Fe-Doped MoS2 Nanozyme for Antibacterial Activity and Detoxification of Mustard Gas Simulant

Alpha to omega for molybdenum disulfide (MoS2)-based antibacterial nanomaterials

Addressing antimicrobial resistance is crucial in microbial studies, especially in creating alternative drug candidates vital for protecting human health from multidrug-resistant microorganisms. Nanomaterials (NMs) have emerged as a potential solution, drawing considerable interest owing to their unique structural and functional characteristics that render them effective against microbes. Two-dimensional NMs, particularly those based on molybdenum disulfide (MoS2), have shown promise as antimicrobial agents owing to their exceptional properties. Although research has advanced in exploring and applying MoS2 NMs for antimicrobial purposes, strategies for optimizing and modifying their use as antimicrobial agents remain in their early developmental stages. This review presents a comprehensive overview of the current MoS2 NMs for antimicrobial applications, including their synthesis, properties, optimization techniques, and modifications, as well as their mechanisms of action. This review also addresses the limitations of the individual materials and proposes future directions for overcoming these challenges. This compilation serves as an invaluable resource for scientists working on the development of targeted antimicrobial agents.

The Construction of a Library of Nanozyme with High Nitrogen Content for Efficient Antibacterial Applications

High catalytic efficiency is persistently pursued to generate high-performance nanozymes. Metal elements are active centers where metal-organic frameworks (MOFs) play a catalytic role. In this work, a library of MOFs-derived nanozyme is constructed based on metal salts and 1H-1,2,3-triazole (MET). Triazole has three N atoms; the intrinsic high N content is beneficial to improve the affinity of substrate H2O2. Meanwhile, different kinds of metals can be introduced by changing the metal salts, through which bimetallic or trimetallic MOFs can be constructed. Amongst various single-, bi-, or trimetallic MET nanozymes, MET-Fe1Zn0.5 nanozyme exhibits the best peroxidase (POD)-like activity. The results demonstrate that the introduction of Zn accelerates electron transfer and promotes the conversion of Fe3+ to Fe2+ in MET-Fe1Zn0.5 nanozyme, thus enhancing the POD-like activity of MET-Fe1Zn0.5 nanozyme. In particular, MET-Fe1Zn0.5 nanozyme exhibits excellent antibacterial efficiency. A study on antibacterial mechanism indicates that MET-Fe1Zn0.5 nanozyme has good adhesion to the bacterial membrane and can work in conjunction with reactive oxygen species, disrupting the oxidative phosphorylation, DNA replication, and biosynthesis of essential amino acids and cofactors within bacteria, leading to membrane damage and, eventually death of bacteria. These results suggest that a high N-coordination number MET has great potential as a new-generation nanozyme.

Ultra-Fast Degradation of Mustard Gas Simulant by Titanium Dioxide-Phosphomolybdic Acid Sub-1 nm Nanobelts

The development of novel catalysts for the rapid detoxification of sulfur mustard holds paramount importance in the field of military defense. In this work, titanium dioxide-phosphomolybdic acid sub-1 nm nanobelts (TiO2/PMA SNBs) are employed as effective catalysts for the ultra-fast degradation of mustard gas simulants (2-chloroethyl ethyl sulfide, CEES) with 100% selectivity and a half-life (t1/2, time required for 50% conversion) as short as 12 s, which is the fastest time to the best of the knowledge. Even in dark conditions, this material can still achieve over 90% conversion within 5 min. A mechanism study reveals that the rapid generation rate of 1O2 and O2 •- in the presence of TiO2/PMA SNBs and H2O2 plays a crucial role in facilitating the efficient oxidation of CEES. A filter layer of a gas mask loaded with TiO2/PMA SNBs and H2O2/polyvinylpyrrolidone cross-linked complex (PHP) is constructed, which demonstrates remarkable stability and exhibits exceptional efficacy in the detoxification of CEES in the presence of a small amount of water. This innovation offers great potential for enhancing personal protective equipment in practical applications.

