Switching Peroxidase-Mimic Activity of Protein Stabilized Platinum Nanozymes by Sulfide Ions: Substrate Dependence, Mechanism, and Detection

Arginine-Rich Peptide-Rhodium Nanocluster@Reduced Graphene Oxide Composite as a Highly Selective and Active Uricase-like Nanozyme for the Degradation of Uric Acid and Inhibition of Urate Crystal

Metal nanozymes have offered attractive opportunities for biocatalysis and biomedicine. However, fabricating nanozymes simultaneously possessing highly catalytic selectivity and activity remains a great challenge due to the lack of three-dimensional (3D) architecture of the catalytic pocket in natural enzymes. Here, we integrate rhodium nanocluster (RhNC), reduced graphene oxide (rGO), and protamine (PRTM, a typical arginine-rich peptide) into a composite facilely based on the single peptide. Remarkably, the PRTM-RhNC@rGO composite displays outstanding selectivity, activity, and stability for the catalytic degradation of uric acid. The reaction rate constant of the uric acid oxidation catalyzed by the PRTM-RhNC@rGO composite is about 1.88 × 10-3 s-1 (4 μg/mL), which is 37.6 times higher than that of reported RhNP (k = 5 × 10-5 s-1, 20 μg/mL). Enzyme kinetic studies reveal that the PRTM-RhNC@rGO composite exhibits a similar affinity for uric acid as natural uricase. Furthermore, the uricase-like activity of PRTM-RhNC@rGO nanozymes remains in the presence of sulfur substances and halide ions, displaying incredibly well antipoisoning abilities. The analysis of the structure-function relationship indicates the PRTM-RhNC@rGO composite features the substrate binding site near the catalytic site in a confined space contributed by 2D rGO and PRTM, resulting in the high-performance of the composite nanozyme. Based on the outstanding uricase-like activity and the interaction of PRTM and uric acid, the PRTM-RhNC@rGO composite can retard the urate crystallization significantly. The present work provides new insights into the design of metal nanozymes with suitable binding sites near catalytic sites by mimicking pocket-like structures in natural enzymes based on simple peptides, conducing to broadening the practical application of high-performance nanozymes in biomedical fields.

Nanozyme as detector and remediator to environmental pollutants: between current situation and future prospective

The term "nanozyme" refers to a nanomaterial possessing enzymatic capabilities, and in recent years, the field of nanozymes has experienced rapid advancement. Nanozymes offer distinct advantages over natural enzymes, including ease of production, cost-effectiveness, prolonged storage capabilities, and exceptional environmental stability. In this review, we provide a concise overview of various common applications of nanozymes, encompassing the detection and removal of pollutants such as pathogens, toxic ions, pesticides, phenols, organic contaminants, air pollution, and antibiotic residues. Furthermore, our focus is directed towards the potential challenges and future developments within the realm of nanozymes. The burgeoning applications of nanozymes in bioscience and technology have kindled significant interest in research in this domain, and it is anticipated that nanozymes will soon become a topic of explosive discussion.

A highly sensitive colorimetric DNA sensor for MicroRNA-155 detection: leveraging the peroxidase-like activity of copper nanoparticles in a double amplification strategy

A novel and highly sensitive colorimetric DNA sensor for determination of miRNA-155 at attomolar levelsis presented that combines the peroxidase-like activity of copper nanoparticles (CuNPs) with the hybridization chain reaction (HCR) . The utilization of CuNPs offers advantages such as strong interaction with double-stranded DNA, excellent molecular recognition, and mimic catalytic activity. Herein, a capture probe DNA (P1) was immobilized on carboxylated magnetic beads (MBs), allowing for amplified immobilization due to the 3D surface. Subsequently, the presence of the target microRNA-155 led to the formation of a sandwich structure (P2/microRNA-155/P1/MBs) when P2 was introduced to the modified P1/MBs. The HCR reaction was then triggered by adding H1 and H2 to create a super sandwich (H1/H2)n. Following this, Cu2+ ions were attracted to the negatively charged phosphate groups of the (H1/H2)n and reduced by ascorbic acid, resulting in the formation of CuNPs, which were embedded into the grooves of the (H1/H2)n. The peroxidase-like activity of CuNPs catalyzed the oxidation reaction of 3,3',5,5'-Tetramethylbenzidine (TMB), resulting in a distinct blue color measured at 630 nm. Under optimal conditions, the colorimetric biosensor exhibited a linear response to microRNA-155 concentrations ranging from 80 to 500 aM, with a detection limit of 22 aM, and discriminate against other microRNAs. It was also successfully applied to the determination of microRNA-155 levels in spiked human serum.

