Enhanced peroxidase activity and tumour tissue visualization by cobalt-doped magnetoferritin nanoparticles

Nature-inspired protein mineralization strategies for nanoparticle construction: advancing effective cancer therapy

Recently, nanotechnology has shown great potential in the field of cancer therapy due to its ability to improve the stability and solubility and reduce side effects of drugs. The biomimetic mineralization strategy based on natural proteins and metal ions provides an innovative approach for the synthesis of nanoparticles. This strategy utilizes the unique properties of natural proteins and the mineralization ability of metal ions to combine nanoparticles through biomimetic mineralization processes, achieving the effective treatment of tumors. The precise control of the mineralization process between proteins and metal ions makes it possible to obtain nanoparticles with the ideal size, shape, and surface characteristics, thereby enhancing their stability and targeting ability in vivo. Herein, initially, we analyze the role of protein molecules in biomineralization and comprehensively review the functions, properties, and applications of various common proteins and metal particles. Subsequently, we systematically review and summarize the application directions of nanoparticles synthesized based on protein biomineralization in tumor treatment. Specifically, we discuss their use as efficient drug delivery carriers and role in mediating monotherapy and synergistic therapy using multiple modes. Also, we specifically review the application of nanomedicine constructed through biomimetic mineralization strategies using natural proteins and metal ions in improving the efficiency of tumor immunotherapy.

Advancements of the Molecular Directed Design and Structure-Activity Relationship of Ferritin Nanocage

Ferritin nanocages possess remarkable structural properties and biological functions, making them highly attractive for applications in functional materials and biomedicine. This comprehensive review presents an overview of the molecular characteristics, extraction and identification of ferritin, ferritin receptors, as well as the advancements in the directional design of high-order assemblies of ferritin and the applications based on its unique structural properties. Specifically, this Review focuses on the regulation of ferritin assembly from one to three dimensions, leveraging the symmetry of ferritin and modifications on key interfaces. Furthermore, it discusses targeted delivery of nutrition and drugs through facile loading and functional modification of ferritin. The aim of this Review is to inspire the design of micro/nano functional materials using ferritin and the development of nanodelivery vehicles for nutritional fortification and disease treatment.

Aptamer-Modified Homogeneous Catalysts, Heterogenous Nanoparticle Catalysts, and Photocatalysts: Functional "Nucleoapzymes", "Aptananozymes", and "Photoaptazymes"

Conjugation of aptamers to homogeneous catalysts ("nucleoapzymes"), heterogeneous nanoparticle catalysts ("aptananozymes"), and photocatalysts ("photoaptazymes") yields superior catalytic/photocatalytic hybrid nanostructures emulating functions of native enzymes and photosystems. The concentration of the substrate in proximity to the catalytic sites ("molarity effect") or spatial concentration of electron-acceptor units in spatial proximity to the photosensitizers, by aptamer-ligand complexes, leads to enhanced catalytic/photocatalytic efficacies of the hybrid nanostructures. This is exemplified by sets of "nucleoapzymes" composed of aptamers conjugated to the hemin/G-quadruplex DNAzymes or metal-ligand complexes as catalysts, catalyzing the oxidation of dopamine to aminochrome, oxygen-insertion into the Ar─H moiety of tyrosinamide and the subsequent oxidation of the catechol product into aminochrome, or the hydrolysis of esters or ATP. Also, aptananozymes consisting of aptamers conjugated to Cu2+ - or Ce4+ -ion-modified C-dots or polyadenine-stabilized Au nanoparticles acting as catalysts oxidizing dopamine or operating bioreactor biocatalytic cascades, are demonstrated. In addition, aptamers conjugated to the Ru(II)-tris-bipyridine photosensitizer or the Zn(II) protoporphyrin IX photosensitizer provide supramolecular photoaptazyme assemblies emulating native photosynthetic reaction centers. Effective photoinduced electron transfer followed by the catalyzed synthesis of NADPH or the evolution of H2 is demonstrated by the photosystems. Structure-function relationships dictate the catalytic and photocatalytic efficacies of the systems.

