogels as catalytic platforms for alcohol detoxification

Constructing effective antidotes to reduce global health impacts induced by alcohol prevalence is a challenging topic. Despite the positive effects observed with intravenous applications of natural enzyme complexes, their insufficient activities and complicated usage often result in the accumulation of toxic acetaldehyde, which raises important clinical concerns, highlighting the pressing need for stable oral strategies. Here we present an effective solution for alcohol detoxification by employing a biomimetic-nanozyme amyloid hydrogel as an orally administered catalytic platform. We exploit amyloid fibrils derived from β-lactoglobulin, a readily accessible milk protein that is rich in coordinable nitrogen atoms, as a nanocarrier to stabilize atomically dispersed iron (ferrous-dominated). By emulating the coordination structure of the horseradish peroxidase enzyme, the single-site iron nanozyme demonstrates the capability to selectively catalyse alcohol oxidation into acetic acid, as opposed to the more toxic acetaldehyde. Administering the gelatinous nanozyme to mice suffering from alcohol intoxication significantly reduced their blood-alcohol levels (decreased by 55.8% 300 min post-alcohol intake) without causing additional acetaldehyde build-up. Our hydrogel further demonstrates a protective effect on the liver, while simultaneously mitigating intestinal damage and dysbiosis associated with chronic alcohol consumption, introducing a promising strategy in effective alcohol detoxification.

Nanomaterials with Enzyme-like Properties for Combatting Foodborne Pathogen Infections: Classifications, Mechanisms, and Applications in Food Preservation

During the transportation and storage of food, foodborne spoilage caused by bacterial and biofilm infection is prone to occur, leading to issues such as short shelf life, economic loss, and sensory quality instability. Therefore, the development of novel and efficient antibacterial agents capable of efficiently inhibiting bacteria throughout various stages of food processing, transportation, and storage is strongly recommended by researchers. The emergence of nanozymes is considered to be an effective candidate for inhibiting foodborne bacteria agents in the food industry. As potent antibacterial agents, nanozymes have the advantages of low cost, high stability, strong broad-spectrum antibacterial ability, and biocompatibility. Herein, we aim to summarize the classification status of various nanozymes. Furthermore, the general catalytic bacteriostatic mechanism of nanozymes against intracellular bacteria, planktonic bacteria, and biofilm activities are highlighted, mainly concerning the destruction of cell walls and/or membranes, reactive oxygen species regulation, HOBr/Cl generation, damage of intracellular components, and so forth. In particular, the review focuses on the pivotal role of nanozymes as antibacterial agents and delivery vehicles in the fields of food preservation applications. We look forward to the future prospects, especially in the field of food preservation, to promote broader applications based on antimicrobial nanozymes.

Biocompatible Gold Nanoparticles-Modified Fluorine Doped Tin Oxide Electrode for the Fabrication of Enzyme-Free Glucose Sensor

This work demonstrates the use of jute stick extract as a reducing and stabilizing agent for the synthesis of spherical gold nanoparticles (AuNPs). In UV-Vis spectroscopy, peak at 550 nm was used to confirm the formation of AuNPs. The spherical surface morphology of AuNPs was determined through SEM and TEM analysis. While XRD investigation revealed the crystallinity of the prepared AuNPs. To ensure the biocompatibility of synthesized AuNPs, a bacterial investigation was conducted with negative results towards bacterial strain. The, modified FTO with AuNPs were able to detect glucose in CV analysis and the constructed sensor displayed a wide linear range of 50 μM to 40 mM with a detection limit of 20 μM. Scan rate analysis was performed to determine the charge transfer coefficient (0.42) and Tafel slope (102 mV/decade). Furthermore, the interfacial surface mechanism is illustrated to understand the interaction of glucose with the electrode surface in an alkaline medium and the product formation through the dehydrogenation and hydrolysis process. The prepared sensor also showed good stability, reproducibility, and anti-interference capabilities. In the case of real sample analysis, we used a blood serum sample. A low RSD value (<10 %) suggests the practical use of AuNPs/FTO in real-life applications.

