Partially oxidized MoS2 nanosheets with high water-solubility to enhance the peroxidase-mimic activity for sensitive detection of glutathione

Surface oxidation engineering is an effective strategy to construct nanomaterials with enhanced biocatalytic activity. In this study, a facile one-pot oxidation strategy was proposed to synthesize partially oxidized molybdenum disulfide nanosheets (ox-MoS₂ NSs), which exhibit good water solubility and can be used as an excellent peroxidase substitute. Under the oxidation process, Mo-S bonds are partially broke and S atoms are replaced by excess oxygen atoms, and the released abundant heat and gases efficiently expended the interlayer distance and weaken the van der Waals forces between adjacent layers. Porous ox-MoS₂ NSs can be easily exfoliated by further sonication, and the nanosheets exhibits excellent water dispersibility and no obvious sediment appear even after store for months. Benefiting from the desirable affinity property with enzyme substrates, optimized electronic structure and prominent electron transfer efficiency, the ox-MoS₂ NSs exhibit enhanced peroxidase-mimic activity. Furthermore, the ox-MoS₂ NSs catalyzed 3,3',5,5'-tetramethylbenzidine (TMB) oxidation reaction could be inhibited by the redox reaction that take place between glutathione (GSH) as well as the direct interaction between GSH and ox-MoS₂ NSs. Thus, a colorimetric sensing platform was constructed for GSH detection with good sensitivity and stability. This work provides a facile strategy for engineering structure of nanomaterials and improving enzyme-mimic performance.

316 stainless steel wire mesh for visual detection of H2O2, glutathione and glucose based on the peroxidase-like activity

Stainless steel is a frequently used and cost-effective material. In this study, we discovered for the first time that fresh 316ss possessed an intrinsic peroxidase (POD) catalytic activity, which can catalyze the substrate of POD-like reaction 3,3',5,5'-tetramethylbenzidine (TMB) changing to a blue-colored product, oxidation of TMB, in the presence of hydrogen peroxide (H₂O₂). Subsequently, a rapid method was conducted to enable the active composites of the 316ss with reused POD activity for 25 circles at least. Based on this finding, the method exhibits a highly sensitive and selective application for H₂O₂, glutathione (GSH), and Glucose determination. The linear range of glucose detection was 5-100 μM and the detection limit was 3 μM. Finally, this method was further used for detection of glucose in human serum. This work finds a new function of 316ss and develops its novel application, which promotes the potential application of nanozyme in nanoscience and nanotechnology. Schematic representation of the enzyme mimic activities of 316ss wire mesh for the colorimetric detection of hydrogen peroxide H₂O₂ and GSH with a superior reusability for more than 25 cycles. Based on this, the colorimetric detection of glucose can be constructed combined with GOx.

3D V2O5-MoS2/rGO nanocomposites with enhanced peroxidase mimicking activity for sensitive colorimetric determination of H2O2 and glucose

In this work, we reported a novel nanozyme (3D V₂O₅-MoS₂/rGO) by decorating MoS₂ nano-flowers and V₂O₅ nanoparticles on reduced graphene oxide (rGO). The 3D V₂O₅-MoS₂/rGO nanocomposites exhibited intrinsic peroxidase mimicking activity and catalyzed the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) to produce a blue colored product in the presence of H₂O₂. Compared with horseradish peroxidase (HRP), 3D V₂O₅-MoS₂/rGO nanocomposites displayed high catalytic velocity (V_max) and affinity (K_m) for substrates (H₂O₂ and TMB). The study of the catalytic mechanism showed that the reduction of V⁵⁺ and the oxidation of S^2- in the 3D V₂O₅-MoS₂/rGO nanocomposites accelerate electron transfer between H₂O₂ and TMB, which enhanced the peroxidase mimicking activity of 3D V₂O₅-MoS₂/rGO nanocomposites. The as-synthetized 3D V₂O₅-MoS₂/rGO could be used for the colorimetric detection of H₂O₂ in the range of 20.00-800.00 μM with the LOD of 12.40 μM (3σ/S). Moreover, the 3D V₂O₅-MoS₂/rGO could also be used for the detection of glucose in the range of 4.00-300.00 μM with the LOD of 3.99 μM (3σ/S). In addition, the as-synthetized novel peroxidase mimics has good applicability for sensitive colorimetric determination of glucose in human blood samples and artificial urine samples, and has broad application prospects as a multi-functional sensing platform in clinical diagnosis.