Synthesis of Fe-Doped Peroxidase Mimetic Nanozymes from Natural Hemoglobin for Colorimetric Biosensing and In Vitro Anticancer Effects

Despite their efficiency and specificity, the instability of natural enzymes in harsh conditions has inspired researchers to replace them with nanomaterials. In the present study, extracted hemoglobin from blood biowastes was hydrothermally converted to catalytically active carbon nanoparticles (BDNPs). Their application as nanozymes for the colorimetric biosensing of H₂O₂ and glucose and selective cancer cell-killing ability was demonstrated. Particles that were prepared at 100 °C (BDNP-100) showed the highest peroxidase mimetic activity, with Michaelis-Menten constants (K_m) of 11.8 mM and 0.121 mM and maximum reaction rates (V_max) of 8.56 × 10^-8 mol L^-1 s^-1 and 0.538 × 10^-8 mol L^-1 s^-1, for H₂O₂ and TMB, respectively. The cascade catalytic reactions, catalyzed by glucose oxidase and BDNP-100, served as the basis for the sensitive and selective colorimetric glucose determination. A linear range of 50-700 µM, a response time of 4 min, a limit of detection (3σ/N) of 40 µM, and a limit of quantification (10σ/N) of 134 µM was achieved. In addition, the reactive oxygen species (ROS)-generating ability of BDNP-100 was employed for evaluating its potential in cancer therapy. Human breast cancer cells (MCF-7), in the forms of monolayer cell cultures and 3D spheroids, were studied by MTT, apoptosis, and ROS assays. The in vitro cellular experiments showed dose-dependent cytotoxicity of BDNP-100 toward MCF-7 cells in the presence of 50 µM of exogenous H₂O₂. However, no obvious damage was induced to normal cells in the same experimental conditions, verifying the selective cancer cell-killing ability of BDNP-100.

A Catalytic Immune Activator Based on Magnetic Nanoparticles to Reprogram the Immunoecology of Breast Cancer from "Cold" to "Hot" State

Triple-negative breast cancer (TNBC) as "cold" tumor is characterized by severe immunosuppression of the tumor microenvironment (TME). To effectively activate the immune response of TNBC, a new kind of therapy strategy called cancer catalytic immunotherapy is proposed based on magnetic nanoparticles (NPs) as immune activators. Utilizing the weak acidity and excessive hydrogen peroxide of TME, these magnetic NPs can release ferrous ions to promote Fenton reaction, leading to abundant ·OH and reactive oxygen species (ROS) for ultimately killing cancer cells. Mechanistically, these magnetic NPs activate the ROS-related signaling pathway to generate more ROS. Meanwhile, these magnetic NPs with unique immunological properties can promote the maturation of dendritic cells and the polarization of macrophages from M2 to M1, resulting in the infiltration of more T cells to reprogram the immunoecology of TNBC from "cold" to "hot" state. Besides directly affecting immune cells, these magnetic NPs can also affect the secretion of some immune-related cytokines by cancer cells, to further indirectly activate the immune response. In conclusion, these catalytic immune activators are designed to achieve the synergistic treatment of chemodynamic therapy-enhanced immunotherapy guided by computed tomography (CT)/near-infrared region-II (NIR-II) dual-mode imaging, providing a new strategy for TNBC treatment.

Ferritin: A Promising Nanoreactor and Nanocarrier for Bionanotechnology

The essence of bionanotechnology lies in the application of nanotechnology/nanomaterials to solve the biological problems. Quantum dots and nanoparticles hold potential biomedical applications, but their inherent problems such as low solubility and associated toxicity due to their interactions at nonspecific target sites is a major concern. The self-assembled, thermostable, ferritin protein nanocages possessing natural iron scavenging ability have emerged as a potential solution to all the above-mentioned problems by acting as nanoreactor and nanocarrier. Ferritins, the cellular iron repositories, are hollow, spherical, symmetric multimeric protein nanocages, which sequester the excess of free Fe(II) and synthesize iron biominerals (Fe₂O₃·H₂O) inside their ∼5-8 nm central cavity. The electrostatics and dynamics of the pore residues not only drives the natural substrate Fe²⁺ inside ferritin nanocages but also uptakes a set of other metals ions/counterions during in vitro synthesis of nanomaterial. The current review aims to report the recent developments/understanding on ferritin structure (self-assembly, surface/pores electrostatics, metal ion binding sites) and chemistry occurring inside these supramolecular protein cages (protein mediated metal ion uptake and mineralization/nanoparticle formation) along with its surface modification to exploit them for various nanobiotechnological applications. Furthermore, a better understanding of ferritin self-assembly would be highly useful for optimizing the incorporation of nanomaterials via the disassembly/reassembly approach. Several studies have reported the successful engineering of these ferritin protein nanocages in order to utilize them as potential nanoreactor for synthesizing/incorporating nanoparticles and as nanocarrier for delivering imaging agents/drugs at cell specific target sites. Therefore, the combination of nanoscience (nanomaterials) and bioscience (ferritin protein) projects several benefits for various applications ranging from electronics to medicine.

