Highly Conductive Peroxidase-like Ce-MoS2 Nanoflowers for the Simultaneous Electrochemical Detection of Dopamine and Epinephrine

The accurate and simultaneous detection of neurotransmitters, such as dopamine (DA) and epinephrine (EP), is of paramount importance in clinical diagnostic fields. Herein, we developed cerium-molybdenum disulfide nanoflowers (Ce-MoS2 NFs) using a simple one-pot hydrothermal method and demonstrated that they are highly conductive and exhibit significant peroxidase-mimicking activity, which was applied for the simultaneous electrochemical detection of DA and EP. Ce-MoS2 NFs showed a unique structure, comprising MoS2 NFs with divalent Ce ions. This structural design imparted a significantly enlarged surface area of 220.5 m2 g-1 with abundant active sites as well as enhanced redox properties, facilitating electron transfer and peroxidase-like catalytic action compared with bare MoS2 NFs without Ce incorporation. Based on these beneficial features, Ce-MoS2 NFs were incorporated onto a screen-printed electrode (Ce-MoS2 NFs/SPE), enabling the electrochemical detection of H2O2 based on their peroxidase-like activity. Ce-MoS2 NFs/SPE biosensors also showed distinct electrocatalytic oxidation characteristics for DA and EP, consequently yielding the highly selective, sensitive, and simultaneous detection of target DA and EP. Dynamic linear ranges for both DA and EP were determined to be 0.05~100 μM, with detection limits (S/N = 3) of 28 nM and 44 nM, respectively. This study shows the potential of hierarchically structured Ce-incorporated MoS2 NFs to enhance the detection performances of electrochemical biosensors, thus enabling extensive applications in healthcare, diagnostics, and environmental monitoring.

Green Synthesis of Au Magnetic Nanocomposites Using Waste Chestnut Skins and Their Application as a Peroxidase Mimic Nanozyme Electrochemical Sensing Platform for Sodium Nitrite

An electrochemical sensor with high sensitivity for the detection of sodium nitrite was constructed based on the peroxidase-like activity of Au magnetic nanocomposites (Au@Fe3O4). The Au@Fe3O4 composite nanoparticles were green-synthesized via the reduction of gold nanoparticles (AuNPs) from waste chestnut skins combined with the sonochemical method. The nanoparticles have both the recoverability of Fe3O4 and the advantage of being able to amplify electrical signals. Furthermore, the synergistic effect of green reduction and sonochemical synthesis provides a functional approach for the preparation of Au@Fe3O4 with significant peroxidase-like activities. The physicochemical properties were characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), the Brunauer-Emmett-Teller (BET) method, and Fourier transform infrared spectroscopy (FT-IR). The electrochemical properties of sodium nitrite were determined with cyclic voltammetry (CV) and chronoamperometry (i-t). The results revealed that Au@Fe3O4 acted as a peroxidase mimic to decompose hydrogen peroxide to produce free radicals, while ·OH was the primary free radical that promoted the oxidation of sodium nitrite. With the optimal detection system, the constructed electrochemical sensor had a high sensitivity for sodium nitrite detection. In addition, the current response had a good linear relationship with the sodium nitrite concentration in the range of 0.01-100 mmol/L. The regression equation of the working curve was y = 1.0752x + 4.4728 (R2 = 0.9949), and the LOD was 0.867 μmol/L (S/N = 3). Meanwhile, the constructed detection system was outstanding in terms of recovery and anti-interference and had a good detection stability of more than 96.59%. The sensor has been successfully applied to a variety of real samples. In view of this, the proposed novel electrochemical analysis method has great prospects for application in the fields of food quality and environmental testing.

