ATP-mediated intrinsic peroxidase-like activity of Fe3O4-based nanozyme: One step detection of blood glucose at physiological pH

Dual Enzyme-Like Performances of PLGA Grafted Maghemite Nanocrystals and Their Synergistic Chemo/Chemodynamic Treatment for Human Lung Adenocarcinoma A549 Cells

In recent years, the emergence of non-toxic but catalytically active inorganic nanoparticles has attracted great attention for cancer treatment, but the therapeutic effect has been affected by the limited reactive oxygen species in tumors. Therefore, the combination of chemotherapy and chemodynamic therapy is regarded as a promising therapeutic strategy. In this paper, we reported the preparation and bioactivity evaluation of poly(lactic acid-co-glycolic acid) (PLGA) grafted-γ-Fe₂O₃ nanoparticles with dual response of endogenous peroxidase and catalase like activities. Our hypothesis is that PLGAgrafted γ-Fe₂O₃ nanoparticles could be used as a drug delivery system for the anti-tumor drug doxorubicin to inhibit the growth of lung adenocarcinoma A549 cells; meanwhile, based on its mimic enzyme properties, this kind of nanoparticles could be combined with doxorubicin in the treatment of A549 cells. Our experimental results showed that the PLGAgrafted γ-Fe₂O₃ nanoparticles could simulate the activity of catalase and decompose hydrogen peroxide into H₂O and oxygen in neutral tumor microenvironment, thus reducing the oxidative damage caused by hydrogenperoxide to lung adenocarcinoma A549 cells. In acidic microenvironment, PLGA grafted γ-Fe₂O₃ nanoparticles could simulate the activity of peroxidase and effectively catalyze the decomposition of hydrogen peroxide to generate highly toxic hydroxyl radicals, which could cause the death of A549 cells. Furthermore, the synergistic effect of peroxidase-like activity of PLGA-grafted γ-Fe₂O₃ nanoparticles and doxorubicin could accelerate the apoptosisand destruction of A549 cells, thus enhancing the antitumor effect of doxorubicin-loaded PLGA-grafted γ-Fe₂O₃ nanoparticles. Therefore, this study provides an effective nanoplatform based on dual inorganic biomimetic nanozymes for the treatment of lung cancer.

The electrochemical immunosensor of the "signal on" strategy that activates MMoO4 (M = Co, Ni) peroxidase with Cu2+ to achieve ultrasensitive detection of CEA

A new type of ultrasensitive electrochemical immunosensor with "signal on" strategy was designed for quantitative detection of CEA. The sensing strategy design is based on the following principles: We use HMSNs-Cu²⁺@HA as the signal probe, the structure of HA is destroyed under acidic conditions, and the released Cu²⁺ activates the substrate material MMoO₄ (M = Co, Ni) Peroxidase activity initiates the reaction of catalytic H₂O₂ and realizes the "signal on" condition of electrical signals. This strategy has the following advantages: (1) HA coating of HMSNs-Cu²⁺ can prevent Cu²⁺ leakage, has good biocompatibility and can be connected with more antibodies. (2) The prepared sensor has the characteristics of high sensitivity and a low detection limit. When the electrode substrate was CoMoO₄, the detection range of the immunosensor was 0.01 pg/mL-40 ng/mL, and the detection limit was 0.0035 pg/mL (S/N = 3). This work innovatively applies the catalytic activity of metal ion-activated nanozymes in the detection of CEA, providing a new perspective for the monitoring and analysis of cancer markers.

L-Cysteine as an Irreversible Inhibitor of the Peroxidase-Mimic Catalytic Activity of 2-Dimensional Ni-Based Nanozymes

The ability to modulate the catalytic activity of inorganic nanozymes is of high interest. In particular, understanding the interactions of inhibitor molecules with nanozymes can bring them one step closer to the natural enzymes and has thus started to attract intense interest. To date, a few reversible inhibitors of the nanozyme activity have been reported. However, there are no reports of irreversible inhibitor molecules that can permanently inhibit the activity of nanozymes. In the current work, we show the ability of L-cysteine to act as an irreversible inhibitor to permanently block the nanozyme activity of 2-dimensional (2D) NiO nanosheets. Determination of the steady state kinetic parameters allowed us to obtain mechanistic insights into the catalytic inhibition process. Further, based on the irreversible catalytic inhibition capability of L-cysteine, we demonstrate a highly specific sensor for the detection of this biologically important molecule.

Polyoxometalate-Mediated Vacancy-Engineered Cerium Oxide Nanoparticles Exhibiting Controlled Biological Enzyme-Mimicking Activities

The biological enzyme-mimetic activity of cerium oxide nanoparticles (CeNPs) is well known to scavenge the reactive oxygen and nitrogen species in cell culture and animal models, imparting protection from the deleterious effects of oxidative and nitrosative stress. The superoxide dismutase (SOD)- and catalase-mimicking activity of CeNPs is reported to be controlled by the oxidation state of the surface "Ce" ions, where a high ratio of Ce^3+/4+ or Ce^4+/3+ has been considered for the displayed SOD and catalase-like activity, respectively. However, the redox behavior of CeNPs can be controlled by certain ligands that could offer changes in their enzyme-mimetic properties. Therefore, in this work, we have studied the enzyme-mimetic activities of CeNPs under the influence of polyoxometalates [phosphomolybdic acid (PMA) and phosphotungstic acid (PTA)], which are electron-dense molecules displaying quick and reversible multielectron redox reactions. Results revealed that the interaction of PMA with CeNPs results in the inhibition of the SOD-like activity; however, it has no impact on the catalase-like activity. Contrary to this, the interaction of PTA with CeNPs improved the SOD as well as catalase-like activities of CeNPs (3+), which generally do not exhibit catalase activity in the bare form. Although CeNPs (3+) did not show any peroxidase-like activity, CeNPs (4+) showed excellent activity, which was enhanced after the interaction with polyoxometalates. Further, the autoregeneration ability of CeNPs was found to be intact even after PTA or PMA interaction; however, the full catalytic activity was observed in the case of PTA but partially with PMA.