Au3+ -Functionalized UiO-67 Metal-Organic Framework Nanoparticles: O2•- and •OH Generating Nanozymes and Their Antibacterial Functions

The synthesis and characterization of Au³⁺ -modified UiO-67 metal-organic framework nanoparticles, Au³⁺ -NMOFs, are described. The Au³⁺ -NMOFs reveal dual oxidase-like and peroxidase-like activities and act as an active catalyst for the catalyzed generation of O₂^•- under aerobic conditions or •OH in the presence of H₂ O₂ . The two reactive oxygen species (ROS) agents O₂^•- and •OH are cooperatively formed by Au³⁺ -NMOFs under aerobic conditions, and in the presence of H₂ O_2. The Au³⁺ -NMOFs are applied as an effective catalyst for the generation ROS agents for antibacterial and wound healing applications. Effective antibacterial cell death and inhibition of cell proliferation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacterial colonies are demonstrated in the presence of the Au³⁺ -NMOFs. In addition, in vivo experiments demonstrate effective wound healing of mice wounds infected by S. aureus, treated by the Au³⁺ -NMOFs.

Amelioration of systemic antitumor immune responses in cocktail therapy by immunomodulatory nanozymes

Nanozymes that mimic natural enzyme-like activities have gradually emerged in cancer therapy. To overcome the bottlenecks of single-mode nanozymes, including "off-target" toxicity and ineffectiveness toward metastatic cancers, we designed magnetic nanoparticle-based multifunctional visualized immunomodulatory nanozymes. Besides the partial initiation of the prime immune response by intrinsic immunogenicity, as a smart drug delivery system with a temperature- and pH-sensitive dual response to the tumor microenvironment, these nanozymes released immune agonists to boost enhanced systemic immune response, eventually ameliorating the cancer immune microenvironment through many aspects: activating dendritic cells, improving the function of CD8⁺ T cells, and decreasing the population of myeloid-derived suppressor cells, which inhibited both primary and metastatic cancers. Mechanistically, these nanozymes regulated the reactive oxygen species-related Akt signaling pathway and consequently activated cell apoptosis-related signaling pathways, which provided a deeper understanding of the synergistic mechanism of multifunctional nanozymes. Our findings offer a promising imaging-guided cocktail therapy strategy through immunomodulatory nanozymes.

Magnetic Nanostructures: Rational Design and Fabrication Strategies toward Diverse Applications

In recent years, the continuous development of magnetic nanostructures (MNSs) has tremendously promoted both fundamental scientific research and technological applications. Different from the bulk magnet, the systematic engineering on MNSs has brought a great breakthrough in some emerging fields such as the construction of MNSs, the magnetism exploration of multidimensional MNSs, and their potential translational applications. In this review, we give a detailed description of the synthetic strategies of MNSs based on the fundamental features and application potential of MNSs and discuss the recent progress of MNSs in the fields of nanomedicines, advanced nanobiotechnology, catalysis, and electromagnetic wave adsorption (EMWA), aiming to provide guidance for fabrication strategies of MNSs toward diverse applications.

Ferritin: A Multifunctional Nanoplatform for Biological Detection, Imaging Diagnosis, and Drug Delivery