Biomimetic and bioorthogonal nanozymes for biomedical applications

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

Detection of Glucose Based on Noble Metal Nanozymes: Mechanism, Activity Regulation, and Enantioselective Recognition

Glucose monitoring is essential to evaluate the degree of glucose metabolism disorders. The enzymatic determination has been the most widely used method in glucose detection because of its high efficiency, accuracy, and sensitivity. Noble metal nanomaterials (NMs, i.e., Au, Ag, Pt, and Pd), inheriting their excellent electronic, optical, and enzyme-like properties, are classified as noble metal nanozymes (NMNZs). As the NMNZs are often involved in two series of reactions, the oxidation of glucose and the chromogenic reaction of peroxide, here the chemical mechanism by employing NMNZs with glucose oxidase (GOx) and peroxidase (POD) mimicking activities is briefly summarized first. Subsequently, the regulation strategies of the GOx-like, POD-like and tandem enzyme-like activities of NMNZs are presented in detail, including the materials, size, morphology, composition, and the reaction condition of the representative NMs. In addition, in order to further mimic the enantioselectivity of enzyme, the design of NMNZs with enantioselective recognition of d-glucose and l-glucose by using different chiral compounds (DNA, amino acids, and cyclodextrins) and molecular imprinting is further described in this review. Finally, the feasible solutions to the existing challenges and a vision for future development possibilities are discussed.

Structure design mechanisms and inflammatory disease applications of nanozymes

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

Highly Sensitive Colorimetric Detection of Glutathione in Human Serum Based on Iron-Copper Metal-Organic Frameworks

Emerging metal-organic framework (MOF)-based mimic enzymes have been exploited to design a colorimetric sensor for the detection of biomolecules. However, it is challenging to figure out the glutathione (GSH) detection method and the corresponding sensing mechanism using an MOF-based colorimetric sensor. In this work, a novel iron-copper MOF with high activity is synthesized by a wet-chemical method. A GSH colorimetric sensor based on the peroxidase-like properties of the iron-copper MOF is developed. Hydrogen peroxide is converted to hydroxyl radicals by the peroxidase-like properties of the iron-copper MOF mimic enzyme, which can catalyze the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (ox-TMB). The kinetic constant of the MOF mimic enzyme (0.02 mM for H₂O₂) is superior to horseradish peroxidase (HRP). The GSH content can be quantified by proposing a sensor based on the colorimetric method and color turn-off mechanism. The turn-off mechanism of GSH analysis includes two aspects. On the one hand, the blue ox-TMB can be deoxidized to colorless TMB by GSH. On the other hand, hydroxyl radicals (^•OH) can be consumed by GSH. The linear range and limit of detection are 2-20 and 0.439 μM, respectively. At the same time, GSH detection also shows good specificity and anti-interference characteristics. Therefore, MOF-based colorimetric sensors have been used to qualitatively and quantitatively measure GSH contents in human serum. The mechanism and application of the iron-copper MOF pave a way for the development of mimic enzymes with polymetallic active sites in the field of colorimetric sensing.

