Adsorption enhanced the oxidase-mimicking catalytic activity of octahedral-shape Mn3O4 nanoparticles as a novel colorimetric chemosensor for ultrasensitive and selective detection of arsenic

Mn2O3 NPs-induced liver injury is potentially associated with gut microbiota dysbiosis in broiler chicken

Mn2O3 nanometer particles(Mn2O3 NPs), a new material, is widely used in medicine, electrochemical sensing and energy storage fields. The widespread use of Mn2O3 NPs has caused health concerns, and it is necessary to clarify the toxic mechanism of Mn2O3 NPs exposure. Our findings showed that Mn2O3 NPs exposure could lead to liver histological abnormalities, mitochondrial dysfunction in liver, as well as mitochondrial-mediated apoptosis, autophagy and mitochondrial dynamics disorder, and eventually lead to liver injury. At the same time, the ileal epithelium suffered physiological damage and inflammation after Mn2O3 NPs exposure, and the expression levels of genes and proteins related to intestinal barrier function (MUC1 ZO-1 Claudin1 and Occludin) were significantly down-regulated. Meanwhile, 16s sequencing analysis of intestinal bacteria showed that Mn2O3 NPs exposure caused significant changes in intestinal flora abundance. The Firmicutes/Bacteroidetes ratio increased, and the abundance of probiotics (Bacteroides, Bifidobacterium, Faecalibacterium) decreased, while the abundance of harmful bacteria (Streptococcus, Enterococcus, Pseudomonas) increased. The changes in these microflorae may potentially impact the development of liver injury. Altogether, these results provide novel insights into the potential mechanism of Mn2O3 NPs related hepatotoxicity induced by gut microbiota via the gut-liver axis, and contribute to a better interpretation of the health impact of Mn2O3 NPs.

Phyto-assisted eco-benevolent synthesis of oxidase-mimic Cu-Mn3O4 as an antibacterial and antiproliferative agent

In recent years, the marked augment of antibiotic resistance hampered the development of antibacterial agent. Nanozymes by their in situ ROS production capability oxidize cellular substances of bacterial cell and eliminate MDR bacteria. Therefore, synthesis of effective nanozymes from green precursors is rarely reported, so the prime objective of this study was to synthesize Cu-Mn3O4 nanozymes from aqueous extracts of medicinal plant Azadirachta indica via co-precipitation approach and to endorse their biomedical applications. The synthesized materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectrometer (FTIR), Scanning Electron Images (SEM), and Field-Emission Scanning Electron Microscopy (FESEM) images. X-ray Diffraction (XRD) patterns revealed the formation of hausmannite Mn3O4 crystal system. Fourier Transform Infrared spectrometer (FTIR) spectra revealed functional groups on the surface nanoparticles for their stabilization. Energy-Dispersive X-ray spectroscopy (EDAX) profile confirmed the existence of desired elements in the synthesized nanozymes. B1 mimics oxidase enzyme most effectively with Km = 0.175 mM and Vmax = 10.34 µM/min. The low Km and high Vmax indicates the strong binding affinity and high catalytic activity. From the agar diffusion antibacterial assay, it can be concluded that B3 is the most potent antibacterial agent specifically against Gram-positive bacteria Bacillus subtilis with inhibition zone of 27 mm at 250 µg/mL. Their cytotoxic activities on neuroblastoma (SHSY5) cell line were investigated for the first time. The data revealed that synthesized nanooctahedrons possess a significant cytotoxicity against cancer cell lines SHSY5Y (IC50 = 137.47 ± 14.11 µg/mL) and SKOV3 (IC50 = 72.72 ± 9.33 µg/mL). Overall, with increasing Cu amount, the percentage growth inhibition of Mn3O4 crystal system enhanced. The improved antibacterial activity and cytotoxicity is due to synergy between metal and phytochemicals. Radical scavenging activity of synthesized nanozymes is comparatively lower than their green source and the comparatively lower IC50 values of B1, 234.12 ± 15.13 and 220.12 ± 10.37 respectively, which indicates that it is more active in scavenging DPPH and ABTS radical. B2 (IC50 = 310.56 ± 5.92 µg/mL) and B3 (IC50 = 43.56 ± 3.03 µg/mL) scavenge superoxide radicals and FRAP more effectively. It is noticed that synthesized nanozymes have greater antibacterial and anticancer activity but low scavenging ability compared to green extract. Thus, Cu-Mn3O4 NPs from Azadirachta indica leaf extract could be utilized as a replacement of potential antibiotic drug candidate against MDR bacteria and in cancer avenues.