Co-Doped CeO2/Activated C Nanocomposite Functionalized with Ionic Liquid for Colorimetric Biosensing of H2O2 via Peroxidase Mimicking

Hydrogen peroxide acts as a byproduct of oxidative metabolism, and oxidative stress caused by its excess amount, causes different types of cancer. Thus, fast and cost-friendly analytical methods need to be developed for H₂O₂. Ionic liquid (IL)-coated cobalt (Co)-doped cerium oxide (CeO₂)/activated carbon (C) nanocomposite has been used to assess the peroxidase-like activity for the colorimetric detection of H₂O₂. Both activated C and IL have a synergistic effect on the electrical conductivity of the nanocomposites to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The Co-doped CeO₂/activated C nanocomposite has been synthesized by the co-precipitation method and characterized by UV-Vis spectrophotometry, FTIR, SEM, EDX, Raman spectroscopy, and XRD. The prepared nanocomposite was functionalized with IL to avoid agglomeration. H₂O₂ concentration, incubation time, pH, TMB concentration, and quantity of the capped nanocomposite were tuned. The proposed sensing probe gave a limit of detection of 1.3 × 10^-8 M, a limit of quantification of 1.4 × 10^-8 M, and an R² of 0.999. The sensor gave a colorimetric response within 2 min at pH 6 at room temperature. The co-existing species did not show any interference during the sensing probe. The proposed sensor showed high sensitivity and selectivity and was used to detect H₂O₂ in cancer patients' urine samples.

A Cascade Enzyme System Integrating Peroxidase Mimic with Catalase for Linear Range Expansion of H2 O2 Assay: A Mechanism and Application Study

Peroxidase (POD) Nanozyme-based hydrogen peroxide (H₂ O₂ ) detection is popular, but hardly adapt to high concentration of H₂ O₂ owing to narrow linear range (LR) and low LR maximum. Here, a solution of combining POD and catalase (CAT) is raised to expand the LR of H₂ O₂ assay via decomposing part of H₂ O₂ . As a proof of concept, a cascade enzyme system (rGRC) is constructed by integrating ruthenium nanoparticles (RuNPs), CAT and graphene together. The rGRC-based sensor does perform an expanded LR and higher LR maximum for H₂ O₂ detection. Meanwhile, it is confirmed that LR expansion is closely associated with apparent K_m of rGRC, which is determined by the relative enzyme activity between CAT and POD both in theory and in experiment. At last, rGRC is successfully used to detect high concentration of H₂ O₂ (up to 10 mm) in contact lens care solution, which performs higher assay accuracy (close to 100% recovery at 10 mm of H₂ O₂ ) than traditional POD nanozymes. This study brings up a kind of POD/CAT cascade enzyme system and provides a new concept for accurate and facile H₂ O₂ detection. Additionally, it replenishes a new enzyme-substrate model of achieving the same pattern with competitive inhibition in enzyme reactions.

Spherical Hydrogel Sensor Based on PB@Fe-COF@Au Nanoparticles with Triplet Peroxidase-like Activity and Multiple Capture Sites for Effective Detection of Organophosphorus Pesticides

The residues of organophosphorus pesticides (OPs) have drawn worldwide increasing attention because of their potential fatal effects on human health and ecological systems. It is of great significance to develop an efficient and portable method for in-field detection of OPs. Herein, a novel core-shell nanocomposite of prussian blue@Fe-covalent organic framework@Au (PB@Fe-COF@Au) was constructed. Fe²⁺ and Fe³⁺ in PB nanoparticle (PBNP) cores, Fe-porphyrin in COF shells, and AuNPs grown on shells all acted as peroxidase-like catalytic active sites, enabling PB@Fe-COF@Au to possess triplet peroxidase-like activity. A colorimetric, affordable, sensitive, and selective strategy was designed to detect OPs. Compared with previous reports, this sensor realized a wider linear range for chlorpyrifos of 10-800 ng mL^-1 with a relatively lower detection limit of 0.61 ng mL^-1, which was attributed to the overlapping triple catalytic sites of PB@Fe-COF@Au and triple response sites to OPs. The assay was successfully employed to detect chlorpyrifos in food and environmental samples. Moreover, to meet the demand of in-field detection for OPs, a spherical hydrogel method based on PB@Fe-COF@Au with visual, portable, and equipment-free features was fabricated. This work provides a new pathway to design and apply effective nanozymes for on-site monitoring of pesticides.