Enzyme-integrated metal-organic framework platform for cascade detection of α-amylase

As one of the most important industrial enzymes, α-amylase is widely used in food processing, such as starch sugar and fermentation, bringing high added value to industry of more than a trillion dollars. We developed a multi-enzyme system (Glu&Gox@Cu-MOF-74) prepared by embedding α-glucosidase (Glu) and glucose oxidase (Gox) into the biomimetic metal-organic framework Cu-MOF-74 using in situ encapsulation within 15 min at room temperature for efficient and sensitive detection of α-amylase activity. Benefitting from the remarkable peroxidase-mimicking property and rigid skeleton of Cu-MOF-74, the biocatalytic platform exhibited excellent cascade activity and tolerance in various extremely harsh environments compared to natural enzymes. On this basis, a cascade biocatalytic platform was constructed for the detection of α-amylase activity with wide linear range (5-100 U/L) and low limit of detection (1.45 U/L). The colorimetric cascade scheme is important for the sensitive and selective determination of α-amylase in complex fermentation samples, and the detection time is short (∼0.5 h). This work provides new ideas for the detection of α-amylase based on the cascade amplification method.

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.

Current Advances on the Single-Atom Nanozyme and Its Bioapplications

Nanozymes, a class of nanomaterials mimicking the function of enzymes, have aroused much attention as the candidate in diverse fields with the arbitrarily tunable features owing to the diversity of crystalline nanostructures, composition, and surface configurations. However, the uncertainty of their active sites and the lower intrinsic deficiencies of nanomaterial-initiated catalysis compared with the natural enzymes promote the pursuing of alternatives by imitating the biological active centers. Single-atom nanozymes (SAzymes) maximize the atom utilization with the well-defined structure, providing an important bridge to investigate mechanism and the relationship between structure and catalytic activity. They have risen as the new burgeoning alternative to the natural enzyme from in vitro bioanalytical tool to in vivo therapy owing to the flexible atomic engineering structure. Here, focus is mainly on the three parts. First, a detailed overview of single-atom catalyst synthesis strategies including bottom-up and top-down approaches is given. Then, according to the structural feature of single-atom nanocatalysts, the influence factors such as central metal atom, coordination number, heteroatom doping, and the metal-support interaction are discussed and the representative biological applications (including antibacterial/antiviral performance, cancer therapy, and biosensing) are highlighted. In the end, the future perspective and challenge facing are demonstrated.

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.

Biosystem-Inspired Engineering of Nanozymes for Biomedical Applications

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

Nanozyme-Based Regulation of Cellular Metabolism and Their Applications

Metabolism is the sum of the enzyme-dependent chemical reactions, which produces energy in catabolic process and synthesizes biomass in anabolic process, exhibiting high similarity in mammalian cell, microbial cell, and plant cell. Consequently, the loss or gain of metabolic enzyme activity greatly affects cellular metabolism. Nanozymes, as emerging enzyme mimics with diverse functions and adjustable catalytic activities, have shown attractive potential for metabolic regulation. Although the basic metabolic tasks are highly similar for the cells from different species, the concrete metabolic pathway varies with the intracellular structure of different species. Here, the basic metabolism in living organisms is described and the similarities and differences in the metabolic pathways among mammalian, microbial, and plant cells and the regulation mechanism are discussed. The recent progress on regulation of cellular metabolism mainly including nutrient uptake and utilization, energy production, and the accompanied redox reactions by different kinds of oxidoreductases and their applications in the field of disease therapy, antimicrobial therapy, and sustainable agriculture is systematically reviewed. Furthermore, the prospects and challenges of nanozymes in regulating cell metabolism are also discussed, which broaden their application scenarios.