Laccase-mimicking activity of octahedral Mn3O4 nanoparticles and fluorescence of carbon dots as dual-mode signals for the specific detection of arsenic(V) in environmental water samples

The detrimental growth of water pollutants such as heavy metals has become a life-threatening problem in the modern era. Challenges remain in the development of rapid and accurate methods for detecting pentavalent arsenic [As(V)] in environmental water. The octahedral Mn3O4 nanoparticles (NPs) did not display excellent laccase-mimicking catalytic activity, whereas the adsorbed As(V) on the surface significantly enhanced the catalytic activity. Meanwhile, the quinone imine generated from the substrates 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AAP) catalyzed by octahedral Mn3O4 NPs further quenched the carbon dots fluorescence. Thus, it is possible to establish a fast and accurate dual-mode sensor for detecting As(V). The developed dual-mode method of As(V) detection has good sensitivity and selectivity. The limit of detection for As(V) in colorimetric mode is 6.96 μg·L-1, whereas in the fluorescent mode, it is as low as 2.56 μg·L-1. Moreover, the detection data obtained by the dual-mode method can be validated by each other, thereby ensuring the dependability of the sensing system. The constructed dual-mode method with merits of sensitivity, speed and accuracy can offer a powerful tool for As(V) detection in environmental water. Furthermore, the application of laccase-mimicking activity in dual-mode detection provides new strategies for other environmental hazard detection.

Applications of nanomaterials with enzyme-like activity for the detection of phytochemicals and hazardous substances in plant samples

Plants such as herbs, vegetables, fruits, and cereals are closely related to human life. Developing effective testing methods to ensure their safety and quantify their active components are of significant importance. Recently, nanomaterials with enzyme-like activity (known as nanozymes) have been widely developed in various assays, including colorimetric, fluorescence, chemiluminescence, and electrochemical analysis. This review presents the latest advances in analyzing phytochemicals and hazardous substances in plant samples based on nanozymes, including some active ingredients, organophosphorus pesticides, heavy metal ions, and mycotoxins. Additionally, the current shortcomings and challenges of the actual sample analysis were discussed.

Recent advances in metal oxide nanozyme-based optical biosensors for food safety assays

Metal oxide nanozymes are emerging as promising materials for food safety detection, offering several advantages over natural enzymes, including superior stability, cost-effectiveness, large-scale production capability, customisable functionality, design options, and ease of modification. Optical biosensors based on metal oxide nanozymes have significantly accelerated the advancement of analytical research, facilitating the rapid, effortless, efficient, and precise detection and characterisation of contaminants in food. However, few reviews have focused on the application of optical biosensors based on metal oxide nanozymes for food safety detection. In this review, the catalytic mechanisms of the catalase, oxidase, peroxidase, and superoxide dismutase activities of metal oxide nanozymes are characterized. Research developments in optical biosensors based on metal oxide nanozymes, including colorimetric, fluorescent, chemiluminescent, and surface-enhanced Raman scattering biosensors, are comprehensively summarized. The application of metal oxide nanozyme-based biosensors for the detection of nitrites, sulphites, metal ions, pesticides, antibiotics, antioxidants, foodborne pathogens, toxins, and other food contaminants has been highlighted. Furthermore, the challenges and future development prospects of metal oxide nanozymes for sensing applications are discussed. This review offers insights and inspiration for further investigations on optical biosensors based on metal oxide nanozymes for food safety detection.

Advances in Nanomaterials and Colorimetric Detection of Arsenic in Water: Review and Future Perspectives

Arsenic, existing in various chemical forms such as arsenate (As(V)) and arsenite (As(III)), demands serious attention in water and environmental contexts due to its significant health risks. It is classified as "carcinogenic to humans" by the International Agency for Research on Cancer (IARC) and is listed by the World Health Organization (WHO) as one of the top 10 chemicals posing major public health concerns. This widespread contamination results in millions of people globally being exposed to dangerous levels of arsenic, making it a top priority for the WHO. Chronic arsenic toxicity, known as arsenicosis, presents with specific skin lesions like pigmentation and keratosis, along with systemic manifestations including chronic lung diseases, liver issues, vascular problems, hypertension, diabetes mellitus, and cancer, often leading to fatal outcomes. Therefore, it is crucial to explore novel, cost-effective, and reliable methods with rapid response and improved sensitivities (detection limits). Most of the traditional detection techniques often face limitations in terms of complexity, cost, and the need for sophisticated equipment requiring skilled analysts and procedures, which thereby impedes their practical use, particularly in resource-constrained settings. Colorimetric methods leverage colour changes which are observable and quantifiable using simple instrumentation or even visual inspection. This review explores the colorimetric techniques designed to detect arsenite and arsenate in water. It covers recent developments in colorimetric techniques, and advancements in the role of nanomaterials in colorimetric arsenic detection, followed by discussion on current challenges and future prospects. The review emphasizes efforts to improve sensitivity, selectivity, cost, and portability, as well as the role of advanced materials/nanomaterials to boost the performance of colorimetric assays/sensors towards combatting this pervasive global health concern.