Ferritins are spherical iron storage proteins within cells that are composed of a combination of 24 subunits of two types, heavy-chain ferritin (HFn) and light-chain ferritin (LFn). They autoassemble naturally into a spherical hollow nanocage with an outer diameter of 12 nm and an interior cavity that is 8 nm in diameter. In recent years, with the constantly emerging safety issues and the concerns about unfavorable uniformity and indefinite in vivo behavior of traditional nanomedicines, the characteristics of native ferritin nanocages, such as the unique nanocage structure, excellent safety profile, and definite in vivo behavior, make ferritin-based formulations uniquely attractive for nanomedicine development. To date, a variety of cargo molecules, including therapeutic drugs (e.g., cisplatin, carboplatin, paclitaxel, curcumin, atropine, quercetin, gefitinib, daunomycin, epirubicin, doxorubicin, etc.), imaging agents (e.g., fluorescence dyes, radioisotopes, and MRI contrast agents), nucleic acids (e.g., siRNA and miRNA), and metal nanoparticles (e.g., Fe₃O₄, CeO₂, AuPd, CuS, CoPt, FeCo, Ag, etc.) have been loaded into the interior cavity of ferritin nanocages for a broad range of biomedical applications from in vitro biosensing to targeted delivery of cargo molecules in living systems with the aid of modified targeting ligands either genetically or chemically. We reported that human HFn could selectively deliver a large amount of cargo into tumors in vivo via transferrin receptor 1 (TfR1)-mediated tumor-cell-specific targeting followed by rapid internalization. By the use of the intrinsic tumor-targeting property and unique nanocage structure of human HFn, a broad variety of cargo-loaded HFn formulations have been developed for biological analysis, imaging diagnosis, and medicine development. In view of the intrinsic tumor-targeting property, unique nanocage structure, lack of immunogenicity, and definite in vivo behavior, human HFn holds promise to promote therapeutic drugs, diagnostic imaging agents, and targeting moieties into multifunctional nanomedicines.Since the report of the intrinsic tumor-targeting property of human HFn, we have extensively explored human HFn as an ideal nanocarrier for tumor-targeted delivery of anticancer drugs, MRI contrast agents, inorganic nanoparticles, and radioisotopes. In particular, by the use of genetic tools, we also have genetically engineered human HFn nanocages to recognize a broader range of disease biomarkers. In this Account, we systematically review human ferritins from characterizing their tumor-binding property and understanding their mechanism and kinetics for cargo loading to exploring their biomedical applications. We finally discuss the prospect of ferritin-based formulations to become next-generation nanomedicines. We expect that ferritin formulations with unique physicochemical characteristics and intrinsic tumor-targeting property will attract broad interest in fundamental drug research and offer new opportunities for nanomedicine development.

Aptamer-Modified Cu2+-Functionalized C-Dots: Versatile Means to Improve Nanozyme Activities-"Aptananozymes"

The covalent linkage of aptamer binding sites to nanoparticle nanozymes is introduced as a versatile method to improve the catalytic activity of nanozymes by concentrating the reaction substrates at the catalytic nanozyme core, thereby emulating the binding and catalytic active-site functions of native enzymes. The concept is exemplified with the synthesis of Cu²⁺ ion-functionalized carbon dots (C-dots), modified with the dopamine binding aptamer (DBA) or the tyrosinamide binding aptamer (TBA), for the catalyzed oxidation of dopamine to aminochrome by H₂O₂ or the oxygenation of l-tyrosinamide to the catechol product, which is subsequently oxidized to amidodopachrome, in the presence of H₂O₂/ascorbate mixture. Sets of structurally functionalized DBA-modified Cu²⁺ ion-functionalized C-dots or sets of structurally functionalized TBA-modified Cu²⁺ ion-functionalized C-dots are introduced as nanozymes of superior catalytic activities (aptananozymes) toward the oxidation of dopamine or the oxygenation of l-tyrosinamide, respectively. The aptananozymes reveal enhanced catalytic activities as compared to the separated catalyst and respective aptamer constituents. The catalytic functions of the aptananozymes are controlled by the structure of the aptamer units linked to the Cu²⁺ ion-functionalized C-dots. In addition, the aptananozyme shows chiroselective catalytic functions demonstrated by the chiroselective-catalyzed oxidation of l/d-DOPA to l/d-dopachrome. Binding studies of the substrates to the different aptananozymes and mechanistic studies associated with the catalytic transformations are discussed.

Peroxidase Mimetic Nanozymes in Cancer Phototherapy: Progress and Perspectives

Nanomaterial-mediated cancer therapeutics is a fast developing field and has been utilized in potential clinical applications. However, most effective therapies, such as photodynamic therapy (PDT) and radio therapy (RT), are strongly oxygen-dependent, which hinders their practical applications. Later on, several strategies were developed to overcome tumor hypoxia, such as oxygen carrier nanomaterials and oxygen generated nanomaterials. Among these, oxygen species generation on nanozymes, especially catalase (CAT) mimetic nanozymes, convert endogenous hydrogen peroxide (H2O2) to oxygen (O2) and peroxidase (POD) mimetic nanozymes converts endogenous H2O2 to water (H2O) and reactive oxygen species (ROS) in a hypoxic tumor microenvironment is a fascinating approach. The present review provides a detailed examination of past, present and future perspectives of POD mimetic nanozymes for effective oxygen-dependent cancer phototherapeutics.