Dual Glutathione Depletion Enhanced Enzyme Catalytic Activity for Hyperthermia Assisted Tumor Therapy on Semi-Metallic VSe2/Mn-CS

Semimetallic nanomaterials as photothermal agents for bioimaging and cancer therapy have attracted tremendous interest. However, the poor photothermal stability, low biocompatibility, and single component limit their therapeutic efficiency in cancer treatment. Here, manganese-doped VSe₂ semimetallic nanosheets were prepared and subsequently modified with chitosan (named VSe₂/Mn-CS NSs) for combined enzyme catalytic and photothermal therapy. VSe₂/Mn-CS NSs show high photothermal property with a photothermal conversion efficiency of 34.61% upon 808 nm near-infrared laser irradiation. In the tumor microenvironment, VSe₂/Mn-CS NSs can convert endogenous H₂O₂ into lethal hydroxyl radicals (•OH) to induce cancer cell apoptosis. The interaction between glutathione (GSH) and Se-Se bonds in VSe₂/Mn-CS NSs results in the depletion of GSH level, and the valence states transition of manganese ions is also beneficial for the GSH consumption. This dual depletion of GSH markedly enhances the peroxidase (POD) activity, leading to the high •OH production and the improved therapeutic effect. What is more, the T₁-weighted magnetic resonance and photoacoustic imaging endow VSe₂/Mn-CS NSs with the ability to guide and track the treatment process. Our study provides a research strategy for the application of semimetallic nanomaterials in cancer diagnosis and treatment.

B,N-Doped PdRu Aerogels as High-Performance Peroxidase Mimics for Sensitive Detection of Glucose

Among plentiful porous nanomaterials, noble metal aerogels taken as nanozymes attract broad attention in sensing applications with their distinct enzyme mimic functions. In the catalytic field, the heteroatom doping strategy is a kind of way with great promise in improving the enzyme mimic activity of noble metal aerogels. In this experiment, we find a type of creative materials that were prepared by the fast and simple method. Due to the unique porous structure and synergetic effect from doped atoms, PdRu aerogels co-doped with boron and nitrogen (B, N-PdRu aerogels) were prepared using NH₃BH₃ as a reductant, which present improved peroxidase mimicking activity. With the existence of H₂O₂, the oxidation of 3,3',5,5'-tetramethylbenzidine was catalyzed by B, N-PdRu aerogels fairly efficiently, whose solution would be a blue appearance at optimum absorption wavelength 652 nm. Thus, by the tandem reaction bound to the enzyme glucose oxidase, the B, N-PdRu aerogels can be used for the sensitive determination of glucose. The new method has a good linear detection effect for glucose in the range of 10 μM to 2 mM. The minimum limit of detection can reach as low as 6 μM. This work will contribute to research on the rational design of metal aerogels based on the heteroatomic doping strategy and enhance the corresponding performance for a variety of applications.

Bimetallic Metal-Organic Frameworks: Enhanced Peroxidase-like Activities for the Self-Activated Cascade Reaction

Metal-organic frameworks (MOFs) are significant useful molecular materials as a result of their high surface area and flexible catalytic activities by tuning the metal centers and ligands. MOFs have attracted great attention as efficient nanozymes recently; however, it is still difficult to understand polymetallic MOFs for enzymatic catalysis because of their complicated structure and interactions. Herein, bimetallic NiFe₂ MOF octahedra were well prepared and exhibited enhanced peroxidase-like activities. The synergistic effect of Fe and Ni atoms was systematically investigated by electrochemistry, X-ray photoelectron spectrometry, (XPS) and in situ Raman techniques. The electrons tend to transfer from Ni²⁺ to Fe³⁺ in NiFe₂ MOFs, and the resulting Fe²⁺ is ready to decompose H₂O₂ and generate ^·OH by a Fenton-like reaction. After integration with glucose oxidase (GOx), which can downgrade the pH value and generate H₂O₂ by oxidation of glucose, a self-activated cascade reagent is therefore established for efficiently inducing cell death. The changes of cell morphology, DNA, and protein are also successfully recorded during the cell death process by Raman spectroscopy and fluorescence imaging.