Advanced nanozymes possess peroxidase-like catalytic activities in biomedical and antibacterial fields: review and progress

Infectious diseases caused by bacterial invasions have imposed a significant global health and economic burden. More worryingly, multidrug-resistant (MDR) pathogenic bacteria born under the abuse of antibiotics have further escalated the status quo. Nowadays, at the crossroads of multiple disciplines such as chemistry, nanoscience and biomedicine, nanozymes, as enzyme-mimicking nanomaterials, not only possess excellent bactericidal ability but also reduce the possibility of inducing resistance. Thus, nanozymes are promising to serve as an alternative to traditional antibiotics. Nanozymes that mimic peroxidase (POD) activity are also known as POD nanozymes. In recent years, POD nanozymes have become one of the most frequently reported and effective nanozymes due to their broad-spectrum bactericidal properties and unique sterilization mechanism. In this review, we introduce the mechanism as well as the classification of POD nanozymes. More importantly, to further improve the antibacterial efficacy of POD nanozymes, we elaborate on three aspects: (1) improving the physicochemical properties; (2) regulating the catalytic microenvironment; and (3) designing multimodel POD nanozymes. In addition, we review the nanosafety of POD nanozymes for discussing their potential toxicity. Finally, the remaining challenges of POD nanozymes and possible future directions are discussed. This work provides a systematic summary of POD nanozymes and hopefully contributes to the early clinical translation.

Novel dual-responsive hydrogel composed of polyacrylamide/Fe-MOF/zinc finger peptide for construction of electrochemical sensing platform

Responsive hydrogels have received much attention for improving the detection performance of electrochemical sensors because of their special responsiveness. However, current responsive hydrogels generally suffer from long response times, ranging from tens of minutes to several hours. This situation severely limits the detection performance and practical application of electrochemical sensors. Here, an electrochemical sensing platform was constructed by employing dual-responsive polyacrylamide/zinc finger peptide/Fe-MOF hydrogel (PZFH) as the silent layer, sodium alginate-Ni2+-graphene oxide hydrogel as the signal layer. GOx@ZIF-8, as the immunoprobe, catalyzed glucose to H2O2 and gluconic acid, resulting in the cleavage of immunoprobe as the pH decreased and subsequent release of Zn2+ ions. During the process of Fe-MOF converting from Fe3+ to Fe2+, free radicals were generated and used to destroy the structure of the PZFH. Cysteine and histidine in the zinc finger peptide can specifically bind to Zn2+ to create many pores in PZFH, exposing the signal layer. These synergistic effects rapidly decreased the impedance of PZFH and increased the electrochemical signal of Ni2+. The electrochemical sensing platform was used to detect pro-gastrin-releasing peptide with response times as short as 7 min of PZFH, a wide linear range from 100 ng mL-1 to 100 fg mL-1, and an ultra-low limit of detection of 14.24 fg mL-1 (S/N = 3). This strategy will provide a paradigm for designing electrochemical sensors.

Swellable colorimetric microneedles for glucose detection based on glucose oxidase-like gold nanoparticles

BACKGROUND

Regular blood glucose monitoring is very important for diabetic patients. The composition of skin interstitial fluid (ISF) is similar to that of blood, which can be used for daily blood sugar detection and disease care. However, most methods of ISF extraction have complicated steps, may cause skin damage, and can only extract a limited amount of ISF, resulting in low detection efficiency. Therefore, it is very necessary to develop a detection method that can not only extract a large amount of ISF safely, efficiently, and conveniently, but also realize rapid detection of glucose level in ISF.

RESULTS

Here, we developed a gold nanoparticle (AuNP)-based swellable colorimetric MN patch with minimally invasive sampling function and real-time ISF glucose analysis ability. The MN patch could quickly absorb a large amount of skin ISF, and 60.2 mg of ISF was extracted within 10 min in vitro. It was divided into two layers: the tip layer was embedded with AuNPs with glucose oxidase (GOx)-like activity, which catalyzed the oxidation of glucose extracted from ISF and produced hydrogen peroxide (H2O2); horseradish peroxidase (HRP) encapsulated in the backing layer catalyzed the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) by H2O2 to produce oxTMB, which led to a visible color shift in the backing layer. The ISF glucose level was judged by naked eyes and further quantified by color analysis with Image J software. As a result, the colorimetric MN patch successfully identified the normal blood sugar and hyperglycemia state in vivo.

SIGNIFICANCE

The colorimetric MN patch combined in-situ colorimetric sensing based on AuNP nanozyme with MN patch, which detected glucose level without blood drawing, increasing patients' compliance and reducing detection steps and time. Compared with the detection methods based on natural nanozymes, our method had better stability and sensitivity to complex environments (extreme pH and high temperature, etc.) in actual detection.