Magnetic nanocatalysts as multifunctional platforms in cancer therapy through the synthesis of anticancer drugs and facilitated Fenton reaction

Background

Heterocyclic compounds have always been used as a core portion in the development of anticancer drugs. However, there is a pressing need for developing inexpensive and simple alternatives to high-cost and complex chemical agents-based catalysts for large-scale production of heterocyclic compounds. Also, development of some smart platforms for cancer treatment based on nanoparticles (NPs) which facilitate Fenton reaction have been widely explored by different scientists. Magnetic NPs not only can serve as catalysts in the synthesis of heterocyclic compounds with potential anticancer properties, but also are widely used as smart agents in targeting cancer cells and inducing Fenton reactions.

Aim of Review

Therefore, in this review we aim to present an updated summary of the reports related to the main clinical or basic application and research progress of magnetic NPs in cancer as well as their application in the synthesis of heterocyclic compounds as potential anticancer drugs. Afterwards, specific tumor microenvironment (TME)-responsive magnetic nanocatalysts for cancer treatment through triggering Fenton-like reactions were surveyed. Finally, some ignored factors in the design of magnetic nanocatalysts- triggered Fenton-like reaction, challenges and future perspective of magnetic nanocatalysts-assisted synthesis of heterocyclic compounds and selective cancer therapy were discussed.Key Scientific Concepts of Review:This review may pave the way for well-organized translation of magnetic nanocatalysts in cancer therapy from the bench to the bedside.

Chemical design of nanozymes for biomedical applications

With the advancement of nanochemistry, artificial nanozymes with high catalytic stability, low manufacturing and storage cost, and greater design flexibility over natural enzymes, have emerged as a next-generation nanomedicine. The catalytic activity and selectivity of nanozymes can be readily controlled and optimized by the rational chemical design of nanomaterials. This review summarizes the various chemical approaches to regulate the catalytic activity and selectivity of nanozymes for biomedical applications. We focus on the in-depth correlation between the physicochemical characteristics and catalytic activities of nanozymes from several aspects, including regulating chemical composition, controlling morphology, altering the size, surface modification and self-assembly. Furthermore, the chemically designed nanozymes for various biomedical applications such as biosensing, infectious disease therapy, cancer therapy, neurodegenerative disease therapy and injury therapy, are briefly summarized. Finally, the current challenges and future perspectives of nanozymes are discussed from a chemistry point of view. STATEMENT OF SIGNIFICANCE: As a kind of nanomaterials that performs enzyme-like properties, nanozymes perform high catalytic stability, low manufacturing and storage cost, attracting the attention of researchers from various fields. Notably, chemically designed nanozymes with robust catalytic activity, tunable specificity and multi-functionalities are promising for biomedical applications. It's crucial to define the correlation between the physicochemical characteristics and catalytic activities of nanozymes. To help readers understand this rapidly expanding field, in this review, we summarize various chemical approaches that regulate the catalytic activity and selectivity of nanozymes together with the discussion of related mechanisms, followed by the introduction of diverse biomedical applications using these chemically well-designed nanozymes. Hopefully our review will bridge the chemical design and biomedical applications of nanozymes, supporting the extensive research on high-performance nanozymes.

Microwave assisted polyol process for time-saving synthesis of superparamagnetic nanoparticles and application in artificial mimic enzyme

A microwave assisted polyol process accomplished within 10 min was developed for synthesis of superparamagnetic Fe3O4 nanoparticles (MNPs) with well controlled size between 2 and 6 nm. Effects of reaction time and temperature on the size of the MNPs were investigated through transmission electronic microscope, x-ray diffraction pattern, thermogravimetic and magnetic analysis. The results indicates that longer reaction time or higher temperature lead to formation of MNPs with larger size. As a proof-of-concept, the MNPs were utilized as peroxidase and their activity was also investigated. Oxidation of typical substrate, 3, 3’, 5, 5’ -tetramethylbenzidine, can be proceeded by using the MNPs as artificial mimic enzyme. The MNPs display the maximal catalyzed activity under the optimum condition as pH = 3.5, 40 °C and concentration of TMB and H2O2 with 120 and 110 mmol·l−1, respectively. This work provides a new way for fast synthesis of MNPs, which are of potential application in artificial mimic enzyme.

Incorporation of a Biocompatible Nanozyme in Cellular Antioxidant Enzyme Cascade Reverses Huntington's Like Disorder in Preclinical Model

The potentiality of nano-enzymes in therapeutic use has directed contemporary research to develop a substitute for natural enzymes, which are suffering from several disadvantages including low stability, high cost, and difficulty in storage. However, inherent toxicity, inefficiency in the physiological milieu, and incompatibility to function in cellular enzyme networks limit the therapeutic use of nanozymes in living systems. Here, it is shown that citrate functionalized manganese-based biocompatible nanoscale material (C-Mn₃ O₄ NP) efficiently mimics glutathione peroxidase (GPx) enzyme in the physiological milieu and easily incorporates into the cellular multienzyme cascade for H₂ O₂ scavenging. A detailed computational study reveals the mechanism of the nanozyme action. The in vivo therapeutic efficacy of C-Mn₃ O₄ nanozyme is further established in a preclinical animal model of Huntington's disease (HD), a prevalent progressive neurodegenerative disorder, which has no effective medication to date. Management of HD in preclinical animal trial using a biocompatible (non-toxic) nanozyme as a part of the metabolic network may uncover a new paradigm in nanozyme based therapeutic strategy.