Fe/Pt-doped carbon nanoparticles with peroxidase-like activity for point-of-care determination of uric acid

A pasting-3D microfluidic paper-based analytical device (P-3D μPAD) was developed. It enabled an efficient cascade reaction between urate oxidase (UOX) and Fe/Pt-doped carbon nanoparticles (Fe/Pt-CNPs) for visual colorimetric detection of uric acid (UA). The novel Fe/Pt-CNP nanozyme performed high peroxidase-like activity toward 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 with Michaelis - Menten constants (Km) of 0.97 and 2.30 mM, respectively. The UOX-Fe/Pt-CNP system was incorporated into P-3D μPAD: the 1st layer was UOX hydrolysis reaction under alkaline pH, and the 2nd layer was Fe/Pt-CNPs catalyzing H2O2 to oxidize TMB at acidic pH. The separated two layers allowed cascade reaction under different working pH without sacrificing the activity of UOX or Fe/Pt-CNPs. The images were captured and analyzed by the camera and "Color Recognition" application using a  smartphone. The linear range of P-3D μPAD for UA was 25-1000 μM with a limit of detection of 10 μM which met the requirements for clinical applications. The high accuracy of P-3D μPAD for UA detection in invasive (blood) and noninvasive (saliva) samples has been confirmed by the biochemical analyzer. This work offers a sensitive, flexible, affordable, and disposable tool for on-site UA level monitoring and provides new insight into natural enzyme and nanozyme tandem systems for biosensing.

A simple Ag-MoS2 hybrid nanozyme-based sensor array for colorimetric identification of biothiols and cancer cells

The intracellular levels of biothiols are associated with various diseases including cancer, and biothiols are regarded as tumor biomarker. Due to the similarity of the molecular structure of biothiols, the development of simple, rapid, efficient, and sensitive colorimetric sensor arrays holds great promise for clinical cancer diagnosis. Here, we developed a simple Ag-MoS2 hybrid nanozyme-based sensor array for colorimetric identification of biothiols and cancer cells. The novel Ag-MoS2 nanoprobe was synthesized in a simple and efficient way through the in situ self-reduction reaction between MoS2 and noble metal precursor. Benefiting from to the formation of heterogeneous metal structures, the peroxidase (POD)-like catalytic activity of the synthesized Ag-MoS2 hybrid nanocomposites is significantly enhanced compared to MoS2 alone. Moreover, the catalytic activity of Ag-MoS2 nanozyme was correlated with the pH of the reaction solution and the inhibitory effects of the three biothiols on the nanozyme-triggered chromogenic system differed in the specific pH environments. Therefore, each sensing unit of this electronic tongue generated differential colorimetric fingerprints of different biothiols. After principal component analysis (PCA), the developed novel colorimetric sensor array can accurately discriminate biothiols between different types, various concentrations, and different mixture proportions. Further, the sensor array was used for the colorimetric identification of real serum and cellular samples, demonstrating its great potential in tumor diagnostic applications.

Synthesis of Pt-MoS2 with enhanced photothermal and peroxidase-like properties and its antibacterial application

Despite tremendous efforts, bacterial infection and contamination remain a major clinical challenge to modern humans. Nanozyme materials with stimuli-responsive properties are expected to be powerful tools for the next generation of antibacterial therapy. Here, MoS2 nanosheet was firstly prepared by liquid phase exfoliation method, and Pt-MoS2 hybrid biomaterial was then successfully synthesized by a simple self-reduction method. The Pt decoration significantly improves the photothermal effect of MoS2 nanosheet under 808 nm NIR laser irradiation. Besides, benefiting from the formation of heterogeneous structure, the Pt-MoS2 has significantly enhanced peroxidase mimetic catalytic activity, which can kill bacteria through catalysis of H2O2 to generate antimicrobial hydroxyl radicals. Moreover, the temperature rise brought about by NIR laser stimulation further amplifies the nanozyme activity of the composites. After treatment by the synergistic platform, both Staphylococcus aureus and Escherichia coli can be effectively inhibited, demonstrating its broad-spectrum antibacterial properties. In addition, the developed antibacterial Pt-MoS2 nanozyme have the excellent biocompatibility, which makes them well suited for infection elimination in biological systems. Overall, this work shows great potential for rationally combining the multiple functions of MoS2-based nanomaterials for synergistic antibacterial therapy. In the future, the Pt-MoS2 nanozyme may find wider applications in areas such as personal healthcare or surface disinfection treatment of medical devices.