Single-atom nanozymes for biological applications

Nanozymes have been widely used as highly active and stable arterial enzymes due to their controllable electronic transfer and unique catalytic reaction route. However, the development of nanozymes is hindered by their ambiguous structure, insufficient activity and inadequate substrate selectivity. In comparison, single-atom nanozymes (SAzymes) hold superior catalytic activity 10-100 times higher than conventional nanozymes by maximizing the utilization of metal atom dispersion, and exhibit versatile catalytic selectivity through precisely adjusting the atom spatial configuration. In this review, we highlight several well-defined SAzymes, and discuss their accurate atom configuration, catalytic mechanisms, enzyme-like activity, and applications in cancer treatment, brain disease, and wound healing. It is of great significance to understand the advantages and properties of SAzymes for further medical development.

Iron-Based Nanozymes in Disease Diagnosis and Treatment

Iron-based nanozymes are currently one of the few clinical inorganic nanoparticles for disease diagnosis and treatment. Overcoming the shortcomings of natural enzymes, such as easy inactivation and low yield, combined with their special nanometer properties and magnetic functions, iron-based nanozymes have broad prospects in biomedicine. This minireview summarizes their preparation, biological activity, catalytic mechanism, and applications in diagnosis and treatment of diseases. Finally, challenges to their future development and the trends of iron-based nanozymes are discussed. The purpose of this minireview is to better understand and reasonably speculate on the rational design of iron-based nanozymes as an increasingly important new paradigm for diagnostics.

Synthesis of niobium substituted cobalt-nickel nano-ferrite (Co0.5Ni0.5NbxFe2-xO4 (x ≤ 0.1) by hydrothermal approach show strong anti-colon cancer activities

The combination of two or more nanoparticles found to be effective strategy to synthesize nanocomposites for better drug delivery and treatment. In the present study, we have combined cobalt (Co), nickel (Ni), niobium (Nb), and iron oxide (Fe₂O₄) and prepared niobium substituted cobalt-nickel nano-ferrite nanocomposites (Co_0.5Ni_0.5Nb_xFe_2-xO₄ (x ≤ 0.1) by using hydrothermal approach. We have characterized the structure and morphology of nanocomposites by using XRD, EDX, TEM and SEM methodologies. We have examined the impact of nanocomposites (Co_0.5Ni_0.5Nb_xFe_2-xO₄ (x ≤ 0.1) on cancerous cells (human colorectal carcinoma cells, HCT-116) by using MTT assay. We have also checked the impact of nanocomposites on normal and non-cancerous cells (human embryonic kidney cells, HEK-293) to confirm the specificity of their actions. Post- 48 h treatment of Co_0.5Ni_0.5Nb_xFe_2-xO₄ (x ≤ 0.1) led to dose-dependent inhibition of cancer cells growth and proliferation. However, no cytotoxic effect was observed on the normal cells (HEK-293). In addition, DAPI stained nuclear DNA staining analysis demonstrates that the Co_0.5Ni_0.5Nb_xFe_2-xO₄ (x ≤ 0.1) treatment also caused nuclear DNA disintegration which is the marker for programmed cell death. These results demonstrate that synthesized nanocomposites Co_0.5Ni_0.5Nb_xFe_2-xO₄ (x ≤ 0.1) selectively target the colon cancer cells and induce cancer cell death.Communicated by Ramaswamy H. Sarma.

Nanozymes: A New Disease Imaging Strategy

Nanozymes are nanomaterials with intrinsic enzyme-like properties. They can specifically catalyze substrates of natural enzymes under physiological condition with similar catalytic mechanism and kinetics. Compared to natural enzymes, nanozymes exhibit the unique advantages including high catalytic activity, low cost, high stability, easy mass production, and tunable activity. In addition, as a new type of artificial enzymes, nanozymes not only have the enzyme-like catalytic activity, but also exhibit the unique physicochemical properties of nanomaterials, such as photothermal properties, superparamagnetism, and fluorescence, etc. By combining the unique physicochemical properties and enzyme-like catalytic activities, nanozymes have been widely developed for in vitro detection and in vivo disease monitoring and treatment. Here we mainly summarized the applications of nanozymes for disease imaging and detection to explore their potential application in disease diagnosis and precision medicine.