Interactions of proteins with metal-based nanoparticles from a point of view of analytical chemistry - Challenges and opportunities

Interactions of proteins with nanomaterials draw attention of many research groups interested in fundamental phenomena. However, alongside with valuable information regarding physicochemical aspects of such processes and their mechanisms, they more and more often prove to be useful from a point of view of bioanalytics. Deliberate use of processes based on adsorption of proteins on nanoparticles (or vice versa) allows for a development of new analytical methods and improvement of the existing ones. It also leads to obtaining of nanoparticles of desired properties and functionalities, which can be used as elements of analytical tools for various applications. Due to interactions with nanoparticles, proteins can also gain new functionalities or lose their interfering potential, which from perspective of bioanalytics seems to be very inviting and attractive. In the framework of this article we will discuss the bioanalytical potential of interactions of proteins with a chosen group of nanoparticles, and implementation of so driven processes for biosensing. Moreover, we will show both positive and negative (opportunities and challenges) aspects resulting from the presence of proteins in media/samples containing metal-based nanoparticles or their precursors.

Supramolecule self-assembly synthesis of amyloid phenylalanine-Cu fibrils with laccase-like activity and their application for dopamine determination

Laccases are multicopper proteins for dioxygen-involved oxidation of a broad spectrum of organic compounds. I Novel amyloid-like phenylalanine-Cu (F-Cu(II)) fibrils were developed, which were obtained via supramolecular self-assembly of Cu²⁺ and phenylalanine (F) under basic condition. The obtained amyloid-like fibrils represented highly periodic structure, of which the lattice unit was constructed via alternating hydrophobic (aromatic environment) and hydrophilic (both hydrogen bonding and Cu(II) coordination) interactions. Relative to natural laccases, the amyloid-like F-Cu(II) architecture exhibited comparable substrate affinity (Michaelis constant, K_m = 0.75 mM) and higher catalytic efficiency (k_cat/K_m = 773.33 × 10^-3 g^-1 min^-1L). Moreover, it exhibited remarkable tolerances in pH (4 ~ 10), temperature (room temperature ~ 200 ℃), organic solvent, and long-term storage (> 15 days). These stabilities were superior among the reported nature and artificial laccases, presenting a more promising candidate in various chemo- or bio-applications. In addition, F-Cu(II) fibrils could catalyze the oxidation of dopamine (DA) to a brown product, in which a new absorption band at 470 nm was observed. Based on this, a simple colorimetric assay for the detection of DA could be performed. We reported a novel amyloid-like phenylalanine-Cu fibrils, in which F-Cu⁺ complex can mimick the T1 site of natural laccase to oxidize the substrates. Then electrons transferred to F-Cu²⁺ complex via N-H···O=C hydrogen binding pathway. Finally, the dioxygen was transformed to water though radical reaction.

Hexavalent Chromium as a Smart Switch for Peroxidase-like Activity Regulation via the Surface Electronic Redistribution of Silver Nanoparticles Anchored on Carbon Spheres

Although some ions, due to their unique chemical properties, can regulate the enzyme-like activity of nanomaterials, it is still a huge challenge to explore the mechanism of regulation. Herein, we found that Cr⁶⁺ (CrO₄^2-) as a smart switch can significantly increase the peroxidase-like (POD-like) activity of silver nanoparticles (Ag NPs), which were anchored efficiently on carbon spheres (Cal-CS/PEG/Ag) using amino-modified poly(ethylene glycol) (PEG) as a bridge. Density functional theory (DFT) calculations demonstrated that the addition of Cr⁶⁺ can not only adjust the surface electronic redistribution of Ag atoms but also improve the geometric structure of the adsorbed intermediate, which resulted in the optimization of free energy and change of bond lengths in the catalytic reaction process, increasing the POD-like activity of Cal-CS/PEG/Ag. Based on the Cr⁶⁺-increased POD-like activity of Cal-CS/PEG/Ag, we successfully constructed a visual sensor of Cr⁶⁺ along with quantitative analysis by the UV spectrum. The sensor has good selectivity for other 29 interfering ions and molecules with a detection limit of 79 nM. In this work, the detailed mechanism of the Cr⁶⁺-increased POD-like activity of Ag NPs was studied and a new possibility for the rational design of ion visual sensors using nanomaterials was proposed.