A colorimetric detection of dopamine in urine and serum based on the CeO2 @ZIF-8/Cu-CDs laccase-like nanozyme activity

This study reports a sensitive and selective colorimetric approach for the analysis of dopamine (DA) based on CeO2 @ZIF-8/Cu-CDs laccase-like nanozymes activity. The CeO2 @ZIF-8/Cu-CDs was synthesized using cerium oxide (CeO2 ) and copper-doped carbon dots (Cu-CDs) with 2-methylimidazole by a facilely hydrothermal approach. The CeO2 @ZIF-8/Cu-CDs exhibited excellent laccase-like nanozymes activity and can oxidize the colorless substrate (DA) to red product with 4-aminoantipyrine as the chromogenic agent. The Michaelis-Menten constant (Km ) and the maximal velocity (Vmax ) of CeO2 @ZIF-8/Cu-CDs are 0.20 mM and 1.48 μM/min, respectively. The detection method has a linear range of 0.05-7.5 μg/mL and a detection limit as low as 8.5 ng/mL with good reproducibility. The developed colorimetric sensor was applied to rapid and precise quantitative evaluation of DA levels in serum and urine samples. This study presents a new approach for detecting biological molecules by utilizing the controlled regulation of nanozymes' laccase-like activity.

A natural biogenic nanozyme for scavenging superoxide radicals

Biominerals, the inorganic minerals of organisms, are known mainly for their physical property-related functions in modern living organisms. Our recent discovery of the enzyme-like activities of nanomaterials, coined as nanozyme, inspires the hypothesis that nano-biominerals might function as enzyme-like catalyzers in cells. Here we report that the iron cores of biogenic ferritins act as natural nanozymes to scavenge superoxide radicals. Through analyzing eighteen representative ferritins from three living kingdoms, we find that the iron core of prokaryote ferritin possesses higher superoxide-diminishing activity than that of eukaryotes. Further investigation reveals that the differences in catalytic capability result from the iron/phosphate ratio changes in the iron core, which is mainly determined by the structures of ferritins. The phosphate in the iron core switches the iron core from single crystalline to amorphous iron phosphate-like structure, resulting in decreased affinity to the hydrogen proton of the ferrihydrite-like core that facilitates its reaction with superoxide in a manner different from that of ferric ions. Furthermore, overexpression of ferritins with high superoxide-diminishing activities in E. coli increases the resistance to superoxide, whereas bacterioferritin knockout or human ferritin knock-in diminishes free radical tolerance, highlighting the physiological antioxidant role of this type of nanozymes.

Atomic-level design of metalloenzyme-like active pockets in metal-organic frameworks for bioinspired catalysis

Natural metalloenzymes with astonishing reaction activity and specificity underpin essential life transformations. Nevertheless, enzymes only operate under mild conditions to keep sophisticated structures active, limiting their potential applications. Artificial metalloenzymes that recapitulate the catalytic activity of enzymes can not only circumvent the enzymatic fragility but also bring versatile functions into practice. Among them, metal-organic frameworks (MOFs) featuring diverse and site-isolated metal sites and supramolecular structures have emerged as promising candidates for metalloenzymes to move toward unparalleled properties and behaviour of enzymes. In this review, we systematically summarize the significant advances in MOF-based metalloenzyme mimics with a special emphasis on active pocket engineering at the atomic level, including primary catalytic sites and secondary coordination spheres. Then, the deep understanding of catalytic mechanisms and their advanced applications are discussed. Finally, a perspective on this emerging frontier research is provided to advance bioinspired catalysis.

Complete Glucose Electrooxidation Enabled by Coordinatively Unsaturated Copper Sites in Metal-Organic Frameworks

The electrocatalytic oxidation of glucose plays a vital role in biomass conversion, renewable energy, and biosensors, but significant challenges remain to achieve high selectivity and high activity simultaneously. In this study, we present a novel approach for achieving complete glucose electrooxidation utilizing Cu-based metal-hydroxide-organic framework (Cu-MHOF) featuring coordinatively unsaturated Cu active sites. In contrast to traditional Cu(OH)2 catalysts, the Cu-MHOF exhibits a remarkable 40-fold increase in electrocatalytic activity for glucose oxidation, enabling exclusive oxidation of glucose into formate and carbonate as the final products. The critical role of open metal sites in enhancing the adsorption affinity of glucose and key intermediates was confirmed by control experiments and density functional theory simulations. Subsequently, a miniaturized nonenzymatic glucose sensor was developed showing superior performance with a high sensitivity of 214.7 μA mM-1  cm-2 , a wide detection range from 0.1 μM to 22 mM, and a low detection limit of 0.086 μM. Our work provides a novel molecule-level strategy for designing catalytically active sites and could inspire the development of novel metal-organic framework for next-generation electrochemical devices.