Facile colorimetric sensor using oxidase-like activity of octahedral Ag2O particles for highly selective detection of Pb(II) in water

Pb(II) is a prevalent heavy metal ion classified as a 2B carcinogen. Excessive intake of Pb(II) in the human body can damage the central nervous system, kidneys, liver, and immune system, leading to permanent brain damage, anemia, and cancer. Colorimetry can be applied to rapidly determine Pb(II) residues, but there are still many challenges in the accuracy and sensitivity of detection. Based on the inhibitory impact of Pb(II) on the oxidase-like activity of octahedral silver oxide (Ag2O), a colorimetric sensor with smartphone-assisted analysis for the Pb(II) detection was first developed. Herein, it has been found that Pb(II) can adsorb onto the surface of octahedral Ag2O, hindering the production of O2- in the reaction system. This ultimately results in the suppression of oxidase-like activity, leading to a lighter purple appearance of the colorimetric reaction solution. The sensor exhibits a high degree of sensitivity and a limit of detection (LOD) for Pb(II) was calculated as 2.2 μg L-1. Hence, the developed colorimetric sensor with high sensitivity, excellent specificity, and high tolerance to sodium ions is hopeful to have practical applications in Pb(II) detection in environmental water samples. Moreover, the sensor will provide a novel strategy for heavy metal ion detection and other substances.

Nanomaterial-based optical colorimetric sensors for rapid monitoring of inorganic arsenic species: a review

Health concerns about the toxicity of arsenic compounds have therefore encouraged the development of new analytical tools for quick monitoring of arsenic in real samples with improved sensitivity, selectivity, and reliability. An overview of advanced optical colorimetric sensor techniques for real-time monitoring of inorganic arsenic species in the environment is given in this review paper. Herein, several advanced optical colorimetric sensor techniques for arsenite (As+3) and arsenate (As+5) based on doping chromogenic dyes/reagents, biomolecule-modified nanomaterials, and arsenic-binding ligand tethered nanomaterials are introduced and discussed. This review also highlights the benefits and limitations of the colorimetric sensor for arsenic species. Finally, prospects and future developments of an optical colorimetric sensor for arsenic species are also proposed. For future study in this sector, particularly for field application, authors recommend this review paper will be helpful for readers to understand the design principles and their corresponding sensing mechanisms of various arsenic optical colorimetric sensors.

Smartphone-assisted colorimetric aptasensor for rapid detection of carbendazim residue in agriculture products based on the oxidase-mimicking activity of octahedral Ag2O nanoparticles

Carbendazim (CBZ) is a widely used pesticides, and its excessive intake is serious damage to humans and animals. Herein, a stable and sensitive colorimetric aptasensor for rapid detection of CBZ residue has been established based on the enhancement of CBZ-specific aptamer (CZ-13) on oxidase-mimicking activity of octahedral Ag2O nanoparticles (NPs). The CZ-13 aptamer can significantly increase the catalytic activity by promoting the production of superoxide anion (·O2-) on the surface of Ag2O NPs and enhancing the affinity of octahedral Ag2O NPs to 3,3',5,5'-tetramethylbenzidine (TMB) molecules. In the presence of CBZ, the quantity of CZ-13 aptamer will be exhausted due to the specific binding to CBZ pesticide. Thus, the rest CZ-13 aptamer no longer enhanced the catalytic activity of octahedral Ag2O NPs, which leads to the change in color of sensing solution. The color change of sensing solution can be easily converted to the corresponding RGB value by a smartphone for quantitative and rapid detection of CBZ. The designed aptasensor has excellent sensitivity and specificity, and the limit of detection was determined as low as 7.35 μg L-1 for CBZ assay. Besides, the aptasensor exhibited good recoveries in the spiked cabbage, apple and cucumber, showing that it may have broad application prospects for detecting CBZ residues in agriculture products.