A direct competitive nanozyme-linked immunosorbent assay based on MnO2 nanosheets as a catalytic label for the determination of fumonisin B1

A direct competitive nanozyme-linked immunosorbent assay (dcNLISA) based on MnO₂ nanosheets (MnO₂ NSs) as a nanozyme label was developed for the highly sensitive determination of fumonisin B₁ (FB₁). MnO₂ NS-labeled fumonisin B₁-bovine serum albumin was easily synthesized as a competing antigen for the dcNLISA. And color changes derived from the MnO₂-3,3',5,5'-tetramethylbenzidine (TMB) system were exploited as the output signals of the dcNLISA. Several experimental parameters including the concentrations of the coating antibody, pH values, ionic strength and methanol concentration were optimized. Under the optimal conditions, the proposed method demonstrated a linear range (1.17-20.74 ng mL^-1) with a reliable correlation coefficient (R² = 0.9989), a satisfactory limit of detection (0.63 ng mL^-1) and high selectivity for the detection of FB₁. The recoveries of FB₁ in spiked corn and wheat samples were in the range of 85.31-108.16% with coefficients of variation (CVs) ranging from 6.14% to 9.23%. Meanwhile, the testing results showed good consistency (R² = 0.9892) between the developed dcNLISA and the reference method, liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) method. The proposed method was proven to be simple, sensitive, cost-effective and reliable for the screening of FB₁ in cereals.

Photoenzymatic Activity of Artificial-Natural Bienzyme Applied in Biodegradation of Methylene Blue and Accelerating Polymerization of Dopamine

Enzymes as biocatalysts have attracted extensive attention. In addition to immobilizing or encapsulating various enzymes for combating the easy loss of enzymatic activity, strengthening the enzymatic activity upon light irradiation is a challenge. To the best of our knowledge, the work of spatiotemporally modulating the catalytic activity of artificial-natural bienzymes with a near-infrared light irradiation has not been reported. Inspired by immobilized enzymes and nanozymes, herein a platinum nanozyme was synthesized; subsequently, the platinum nanozyme was grafted on the body of laccase, thus successfully obtaining the artificial-natural bienzyme. The three-dimensional structure of the artificial-natural bienzyme was greatly different from that of the immobilized enzyme or the encapsulated enzyme. The platinum nanozyme possessed excellent laccase-like activity, which was 3.7 times higher than that of laccase. Meanwhile, the coordination between the platinum nanozyme and laccase was proved. Besides, the cascaded catalysis of artificial-natural bienzyme was verified with hydrogen peroxide as a mediator. The enzymatic activities of artificial-natural bienzyme with and without near-infrared light irradiation were, respectively, 46.2 and 29.5% higher than that of free laccase. Moreover, the reversible catalytic activity of the coupled enzyme could be manipulated with and without a near-infrared light at 808 nm. As a result, the degradation rates of methylene blue catalyzed by the coupled enzyme and the platinum nanozyme were higher than that of laccase. Furthermore, accelerating polymerization of the dopamine was also demonstrated. Briefly, this facile strategy may provide a universal approach to control the catalytic activity of other natural enzymes.

Recent advances in enzyme-enhanced immunosensors

Among the products for rapid detection in different fields, enzyme-based immunosensors have received considerable attention. Recently, great efforts have been devoted to enhancing the output signals of enzymes through different strategies that can significantly improve the sensitivity of enzyme-based immunosensors for the need of practical applications. In this manuscript, the significance of enzyme-based signal transduction patterns in immunoassay and the central role of enzymes in achieving precise control of reaction systems are systematically described. In view of the rapid development of this field, we classify these strategies based on the combination of immune recognition and enzyme amplification into three categories, namely enzyme-based enhancement strategies, combination of the catalytic amplification of enzymes with other signal amplification methods, and substrate-based enhancement strategies. The current focus and future direction of enzyme-based immunoassays are also discussed. This article is not exhaustive, but focuses on the latest advances in different signal generation methods based on enzyme-initiated catalytic reactions and their applications in the detection field, which could provide an accessible introduction of enzyme-based immunosensors for the community with a view to further improving its application efficiency.

