Intrinsic Peroxidase Activity Research Articles

In-Situ Grown Nanocrystal TiO2 on 2D Ti3C2 Nanosheets with Anti-Tumor Activity from Photo-Sonodynamic Treatment and Immunology.

Traditional cancer treatment strategies often have severe toxic side effects and poor therapeutic efficacy. To address the long-standing problems related to overcoming the complexity of tumors, we develop a novel nanozyme based on the in situ oxidation of 2D Ti3C2 structure to perform simultaneous phototherapy and sonodynamic therapy on tumors. Ti3C2 nanozymes exhibit multi-enzyme activity, including intrinsic peroxidase (POD) activities, which can react with H2O2 in the tumor microenvironment. This new material can construct Ti3C2/TiO2 heterostructures in vivo. Photothermal (PTT), sonodynamic (SDT) effects, and photoacoustic (PA) image-guided synergy therapy can be achieved. Finally, anticancer immune responses occur with this nanozyme. In vivo experiments revealed that the Ti3C2/TiO2 heterostructure inhibited tumor growth. Complementarily, our results showed that the Ti3C2/TiO2 heterostructure enhanced the immunogenic activity of tumors by recruiting cytotoxic T cells, thereby enhancing the tumor ablation effect. Mechanistic studies consistently indicated that Reactive Oxygen Species (ROS) regulates apoptosis of HCC cells by modulating NRF2/OSGIN1 signaling both in vitro and in vivo. As a result, Ti3C2 nanozyme effectively inhibited tumor through its synergistic ability to modulate ROS and enhance immune infiltration of cytotoxic T cells in the tumor microenvironment. These findings open up new avenues for enhancing 2D Ti3C2 nanosheets and suggest a new way to develop more effective sonosensitizers for the treatment of cancer.

Borophene Quantum Dots as Novel Peroxidase-Mimicking Nanozyme: A Dual-Mode Assay for the Detection of Oxytetracycline and Tetracycline Antibiotics.

The greater advantages and wide applications of zero-dimensional nanodots inspire researchers to develop new materials. Therefore, novel borophene quantum dots (QDs) were prepared by a hydrothermal liquid exfoliation technique using water medium. The borophene QDs proved to be highly stable in water medium for more than 120 days. The synthesized borophene QDs revealed intrinsic peroxidase mimetic activity using two chromogenic substrates, 3,3',5,5'-tetramethylbenzidine (TMB) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS). The excellent intrinsic peroxidase activity toward TMB and ABTS substrates was executed using optimal reaction conditions (pH, borophene QDs' concentration, incubation time, and temperature). The formation of hydroxyl radicals in the presence of H2O2 upon TMB and ABTS oxidation played a significant role in the peroxidase reaction. The borophene QDs further proved to be successful for the colorimetric detection of antibiotics (oxytetracycline and tetracycline) using both TMB and ABTS peroxidase substrates. The limit of detection (LOD) for oxytetracycline and tetracycline was found to be 1.10 and 1.02 μM using TMB and 1.03 and 1.02 μM using ABTS chromogenic substrates, respectively. In addition, the fluorescence sensing of oxytetracycline and tetracycline over borophene QDs was also examined. The high fluorescence of borophene QDs (turn ON) was quenched (turn OFF) by oxytetracycline and tetracycline through the inner filter effect mechanism. The LOD of the fluorescence sensing of oxytetracycline and tetracycline was 1.14 and 1.08 μM, respectively. Interestingly, the borophene QDs could be used for the sensitive and selective colorimetric and fluorometric sensing of oxytetracycline and tetracycline after 120 days of storage. The synthesized borophene QDs with long-term stability and real sample analysis provide new insight as nanozymes with higher peroxidase mimetic and fluorescence performance and can be further exploited for medical diagnosis and environmental toxicants' detection.

Extracellular G-quadruplexes and Z-DNA protect biofilms from DNase I, and G-quadruplexes form a DNAzyme with peroxidase activity.