Ferritins as natural and artificial nanozymes for theranostics

Nanozymes are a class of nanomaterials with intrinsic enzyme-like characteristics which overcome the limitations of natural enzymes such as high cost, low stability and difficulty to large scale preparation. Nanozymes combine the advantages of chemical catalysts and natural enzymes together, and have exhibited great potential in biomedical applications. However, the size controllable synthesis and targeting modifications of nanozymes are still challenging. Here, we introduce ferritin nanozymes to solve these problems. Ferritins are natural nanozymes which exhibit intrinsic enzyme-like activities (e.g. ferroxidase, peroxidase). In addition, by biomimetically synthesizing nanozymes inside the ferritin protein shells, artificial ferritin nanozymes are introduced, which possess the advantages of versatile self-assembly ferritin nanocage and enzymatic activity of nanozymes. Ferritin nanozymes provide a new horizon for the development of nanozyme in disease targeted theranostics research. The emergence of ferritin nanozyme also inspires us to learn from the natural nanostructures to optimize or rationally design nanozymes. In this review, the intrinsic enzyme-like activities of ferritin and bioengineered synthesis of ferritin nanozyme were summarized. After that, the applications of ferritin nanozymes were covered. Finally, the advantages, challenges and future research directions of advanced ferritin nanozymes for biomedical research were discussed.

Thermostable iron oxide nanoparticle synthesis within recombinant ferritins from the hyperthermophile Pyrococcus yayanosii CH1

Thermostable nanoparticles have numerous applications in catalysis and in the oil/gas industry. However, synthesizing these nanoparticles requires expensive polymers. Here, a novel thermostable ferritin named PcFn, originally from the hyperthermophilic archaeon Pyrococcus yayanosii CH1, was overexpressed in Escherichia coli, purified and characterized, which could successfully direct the synthesis of thermostable magnetoferritins (M-PcFn) with monodispersed iron oxide nanoparticles in one step. Transmission electron microscopy and magnetic measurements show that the cores of the M-PcFn have an average diameter of 4.7 nm, are well-crystalline and superparamagnetic. Both the PcFn and M-PcFn can resist temperatures up to 110 °C, which is significantly higher than for human H-chain ferritin (HFn) and M-HFn, and comparable to temperatures previously reported for Pyrococcus furiosus ferritin (PfFn) and M-PfFn. After heating at 110 °C for 30 minutes, PcFn and M-PcFn maintained their secondary structures and PcFn retained 87.4% of its iron uptake activity. This remarkable thermostability of PcFn and M-PcFn suggests potential applications in elevated temperature environments.

Ferritin nanocage-based antigen delivery nanoplatforms: epitope engineering for peptide vaccine design

Biomedical applications and nanotechnological advances, including constrained synthesis, multimodal imaging, drug delivery, and bioassay, have strongly benefited from employing ferritin nanocages due to their remarkable properties of easy engineering, great biocompatible features, large capacity and so on. In this study, ferritin nanocages were used to display epitopes (model antigens derived from Enterovirus 71 (EV71) with different length) on C- and N-terminals and the loop zone to search for the optimal position for the fusion of the epitopes to the vaccine platform. The longest epitope displayed on the N-terminal and loop zone as well as the second longest peptide displayed on the loop zone of ferritin resulted in 100% passive protection of newborn BALB/c mice from the lethal EV71. This suggests that peptides fused onto the loop zone of ferritin could induce strong immune response. Our results increase the versatility of the vaccine platform and provide more options for the production of stable constructs, suggesting the potential future clinical applicability of ferritin-based antigen delivery nanoplatforms.