Protein-Assisted Osmium Nanoclusters with Intrinsic Peroxidase-like Activity and Extrinsic Antifouling Behavior

Extensive studies have laid the groundwork for understanding peroxidase-like nanozymes. However, improvements are still required before their practical applications. On one hand, it is significant to explore highly reactive nanozymes. On the other hand, it is necessary to avoid fouling formed on the surface of nanozymes, which will affect their activity and the results of H₂O₂ sensors or H₂O₂-related applications. Herein, a strategy is reported to design osmium nanoclusters (Os NCs) with the existence of bovine serum albumin (BSA) through biomineralization. BSA-Os NCs were found to possess intrinsic peroxidase-like activity with a high specific activity (6120 U/g). Studies also found that the catalytic activity of BSA-Os NCs was better than those of reported protein-assisted metal nanozymes (e.g., BSA-Pt NPs and BSA-Au NCs). More significantly, BSA has been confirmed as a protective shell to give Os NCs extrinsic antifouling property in some typical ions (e.g., Hg²⁺, Ag⁺, Pb²⁺, I^-, Cr⁶⁺, Cu²⁺, Ce³⁺, S^2-, etc.), saline (0-2 M), or protein (0-100 mg/mL) conditions. Under optimal conditions, a colorimetric sensor was established to realize a linear range of H₂O₂ from 1.25 to 200 μM with a low detection limit of 300 nM. On this basis, remarkable features enable a BSA-Os NCs-based colorimetric sensor to detect H₂O₂ from complex systems with clear color gradients. Together, this work highlights the advantages of protein-assisted Os nanozymes and provides a paragon for peroxidase-like nanozymes in H₂O₂-related applications.

A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

Platinum-Copper Bimetallic Colloid Nanoparticle Cluster Nanozymes with Multiple Enzyme-like Activities for Scavenging Reactive Oxygen Species

Fabrication of high-performance artificial antioxidant enzyme (AAE) systems based on a single nanozyme possessing multi-enzymatic activities is fascinating but challenging. Here, polyvinylpyrrolidone (PVP)-platinum-copper nanoparticle clusters (PVP-PtCuNCs) are prepared by a facile one-pot chemical coreduction method. PVP-PtCuNCs possess efficient superoxide dismutase (SOD)-like, peroxidase (POD)-like, and catalase (CAT)-like activities, and the multi-enzymatic activities depend on the bimetal component and cluster structure. Compared with individual platinum nanoparticle clusters (PVP-PtNCs), PVP-PtCuNCs can effectively eliminate reactive oxygen species (ROS) including superoxide anions, hydrogen peroxide, and hydroxyl radicals. The doping of copper not only reduces the usage of Pt content but also improves the catalytic efficiency and versatility effectively through the synergistic effect of bimetal components and the nanocluster structure. The results not only demonstrate that a single bimetallic nanozyme has the potential as an efficient AAE system in the biomedical application but also demonstrate that traditional concepts of structure-activity relationships can be used to fabricate nanozymes with the desired multi-enzymatic activities.

A review on metal nanozyme-based sensing of heavy metal ions: Challenges and future perspectives

Large scale mining, manufacturing industries, exploitation of underground water, depletion of groundwater level, and uncontrolled discharge of industrial wastes have caused severe heavy metal ion pollution to the environment throughout the world. Therefore, the rapid detection of such toxic metal ions is inevitable. However, conventional methods require sophisticated instruments and skilled manpower and are difficult to operate in on-field conditions. Recently, metal nanozyme-based assays have been found to have the potential as an alternative to conventional methods due to their portability, simplicity, and high sensitivity to detect metal ion concentration to as low as parts per trillion (ppt). Metal nanozyme-based systems for heavy metal ions enable rapid and cheap screening on the spot with a very simple instrument such as a UV-vis absorption spectrophotometer and therefore, are convenient for use in field operations, especially in remote parts of the world. The sensing mechanism of a nanozyme-based sensor is highly dependent on its surface properties and specific interactions with particular metal ion species. Such method often encounters selectivity issues, unlike natural enzyme-based assays. Therefore, in this review, we mainly focus our discussion on different types of target recognition and inhibition/enhancement mechanisms, and their responses toward the catalytic activity in the sensing of target metal ions, design strategies, challenges, and future perspectives.