Amplified Electrochemical Hydrogen Peroxide Sensing Based on Cu-Porphyrin Metal-Organic Framework Nanofilm and G-Quadruplex-Hemin DNAzyme

A novel electrochemical hydrogen peroxide (H₂O₂) sensor based on Cu-porphyrin(Cu-TCPP)/G-quadruplex-hemin nanocomposite was constructed by assembling two-dimensional Cu-TCPP metal-organic framework (MOF) nanofilm and G-quadruplex-hemin DNAzyme. The Cu-TCPP synthesized by the surfactant-assisted method has a wrinkled two-dimensional nanofilm morphology, which gives it a large surface area and accessible active sites. Cu-TCPP exhibits peroxidase activity and good stability and can catalyze the reduction of H₂O₂. In addition, Cu-TCPP can be used as a nanocarrier for G-quadruplex-hemin DNAzyme with strong peroxidase activity to achieve "biological barcode" amplification and improve stability. The cooperative interaction of Cu-TCPP and G-quadruplex-hemin DNAzyme effectively amplifies the electrochemical response signal. Electrochemical studies have shown that the constructed sensor exhibits good electrochemical sensing performance with three linear ranges: 0.08 μM to 0.11 mM, 0.11-0.91 mM, and 0.91-8.1 mM, with sensitivities of 2315.86, 301.00, and 65.71 μA/(mM cm²), respectively, and the detection limit was 0.03 μM. In addition, the sensor shows good selectivity. In summary, this study provides a simple and effective new strategy for electrochemical sensing based on two-dimensional MOFs and artificial enzymes.

Ruthenium Ion-Complexed Carbon Nitride Nanosheets with Peroxidase-like Activity as a Ratiometric Fluorescence Probe for the Detection of Hydrogen Peroxide and Glucose

Detection of hydrogen peroxide is of great significance for clinical diagnosis and biomedical research. Ratiometric detection represents an effective method that is generally based on horseradish peroxidase. In the present study, ruthenium ion-complexed carbon nitride (Ru-C₃N₄) nanosheets are found to serve as a peroxidase mimic and can catalyze the conversion of o-phenylenediamine to fluorescent 2,3-diaminophenazine in the presence of H₂O₂. The produced 2,3-diaminophenazine also results in the apparent quenching of the Ru-C₃N₄ photoluminescence due to the inner filter effect. These unique characteristics can be exploited for the construction of an effective, peroxidase-free ratiometric fluorescence framework for the detection of H₂O₂ and glucose, which has also been used in the successful detection of glucose in human serum. Results from this study not only demonstrate a new peroxidase mimic but also provide a novel ratiometric fluorescence platform for the detection of H₂O₂ and metabolites involving reactions of H₂O₂ generation in the absence of horseradish peroxidase.

Fe₃O₄Nanoparticles Loaded on Lignin Nanoparticles Applied as a Peroxidase Mimic for the Sensitively Colorimetric Detection of H₂O₂

Lignin is the second largest naturally renewable resource and is primarily a by-product of the pulp and paper industry; however, its inefficient use presents a challenge. In this work, Fe₃O₄ nanoparticles loaded on lignin nanoparticles (Fe₃O₄@LNPs) were prepared by the self-assembly method and it possessed an enhanced peroxidase-like activity. Fe₃O₄@LNPs catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate a blue color, was observable by the naked eye. Under the optimal conditions, Fe₃O₄@LNPs showed the ability of sensitive colorimetric detection of H₂O₂within a range of 5⁻100 μM and the limit of detection was 2 μM. The high catalytic activity of Fe₃O₄@LNPs allows its prospective use in a wide variety of applications, including clinical diagnosis, food safety, and environmental monitoring.