Rational Design and Biological Application of Antioxidant Nanozymes

Nanozyme is a type of nanostructured material with intrinsic enzyme mimicking activity, which has been increasingly studied in the biological field. Compared with natural enzymes, nanozymes have many advantages, such as higher stability, higher design flexibility, and more economical production costs. Nanozymes can be used to mimic natural antioxidant enzymes to treat diseases caused by oxidative stress through reasonable design and modification. Oxidative stress is caused by imbalances in the production and elimination of reactive oxygen species (ROS) and reactive nitrogen species (RNS). This continuous oxidative stress can cause damage to some biomolecules and significant destruction to cell structure and function, leading to many physiological diseases. In this paper, the methods to improve the antioxidant properties of nanozymes were reviewed, and the applications of nanozyme antioxidant in the fields of anti-aging, cell protection, anti-inflammation, wound repair, cancer, traumatic brain injury, and nervous system diseases were introduced. Finally, the future challenges and prospects of nanozyme as an ideal antioxidant were discussed.

A long-term stable paper-based glucose sensor using a glucose oxidase-loaded, Mn2BPMP-conjugated nanocarrier with a smartphone readout

A simple paper-based analytical device (PAD) for the one-pot detection of glucose was developed herein using an artificial peroxidase-functionalized and glucose oxidase (GOx)-loaded pluronic-based nanocarrier (PNC). Mn₂BPMP (BPMP; 2,6-bis[(bis(2-pyridylmethyl)amino)-methyl]-4-methylphenolate), an artificial peroxidase, was conjugated to PNC, allowing GOx to be loaded with a very high encapsulation efficiency. In solution, Mn₂BPMP-PNC showed higher peroxidase-like catalytic efficiency than did Mn₂BPMP at physiological pH. In addition, glucose detection via enzyme cascade reaction between GOx and Mn₂BPMP in the GOx loaded-Mn₂BPMP-PNC was more sensitive than the simple combination of Mn₂BPMP and GOx with excellent selectivity. Subsequently, a PAD was fabricated using a laser printer with an assay substance containing GOx loaded-Mn₂BPMP-PNC and peroxidase chromogenic substrate. The prepared Mn₂BPMP-PNC-based PAD quantitatively measured glucose in human serum ranging from normal levels to those typical for diabetics as well as in buffer by obtaining RGB (red, green, and blue) color values through smartphone readout or the naked eye. Importantly, the present PNC-based PAD maintained the detection efficiency during storage at room temperature for 6 weeks in contrast to the rapid decrease in detection efficiency obtained for PAD containing Mn₂BPMP and GOx without PNC.

Iron Oxide Nanoparticles Combined with Cytosine Arabinoside Show Anti-Leukemia Stem Cell Effects on Acute Myeloid Leukemia by Regulating Reactive Oxygen Species

BACKGROUND AND AIM

Acute myeloid leukemia (AML), initiated and maintained by leukemia stem cells (LSCs), is often relapsed or refractory to therapy. The present study aimed at assessing the effects of nanozyme-like Fe3O4 nanoparticles (IONPs) combined with cytosine arabinoside (Ara-C) on LSCs in vitro and in vivo.

METHODS

The CD34+CD38-LSCs, isolated from human AML cell line KG1a by a magnetic activated cell sorting method, were treated with Ara-C, IONPs, and Ara-C+ IONPs respectively in vitro. The cellular proliferation, apoptosis, reactive oxygen species (ROS), and the related molecular expression levels in LSCs were analyzed using flow cytometry, RT-qPCR, and Western blot. The nonobese diabetic/severe combined immune deficiency mice were transplanted with LSCs or non-LSCs via tail vein, and then the mice were treated with Ara-C, IONPs and IONPs plus Ara-C, respectively. The therapeutic effects on the AML bearing mice were further evaluated.

RESULTS

LSCs indicated stronger cellular proliferation, more clone formation, and more robust resistance to Ara-C than non-LSCs. Compared with LSCs treated with Ara-C alone, LSCs treated with IONPs plus Ara-C showed a significant increase in apoptosis and ROS levels that might be regulated by nanozyme-like IONPs via improving the expression of pro-oxidation molecule gp91-phox but decreasing the expression of antioxidation molecule superoxide dismutase 1. The in vivo results suggested that, compared with the AML bearing mice treated with Ara-C alone, the mice treated with IONPs plus Ara-C markedly reduced the abnormal leukocyte numbers in peripheral blood and bone marrow and significantly extended the survival of AML bearing mice.

CONCLUSION

IONPs combined with Ara-C showed the effectiveness on reducing AML burden in the mice engrafted with LSCs and extending mouse survival by increasing LSC's ROS level to induce LSC apoptosis. Our findings suggest that targeting LSCs could control the AML relapse by using IONPs plus Ara-C.