DNA-based FeCuAg nanoclusters with peroxidase-like and GSH depletion activities for toxicity of in vitro cancer cells

Developing the efficient nanozymes for reactive oxygen species (ROS)-mediated highly potent tumor catalytic therapy has become a great challenge. In this study, we prepared the DNA-Fe, -FeAg, and -FeCuAg nanocluster (NCs) using the G-/C-rich single-stranded DNA (ssDNA) templates. The steady-state kinetic and the catalytic performances and mechanisms of DNA-metal NCs were first systematically investigated. The results indicated that c-kit-TBA-Fe, c-kit-TBA-FeAg, and c-kit-TBA-FeCuAg NCs exhibited the high peroxidase-like activity. All of three types of NCs presented the higher affinity to the substrate TMB and better storage stability at 4 °C than horseradish peroxidase (HRP). Moreover, c-kit-TBA-FeAg and c-kit-TBA-FeCuAg NCs presented the 6.7- and 4.7-fold stronger affinity to TMB than c-kit-TBA-Fe, respectively. However, the maximum reaction rate (Vmax) of c-kit-TBA-FeCuAg NCs with H2O2 was the largest, which promoted the generation of much more •OH in the reaction system. More importantly, c-kit-TBA-FeCuAg NCs were able to deplete largely the intracellular GSH and thus generate lots of endogenous ROS in HeLa cells, thereby exhibiting the significant and specific in vitro cancer cells toxicity. Therefore, c-kit-TBA-FeCuAg NCs, with peroxidase-like activity and glutathione (GSH) consumption ability, hold the ROS-based promising therapeutic effects for cancer.

Structural engineering of Pt-on-Rh hollow nanorods with high-performance peroxidase-like specific activity for colorimetric detection

The preparation of nanozymes with high specific activity is highly important for various applications. However, only a few nanozymes have specific activities comparable to natural enzymes. Herein, novel Pt-on-Rh hollow nanorods (PtRh HNRs) were developed, in which surface Pt exhibited adjustable dispersity and interior Rh served as the support. The optimized PtRh HNRs demonstrated high-performance peroxidase (POD)-like activity, with a specific activity as high as 1352 U mg-1, which was 3.86 times that of their monometallic Pt counterparts. Density functional theory (DFT) calculations illustrated that the presence of Rh decreased the energy barrier of the rate-determining step. When PtRh HNRs were used as nanozymes in the colorimetric detection of hydrogen peroxide (H2O2) and ascorbic acid (AA), the limits of detection (LODs) were as low as 9.97 μM and 0.039 μM, respectively. The current work highlights a facile and powerful strategy for manufacturing nanozymes with high specific activity and demonstrates that the prepared PtRh HNRs have the potential for analysis and determination.

Chitosan-chelated carbon dots-based nanozyme of extreme stability with super peroxidase activity and antibacterial ability for wound healing

Bacterial infection often leads to failed wound healing, causing one-third of death cases globally. However, antibacterial nanomaterials and natural enzymes face limitations including low antibacterial efficiency, lack of catalytic performance, low safety, and instability. Therefore, a new Fe/N-doped chitosan-chelated carbon dot-based nanozyme CS@Fe-N CDs was developed, which showed multiple advantages such as highly efficient antibacterial activity, excellent peroxidase-like activity, high stability, and high biocompatibility, shortening the wound healing time. The ultra-small (6.14 ± 3.38 nm) CS@Fe-N CDs nanozyme accelerated the H2O2 to ·OH conversion, exhibiting excellent antibacterial performance against Staphylococcus aureus. The antibacterial activity was increased by over 2000-fold after catalysis. The CS@Fe-N CDs nanozyme also displayed outstanding peroxidase activity (Vmax/Km = 1.77 × 10-6/s), 8.8-fold higher than horseradish peroxidase. Additionally, the CS@Fe-N CDs nanozyme exhibited high stability at broad pH values (pH 1-12) and temperature ranges (20-90 °C). In vitro evaluation of cell toxicity proved that the CS@Fe-N CDs nanozyme had negligible cytotoxicity. In vivo, wound healing experiments demonstrated that the CS@Fe-N CDs could shorten the healing time of rat wounds by at least 4 days, and even had a better curative effect than penicillin. In conclusion, this therapeutic platform provides an effective antibacterial and biologically safe healing strategy for skin wounds.