Adenosine-Related Compounds as an Enhancer for Peroxidase-Mimicking Activity of Nanomaterials: Application to Sensing of Heparin Level in Human Plasma and Total Sulfate Glycosaminoglycan Content in Synthetic Cerebrospinal Fluid

A variety of compounds, such as DNA and protein, have been demonstrated to be effective in suppressing the catalytic activity of peroxidase-like nanomaterials. However, little investigations have been conducted to discover new chemical compounds for amplifying the catalytic activity of peroxidase-mimicking nanomaterials. This study discloses that adenosine analogues were useful as a universal enhancer for peroxidase-mimicking nanomaterials in the hydrogen peroxide-mediated oxidation of amplex ultrared at neutral pH. The optimal adenosine analogues for improving the peroxidase-like performance of citrate-stabilized gold nanoparticles (Au NPs), citrate-capped platinum NPs, bovine serum albumin-encapsulated gold nanoclusters, and unmodified magnetite NPs were found to be adenosine diphosphate (ADP), ADP, ADP, and adenosine monophosphate, respectively. The results show that adenosine analogue-induced enhancement in the peroxidase-like activity of nanomaterials was heavily associated with the number of adsorbed adenosine analogues onto the nanomaterial surface. The analysis of ADP-modified Au NPs by electron paramagnetic resonance spectroscopy indicates that the adsorbed ADP molecules on the Au NP surface not only activated H₂O₂ but also strengthened the interaction between hydroxyl radicals and nanomaterials. By integrating the ADP-boosted catalytic activity of peroxidase-like Au NPs, surfen-triggered NP aggregation, and specific surfen-sulfated glycosaminoglycan (GAG) interaction, a turn-on fluorescent probe was constructed to quantify the heparin level in human plasma and total sulfate GAG content in synthetic cerebrospinal fluid.

Umbelliferone as a Small Molecular Peroxidase Mimic towards Sensitive Detection of H2O2 and Glucose

In this work, umbelliferone, a kind of coumarin derivative, was proved to exhibit peroxidase-like activity that could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide to generate a blue-colored oxide (oxTMB). The catalytic mechanism is similar to that of native enzymes (e.g. horseradish peroxidase, HRP) and nanozymes, which follow the Michaelis-Menten kinetics behavior. Meanwhile, the 7-hydroxyl group of umbelliferone plays a significant role in the peroxidase-like activity. Compared with enzymes and nanozymes, this small molecular mimic enzyme possesses the advantages of low cost, simple molecular structures, small molecular weight and high stability against harsh conditions. Based on the favorable peroxidase mimetic activity of umbelliferone, a convenient, practical and sensitive H₂O₂ and glucose detection method was successfully established. This work not only opens some new inspirations into seeking for novel molecular enzyme mimetics with excellent catalytic activities, but also provides promising assays for clinical diagnosis.

Rational Design of Mimic Multienzyme Systems in Hierarchically Porous Biomimetic Metal-Organic Frameworks

A facile approach was reported to establish mimic multienzyme systems with hierarchically porous (HP) biomimetic metal-organic frameworks (MOFs) and natural enzymes for tandem catalysis. The hierarchically porous MOF HP-PCN-224(Fe) with peroxidase-like activity and tunable hierarchical porosity was synthesized via a modulator-induced strategy. HP-PCN-224(Fe) not only acts as the enzyme-immobilization matrix but also as an effective enzyme mimic, which could cooperate with the immobilized natural enzyme to catalyze the cascade reactions. The mimic multienzyme systems were used for the efficient colorimetric detection of a series of biomolecules, including glucose and uric acid. This work displays the great potential to construct highly functional biocatalysts by integrating the merits of both natural enzymes and MOF mimics, which are promising for applications in biosensing and biomimetic catalysis.

Integrated Antibody with Catalytic Metal-Organic Framework for Colorimetric Immunoassay