Nanozyme's catching up: activity, specificity, reaction conditions and reaction types

Nanozymes aim to mimic enzyme activities. In addition to catalytic activity, nanozymes also need to have specificity and catalyze biologically relevant reactions under physiological conditions to fit in the definition of enzyme and to set nanozymes apart from typical inorganic catalysts. Previous discussions in the nanozyme field mainly focused on the types of reactions or certain analytical, biomedical or environmental applications. In this article, we discuss efforts made to mimic enzymes. First, the catalytic cycles are compared, where a key difference is specific substrate binding by enzymes versus non-specific substrate adsorption by nanozymes. We then reviewed efforts to engineer and surface-modify nanomaterials to accelerate reaction rates, strategies to graft affinity ligands and molecularly imprinted polymers to achieve specific catalysis, and methods to bring nanozyme reactions to neutral pH and ambient temperature. Most of the current nanozyme reactions used a few model chromogenic substrates of no biological relevance. Therefore, we also reviewed efforts to catalyze the conversion of biomolecules and biopolymers using nanozymes. By the efforts to close the gaps between nanozymes and enzymes, we believe nanozymes are catching up rapidly. Still, challenges exist in materials design to further improve nanozymes as true enzyme mimics and achieve impactful applications.

Facile one-pot synthesis of Mn3O4 nanorods and their analytical application

One-pot synthesis of Mn3O4 nanorods in aqueous solution at room temperature without using templates and surfactants was achieved for the first time, opening a new route for preparing various metal nanorods for detecting H2O2-related targets.

Perspectives for Single-Atom Nanozymes: Advanced Synthesis, Functional Mechanisms, and Biomedical Applications

Single-atom nanozymes (SANs) are one of the newest generations of nanozymes, which have been greatly developed in the past few years and exploited widely for many applications, such as biosensing, disease diagnosis and therapy, bioimaging, and so on. SANs, possessing dispersed single-atom structures and a well-defined coordination environment, exhibit remarkable catalytic performance with both high activity and stability. In this paper, the most recent progress in SANs is reviewed in terms of their advanced synthesis, characterization, functional mechanisms, performance validation/optimization, and biomedical applications. Several technical challenges hindering practical applications of SANs are analyzed, and possible research directions are also proposed for overcoming the challenges.

Phosphotungstate-sandwiched between cerium oxide and gold nanoparticles exhibit enhanced catalytic reduction of 4-nitrophenol and peroxidase enzyme-like activity

The catalytic performance of gold (Au) decorated cerium oxide nanoparticles (nanoceria) can be potentially crucial because such a defined arrangement of multiple materials may provide improved chemical and biological catalytic activities. In this work, we have utilized a highly localized approach to reduce Au nanoparticles (AuNPs) on the nanoceria-phosphotungstate composite's surface. Phosphotungstic acid (PTA) bound on nanoceria's surface acts as a UV-light dependent redox molecule that specifically reduces AuNPs. The mechanistic study demonstrates that PTA* molecules outstanding electron transfer ability leads to an excellent improvement in the catalytic performance of nanoceria-PTA*-AuNPs composite. Nanoceria-PTA*-AuNPs showed better and faster degradation of 4-nitrophenol than either nanoceria or PTA*-AuNPs. The developed nanoceria-PTA*-AuNPs exhibited efficient (>80 % in 5 min) conversion of 4-NP into 4-AP at room temperature and neutral pH. Additionally, the nanoceria-PTA*-AuNPs also showed improved peroxidase enzyme-like activity than the corresponding control samples. The observed catalytic activity could be due to the rapid electron transfer from nanoceria to AuNPs, where the metal nanoparticle acts as an electron sink, mediated by PTA*. Nanoceria-PTA*-AuNPs showed ∼ 2-fold better catalytic oxidation of peroxidase substrate than PTA*-AuNPs. The reported nanoceria-PTA*-AuNPs nanocomposites are expected to display improved biological enzyme-like activities, photocatalysis, and other biomedical applications.

Polymer-Coated Cerium Oxide Nanoparticles as Oxidoreductase-like Catalysts

Cerium oxide nanoparticles have been shown to mimic oxidoreductase enzymes by catalyzing the decomposition of organic substrates and reactive oxygen species. This mimicry can be found in superoxide radicals and hydrogen peroxides, which are harmful molecules produced in oxidative stress-associated diseases. Despite the fact that nanoparticle functionalization is mandatory in the context of nanomedicine, the influence of polymer coatings on their enzyme-like catalytic activity is poorly understood. In this work, six polymer-coated cerium oxide nanoparticles are prepared by the association of 7.8 nm cerium oxide cores with two poly(sodium acrylate) and four poly(ethylene glycol) (PEG)-grafted copolymers with different terminal or anchoring end groups, such as phosphonic acids. The superoxide dismutase-, catalase-, peroxidase-, and oxidase-like catalytic activities of the coated nanoparticles were systematically studied. It is shown that the polymer coatings do not affect the superoxide dismutase-like, impair the catalase-like and oxidase-like, and surprisingly improves peroxidase-like catalytic activities of cerium oxide nanoparticles. It is also demonstrated that the particles coated with the PEG-grafted copolymers perform better than the poly(acrylic acid)-coated ones as oxidoreductase-like enzymes, a result that confirms the benefit of having phosphonic acids as anchoring groups at the particle surface.

Synthesis, Catalytic Properties and Application in Biosensorics of Nanozymes and Electronanocatalysts: A Review

The current review is devoted to nanozymes, i.e., nanostructured artificial enzymes which mimic the catalytic properties of natural enzymes. Use of the term "nanozyme" in the literature as indicating an enzyme is not always justified. For example, it is used inappropriately for nanomaterials bound with electrodes that possess catalytic activity only when applying an electric potential. If the enzyme-like activity of such a material is not proven in solution (without applying the potential), such a catalyst should be named an "electronanocatalyst", not a nanozyme. This paper presents a review of the classification of the nanozymes, their advantages vs. natural enzymes, and potential practical applications. Special attention is paid to nanozyme synthesis methods (hydrothermal and solvothermal, chemical reduction, sol-gel method, co-precipitation, polymerization/polycondensation, electrochemical deposition). The catalytic performance of nanozymes is characterized, a critical point of view on catalytic parameters of nanozymes described in scientific papers is presented and typical mistakes are analyzed. The central part of the review relates to characterization of nanozymes which mimic natural enzymes with analytical importance ("nanoperoxidase", "nanooxidases", "nanolaccase") and their use in the construction of electro-chemical (bio)sensors ("nanosensors").