Designing signal-on sensors by regulating nanozyme activity

Nanozymes are nanomaterials with enzyme-like activities. Compared to natural enzymes, nanozymes are more stable and cost-effective, and they have unique properties due to their nanoscale size and surface chemistry. In this review, we summarize 'signal-on' nanozyme-based sensors for detecting metal ions, anions, small molecules and proteins. Since protein-based enzymes are already highly active, they were used to detect their inhibitors, resulting in 'signal-off' sensors. On the other hand, for nanozymes, target molecules were detected either as a promotor of nanozyme activity or for its ability to selectively remove nanozyme inhibitors. In both cases, 'signal-on' detection was achieved. We classify the commonly used nanozymes based on their composition such as metal oxide, gold nanoparticles and other nanomaterials, most of which belong to the oxidase, peroxidase and catalase mimics. The nanozymes can catalyze the oxidation of colorless or non-fluorescent substrates to produce a visual or fluorescent signal. Based on this, this article presents some typical 'turn-on' and 'turn-off-on' sensors, and we critically review their design principles. At the end, further perspectives for the nanozyme-based sensors are outlined.

Engineering Inorganic Nanoflares with Elaborate Enzymatic Specificity and Efficiency for Versatile Biofilm Eradication

Nanozyme has emerged as a versatile nanocatalyst yet is constrained with limited catalytic efficiency and specificity for various biomedical applications. Herein, by elaborately integrating the recognition/transduction carbon dots (CDs) with platinum nanoparticles (PtNPs), an exquisite CDs@PtNPs (CPP) nanoflare is engineered as an efficient and substrate-specific peroxidase-mimicking nanozyme for high-performance biosensing and antibacterial applications. The intelligent CPP-catalyzed hydrogen peroxide (H₂ O₂ )-generated reactive oxygen species realize the sensitive diagnosis-guided enhanced disinfection of pathogens. Significantly, the CPP nanozyme shows the prominent biofilm eradication and wound healing in vivo by virtue of endogenous H₂ O₂ in acidic infection tissues, which can substantially preclude the annoying antibiotics resistance. A fundamental understanding on the present CPP nanoflare would not only facilitate the advancement of various prospective biocatalysts, but also establish a multifunctional means for versatile biosensing and smart diagnostic applications.

Influence of the Alkyl Chain Length of the Imidazole Ionic Liquid-Type Surfactants on Their Aggregation Behavior with Sodium Dodecyl Sulfate

The influence of the alkyl chain length of the ionic liquid surfactants 1-hexadecyl-3-alkyl imidazolium bromide [C₁₆imC_n]Br (n = 2-16) on their aggregation behavior with sodium dodecyl sulfate (SDS) in water was studied. The rheological properties, thermostability, and microstructure of the samples were characterized via a combination of rheology, cryo-transmission electron microscopy, polarization optical microscopy, and small-angle X-ray scattering. Upon the addition of SDS, the [C₁₆imC_n]Br (n = 2, 4, 6) rodlike micelles transit into the gels with high water content. The effects of molar ratio and alkyl chain length on the viscoelasticity and thermal stability of the SDS/[C₁₆imC_n]Br (n = 2, 4, 6) gels were studied. However, the [C₁₆imC_n]Br (n = 8, 10, 12, 14, 16) rodlike micelles precipitate with the addition of SDS. The [C₁₆imC_n]Br (n = 10, 12, 14, 16) gels transit to the rodlike micelles with the proper addition of SDS. The mechanism of the influence of the alkyl chain length of the [C₁₆imC_n]Br on their aggregation behavior with SDS was proposed.

Triggered peroxidase-like activity of Au decorated carbon dots for colorimetric monitoring of Hg2+ enrichment in Chlorella vulgaris

Developing a rapid, low-cost, and multimode detection method for heavy metal ions remains a compelling goal for many applications, including food safety, environmental and biological analysis. This study investigated the influence of Hg²⁺ on the peroxidase-like activity of gold nanoparticles (GNPs) decorated on carbon dots (CDs) from lysine (denoted as GNP@CDs). A new type of Hg²⁺-triggered peroxidase-like activity of GNP@CDs was discovered, which could catalyze the oxidation of the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue TMB. Based on the regulation of the catalytically triggered activity, a sensitive colorimetric method for the detection of Hg²⁺ was developed, with a linear range of 7-150 nM, providing a limit of detection as low as 3.7 nM. The sensor is simple and rapid, and was successfully applied to the detection of Hg²⁺ enrichment in chlorella, suggesting a promising application in biological analysis.