Unveiling the antibacterial strategies and mechanisms of MoS2: a comprehensive analysis and future directions

Antibiotic resistance is a growing problem that requires alternative antibacterial agents. MoS2, a two-dimensional transition metal sulfide, has gained significant attention in recent years due to its exceptional photocatalytic performance, excellent infrared photothermal effect, and impressive antibacterial properties. This review presents a detailed analysis of the antibacterial strategies and mechanism of MoS2, starting with its morphology and synthesis methods and focusing on the different interaction stages between MoS2 and bacteria. The paper summarizes the main antibacterial mechanisms of MoS2, such as photocatalytic antibacterial, enzyme-like catalytic antibacterial, physical antibacterial, and photothermal-assisted antibacterial. It offers a comprehensive discussion focus on recent research studies of photocatalytic antibacterial mechanisms and categorizes them, guiding the application of MoS2 in the antibacterial field. Overall, the review provides an in-depth understanding of the antibacterial mechanisms of MoS2 and presents the challenges and future directions for the improvement of MoS2 in the field of high-efficiency antibacterial materials.

PdMo bimetallene nanozymes for photothermally enhanced antibacterial therapy and accelerated wound healing

Although antibacterial platforms involving nanozymes have been extensively investigated, there are still problems of poor reactive oxygen species generation efficiency and obstinate bacterial biofilms. Developing a nanozyme-photothermal therapy nanoplatform with superior sterilization effects and minimal side effects would be a good alternative for completely eliminating bacteria and biofilms. Herein, an ultrathin PdMo bimetallene nanozyme with a planar topology and boosted metal utilization, exhibiting excellent photothermal and peroxidase-like activity, is designed for synergistic nanozyme-photothermal sterilization applications and accelerated wound healing. The superior catalytic activity of PdMo bimetallene nanozymes could convert a biosafe concentration of hydrogen peroxide (H2O2) into large quantities of toxic hydroxyl radicals (•OH) under laser irradiation, enhancing bacterial membrane permeability and thermal sensitivity for efficient removal of bacteria and biofilms. In addition, PdMo bimetallene presents a good wound-healing ability according to the results of fibroblast proliferation and collagen deposition with minor side effects. This work would provide an innovative avenue for developing metallene-based nanozymes for biomedical applications.

2D-MoS2-supported copper peroxide nanodots with enhanced nanozyme activity: application in antibacterial activity

Peroxidase (POD)-like nanozymes are an upcoming class of new-generation antibiotics that are efficient for broad-spectrum antibacterial action. The POD-like activity employs the generation of reactive oxygen species (ROS), which have been utilized for bactericidal action. However, their intrinsic low catalytic activity and stability limit their bactericidal properties. In this study, we prepared a MoS2-based nanocomposite with copper peroxide nanodots (MoS2@CP) to achieve pH-dependent light-induced nanozyme-based antibacterial action. It has shown superior peroxidase and antibacterial activity at low pH. The mechanism behind the enhanced POD-like activity and high antibacterial activity was established. The mechanistic pathway involves estimating ROS generation, membrane depolarization, inner membrane permeabilization, metal ion release, and the effect of NIR on photothermal and photodynamic activities. Overall, our work highlighted the combinatorial approach for eradicating bacterial infections using enzyme-based antibacterial agents.

Metal-organic framework-modulated Fe3O4 composite au nanoparticles for antibacterial wound healing via synergistic peroxidase-like nanozymatic catalysis

Bacterial wound infections are a serious threat due to the emergence of antibiotic resistance. Herein, we report an innovative hybrid nanozyme independent of antibiotics for antimicrobial wound healing. The hybrid nanozymes are fabricated from ultra-small Au NPs via in-situ growth on metal-organic framework (MOF)-stabilised Fe3O4 NPs (Fe3O4@MOF@Au NPs, FMA NPs). The fabricated hybrid nanozymes displayed synergistic peroxidase (POD)-like activities. It showed a remarkable level of hydroxyl radicals (·OH) in the presence of a low dose of H2O2 (0.97 mM). Further, the hybrid FMA nanozymes exhibited excellent biocompatibility and favourable antibacterial effects against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The animal experiments indicated that the hybrid nanozymes promoted wound repair with adequate biosafety. Thus, the well-designed hybrid nanozymes represent a potential strategy for healing bacterial wound infections, without any toxic side effects, suggesting possible applications in antimicrobial therapy.