Synthesis of cost-effective magnetic nano-biocomposites mimicking peroxidase activity for remediation of dyes

The present study describes preparation of cellulose incorporated magnetic nano-biocomposites (CNPs) by using cellulose as base material. The prepared CNPs were characterised by SEM, EDAX, TEM, XRD, and FT-IR and found to exhibit an intrinsic peroxidase-like activity with a K_m and V_max of 550 μM and 3.8 μM/ml/min, respectively. The CNPs exhibited higher pH and thermal stability compared to commercial peroxidase. These nanocomposites were able to completely remove (i) a persistent azo dye, methyl orange at a concentration of 50 ppm, within 60 min under acidic conditions (pH 3.0) and also (ii) decolourize commercial textile dye mixture under acidic conditions within 30 min. CNP-mediated degradation of dyes into simple products was further confirmed by UV-Vis and AT-IR spectroscopy The added advantage of CNPs separation after decolourization by simple magnet due to their magnetic properties and consequent reusability makes them fairy attractive system for dye remediation from environmental samples or textile industries effluents.

An ultrasensitive label-free colorimetric biosensor for the detection of glucose based on glucose oxidase-like activity of nanolayered manganese-calcium oxide

During the last years, enzyme-based biosensors have gained much more attention among the researchers and have had great success in the determination of different biological macromolecules. Nanomaterials with intrinsic enzyme-mimic activity are widely used in biomedicine as artificial enzymes. Here, we report glucose oxidase-mimic activity of nanolayered manganese-calcium (Mn-Ca) oxide nanoparticles (NL-MnCaO₂). In this work, NL-MnCaO₂nanoparticles were synthesized and characterized using different techniques including transmission electron microscopy (TEM), scanning electron microscopy (SEM), fourier-transform infrared spectroscopy (FTIR) and powder X-ray diffraction (XRD). Also, the ability of these compounds for the glucose and hydrogen peroxide (H₂O₂) determination was investigated. A non-enzymatic strategy for the colorimetric detection of glucose and H₂O₂ was reported which can be utilized not only for the rapid detection and analysis of glucose by the naked eye but also the quantitative assay of glucose by spectrophotometry. The in situ generated H₂O₂ and gluconic acid (GA) from the oxidation of glucose through the glucose oxidase-mimicking activity of NL-MnCaO₂ was detected using a colorimetric method. Also, the results confirmed the application of these compounds for the detection of glucose in human serum samples with a detection limit (LOD) of 6.12 × 10^-6 M. The results showed that NL-MnCaO₂ can be used as an alternative for the natural enzymes and act as a simple, sensitive and enzyme-free biosensor for the detection of glucose in real samples. The proposed strategy shows some advantages including sensitivity, short detection time and low detection limit.

Intrinsic peroxidase-like activity of 4-amino hippuric acid reduced/stabilized gold nanoparticles and its application in the selective determination of mercury and iron in ground water

Herein, we report a method for the synthesis of 4-aminohippuric acid (4-AHA) reduced/stabilized gold nanoparticles and their peroxidase mimicking properties for the colorimetric detection of Fe³⁺ and Hg²⁺. The synthesis of nanoparticles was evidenced by appearance of bright red color and an absorption peak at 518 nm. Transmission electron microscopic (TEM) characterization revealed the nanoparticles to be spherical with average size of about 5.9 ± 1.7 nm. X-ray diffraction (XRD) analysis established highly crystalline nature of the nanoparticles. The synthesized nanoparticles have shown very good peroxidase mimicking property; exhibiting the catalytic oxidation of the chromogen 3,3',5,5'-tetramethyl benzidine (TMB) to a blue color product, in the presence of hydrogen peroxide. The peroxidase mimicking activity of the nanoparticles was found to be selectivity enhanced in the presence of Fe³⁺ and Hg²⁺ while there was no change in the activity in the presence of other concomitant ions. The mechanism studies revealed that the synthesized gold nanoparticles assisted in electron transfer during the catalytic process however the stimulation of peroxidase-like activity in the presence of Fe³⁺ and Hg²⁺ is owed to both generation of hydroxyl radical and accelerated electron transfer. The assay was made selective for iron by the addition of cysteine in acetate buffer; whereas the selective detection of mercury was achieved by carrying out the assay in citrate buffer. The linear ranges for the determination of Fe³⁺ and Hg²⁺ in deionized water were found to be: 5-50 ppb and 5-200 ppb respectively. The limits of quantification (LOQ) for Fe³⁺ and Hg²⁺ were 4.0 and 2.5 ppb respectively. The assay was applied for the determination of Fe³⁺ and Hg²⁺ in drinking and ground water samples. The method holds potential for the on-field screening of these metal ions in real environmental samples.

Exploring the bactericidal performance and application of novel mimic enzyme Co4S3

Novel and uniform Co₄S₃ nanoparticles were synthesized through a two-step hydrothermal process and testified to possess intrinsic peroxidase (POx)-like activity for the first time. As a fresh POx mimic, we studied its catalytic properties, kinetic, and mechanism to catalyze the oxidation of 3, 3', 5, 5'-tetramethylbenzidine in the presence of H₂O₂. According to the experiments, the bactericidal mechanism is the same as that of simulated enzyme. Based on the ability of Co₄S₃ inducing H₂O₂ to express O₂^-, the bactericidal rate can be as high as 100%. Besides, using the POx-like activity of Co₄S₃, a new off-on sensor for H₂O₂ and l-cysteine (l-Cys) detection is constructed. The sensor reveals a good wide linear response to H₂O₂ in the 40-2000 µM with a detection limit of 18 µM, while l-Cys in the 20-100 mM with a detection limit of 10 mM. The proposed method also shows great stability, high selectivity, and excellent practicability.