Constraint Coupling of Redox Cascade and Electron Transfer Synchronization on Electrode-Nanosensor Interface for Repeatable Detection of Tumor Biomarkers

Quantitative analysis of up-regulated biomarkers in pathological tissues is helpful to tumor surgery yet the loss of biomarker extraction and time-consuming operation limited the accurate and quick judgement in preoperative or intraoperative diagnosis. Herein, an immobilization-free electrochemical sensing platform is developed by constraint coupling of electron transfer cascade on electrode-nanosensor interface. Specifically, electrochemical indicator (Ri)-labeled single-stranded DNA on electroactive nanodonor (polydopamine, PDA) can be responsively detached by formation of DNA complex through the recognition and binding with targets. By applying the oxidation potential of Ri, nanosensor collisions on electrode surface trigger a cascade redox cycling of PDA and Ri through synchronous electron transfer, which boost the amplification of current signal output. The developed nanosensor exhibit excellent linear response toward up-regulated biomarkers (miRNA-21, ATP, and VEGF) with low detection limits (32 fM, 386 pM, and 2.8 pM). Moreover, background influence from physiological interferent is greatly reduced by restricted electron transfer coupling on electrode. The practical applicability is illustrated in sensitive and highly repeatable profiling of miRNA-21 in lysate of tumor cells and tumor tissue, beneficial for more reliable diagnosis. This electrochemical platform by employing electron transfer cascades at heterogeneous interfaces offers a route to anti-interference detection of biomarkers in tumor tissues.

Portable visual and electrochemical detection of hydrogen peroxide release from living cells based on dual-functional Pt-Ni hydrogels

It is important to monitor the intra-/extracellular concentration of hydrogen peroxide (H2O2) in biological processes. However, miniaturized devices that enable portable and accurate H2O2 measurement are still in their infancy because of the difficulty of developing facile sensing strategies and highly integrated sensing devices. In this work, portable H2O2 sensors based on Pt-Ni hydrogels with excellent peroxidase-like and electrocatalytic activities are demonstrated. Thus, simple and sensitive H2O2 sensing is achieved through both colorimetric and electrochemical strategies. The as-fabricated H2O2 sensing chips exhibit favorable performance, with low detection limits (0.030 μM & 0.15 μM), wide linearity ranges (0.10 μM-10.0 mM & 0.50 μM-5.0 mM), outstanding long-term stability (up to 60 days), and excellent selectivity. With the aid of an M5stack development board, portable visual and electrochemical H2O2 sensors are successfully constructed without complicated and expensive equipment or professional operators. When applied to the detection of H2O2 released from HeLa cells, the results obtained by the developed sensors are in good agreement with those from an ultraviolet‒visible spectrophotometer (UV‒vis) (1.97 μM vs. 2.08 μM) and electrochemical station (1.77 μM vs. 1.84 μM).

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.

Confined synthesis of ternary FeCoMn single-atom nanozyme in N-doped hollow mesoporous carbon nanospheres for synergistic chemotherapy and chemodynamic cancer therapy

Recently, nanozymes show increasing biological applications and promising possibilities for therapeutic intervention, while their mediated therapeutic outcomes are severely compromised due to their insufficient catalytic activity and specificity. Herein, ternary FeCoMn single atoms were incorporated into N-doped hollow mesoporous carbon nanospheres by in situ confinement pyrolysis at 800 °C as high-efficiency nanozyme. The confinement strategy endows the as-prepared nanozyme with the enhanced catalase- and oxidase-like activities. Specifically, the FeCoMn TSAs/N-HCSs nanozyme can decompose intracellular H2O2 to generate O2 and subsequently convert O2 to cytotoxic superoxide radicals (O2∙-), which can initiate cascade enzymatic reactions in tumor microenvironment (TME) for chemodynamic therapy (CDT). Moreover, the cancer therapy was largely enhanced by loading with doxorubicin (DOX). Impressively, the FeCoMn TSAs/N-HCSs nanozyme-mediated CDT and the DOX-induced chemotherapy endow the DOX@FeCoMn TSAs/N-HCSs with effective tumor inhibition, showing the superior therapeutic efficacy.