pH-Switchable phenylalanine-templated copper nanoclusters: CO2 probing and efficient peroxidase mimicking activity

Inter-cluster conversion through the strategic tuning of external stimuli and thereby modulation of the optical properties of metal nanoclusters (MNCs) is an emerging domain for exploration. Herein, we report the preparation of blue-emitting CuNCs using phenylalanine (Phe) as a template under acidic conditions (pH ∼ 4). The as-prepared CuNCs exhibit a sequential tuning of the photophysical properties upon varying the pH of the solution from pH ∼4 to pH ∼12. Blue-emitting CuNCs (B-CuNCs, λem = 410 nm) are systematically converted to cyan-emitting CuNCs (C-CuNCs, λem = 490 nm) with a large red-shifted emission maximum by 80 nm as a function of pH. Our present investigation delineates an unprecedented switchability of the photoluminescence (PL) properties of the CuNCs with the variations of the pH from pH ∼4 to pH ∼12. Both the Phe-templated CuNCs (B-CuNCs and C-CuNCs) were broadly characterized by various spectroscopic and morphological techniques. The X-ray photoelectron spectroscopy (XPS) studies reveal the presence of different oxidation states in the metallic core of B-CuNCs and C-CuNCs. These results in turn substantiate the pH-induced intercluster conversion of CuNCs through the substantial change in their core composition as well as valence states. Owing to the pH sensitivity, the CuNCs act as an efficient and highly sensitive probe for CO2, and quantitative estimation of the dissolved CO2 in the form of bicarbonate ions has been achieved through the enhancement of the PL intensity, wherein a very low value of the limit of detection (LOD) of ∼60 μM was obtained. Furthermore, we demonstrated that the CuNCs act as an efficient bio-catalyst with peroxidase mimicking enzymatic activity which has been investigated using OPD as a substrate under physiological conditions (pH ∼7.4 and temperature ∼37 °C). The mechanistic investigations confirmed that the oxidation of OPD mainly proceeds through the generation of hydroxyl radicals (˙OH). We hope the present investigations shed light on a multidimensional aspect of MNCs and uncover an upsurging recent interest in MNCs to act as an artificial enzyme.

Recent Advances in Nanozyme-Mediated Strategies for Pathogen Detection and Control

Pathogen detection and control have long presented formidable challenges in the domains of medicine and public health. This review paper underscores the potential of nanozymes as emerging bio-mimetic enzymes that hold promise in effectively tackling these challenges. The key features and advantages of nanozymes are introduced, encompassing their comparable catalytic activity to natural enzymes, enhanced stability and reliability, cost effectiveness, and straightforward preparation methods. Subsequently, the paper delves into the detailed utilization of nanozymes for pathogen detection. This includes their application as biosensors, facilitating rapid and sensitive identification of diverse pathogens, including bacteria, viruses, and plasmodium. Furthermore, the paper explores strategies employing nanozymes for pathogen control, such as the regulation of reactive oxygen species (ROS), HOBr/Cl regulation, and clearance of extracellular DNA to impede pathogen growth and transmission. The review underscores the vast potential of nanozymes in pathogen detection and control through numerous specific examples and case studies. The authors highlight the efficiency, rapidity, and specificity of pathogen detection achieved with nanozymes, employing various strategies. They also demonstrate the feasibility of nanozymes in hindering pathogen growth and transmission. These innovative approaches employing nanozymes are projected to provide novel options for early disease diagnoses, treatment, and prevention. Through a comprehensive discourse on the characteristics and advantages of nanozymes, as well as diverse application approaches, this paper serves as a crucial reference and guide for further research and development in nanozyme technology. The expectation is that such advancements will significantly contribute to enhancing disease control measures and improving public health outcomes.