Tuning the ATP-triggered pro-oxidant activity of iron oxide-based nanozyme towards an efficient antibacterial strategy

An alarming increase in bacterial resistance towards various types of antibiotics makes it imperative to design alternate or combinational therapies to treat stubborn bacterial infections. In this perspective, emerging tools like nanozymes, nanomaterials with biological enzyme like characteristics, are being utilised to control infections caused by bacterial pathogens. Among several nanozymes used for antibacterial applications, Fe₃O₄ nanoparticles (NP) received great attention due to their effective peroxidase like activity. The pH dependent peroxidase activity of Fe₃O₄ NP results in generation of OH radical via the unique Fenton chemistry of iron. However, their pH dependent activity is restricted to acidic environment and dramatic loss in antibacterial activity is observed at near neutral pH. Here we describe a novel strategy to overcome the pH lacunae of citrate coated Fe₃O₄ NP by utilizing adenosine triphosphate disodium salt (ATP) as a synergistic agent to accelerate the OH radical production and restore its antibacterial activity over a wide range of pH. This synergistic combination (30 µg/mL Fe₃O₄ NP and 2.5 mM ATP) shows a high bactericidal activity against both gram positive (B. subtilis) and gram negative (E. coli) bacterial strains, in presence of H₂O₂, at neutral pH. The synergistic effect (Fe₃O₄ NP + ATP) is determined from the viability assessment and membrane damage studies and is further confirmed by comparing the concentration of generated OH radicals. Over all, this study illustrates ATP assisted and OH-mediated bactericidal activity of Fe₃O₄ nanozyme at near neutral pH.

Iron Oxide Nanoparticles for Breast Cancer Theranostics

BACKGROUND

Breast cancer is the second leading cause of death in women worldwide. The extremely fast rate of metastasis and ability to develop resistance mechanism to all the conventional drugs make them very difficult to treat which are the causes of high morbidity and mortality of breast cancer patients. Scientists throughout the world have been focusing on the early detection of breast tumor so that treatment can be started at the very early stage. Moreover, conventional treatment processes such as chemotherapy, radiotherapy, and local surgery suffer from various limitations including toxicity, genetic mutation of normal cells, and spreading of cancer cells to healthy tissues. Therefore, new treatment regimens with minimum toxicity to normal cells need to be urgently developed.

METHODS

Iron oxide nanoparticles have been widely used for targeting hyperthermia and imaging of breast cancer cells. They can be conjugated with drugs, proteins, enzymes, antibodies or nucleotides to deliver them to target organs, tissues or tumors using external magnetic field.

RESULTS

Iron oxide nanoparticles have been successfully used as theranostic agents for breast cancer both in vitro and in vivo. Furthermore, their functionalization with drugs or functional biomolecules enhance their drug delivery efficiency and reduces the systemic toxicity of drugs.

CONCLUSION

This review mainly focuses on the versatile applications of superparamagnetic iron oxide nanoparticles on the diagnosis, treatment, and detecting progress of breast cancer treatment. Their wide application is because of their excellent superparamagnetic, biocompatible and biodegradable properties.

ATP fosters the tuning of nanostructured CeO2 peroxidase-like activity for promising antibacterial performance

Recyclable nano CeO₂ POD mimic records a K_m reduction (∼30% and ∼19.72% for TMB and H₂O₂, respectively) in 900 seconds at pH 4.5. ATP boosts catalytic feasibility in nano CeO₂ at physiological pH.

Fe3O4 Nanozymes with Aptamer-Tuned Catalysis for Selective Colorimetric Analysis of ATP in Blood

In this work, a simple and highly selective colorimetric method has been developed for quantifying trace-level ATP using Fe₃O₄ nanoparticles (Fe₃O₄ NPs). It was discovered that Fe₃O₄ NPs could present the dramatically enhanced catalysis once anchored with ATP-specific aptamers (Apts), which is about 6-fold larger than that of bare Fe₃O₄ NPs. In the presence of ATP, however, the Apts would be desorbed from Fe₃O₄ NPs due to the Apts-target binding event, leading to the decrease of catalysis rationally depending on ATP concentrations. A colorimetric strategy was thereby developed to facilitate the highly selective detection of ATP, showing the linear concentrations ranging from 0.50 to 100 μM. Subsequently, the developed ATP sensor was employed for the evaluation of ATP in blood with the analysis performances comparably better than those of the documented detection methods, showing the potential applications in the clinical laboratory for the detective diagnosis of some ATP-indicative diseases. Importantly, such a catalysis-based detection strategy should be extended to other kinds of nanozymes with intrinsic catalysis properties (i.e., peroxidase and oxidase-like activities), promising as a universal candidate for monitoring various biological species simply by using target-specific recognition elements like Apts and antibodies.