Many bacteria form biofilms to protect themselves from predators or stressful environmental conditions. In the biofilm, bacteria are embedded in a protective extracellular matrix composed of polysaccharides, proteins and extracellular DNA (eDNA). eDNA most often is released from lysed bacteria or host mammalian cells, and it is the only matrix component most biofilms appear to have in common. However, little is known about the form DNA takes in the extracellular space, and how different non-canonical DNA structures such as Z-DNA or G-quadruplexes might contribute to its function in the biofilm. The aim of this study was to determine if non-canonical DNA structures form in eDNA-rich staphylococcal biofilms, and if these structures protect the biofilm from degradation by nucleases. We grew Staphylococcus epidermidis biofilms in laboratory media supplemented with hemin and NaCl to stabilize secondary DNA structures and visualized their location by immunolabelling and fluorescence microscopy. We furthermore visualized the macroscopic biofilm structure by optical coherence tomography. We developed assays to quantify degradation of Z-DNA and G-quadruplex DNA oligos by different nucleases, and subsequently investigated how these enzymes affected eDNA in the biofilms. Z-DNA and G-quadruplex DNA were abundant in the biofilm matrix, and were often present in a web-like structures. In vitro, the structures did not form in the absence of NaCl or mechanical shaking during biofilm growth, or in bacterial strains deficient in eDNA or exopolysaccharide production. We thus infer that eDNA and polysaccharides interact, leading to non-canonical DNA structures under mechanical stress when stabilized by salt. We also confirmed that G-quadruplex DNA and Z-DNA was present in biofilms from infected implants in a murine implant-associated osteomyelitis model. Mammalian DNase I lacked activity against Z-DNA and G-quadruplex DNA, while Micrococcal nuclease could degrade G-quadruplex DNA and S1 Aspergillus nuclease could degrade Z-DNA. Micrococcal nuclease, which originates from Staphylococcus aureus, may thus be key for dispersal of biofilm in staphylococci. In addition to its structural role, we show for the first time that the eDNA in biofilms forms a DNAzyme with peroxidase-like activity in the presence of hemin. While peroxidases are part of host defenses against pathogens, we now show that biofilms can possess intrinsic peroxidase activity in the extracellular matrix.

Intrinsic peroxidase activity of carbon dots derived from expired drugs and its application in automatic detection of total antioxidant capacity

In the post-COVID-19 pandemic, the stockpiling of medicines by most households could pose a pollution risk as they may expire over time. In this study, an expired amoxicillin act as carbon source to prepare peroxide-like functional carbon dots nanozymes doped Fe (Fe-CDs). Importantly, a high-value treatment technique for expired drugs was proposed. To obtain outstanding catalytic performance, compared with other commonly doped metals, Fe-CDs catalyzed the oxidation of TMB by H2O2 with the highest efficiency. In particular, the oxidation product of TMB (oxTMB) would be alleviated in the presence of antioxidants. Significantly, antioxidants could briefly cause the fading of oxTMB and the fading level was correlated with various concentrations of antioxidants. Importantly, a sequential injection strategy was introduced to control the fading process caused by antioxidants to improve the accuracy. Under the optimum condition, the limit of detection (LOD) was 0.13 mg/L (for ascorbic acid) with the linear concentration range from 0.5 to 15 mg·L−1. Finally, the total antioxidant capacity (TAC) in human serum samples were evaluated successfully.

Magnetite chitosan hydrogel nanozyme with intrinsic peroxidase activity for smartphone-assisted colorimetric sensing of thiabendazole

Although nanozymes proved a promising utility in sensing applications, they often lack a rational approach in their design. Herein, magnetite chitosan hydrogel (MCH) is reported as a rational peroxidase nanozyme for the smartphone-assisted colorimetric detection of thiabendazole (TBZ). Chitosan due to its polycationic nature, renders a microenvironment similar to amino acids in HRP enzyme. Characterizations of the nanozyme using SEM, XRD, and XPS confirmed the distribution of Fe3O4NPs on the chitosan matrix. The peroxidase activity was demonstrated using TMB and H2O2 as substrates which resulted in a characteristic absorption at 652 nm. MCH nanozyme showed a 24% higher peroxidase activity in acidic pH than the pristine Fe3O4 confirming the role of chitosan in boosting the electron transfer. Kinetics result suggested the catalytic reaction followed a Michalis-Menten model with Km and Vmax of 0.45 mM and 15 μM/min for TMB and 2.8 mM and 4.18 μM/min for H2O2 respectively. These values are competitive with natural HRP enzymes reported before. Further, MCH nanozyme showed improved thermal and temporal stability as well as reusability retaining 80% of its activity after the 4th cycle. TBZ showed concentration-dependent inhibition on the peroxidase activity. The degree of inhibition exhibited a linear relationship with the concentration of TBZ from 0.1 to 100 μM (R2 = 0.998) enabling the detection of TBZ down to 0.73 and 1.84 μM in a spectrometer and smartphone-based readouts respectively. The results show the potential of the prepared nanozyme as a point-of-need sensor for food safety monitoring.