Molybdenum disulfide nanosheets-based fluorescent "off-to-on" probe for targeted monitoring and inhibition of β-amyloid oligomers

A novel and simple "off-to-on" fluorescent sensing platform for β-amyloid oligomers (Aβo) was developed based on dye (FAM)-labeled single-strand DNA (FAM-ssDNA)-conjugated molybdenum disulfide nanosheets (MoS2 NSs). Due to strong adsorption of ss-DNA to the surface of MoS2 NSs, the fluorescence of FAM was quenched remarkably, leading to a fluorescent "off" state. However, in the presence of Aβo, a hybrid structure between Aβo and FAM-ssDNA resulted in the dissociation of FAM-ssDNA from MoS2 NSs and an obvious fluorescence recovery transformed the fluorescence to an "on" state. The developed fluorescence sensing assay showed a good linear relationship toward Aβo ranging from 0.01 to 20 μM (R2 = 0.994) with a satisfactory detection limit of 3.1 nM. Practical samples of hippocampus and cortex tissues from APP/PS1 double transgenic AD mice were applied to demonstrate feasibility of the assay. Moreover, we found that similar to MoS2 nanoparticles, MoS2 NSs possessed therapeutic effects on Alzheimer's disease (AD) by inhibiting Aβ aggregations and degrading the previously formed Aβ fibrils. Collectively, the high sensitivity, specificity, and good biocompatibility along with an efficient anti-aggregation ability, the presented fluorescent strategy with MoS2 NSs demonstrated their promising potential for future AD-related research.

Molybdenum disulfide-based materials with enzyme-like characteristics for biological applications

Nanozyme, a kind of nanomaterials with enzymatic activity, has been developing vigorously over the past years owing to its advantages such as low-cost, easy storage, ease of use in harsh environments and so on, compared with natural enzymes. At present, as a typical two-dimensional nanomaterial, molybdenum disulfide (MoS₂) and their hybrids with unexpected enzyme-like activities have caused wide attention. In this review, we mainly investigated the enzyme-like activities of MoS₂ based nanomaterials, including peroxidase-like activity, catalase-like activity and superoxide dismutase-like activity. Furthermore, we systematically introduce recent research progress of MoS₂ based nanomaterials in the fields of biological applications such as radiation protection, cancer therapy, antibacterial, and wound healing. Finally, the current challenges and perspectives of MoS₂ based nanomaterials in the future are also discussed and proposed. We expect this review may be significant to understand the properties of MoS₂ based nanomaterials and the development of two-dimensional nanomaterials with enzyme mimicking activities.

Molybdenum-based hetero-nanocomposites for cancer therapy, diagnosis and biosensing application: Current advancement and future breakthroughs

In recent years, there have been significant advancements in the nanotechnology for cancer therapy. Even though molybdenum disulphide (MoS2)-based nanocomposites demonstrated extensive applications in biosensing, bioimaging, phototherapy, the review article focusing on MoS2 nanocomposite platform has not been accounted for yet. The review summarizes recent strategies on design and fabrication of MoS2-based nanocomposites and their modulated properties in cancer treatment. The review also discussed several therapeutic strategies (photothermal, photodynamic, immunotherapy, gene therapy and chemotherapy) and their combinations for efficient cancer therapy along with certain case studies. The review also inculcates various diagnostic techniques viz. magnetic resonance imaging, computed tomography, photoacoustic imaging and fluorescence imaging for diagnosis of cancer.