Metal and metal-oxide nanozymes: bioenzymatic characteristics, catalytic mechanism, and eco-environmental applications

Phenolic contaminants (R-OH) are a category of highly toxic organic compounds that are widespread in aquatic ecosystems and can induce carcinogenic risk to wildlife and humans; natural enzymes as green catalysts are capable of step-polymerizing these compounds to produce diverse macromolecular self-coupling products via radical-mediated C-C and C-O-C bonding at either the ortho- or para-carbon position, thereby evading the bioavailability and ecotoxicity of these compounds. Intriguingly, certain artificial metal and metal-oxide nanomaterials are known as nanozymes. They not only possess the unique properties of nanomaterials but also display intrinsic enzyme-mimicking activities. These artificial nanozymes are expected to surmount the shortcomings, such as low stability, easy inactivation, difficult recycling, and high cost, of natural enzymes, thus contributing to eco-environmental restoration. This review highlights the available studies on the enzymatic characteristics and catalytic mechanisms of natural enzymes and artificial metal and metal-oxide nanozymes in the removal and transformation of R-OH. These advances will provide key research directions beneficial to the multifunctional applications of artificial nanozymes in aquatic ecosystems.

Magnetic Nanoparticles: Current Trends and Future Aspects in Diagnostics and Nanomedicine

Background:

Biomedical applications of Magnetic Nanoparticles (MNPs) are creating a major impact on disease diagnosis and nanomedicine or a combined platform called theranostics. A significant progress has been made to engineer novel and hybrid MNPs for their multifunctional modalities such as imaging, biosensors, chemotherapeutic or photothermal and antimicrobial agents. MNPs are successfully applied in biomedical applications due to their unique and tunable properties such as superparamagnetism, stability, and biocompatibility. Approval of ferumoxytol (feraheme) for MRI and the fact that several Superparamagnetic Iron Oxide Nanoparticles (SPIONs) are currently undergoing clinical trials have paved a path for future MNPs formulations. Intensive research is being carried out in designing and developing novel nanohybrids for multiple applications in nanomedicine.

Objective:

The objective of the present review is to summarize recent developments of MNPs in imaging modalities like MRI, CT, PET and PA, biosensors and nanomedicine including their role in targeting and drug delivery. Relevant theory and examples of the use of MNPs in these applications have been cited and discussed to create a thorough understanding of the developments in this field.

Conclusion:

MNPs have found widespread use as contrast agents in imaging modalities, as tools for bio-sensing, and as therapeutic and theranostics agents. Multiple formulations of MNPs are in clinical testing and may be accepted in clinical settings in near future.

Red blood cells as an efficient in vitro model for evaluating the efficacy of metallic nanoparticles

Blood and the linings of blood vessels may be regarded as a fifth tissue type. The human body contains 5 × 10⁹ red blood cells (RBCs) per ml, a total of 2.5 × 10¹³ cells in the 5 l of blood present in the body. With an average lifetime of 125 days, human RBCs are destroyed by leukocytes in the spleen and liver. Nowadays red blood cells are extensively used to study various metabolic functions. Nanoparticles (NP) are being widely accepted for drug delivery system. This review summarizes the red blood cells, NPs and their characteristics on the basis of the RBC components along with drug delivery systems through RBCs. Further, we also discussed that how erythrocytes can be used as an efficient in vitro model for evaluating the efficacy of various nanocomposite materials.

Ferroxidase-like and antibacterial activity of PtCu alloy nanoparticles

Many metal nanoparticles are reported to have intrinsic enzyme-like activities and offer great potential in chemical and biomedical applications. In this study, PtCu alloy nanoparticles (NPs), synthesized through hydrothermal treatment of Cu²⁺ and Pt²⁺ in an aqueous solution, were evaluated for ferroxidase-like and antibacterial activity. Electron spin resonance (ESR) spectroscopy and colorimetric methods were used to demonstrate that PtCu NPs exhibited strong ferroxidase-like activity in a weakly acidic environment and that this activity was not affected by the presence of most other ions, except silver. Based on the color reaction of salicylic acid in the presence of Fe³⁺, we tested the ferroxidase-like activity of PtCu NPs to specifically detect Fe²⁺ in a solution of an oral iron supplement and compared these results with data acquired from atomic absorption spectroscopy and the phenanthroline colorimetric method. The results showed that the newly developed PtCu NPs detection method was equivalent to or better than the other two methods used for Fe²⁺ detection. The antibacterial experiments showed that PtCu NPs have strong antibacterial activity against Staphylococcus aureus and Escherichia coli. Herein, we demonstrate that the peroxidase-like activity of PtCu NPs can catalyze H₂O₂ and generate hydroxyl radicals, which may elucidate the antibacterial activity of the PtCu NPs against S. aureus and E. coli. These results showed that PtCu NPs exhibited both ferroxidase- and peroxidase-like activity and that they may serve as convenient and efficient NPs for the detection of Fe²⁺ and for antibacterial applications.

A novel ultrasensitive and non-enzymatic "turn-on-off" fluorescence nanosensor for direct determination of glucose in the serum: As an alternative approach to the other optical and electrochemical methods

A new, simple, rapid, highly sensitive and selective and non-enzymatic fluorometric method for direct determination of glucose in real samples was developed. The method was based on the inhibition of fluorescence resonance energy transfer (FRET) process between terbium (III)-1, 10-phenanthroline (Tb-phen) complex and silver nanoparticles (AgNPs). Upon the addition of glucose, the quenched FRET-based fluorescence of Tb-phen complex was gradually recovered by glucose via its strong adsorption on the surface of AgNPs and removal of Tb-phen complex from AgNPs surface. Therefore the fluorescence of Tb-phen complex switched to "turn-on" state. Under the optimum conditions, a linear relationship was obtained between the enhanced fluorescence intensity and glucose concentration in the range of (5-900) × 10^-8 M with the detection limit of 1.94 × 10^-8 M. The proposed sensing system was successfully applied to determine glucose in the spiked normal and diabetic patient serum samples after deproteinization with acetonitrile. Analytical recoveries from treated serum samples were in the range of 99.97-104.80% and 92.14-105.43%, respectively. The common interfering species, such as ascorbic acid, fructose and galactose did not cause interior interference due to unique emission properties of Tb-phen complex probe. Also the interaction of the Tb-phen complex with AgNPs, which led to the fluorescence intensity quenching of the complex, was further examined by FTIR technique. In short, as compared to most of the existing methods, the newly proposed method, provides some advantages and makes it promising for the direct rapid screening of glucose residues of real samples in clinical diagnosis of diabetes, as an alternative approach to the other exiting optical and electrochemical methods.