Emerging enzyme-based nanocomposites for catalytic biomedicine

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

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

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

Design and Mechanism Insight of Monodispersed AuCuPt Alloy Nanozyme with Antitumor Activity

The abrogation of the self-adaptive redox evolution of tumors is promising for improving therapeutic outcomes. In this study, we designed a trimetallic alloy nanozyme AuCuPt-PpIX (ACPP), which mimics up to five naturally occurring enzymes: glucose oxidase (GOD), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione peroxidase (GPx). Facilitated by these enzyme-mimicking traits, the constructed ACPP nanozymes can not only disrupt the established redox homeostasis in tumors through a series of enzymatic cascade reactions but also achieve cyclic regeneration of the relevant enzyme substrates. Density functional theory (DFT) calculations have theoretically explained the synergistic effect of multimetallic doping and the possible mechanism of enzymatic catalysis. The doped Cu and Pt sites are conducive to the adsorption, activation, and dissociation of reactant molecules, whereas the Au sites are conducive to desorption, which significantly improves catalytic efficiency via a synergistic effect. Additionally, ACPP nanozymes can improve the effect of protoporphyrin (PpIX)-enabled sonodynamic therapy (SDT) by alleviating hypoxia and initiating ferroptosis by inducing lipid peroxidation (LPO) and inhibiting GPX4 activity, thus achieving multimodal synergistic therapy. This study presents a typical paradigm to enable the use of multimetallic alloy nanozymes for the treatment of tumor cells with self-adaptive properties.

A spectroscopy based prototype for the noninvasive detection of diabetes from human saliva using nanohybrids acting as nanozyme

The recent prediction of diabetes to be a global pandemic invites a detection strategy preferably non-invasive, and bloodless to manage the disease and the associated complications. Here, we have synthesized chitosan polymer functionalized, organic-inorganic bio-compatible nano-hybrids of Mn3O4 nanoparticles, and characterized it by utilizing several optical methodologies for the structural characterization which shows the Michaelis Menten (MM) kinetics for glucose and alpha-amylase protein (well-known diabetes biomarkers). We have also studied the potentiality for the detection of alpha-amylase in human salivary secretion which is reported to be strongly correlated with uncontrolled hyperglycemia. Finally, we have developed a prototype for the measurement of glucose (LOD of 0.38 mg/dL, LOQ of 1.15 mg/dL) and HbA1c (LOD of 0.15% and LOQ of 0.45%) utilizing the basic knowledge in the study for the detection of uncontrolled hyperglycemia at the point-of-care. With the limited number of clinical trials, we have explored the potential of our work in combating the diabetic pandemic across the globe in near future.

Self-Powered Biosensor Based on DNA Walkers for Ultrasensitive MicroRNA Detection

A novel self-powered biosensor is fabricated for ultrasensitive microRNA-21 (miRNA-21) detection, which includes an enzymatic biofuel cell (EBFC), DNA walkers, a digital multimeter (DMM), and a capacitor. As a novel strategy for signal amplification, DNA walkers are designed in the cathode, while the capacitor stores electrochemical energy from the EBFC to further boost the instantaneous current displayed by the DMM. When miRNA-21 is present, the DNA walkers are provoked to walk from as-opened hairpin structures to other hairpin structures, generating double-strand DNA structures, which stimulate [Ru(NH3)6]3+ to be adsorbed on the cathode surface by electrostatic interaction. Afterward, [Ru(NH3)6]3+ is reduced to [Ru(NH3)6]2+, and the open circuit voltage (EOCV) is significantly increased. Depending on the approach of signal amplification from DNA walkers, this biosensor displays an ultrasensitive assay toward miRNA-21 in the range of 0.5 to 104 fM, with a detection limit of 0.15 fM. In addition, this self-powered biosensor displays high selectivity for miRNA-21 assay in human serum samples.