A critical review on the applications and potential risks of emerging MoS2 nanomaterials

Molybdenum disulfide (MoS₂) nanomaterials have been widely used in various fields such as energy store and transformation, environment protection, and biomedicine due to their unique physicochemical properties. Unfortunately, such large-scale production and use of MoS₂ nanomaterials would inevitably release into the environmental system and then potentially increase the risks of wildlife/ecosystem and human beings as well. In this review, we first introduce the physicochemichemical properties, synthetic methods and environmental behaviors of MoS₂ nanomaterials and their typical functionalized materials, then summarize their environmental and biomedical applications, next assess their potential health risks, covering in vivo and in vitro studies, along with the underlying toxicological mechanisms, and last point out some special phenomena about the balance between applications and potential risks. This review aims to provide guidance for harm predication induced by MoS₂ nanomaterials and to suggest prevention measures based on the recent research progress of MoS₂' applications and exerting toxicological data.

Fabrication of FeS2/SiO2 Double Mesoporous Hollow Spheres as an Artificial Peroxidase and Rapid Determination of H2O2 and Glutathione

Nanozymes as one of artificial enzymes show many advantages than natural enzymes. The high Michaelis-Menten constant (K_m) to H₂O₂ is the drawback for nanozymes, which means a high H₂O₂ concentration to oxidize 3,3',5,5'-tetramethylbenzidine (TMB). For this problem, FeS₂/SiO₂ double mesoporous hollow spheres (DMHSs) were first synthesized as an artificial peroxidase through a solid reaction. The experimental results demonstrate that Fe₃O₄ vulcanization and DMHS formation were effective strategies to enhance affinity to H₂O₂ for the nanozyme. The K_m of FeS₂/SiO₂ DMHSs (H₂O₂ as the substrate) is 18-fold smaller than that of FeS₂ nanoparticles (NPs). The catalytic efficiency (K_cat/K_m) of FeS₂/SiO₂ DMHSs is about 16 times higher than that of FeS₂ NPs. FeS₂/SiO₂ DMHSs can be used as a nanozyme to sensitively and rapidly detect H₂O₂ and glutathione within 1 min at room temperature.

Multimodal theranostics augmented by transmembrane polymer-sealed nano-enzymatic porous MoS2 nanoflowers

Developing an all-in-one multimodal theranostic platform that can synergistically integrate sensitive photoacoustic (PA) imaging, enhanced photothermal therapy (PTT) and photodynamic therapy (PDT) as well as the nano-enzyme activated chemodynamic therapy (CDT) presents a great challenge for the current nanomedicine design. Herein, a simple hydrothermal method was used to prepare porous molybdenum disulfide (MoS₂) nanoflowers. These nanoflowers were assembled by three dimensional (3D)-stacked MoS₂ nanosheets with plentiful pores and large surfaces, which thus exhibited enhanced photothermal conversion via light trapping and peroxidase (POD)-like activity via active defects exposure. Consequently, this 3D-MoS₂ nanostructure could be well-sealed by polyethylene glycol-polyethylenimine polymer modified with nucleolar translocation signal sequence of the LIM Kinase 2 protein (LNP) via strong electrostatic interaction, which not only benefited to stably deliver anticancer drug doxorubicin (DOX) into the tumor cells for pH/NIR-responsive chemotherapy, but also provided strong photoacoustic, photothermal performances and stimulated generation of reactive oxygen species (ROS) for imaging-guided PTT/PDT/CDT combined therapy. This work promised a simple all-in-one multimodal theranostic platform to augment the potential antitumoral therapeutic outcomes.

Electronic coupling between molybdenum disulfide and gold nanoparticles to enhance the peroxidase activity for the colorimetric immunoassays of hydrogen peroxide and cancer cells

Peroxidase nanoenzymes exhibit a specific affinity toward substrates, thereby demonstrating application potential for realizing the colorimetric immunoassays of hydrogen peroxide (H₂O₂), which can be further used as a probe for imaging cancer cells. To enhance the intrinsic peroxidase activity of molybdenum sulfide (MoS₂) nanomaterials, gold (Au) nanoparticles with an average diameter of approximately 2.1 nm were modified on a MoS₂/carbon surface (denoted as MoS₂/C-Au₆₀₀) via ascorbic acid reduction. MoS₂/C-Au₆₀₀ can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to generate a blue oxidation product in the presence of H₂O₂; this product exhibits peroxidase-like activities, superior to those of most existing MoS₂-based nanoenzymes. Furthermore, MoS₂/C-Au₆₀₀ exhibits a high detection capability for H₂O₂ in the range of 1 × 10^-5 to 2 × 10^-4 mol/L (R² = 0.99), and the lowest detection limit is 1.82 µmol/L in a sodium acetate and acetic acid buffer solution. Steady state kinetics studies indicate that the catalytic mechanism is consistent with the ping-pong mechanism. Given its strong absorption peak at 652 nm in the visible region, MoS₂/C-Au₆₀₀ can be used to image cancer cells due to the enhanced permeability and retention effect. Our findings demonstrate that the synergistic electronic coupling between multiple components can enhance the peroxidase activity, which can facilitate the development of an effective, facile, and reliable method to perform colorimetric immunoassays of H₂O₂ and cancer cells.