Electrodeposition-Assisted Rapid Preparation of Pt Nanocluster/3D Graphene Hybrid Nanozymes with Outstanding Multiple Oxidase-Like Activity for Distinguishing Colorimetric Determination of Dihydroxybenzene Isomers

Here, we demonstrate a facile bottom-up strategy to fabricate Pt nanoclusters (Pt NCs) grafted onto three-dimensional graphene foam (3D GF) assisted by cetyltrimethyl ammonium bromide (CTAB) using the electrodeposition method. The homogeneous grafting of Pt NC onto 3D GF is due to the formation of hemimicelles above some CTAB concentration. With the unique nanocluster structure and the high content of Pt⁰, the Pt NC/3D GF nanohybrid exhibits extremely high activity and shows higher reusability and stability. Apart from the intrinsic oxidase-like activity with 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate, the Pt NC/3D GF nanohybrid can act simultaneously as an effective polyphenol oxidase (PPO) mimic, such as tyrosinase, catechol oxidase, and laccase. More importantly, utilizing intrinsic catechol oxidase-like activity and the oxidase-like activity with TMB as the substrate of the nanohybrid, distinguishing colorimetric determination of dihydroxybenzene isomers (catechol and hydroquinone) is performed. Distinguishing colorimetric analysis of dihydroxybenzene isomers was first developed using nanozymes. The present work provides a simple bottom-up approach for the reasonable fabrication of various nanostructured nanozymes with excellent performance using the electrodeposition method assisted with surfactants.

Protein-mediated sponge-like copper sulfide as an ingenious and efficient peroxidase mimic for colorimetric glucose sensing

Strenuous efforts have been made to develop nanozymes for achieving the performance of natural enzymes to broaden their application in practice, but the fabrication of high-performance and biocompatible nanozymes via facile and versatile approaches has always been a great challenge. Here, sponge-like casein-CuS hybrid has been facilely synthesized in the presence of amphiphilic protein-casein through a simple one-step approach. Casein-CuS hybrid exhibits substrates-dependent peroxidase-like activity. Casein-CuS hybrid exhibits well peroxidase-like activity with 3,3′,5,5′-tetramethylbenzidine (TMB) and 1,2-diaminobenzene (OPD) as substrates, and the affinity of OPD towards the hybrid nanozyme is much higher than that of TMB. More importantly, due to the high affinity of OPD and the well biocompatibility of the hybrid nanozyme, a superior enzyme cascade for glucose based on the well cooperative effect of casein-CuS hybrid and glucose oxidase is developed. The proposed glucose sensor exhibits a wide linear range of 0.083 to 75 μM and a detection limit of 5 nM. This suggests the promising utilization of protein–metal hybrid nanozymes as robust and potent peroxidase mimics in the medical, food and environmental detection fields.

Strenuous efforts have been made to develop nanozymes for achieving the performance of natural enzymes, but the fabrication of high-performance and biocompatible nanozymes via facile and versatile approaches has always been a great challenge.

In-situ generation of nanozymes by natural nucleotides: a biocatalytic label for quantitative determination of hydrogen peroxide and glucose