Enzyme-linked immunosorbent assay has been widely used as a gold standard in biomedical field, but some inevitable drawbacks still exist in its practical applications, especially the laborious preparation of enzyme-antibody conjugates by a covalent linkage. In this work, we proposed a new strategy to prepare enzyme-antibody conjugate by integrating antibody with catalytic metal-organic framework (MOF) to form dual-functional MOF/antibody composite. As models, rabbit antimouse immunoglobulin G antibody (RIgG) and Cu-MOF with peroxidase-like activity were used to fabricate RIgG@Cu-MOF composite for colorimetric immunoassay. It was found that Cu-MOF as a host not only has no influence on the original capture ability of RIgG to its corresponding antigen (mIgG), but also can shield RIgG against long-term storage, high temperature, and biological degradation. More importantly, upon the formation of sandwiched immunocomplex between RIgG@Cu-MOF and capture antibody, Cu-MOF can serve as a signal amplification unit to perform colorimetric immunoassay. The detection limit of RIgG@Cu-MOF toward mIgG was obtained at 0.34 ng/mL, which is 3-fold lower than that of horseradish peroxidase labeled RIgG. Furthermore, the successful determination of mIgG in serum sample demonstrates the applicability of RIgG@Cu-MOF in detecting real sample. Therefore, it is highly anticipated that this study can offer a new way to prepare enzyme-antibody conjugates, facilitating the exploration of MOF composites in biomedical field.

Amplified Peroxidase-Like Activity in Iron Oxide Nanoparticles Using Adenosine Monophosphate: Application to Urinary Protein Sensing

Numerous compounds such as protein and double-stranded DNA have been shown to efficiently inhibit intrinsic peroxidase-mimic activity in Fe₃O₄ nanoparticles (NP) and other related nanomaterials. However, only a few studies have focused on finding new compounds for enhancing the catalytic activity of Fe₃O₄ NP-related nanomaterials. Herein, phosphate containing adenosine analogs are reported to enhance the oxidation reaction of hydrogen peroxide (H₂O₂) and amplex ultrared (AU) for improving the peroxidase-like activity in Fe₃O₄ NPs. This enhancement is suggested to be a result of the binding of adenosine analogs to Fe²⁺/Fe³⁺ sites on the NP surface and from adenosine 5'-monophosphate (AMP) acting as the distal histidine residue of horseradish peroxidase for activating H₂O₂. Phosphate containing adenosine analogs revealed the following trend for the enhanced activity of Fe₃O₄ NPs: AMP > adenosine 5'-diphosphate > adenosine 5'-triphosphate. The peroxidase-like activity in the Fe₃O₄ NPs progressively increased with increasing AMP concentration and polyadenosine length. The Michaelis constant for AMP attached Fe₃O₄ NPs is 5.3-fold lower and the maximum velocity is 2.7-fold higher than those of the bare Fe₃O₄ NPs. Furthermore, on the basis of AMP promoted peroxidase mimicking activity in the Fe₃O₄ NPs and the adsorption of protein on the NP surface, a selective fluorescent turn-off system for the detection of urinary protein is developed.

Cu0.89Zn0.11O, A New Peroxidase-Mimicking Nanozyme with High Sensitivity for Glucose and Antioxidant Detection

Nanomaterial-based enzyme mimetics (nanozymes) is an emerging field of research that promises to produce alternatives to natural enzymes for a variety of applications. The search for the most cost-effective and efficient inorganic nanomaterials, such as metal oxides, cannot be won by pristine CuO. However, unlike CuO, the Zn-doped CuO (Zn-CuO) nanoparticles reported in this paper reveal superior peroxidase-like enzyme activity. This places Zn-CuO in a good position to participate in a range of activities aimed at developing diverse enzyme applications. The peroxidase-like activity was tested and confirmed against various chromogenic substrates in the presence of H2O2 and obeyed the Michaelis-Menten enzymatic pathway. The mechanism of enhanced enzymatic activity was proved by employing terephthalic acid as a fluorescence probe and by electron spin resonance. The nanozyme, when tested for the detection of glucose, showed a substantial enhancement in the detection selectivity. The limit of detection (LOD) was also decreased reaching a limit as low as 0.27 ppm. Such a low LOD has not been reported so far for the metal oxides without any surface modifications. Moreover, the nanozyme (Zn-CuO) was utilized to detect the three antioxidants tannic acid, tartaric acid, and ascorbic acid and the relative strength of their antioxidant capacity was compared.