Facile colorimetric smartphone-based biosensor for rapid detection of organophosphorus pesticides residues in environment using the aptamer-enhanced oxidase activity of octahedral Ag2O particles

The long-term and excessive use of organophosphorus pesticides (OPs) leads to hazardous residues in the environment, which threatens human health to a considerable extent. Colorimetric methods can quickly and readily identify pesticide residue, but they still have various challenges in accuracy and stability. Herein, a smartphone-assisted and non-enzymatic colorimetric biosensor was constructed for rapid monitoring of multiple OPs based on the enhanced effect of aptamer on the catalytic ability of octahedral Ag₂O. It was demonstrated that the aptamer sequence could enhance the affinity of colloidal Ag₂O to chromogenic substrates, and accelerate the generation of oxygen radicals such as superoxide radical (·O₂^-) and singlet oxygen (¹O₂) from dissolved oxygen, thereby significantly increasing the oxidase activity of octahedral Ag₂O. The color change of the solution can be easily converted to the corresponding RGB values by a smartphone for quantitative and rapid detection of multiple OPs. Hence, the smartphone-based and visual biosensor of multiple OPs was acquired with limit of detection of 10 μg L^-1, 28 μg L^-1 and 40 μg L^-1 for isocarbophos, profenofos and omethoate, respectively. The colorimetric biosensor also exhibited good recoveries in several environmental and biological samples, showing that it may have broad application prospects for detecting OPs residues.

Mn3O4 nanoparticles decorated porous reduced graphene oxide with excellent oxidase-like activity for fast colorimetric detection of ascorbic acid

Mn₃O₄ nanoparticles composed of porous reduced graphene oxide nanosheets (Mn₃O₄@p-rGO) with enhanced oxidase-like activity were successfully fabricated through an in-situ approach for fast colorimetric detection of ascorbic acid (AA). The residual Mn²⁺ in the GO suspension of Hummers method was directly reused as the manganese source, improving the atom utilization efficiency. Benefiting from the uniform distribution of Mn₃O₄ nanoparticles on the surface of p-rGO nanosheets, the nanocomposite exhibited larger surface area, more active sites, and accelerated electron transfer efficiency, which enhanced the oxidase-like activity. Mn₃O₄@p-rGO nanocomposite efficiently activate dissolved O₂ to generate singlet oxygen (¹O₂), leading to high oxidation capacity toward the substrate 3,3',5,5'-tetramethylbenzidine (TMB) without the extra addition of H₂O₂. Furthermore, the prominent absorption peak of the blue ox-TMB at 652 nm gradually decreased in the presence of AA, and a facile and fast colorimetric sensor was constructed with a good linear relationship (0.5-80 μM) and low LOD (0.278 μM) toward AA. Owing to the simplicity and excellent stability of the sensing platform, its practical application for AA detection in juices has shown good feasibility and reliability compared with HPLC and the 2, 4-dinitrophenylhydrazine colorimetric method. The oxidase-like Mn₃O₄@p-rGO provides a versatile platform for applications in food testing and disease diagnosis.

Antioxidant Nanozymes: Mechanisms, Activity Manipulation, and Applications

Antioxidant enzymes such as catalase, superoxide dismutase, and glutathione peroxidase play important roles in the inhibition of oxidative-damage-related pathological diseases. However, natural antioxidant enzymes face some limitations, including low stability, high cost, and less flexibility. Recently, antioxidant nanozymes have emerged as promising materials to replace natural antioxidant enzymes for their stability, cost savings, and flexible design. The present review firstly discusses the mechanisms of antioxidant nanozymes, focusing on catalase-, superoxide dismutase-, and glutathione peroxidase-like activities. Then, we summarize the main strategies for the manipulation of antioxidant nanozymes based on their size, morphology, composition, surface modification, and modification with a metal-organic framework. Furthermore, the applications of antioxidant nanozymes in medicine and healthcare are also discussed as potential biological applications. In brief, this review provides useful information for the further development of antioxidant nanozymes, offering opportunities to improve current limitations and expand the application of antioxidant nanozymes.