Four natural nucleotides including 5'-cytidine monophosphate (CMP), 5'-thymidine monophosphate (TMP), guanosine monophosphate (GMP) and 5'-adenosine monophosphate (AMP) were employed to modulate the coordination environment and the valence state of PtCl₄^2-. This is the first report that natural nucleotides have the ability to produce highly active Pt nanoclusters. The latter are shown to act as peroxidase mimetics. Both the size distribution and the charge state of Pt-nucleotide nanozymes vary with the chemical structures of nucleotides, thereby contributing to distinct enzyme-like activities. By adopting Pt-CMP as a signal amplifier, a photometric assay was well-established for quantitative determination of glucose. The assay is based on the oxidation of glucose by glucose oxidase. The oxidation product (H₂O₂) is detected at 652 nm via the Pt-CMP-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine with H₂O₂. Response is linear in the 5 to 100 μM glucose concentration range, and the limit of detection is 0.12 μM (at S/N= 3). The method excels by a low signal background, high sensitivity, and low consumption of energy and materials. Graphical abstract Peroxidase mimicking Pt nanoclusters were synthesized by employing natural nucleotides as both the reducing agent and the stabilization template.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

Additive-based stability assessment of biologically designed CuO and GSH-CuO nanospheres and their applicability as Nano-biosensors

Uncapped and Glutathione capped Cupric oxide nanospheres were synthesized by the interaction of Berberis lycium (Bl) root extract with corresponding salt solution. CuO nanospheres were best optimized by mixing 2% Bl extract solution with 1 mM CuSO₄·5H₂O (pH 11, 90 °C) Reduced glutathione (0.25 mM) in solution form was added in respective emulsion after 24 h. Synthesis of nanospheres was ensured by distinct surface plasmonic resonance peaks shown by CuO (370-420 nm). Addition of glutathione resulted in sharp blue shift and lowered absorbance values in UV spectra suggesting the decrease in nanoparticles' size and concentration. Average particle sizes as deduced with XRD were found to be 18.52 and 16.57 nm for CuO and GSH-CuO nanospheres respectively. Additive based stability assessment of synthesized nanospheres revealed CuO and GSH-CuO nanospheres to be highly stable in the presence of Catechin hydrate among various tested chemical compounds while ascorbic acid appeared as a strong destabilizing agent. TMB was oxidized by H₂O₂ in the presence of synthesized enzymes likewise horseradish peroxidase; though exhibited moderate results. Glutathione stabilized cupric oxide nanospheres exhibited the potential to be modulated further into efficient nanozymes as these showed better affinity towards chromogenic substrate TMB (K_m value 0.32 mM) and better catalytic efficiency (0.075 mM^-1 s^-1) compared to uncapped CuO nanomimetics (1.6 mM, 0.033 mM^-1 s^-1). All of the tested additives served as inhibitors to the peroxidase mimicking potential of CuO and GSH-CuO nanozymes.

Carbon-mediated synthesis of shape-controllable manganese phosphate as nanozymes for modulation of superoxide anions in HeLa cells

Here we present a facile method to fabricate shape-controllable transition metal phosphates by using hollow carbon structures as substrates for superoxide sensing.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Mn3O4 microspheres as an oxidase mimic for rapid detection of glutathione

Exploiting a rapid and sensitive method for biomarker detection has important implications in the early diagnosis of diseases. Here, we synthesized Mn₃O₄ microspheres which worked as a nanozyme to exhibit outstanding oxidase-like activity for rapid colorimetric determination of glutathione (GSH). The Mn₃O₄ microspheres of about 800 nm in size could be prepared through a hydrothermal method, and we found that the as-prepared Mn₃O₄ microspheres could quickly oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to its oxidized form (TMBox) in the absence of H₂O₂. After adding glutathione (GSH), TMBox was able to be changed into to its original form and resulted in the corresponding decrease in absorbance value at 652 nm. The Mn₃O₄-TMB system had good linearity with GSH concatenation in the range of 5–60 μM, and the limit of detection was 0.889 μM. Furthermore, this assay possessed high selectivity specificity, which made it possible to detect GSH in human serum samples. Thus, the obtained assay based on the oxidase mimic of Mn₃O₄ would enlarge and exploit the application fields of nanozymes in bio-analysis.

The oxidase-like activity of Mn₃O₄ was used to detect the GSH level directly and rapidly in the absence of H₂O₂.

Metal-doped carbon nanoparticles with intrinsic peroxidase-like activity for colorimetric detection of H2O2 and glucose

We develop a general hydrothermal approach to fabricate new nanozymes with intrinsic peroxidase-like activity for H₂O₂ and glucose detection.