Magnetoferritin: Process, Prospects, and Their Biomedical Applications

Ferritin is a spherical iron storage protein composed of 24 subunits and an iron core. Using biomimetic mineralization, magnetic iron oxide can be synthesized in the cavity of ferritin to form magnetoferritin (MFt). MFt, also known as a superparamagnetic protein, is a novel magnetic nanomaterial with good biocompatibility and flexibility for biomedical applications. Recently, it has been demonstrated that MFt had tumor targetability and a peroxidase-like catalytic activity. Thus, MFt, with its many unique properties, provides a powerful platform for tumor diagnosis and therapy. In this review, we discuss the biomimetic synthesis and biomedical applications of MFt.

Colorimetric determination of lead(II) or mercury(II) based on target induced switching of the enzyme-like activity of metallothionein-stabilized copper nanoclusters

It is shown that metallothionein-stabilized copper nanoclusters (MT-CuNCs) display catalase-like activity. In the presence of either lead(II) or mercury(II), the catalase-like activity is converted to a peroxidase-like activity. On addition of Pb(II) or Hg(II), the inhibitory effect of MT-CuNCs on the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) with H₂O₂ is weakened. On the other hand, the catalytic effect of the nanoclusters on the chromogenic reaction is increased. The system MT-CuNCs-Pb(II)/Hg(II) exhibits high affinity for the substrates TMB and H₂O₂. Their catalytic behavior follows Michaelis-Menten kinetics. Based on these findings, a method was developed for visual detection (via the blue coloration formed) and spectrophotometric determination (at 450 nm) of Pb(II) and Hg(II). The linear range for Pb(II) extends from 0.7 to 96 μM, and the linear ranges for Hg(II) from 97 nM to 2.3 μM and from 3.1 μM to 15.6 μM. The detection limits are 142 nM for Pb(II) and 43.8 nM for Hg(II). Graphical abstract Metallothionein-stabilized copper nanoclusters (MT-CuNCs) display catalase-like activity. On addition of Pb(II) or Hg(II), the catalase-like activity is converted to a peroxidase-like activity. The latter catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H₂O₂.

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.

Positive magnetic resonance angiography using ultrafine ferritin-based iron oxide nanoparticles

Iron oxide nanoparticles with good biocompatibility can serve as safe magnetic resonance imaging contrast agents. Herein, we report that ultrafine ferritin-based iron oxide (hematite/maghemite) nanoparticles synthesized by controlled biomimetic mineralization using genetically recombinant human H chain ferritin can be used as a positive contrast agent in magnetic resonance angiography. The synthesized magnetoferritin with an averaged core size of 2.2 ± 0.7 nm (hereafter named M-HFn-2.2) shows a r1 value of 0.86 mM-1 s-1 and a r2/r1 ratio of 25.1 at a 7 T magnetic field. Blood pool imaging on mice using the M-HFn-2.2 nanoparticles that were injected through a tail vein by single injection at a dose of 0.54 mM Fe per kg mouse body weight enabled detecting detailed vascular nets at 3 minutes post-injection; the MR signal intensity continuously enhanced up to 2 hours post-injection, which is much longer than that of the commercial magnevist (Gd-DTPA) contrast. Moreover, biodistribution examination indicates that organs such as liver, spleen and kidney safely cleared the injected nanoparticles within one day after the injection, demonstrating no risk of iron overload in test mice. Therefore, this study sheds light on developing high-performance gadolinium free positive magnetic resonance contrast agents for biomedical applications.

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.

Magnetization of active inclusion bodies: comparison with centrifugation in repetitive biotransformations

Background

Physiological aggregation of a recombinant enzyme into enzymatically active inclusion bodies could be an excellent strategy to obtain immobilized enzymes for industrial biotransformation processes. However, it is not convenient to recycle “gelatinous masses” of protein inclusion bodies from one reaction cycle to another, as high centrifugation forces are needed in large volumes. The magnetization of inclusion bodies is a smart solution for large-scale applications, enabling an easier separation process using a magnetic field.

Results

Magnetically modified inclusion bodies of UDP–glucose pyrophosphorylase were recycled 50 times, in comparison, inclusion bodies of the same enzyme were inactivated during ten reaction cycles if they were recycled by centrifugation. Inclusion bodies of sialic acid aldolase also showed good performance and operational stability after the magnetization procedure.

Conclusions

It is demonstrated here that inclusion bodies can be easily magnetically modified by magnetic iron oxide particles prepared by microwave-assisted synthesis from ferrous sulphate. The magnetic particles stabilize the repetitive use of the inclusion bodies .

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0987-7) contains supplementary material, which is available to authorized users.