A review on multi-synergistic transition metal oxide systems towards arsenic treatment: Near molecular analysis of surface-complexation (synchrotron studies/modeling tools)

The science and interface chemistry between the arsenic (As) anions and the different adsorbent systems have been gaining interest in recent years in environmental remediation applications. Metal-oxides and the corresponding hybrid systems have shown promising performance as novel adsorbents in various treatment technologies. The abundance, surface chemistry, high surface area (active-centres), various synthesis and functionalization methodologies, and good recyclability make these metal oxide-based nanomaterials as potential remediating agents for As oxyanions. This work critically reviews eight different platforms focused on the arsenic contamination issue, where the first classification describes the origin of arsenic contamination and presents geographical and demo-graphical considerations. The following section briefs the state-of-the-art remediation techniques for arsenic treatment with a comparative evaluation. An emphasized discussion has been provided regarding the adsorption and classification of various metal oxide adsorbents. In the next classification, various multi-synergism abilities like Redox activity, Surface functional groups, Surface area/morphology, Heterogeneous catalysis, Reactive oxygen species, Photo-catalytic/electro-catalytic reactions, and Electrosorption are detailed. The classification of various characterization tools for accessing the arsenic remediation qualitatively and quantitatively are given in the fifth chapter. The first-of-its-kind dedicated analysis has been given on the surface complexation aspects of the arsenic speciation onto various metal adsorbent systems using synchrotron results, surface-complexation modeling, and molecular simulation (e.g., DFT) in the sixth chapter. The current sensing applications of these novel nano-material systems for arsenic determination using colorimetric and electrochemical-based analytical tools and a note about the economic parameters, i.e., regeneration aspects of various adsorbent systems/the sustainable applications of the treated sludge materials, are provided in the final sections. This work makes a critical analysis of 'Environmental Nanotechnology' towards 'Arsenic Treatment'.

Simultaneous removal of arsenate and arsenite in water using a novel functional halloysite nanotube composite

This work aims at exploring a novel environment-friendly nanomaterial based on natural clay minerals for arsenic removal in aqueous samples. Halloysite nanotubes (HNTs) were selected as the substrate with Mn oxides loaded on the surface to enhance its arsenic adsorption ability and then grafted onto the SiO₂-coated Fe₃O₄ microsphere to get a just enough magnetic performance facilitating the material's post-treatment. The prepared composite (Fe₃O₄@SiO₂@Mn-HNTs) was extensively characterized by various instruments including Fourier transform infrared spectroscope (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TG), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscope (XPS), and X-ray diffraction (XRD). Batch experiments were carried out to get the optimum test conditions for arsenic adsorption by the composite, including pH, loading amount of Mn oxides, adsorbent dosage, and the co-existing ions. The adsorption of As^III and As^V on Fe₃O₄@SiO₂@Mn-HNTs were both well fitted with the pseudo-second-order kinetic model as well as the Langmuir adsorption isotherm model revealing the chemisorption between arsenic and Fe₃O₄@SiO₂@Mn-HNTs. The adsorption process of As^III and As^V were both endothermic and spontaneous displayed by the thermodynamic study. The capacities of the prepared composite are 3.28 mg g^-1 for As^III and 3.52 mg g^-1 for As^V, respectively, which are comparable or better than those of many reported materials in the references. Toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) tests were carried out to access the secondary environmental risk of the composite and showed that it was quite environmentally stable and can be safely disposed. The composite was successfully applied in environmental water samples indicating its great potential applicability in future.

Self-triggered fluorescent metal-organic framework mimic enzyme for competitive immunoassay of hypoglycemic drug in functional tea

Colorimetric or fluorescent biosensors based on mimic enzymes have come into the spotlight in virtue of their visual detection. In traditional visual sensors, fluorescent-changing or color-changing substances should be introduced for the catalytic reaction with mimic enzymes. Herein, a mimic enzyme (Au@Fe-MIL-88B) with self-triggered fluorescent property was prepared. By incorporating Au nanoparticles (Au NPs) in Fe-MIL-88B, a higher peroxidase activity of Au@Fe-MIL-88B was monitored due to the synergistic effect between Au NPs and Fe-MIL-88B. Besides, Au NPs can change the valence of Fe ion in metal organic framework (MOF), thus lower background fluorescence was discovered, but the addition of H₂O₂ can trigger the self-fluorescence of Au@Fe-MIL-88B. By using Au@Fe-MIL-88B as a label to anchor secondary antibody, a competitive immunosensor based on fluorescence and photoelectrochemistry was constructed for the immunoassay of rosiglitazone (RSG), a kind of hypoglycemic drug. Finally, a portable instrument was homemade for the on-site and convenient detection of RSG in functional tea. This self-triggered fluorescent MOF may provide a possible route to design biosensors for the detection of hazardous materials.