In situ polymerization and covalent functionalisation of trithiocyanuric acid by MoS2 nanosheets resulting in a novel nanozyme with enhanced peroxidase activity

MoS₂ catalysed the polymerisation of trithiocyanuric acid, resulting in a network exhibiting peroxidase activity via a ping-pong mechanism.

Accelerating the peroxidase-like activity of MoSe2 nanosheets at physiological pH by dextran modification

One-pot synthesis of dextran-modified MoSe₂ nanosheets with peroxidase-like activity at physiological pH for bio-sensing.

Nanocomposite of Poly(l-Lactic Acid) with Inorganic Nanotubes of WS2

Composites of poly(l-lactic acid) (PLLA) reinforced by adding inorganic nanotubes of tungsten disulfide (INT–WS2) were prepared by solvent casting. In addition to the pristine nanotubes, PLLA nanocomposites containing surface modified nanotubes were studied as well. Several surface-active agents, including polyethylene imine (PEI), were studied in this context. In addition, other biocompatible polymers, like poly d,l-lactic acid (PDLLA) and others were considered in combination with the INT–WS2. The nanotubes were added to the polymer in different proportions up to 3 wt %. The dispersion of the nanotubes in the nanocomposites were analyzed by several techniques, including X-ray tomography microscopy (Micro-XCT). Moreover, high-temperature rheological measurements of the molten polymer were conducted. In contrast to other nanoparticles, which lead to a considerable increase of the viscosity of the molten polymer, the WS2 nanotubes did not affect the viscosity significantly. They did not affect the complex viscosity of the molten PLLA phase, either. The mechanical and tribological properties of the nanocomposites were found to improve considerably by adding the nanotubes. A direct correlation was observed between the dispersion of the nanotubes in the polymer matrix and its mechanical properties.

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.

Functional nanomaterials with unique enzyme-like characteristics for sensing applications

We highlight the recent developments in functional nanomaterials with unique enzyme-like characteristics for sensing applications.

Synergistic Nanozymetic Activity of Hybrid Gold Bipyramid-Molybdenum Disulfide Core@Shell Nanostructures for Two-Photon Imaging and Anticancer Therapy

In recent years, the concept of combined therapy using gold hybrid nanomaterials has been broadly adopted to pioneer new anticancer treatments. However, their synergistic anticancer effects have yet to be thoroughly investigated. Herein,a hybrid gold nanobipyramid nanostructure coated with molybdenum disulfide (MoS₂) semiconductor (AuNBPs@MoS₂) was proposed as a smart nanozyme for anticancer therapy and two-photon bioimaging. The hybrid material showed dramatically enhanced localized surface plasmon resonance property under excitation owing to its anisotropic nature, coupled with the rich electron density in MoS_2, resulting in the superior in situ photogeneration of reactive oxidative species (ROS - ¹O₂, ^•OH). We demonstrated that the synergistic effect of enhanced photothermal conversion and generation of ROS could increase the anticancer effect of AuNBPs@MoS₂. Two-photon luminescence imaging confirmed that AuNBPs@MoS₂ was successfully internalized in cancer cells and that simultaneous anticancer treatments based on catalytic and photothermal therapy could be achieved. This study highlighted, for the first time, a novel approach of plasmon-mediated powerful anticancer therapy and imaging via the unprecedented combination of anisotropic AuNBPs and two-dimensional MoS₂ material.