A Nanozymatic-Mediated Smartphone Colorimetric Sensing Platform for the Detection of Dimethyl Phthalate (DMP) and Dibutyl Phthalate (DBP)

Plasticizers are a type of toxic substance that may remain in food, posing significant health risks including carcinogenic, teratogenic, mutagenic, and other adverse effects. In this study, a novel strategy was employed by combining Pt@Au nanozymes with high catalytic properties to created two catalytic signal probes, designated as Pt@Au@Ab1 and Pt@Au@Ab2, specifically designed for the detection of dimethyl phthalate (DMP) and dibutyl phthalate (DBP). These catalytic signal probes served as the foundation for the development of a colorimetric immunoassay, enabling the simultaneous detection of both DMP and DBP. The colorimetric immunoassay is capable of detecting DMP in the range of 0.5-100 μg/L with a limit of detection as low as 0.1 μg/L and DBP in the range of 1-32 μg/L with a low limit of detection of 0.5 μg/L. The developed immunoassay can be used for the determination of the DMP and DBP in baijiu and plastic bottled drinks. The recovery rate is in the range of 96.4% and 100.5% and the coefficient of variation is between 1.0% and 7.2%. This innovative colorimetric immunoassay offers a robust tool for the simultaneous quantification of DMP and DBP in real samples.

Functional Zonation Strategy of Heterodimer Nanozyme for Multiple Chemiluminescence Imaging Immunoassay

Although nanozymes with intrinsic enzyme-like characteristics have aroused great interest in the biosensing field, the challenge is to keep high enzyme-like activity of the nanozyme after the modification of biomolecules onto nanozymes. Herein, a functional zonation strategy of a heterodimer nanozyme was proposed to tackle the challenge and further construct a multiple chemiluminescence (CL) imaging immunoassay. Here Fe3O4-Au as a heterodimer nanozyme model was divided into two zones, in which Fe3O4 nanoparticles (NPs) were regarded as a nanozyme zone and AuNPs were defined as an antibody immobilization zone. A signal amplification probe (Fe3O4-Au-Ab2) was prepared by modifying the secondary antibody (Ab2) on AuNPs of the Fe3O4-Au heterodimer owing to the Au-S bond. The exposed Fe3O4 of the Fe3O4-Au-Ab2 probe shows very high peroxidase-like activity and can efficiently catalyze H2O2-luminol to produce strong CL imaging signals for multiple antigens detection. Using chicken interleukin-4 (ChIL-4) and chicken gamma interferon (ChIFN-γ) as models, the proposed CL imaging immunoassay shows wide linear ranges (0.005-0.10 ng/mL for both ChIL-4 and ChIFN-γ) and low detection limits (0.58 pg/mL for ChIL-4, 0.47 pg/mL for ChIFN-γ) with the characteristics of high sensitivity, high specificity, and good stability. This work provides a promising functional zonation concept for nanozymes to construct new types of nanozyme probes for immunoassay of multiple biomolecules.

Tailoring the Surface and Composition of Nanozymes for Enhanced Bacterial Binding and Antibacterial Activity

With the advantages of diverse structures, tunable enzymatic activity, and high stability, nanozymes are widely used in medicine, chemistry, food, environment, and other fields. As an alternative to traditional antibiotics, nanozymes attract more and more attention from the scientific researchers in recent years. Developing nanozymes-based antibacterial materials opens up a new avenue for the bacterial disinfection and sterilization. In this review, the classification of nanozymes and their antibacterial mechanisms are discussed. The surface and composition of nanozymes are critical for the antibacterial efficacy, which can be tailored to enhance both the bacterial binding and the antibacterial activity. On the one hand, the surface modification of nanozymes enables binding and targeting of bacteria that improves the antibacterial performance of nanozymes including the biochemical recognition, the surface charge, and the surface topography. On the other hand, the composition of nanozymes can be modulated to achieve enhanced antibacterial performance including the single nanozyme-mediated synergistic and multiple nanozymes-mediated cascade catalytic antibacterial applications. In addition, the current challenges and future prospects of tailoring nanozymes for antibacterial applications are discussed. This review can provide insights into the design of future nanozymes-based materials for the antibacterial treatments.