Catalytic Mechanisms of Nanozymes and Their Applications in Biomedicine

The research on nanozymes has increased dramatically in recent years and a new interdiscipline, nanozymology, has emerged. A variety of nanomaterials have been designed to mimic the characteristics of natural enzymes, which connects an important bridge between nanotechnology and biological science. Unlike natural enzymes, the nanoscale properties of nanozymes endow them with the potential to regulate their enzymatic-like activity from different perspectives. The mechanisms behind those methods are intriguing. In this Review, we introduce these mechanisms from the aspects of surface chemistry, surface modification, molecular imprinting, and hybridization and then focus attention on some specific catalytic mechanisms of several representative nanozymes. The applications of nanozymes ranging from bioassay, imaging, to disease therapy are also discussed in detail to prove the fact that the inherent physicochemical properties of nanomaterials not only make nanozymes the analogues of biological enzymes, but also endow them with incomparable advantages and broad prospects in biomedical fields. Finally, four characteristics and some challenges of nanozymes are summarized.

Peroxidase-Like Activity of Smart Nanomaterials and Their Advanced Application in Colorimetric Glucose Biosensors

Diabetes is a dominating health issue with 425 million people suffering from the disease worldwide and 4 million deaths each year. To avoid further complications, the diabetic patient blood glucose level should be strictly monitored despite there being no cure for diabetes. Colorimetric biosensing has attracted significant attention because of its low cost, simplicity, and practicality. Recently, some nanomaterials have been found that possess unexpected peroxidase-like activity, and great advances have been made in fabricating colorimetric glucose biosensors based on the peroxidase-like activity of these nanomaterials using glucose oxidase. Compared with natural horseradish peroxidase, the nanomaterials exhibit flexibility in structure design and composition, and have easy separation and storage, high stability, simple preparation, and tunable catalytic activity. To highlight the significant progress in the field of nanomaterial-based peroxidase-like activity, this work discusses the various smart nanomaterials that mimic horseradish peroxidase and its mechanism and development history, and the applications in colorimetric glucose biosensors. Different approaches for tunable peroxidase-like activity of nanomaterials are summarized, such as size, morphology, and shape; surface modification and coating; and metal doping and alloy. Finally, the conclusion and challenges facing peroxidase-like activity of nanomaterials and future directions are discussed.

Redox Trimetallic Nanozyme with Neutral Environment Preference for Brain Injury

Metal nanozyme has attracted wide interest for biomedicine, and a highly catalytic material in the physiological environment is highly desired. However, catalytic selectivity of nanozyme is still highly challenging, limiting its wide application. Here, we show a trimetallic (triM) nanozyme with highly catalytic activity and environmental selectivity. Enzyme-mimicked investigations find that the triM system possesses multi-enzyme-mimetic activity for removing reactive oxygen species (ROS) and reactive nitrogen species (RNS), such as ¹O₂, H₂O₂, ^•OH, and ^•NO. Importantly, triM nanozyme exhibits the significant neutral environment preference for removing the ^•OH, ¹O₂, and ^•NO free radical, indicating its highly catalytic selectivity. The density functional theory (DFT) calculations reveal that triM nanozyme can capture electrons very easily and provides more attraction to reactive oxygen and nitrogen species (RONS) radicals in the neutral environment. In vitro experiments show that triM nanozyme can improve the viability of injured neural cell. In the LPS-induced brain injury model, the superoxide dismutase (SOD) activity and lipid peroxidation can be greatly recovered after triM nanozyme treatment. Moreover, the triM nanozyme treatment can significantly improve the survival rate, neuroinflammation, and reference memory of injured mice. Present work provides a feasible route for improving selectivity of nanozyme in the physiological environment as well as exploring potential applications in brain science.

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.

Nanomaterials Exhibiting Enzyme-Like Properties (Nanozymes): Current Advances and Future Perspectives

Biological enzymes are macromolecular catalysts that catalyze the biochemical reactions of the natural systems. Although each enzyme performs a particular function, however, holds several drawbacks, which limits its utilization in broad-spectrum applications. Natural enzymes require strict physiological conditions for performing catalytic functions. Their limited stability in harsh environmental conditions, the high cost of synthesis, isolation, and purification are some of the significant drawbacks. Therefore, as an alternative to natural enzymes, recently several strategies have been developed including the synthesis of molecules, complexes, and nanoparticles mimicking their intrinsic catalytic properties. Nanoparticles exhibiting the properties of an enzyme are termed as “nanozymes.” Nanozymes offer several advantages over natural enzymes, therefore, a rapid expansion of the development of artificial biocatalysts. These advantages include simple methods of synthesis, low cost, high stability, robust catalytic performance, and smooth surface modification of nanomaterials. In this context, nanozymes are tremendously being explored to establish a wide range of applications in biosensing, immunoassays, disease diagnosis and therapy, theranostics, cell/tissue growth, protection from oxidative stress, and removal of pollutants. Considering the importance of nanozymes, this article has been designed to comprehensively discuss the different enzyme-like properties, such as peroxidase, catalase, superoxide dismutase, and oxidase, exhibited by various nanoparticles.