G-/C-rich ssDNA-based Fe and Cu/Fe nanoclusters with peroxidase-like activity for intracellular ROS production and cytotoxicity applications

Five G-/C-rich single-stranded DNA (ssDNA) with different sequences and lengths were templated to prepare the DNA-Cu, DNA-Fe, and bimetallic DNA-Cu/M nanoclusters (NCs). The peroxidase-like activities of these nanomaterials were studied using H₂O₂ and 3,3',5,5''-tetramethylbenzidine (TMB) as the reaction substrates in HAc-NaAc buffer. It was found that T30-G2-Fe NCs and T30-G2-Cu/Fe NCs, with a size of about 2 nm, exhibit similar and the strongest enzyme-like activity under optimal conditions. Both NCs possess a similarly high affinity to substrates, and the Michaelis-Menten constant (K_m) values to TMB and H₂O₂ are about 11 and 2-3 times lower than those of natural horseradish peroxidase (HRP), respectively. The activity of both nanozymes decreases to about 70% after being kept for one week in pH 4.0 buffer at 4 °C, which is comparable with HRP. Hydroxyl radicals (•OH) are the main reactive oxygen species (ROS) produced in the catalytic reaction. Moreover, both NCs can facilitate in situ generation of ROS in HeLa cells using endogenous H₂O₂. MTT assays indicate that the T30-G2-Cu/Fe NCs exhibit the strong selective cytotoxicity to HeLa cells over HL-7702 cells. The cellular viability is about 70% and 50% after incubating with 0.6 M NCs for 24 h without or with 2 mM H₂O₂, respectively. The current study shows that the T30-G2-Cu/Fe NCs have the potential for chemical dynamic treatment (CDT).

Amorphous Fe-Containing Phosphotungstates Featuring Efficient Peroxidase-like Activity at Neutral pH: Toward Portable Swabs for Pesticide Detection with Tandem Catalytic Amplification

Peroxidase-mimetic materials are intensively applied to establish multienzyme systems because of their attractive merits. However, almost all of the nanozymes explored exhibit catalytic capacity only under acidic conditions. The pH mismatch between peroxidase mimics in acidic environments and bioenzymes under neutral conditions significantly restricts the development of enzyme-nanozyme catalytic systems especially for biochemical sensing. To solve this problem, here amorphous Fe-containing phosphotungstates (Fe-PTs) featuring high peroxidase activity at neutral pH were explored to fabricate portable multienzyme biosensors for pesticide detection. The strong attraction of negatively charged Fe-PTs to positively charged substrates as well as the accelerated regeneration of Fe²⁺ by the Fe/W bimetallic redox couples was demonstrated to play important roles in endowing the material with peroxidase-like activity in physiological environments. Consequently, integrating the developed Fe-PTs with acetylcholinesterase and choline oxidase led to an enzyme-nanozyme tandem platform with good catalytic efficiency at neutral pH for organophosphorus pesticide response. Furthermore, they were immobilized onto common medical swabs to fabricate portable sensors for paraoxon detection conveniently based on smartphone sensing, showing excellent sensitivity, good anti-interference capacity, and low detection limit (0.28 ng/mL). Our contribution expands the horizon of acquiring peroxidase activity at neutral pH, and it will also open avenues to construct portable and effective biosensors for pesticides and other analytes.

Ligand-Mediated Exfoliation and Antibacterial Activity of 2H Transition-Metal Dichalcogenides

Transition-metal dichalcogenides (TMDs) exists mainly in two polymorphs, namely, 1T (metallic) and 2H (semiconducting). To tailor the characteristics and practical utility of TMDs for different applications, functionalization is essential. In our earlier studies, we have shown that functionalized 1T and 2H MoS₂ exhibit exceptionally high antibacterial activity. The functionalization and related biological applications of other 1T (chemically exfoliated) TMDs were reported, but regarding other 2H TMDs, the functionalization and antibacterial activity are not explored yet. Hence, here we prepared functionalized 2H TMDs such as WS₂, WSe₂, and MoSe₂ other than MoS₂ by using a positively charged thiolate surfactant ligand. Further, functionalized 2H TMDs were utilized for antibacterial activity against Gram-positive and Gram-negative bacteria for a comparative antibacterial analysis. Interestingly, we found disparity in activity among the functionalized 2H TMDs, that is, MoS₂ shows higher activity than WS₂ followed by MoSe₂ and WSe₂. The intracellular reactive oxygen species measurement was found to be in the order MoS₂ > WS₂ > MoSe₂ > WSe₂, which is solely responsible for variation in the activity of functionalized TMDs. These results indicate that the easy functionalization of all types TMDs by using thiol ligand and importance of core material should be considered while designing functionalized material for specific applications.