A liquid colorimetric chemosensor for ultrasensitive detection of glyphosate residues in vegetables using a metal oxide with intrinsic peroxidase catalytic activity

The control of pesticide residues in food is of increasing importance nowadays due to the over-use and misapplication of herbicides in agricultural production. However, the current colorimetric method for rapid detection of glyphosate still faces many challenges like the low sensitivity and stability. Herein, a simple and ultrasensitive liquid colorimetric chemosensor for glyphosate detection was successfully constructed. Glyphosate pesticide can interact with metallic oxidelike porous Co3O4 nanodisc, and inhibit its inherent peroxidase-mimicking activity, making the colour of the solution change from blue to light blue or even colourless. The colour variation of the colorimetric chemosensor enables us to easily distinguish in less than 20 min even by the naked eye whether glyphosate exceeds the allowable level. The limit of detection (LOD) of the chemosensor for glyphosate was calculated as low as 2.37 μg·L-1, and the chemosensor displays excellent selectivity against other competitive pesticides and metal ions. Further studies have also validated the applicability of the colorimetric chemosensor in actual samples like tomato, cucumber and cabbage, indicating that the proposed strategy may have promising application prospects for detecting glyphosate residues in agricultural products.

L-Cysteine functionalized graphene oxide nanoarchitectonics: A metal-free Hg2+ nanosensor with peroxidase-like activity boosted by competitive adsorption

Developing non-noble metal, even metal-free chemical sensors for the detection of toxic heavy metal ions is significantly desirable for economically and environmentally sustainable application but has heretofore remained elusive. Herein, a _L-cysteine functionalized graphene oxide nanosheet (CGO) nanoarchitectonics, greenly synthesized by a very simple method at room temperature, was utilized to realize the simultaneous enrichment and colorimetric detection of trace mercury ions (Hg²⁺). It was discovered that CGO, as a nanozyme mimic exhibited greatly enhanced peroxidase-like catalytic activity than the pristine graphene oxide. By exploring the interactions of CGO nanozyme with colorimetric substrate, 3,3',5,5'-tetramethylbenzidine (TMB) and target Hg²⁺ ions, we found that the sensing principle was based mainly on the competitive adsorption between Hg²⁺ ions and TMB over CGO. The pre-capture of Hg²⁺ ions hindered the TMB binding on CGO, resulting in the promoted oxidation of TMB by H₂O₂ to produce more colored oxidation products, from which the colorimetric sensing of Hg²⁺ was realized with a good detection effect on 5 μg L^-1 solution. As an enrichment-sensing integration platform, this metal-free sensor is cost-effective and sensitive, and presents considerable anti-interference ability over other metal ions. Overall, this work not only expands the application of graphene-based materials in colorimetric detection but also provides a general sensing principle to construct highly sensitive sensors.

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

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

Recent Advances in Colorimetric Detection of Arsenic Using Metal-Based Nanoparticles

Nowadays, arsenic (III) contamination of drinking water is a global issue. Laboratory and instrument-based techniques are typically used to detect arsenic in water, with an accuracy of 1 ppb. However, such detection methods require a laboratory-based environment, skilled labor, and additional costs for setup. As a result, several metal-based nanoparticles have been studied to prepare a cost-effective and straightforward detector for arsenic (III) ions. Among the developed strategies, colorimetric detection is one of the simplest methods to detect arsenic (III) in water. Several portable digital detection technologies make nanoparticle-based colorimetric detectors useful for on-site arsenic detection. The present review showcases several metal-based nanoparticles that can detect arsenic (III) colorimetrically at a concentration of ~0.12 ppb or lower in water. A literature survey suggests that biomolecule-based metal nanoparticles could serve as low-cost, facile, susceptible, and eco-friendly alternatives for detecting arsenic (III). This review also describes future directions, perspectives and challenges in developing this alternative technology, which will help us reach a new milestone in designing an effective arsenic detector for commercial use.

A fast phosphate colorimetric sensor based on MoS2/UiO-66 (Fe/Zr) nanocomposites as oxidase-/peroxidase-like nanoenzymes

According to the excellent peroxidase activity of MoS2/UiO-66(Fe/Zr) as well as specific recognition towards phosphate (Pi), a fast cheap colorimetric sensing platform has been established to determine phosphate.