Pd-Ir Core-Shell Nanocubes: A Type of Highly Efficient and Versatile Peroxidase Mimic

Peroxidase mimics with dimensions on the nanoscale have received great interest as emerging artificial enzymes for biomedicine and environmental protection. While a variety of peroxidase mimics have been actively developed recently, limited progress has been made toward improving their catalytic efficiency. In this study, we report a type of highly efficient peroxidase mimic that was engineered by depositing Ir atoms as ultrathin skins (a few atomic layers) on Pd nanocubes (i.e., Pd-Ir cubes). The Pd-Ir cubes exhibited significantly enhanced efficiency, with catalytic constants more than 20- and 400-fold higher than those of the initial Pd cubes and horseradish peroxidase (HRP), respectively. As a proof-of-concept demonstration, the Pd-Ir cubes were applied to the colorimetric enzyme-linked immunosorbent assay (ELISA) of human prostate surface antigen (PSA) with a detection limit of 0.67 pg/mL, which is ∼110-fold lower than that of the conventional HRP-based ELISA using the same set of antibodies and the same procedure.

Highly dispersed CeO₂ on TiO₂ nanotube: a synergistic nanocomposite with superior peroxidase-like activity

In this report, a novel nanocomposite of highly dispersed CeO2 on a TiO2 nanotube was designed and proposed as a peroxidase-like mimic. The best peroxidase-like activity was obtained for the CeO2/nanotube-TiO2 when the molar ratio of Ce/Ti was 0.1, which was much higher than that for CeO2/nanowire-TiO2, CeO2/nanorod-TiO2, or CeO2/nanoparticle-TiO2 with a similar molar ratio of Ce/Ti. Moreover, in comparison with other nanomaterial based peroxidase mimics, CeO2/nanotube-TiO2 nanocomposites exhibited higher affinity to H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB). Kinetic analysis indicated that the catalytic behavior was in accordance with typical Michaelis-Menten kinetics. Ce(3+) sites were confirmed as the catalytic active sites for the catalytic reaction. The first interaction of surface CeO2 with H2O2 chemically changed the surface state of CeO2 by transforming Ce(3+) sites into surface peroxide species causing adsorbed TMB oxidation. Compared with CeO2/nanowire-TiO2, CeO2/nanorod-TiO2, and CeO2/nanoparticle-TiO2, the combination of TiO2 nanotube with CeO2 presented the highest concentration of Ce(3+) thus leading to the best peroxidase-like activity. On the basis of the high activity of CeO2/nanotube-TiO2, the reaction provides a simple method for colorimetric detection of H2O2 and glucose with the detection limits of 3.2 and 6.1 μM, respectively.

Artificial evolution of graphene oxide chemzyme with enantioselectivity and near-infrared photothermal effect for cascade biocatalysis reactions

It is highly desirable and challenging when the chemzyme can be not only simply duplicating and imitating the properties of natural enzymes, but also introducing additional new features for practical applications. Herein, we report a zinc-finger-protein like α-helical chiral metallo-supramolecular complex ([Fe2L3](4+)) functionalized graphene oxide (GO-COOH) as a peroxidase mimic. This artificial enzyme integrates the characteristics of both chiral metallo-supramolecular complex and GO-COOH, and shows excellent catalytic activity. More intriguingly, the novel chemzyme turn out to have enantioselectivity and near-infrared photothermal effect. To the best of our knowledge, this is the first example that the chemzyme has such new features. Based on these properties, we have demonstrated three examples for the applications of our designed enzyme: 1) Intracellular H2O2 detection in PC12 cells against Alzheimer's disease; 2) Discrimination between the chiral drug, Levodopa (L-dopa), the gold standard for treating Parkinson's disease and its enantiomer, D-dopa. This is important because L-dopa is the most effective drug at present used to combat Parkinson's disease while D-dopa is inactive and can even cause side effects, thus for drug efficacy it must be free of D-dopa in the formulation; 3) Remote control of enzyme cascade biocatalysis reactions using high transparent, bio-friendly near-infrared (NIR) light. NIR allows remote activation with relatively high spatial and temporal precision. Our work will provide new insights into design and construction of novel chemzyme with more advanced features beyond intrinsic enzyme property.