In-situ synthesized V2CTx MXene-based immune tag for the electrochemical detection of Interleukin 6 (IL-6) from breast cancer cells

Interleukin-6 (IL-6) is a proinflammatory cytokine with a critical role in immune regulation and treatment of many diseases, including breast cancer. Herein, we developed a novel V2CTx MXene-based immunosensor for rapid and accurate IL-6 detection. The chosen substrate was V2CTx, a 2-dimensional (2D) MXene nanomaterial with excellent electronic properties. Prussian blue (Fe4[Fe(CN)6]3), used for its electrochemical properties, and spindle-shaped gold nanoparticles (Au SSNPs), used to combine with antibodies, were in-situ synthesized on the surface of the MXene. The in-situ synthesis ensures a firm chemical connection compared to other tags formed by a less stable physical absorption. Inspired by a sandwich ELISA test, the modified V2CTx tag was captured by the electrode surface with cysteamine to detect the analyte, IL-6, after being attached with a capture antibody (cAb). Benefiting from an increased surface area, an enhanced charge transfer rate, and a firm connection of the tag, this biosensor exhibited excellent analytical performance. The high sensitivity, high selectivity, and wide detection range covering the IL-6 level of both healthy individuals and breast cancer patients were obtained to meet clinical demands. Herein, this V2CTx MXene-based immunosensor is a potential therapeutic and diagnostic point-of-care alternative to routine ELISA IL-6 detection methods.

Nanozymes based on octahedral platinum nanocrystals with {111} surface facets: glucose oxidase mimicking activity in electrochemical sensors

The ability of shape-controlled octahedral Pt nanoparticles to act as nanozyme mimicking glucose oxidase enzyme is reported. Extended {111} particle surface facets coupled with a size comparable to natural enzymes and easy-to-remove citrate coating give high affinity for glucose, comparable to the enzyme as proven by the steady-state kinetics of glucose electrooxidation. The easy and thorough removal of the citrate coating, demonstrated by X-ray photoelectron spectroscopy analysis, allows a highly stable deposition of the nanozymes on the electrode. The glucose electrochemical detection (at -0.2 V vs SCE) shows a linear response between 0.36 and 17 mM with a limit of detection of 110 μM. A good reproducibility has been achieved, with an average relative standard deviation (RSD) value of 9.1% (n = 3). Similarly, a low intra-sensor variability has been observed, with a RSD of 6.6% (n = 3). Moreover, the sensor shows a long-term stability with reproducible performances for at least 2 months (RSD: 7.8%). Tests in saliva samples show the applicability of Pt nanozymes to commercial systems for non-invasive monitoring of hyperglycemia in saliva, with recoveries ranging from 92 to 98%.

Fe(III)-incorporated porphyrin-based conjugated organic polymer as a peroxidase mimic for the sensitive determination of glucose and H2O2

Nanozymes, i.e., nanomaterials that possess intrinsic enzyme-like behaviour, have thrived over the past few decades owing to their advantages of superior stability and effortless storage. Such artificial enzymes can be a perfect alternative to naturally occurring enzymes, which have disadvantages of high cost and limited functionality. In this work, we present the fabrication of an Fe(III)-incorporated porphyrin-based conjugated organic polymer as a nanozyme for the efficient detection of glucose through its intrinsic peroxidase activity and the amperometric detection of hydrogen peroxide. The iron-incorporated porphyrin-based conjugated organic polymer (Fe-DMP-POR) possesses a spherical morphology with high chemical and thermal stability. Exploiting the peroxidase-mimicking activity of the material for the determination of glucose, a detection limit of 4.84 μM is achieved with a linear range of 0-0.15 mM. The Fe-DMP-POR also exhibits a reasonable recovery range for the detection of human blood glucose. The as-synthesized material can also act as an H2O2 sensor, with a sensitivity of 947.67 μA cm-2 mM-1 and a limit of detection of 3.16 μM.