Directed Evolution of a G-Quadruplex Peroxidase DNAzyme and Application in Proteomic DNAzyme-Aptamer Proximity Labeling.

DNAzymes have been limited in application by their low catalytic rates. Here, we evolved a new peroxidase DNAzyme mSBDZ-X-3 through a directed evolution method based on the capture of self-biotinylated DNA catalyzed by its intrinsic peroxidase activity. The mSBDX-X-3 DNAzyme has a parallel G-quadruplex structure and has more favorable catalytic properties than all previously reported peroxidase DNAzyme variants. We applied mSBDZ-X-3 in an aptamer-coupled proximity-based labeling proteomic assay to determine the proteins that bind to cell surface cancer biomarkers EpCAM and nucleolin. Confocal microscopy, western blot analysis, and LC-MS/MS showed that the hybrid DNAzyme aptamer-coupled proximity assay-labeled proteins associated with EpCAM and nucleolin within 6-12 min in fixed cancer cells. The labeled proteins were identified by mass spectrometry. This study provides a highly efficient peroxidase DNAzyme, a methodology for selection of such variants, and a method for its application in spatial proteomics using entirely nucleic acid-based tooling.

A colorimetric biosensor to track Trop-2 status of tumor cells for diagnosis of breast cancer

The emergence of antibody-drug conjugates (ADCs) targeting trophoblast cell-surface antigen-2 (Trop-2) has reshaped the therapeutic landscape of advanced breast cancer. Accurate profiling of the Trop-2 status of tumor cells can facilitate the identification of patients who will benefit from Trop-2-targeting therapy; however limited analytical method has hindered this process. In this study, we have proposed a specific and sensitive biosensor for visual tracking of the Trop-2 status of breast cancer cells based on tetrahedral DNA nanostructure (TDN)-decorated Fe-based metal-organic framework nanoparticles (TDN-PCN-222 (Fe)). In the design, a dual-aptamer-assisted biomimetic capture strategy shows high capture efficiency while maintaining the viability and original phenotype of captured cells, ensuring the accurate profiling of the Trop-2 status. Meanwhile, by using the high intrinsic peroxidase activity and excellent targeting ability of Trop-2-specific aptamer-linked TDN-PCN-222 (Fe), specific detection of Trop-2-positive tumor cells can be achieved with a limit of detection (LOD) of 10 cells/mL, and the Trop-2 status of tumor cells can be visually tracked. Moreover, the proposed biosensor has been successfully used for tracking the Trop-2 status of tumor cells in breast cancer tissues, suggesting that our method has great promise for clinical applications.

Piezoelectric Metal-Organic Frameworks Based Sonosensitizer for Enhanced Nanozyme Catalytic and Sonodynamic Therapies.

The regulation of electrostatic electric fields through electrical stimulation is an efficient method to increase the catalytic activity of nanozymes and improve the therapeutic effect of nanozyme catalytic therapy. Piezoelectric materials, which are capable of generating a built-in electric field under ultrasound (US), not only improve the activity of nanozymes but also enable piezoelectric sonodynamic therapy (SDT). In this study, a sonosensitizer based on a Hf-based metal-organic framework (UIO-66) and Au nanoparticles (NPs) was produced. Under US irradiation, UIO-66 can generate a built-in electric field inside the materials, which promotes electron-hole separation and produces reactive oxygen species (ROS). The introduction of Au NPs facilitated the electron transfer, which inhibited the recombination of the electron-hole pairs and improved the piezoelectric properties of UIO-66. The value of the piezoelectric constant (d33) increased from 71 to 122 pmV-1 after the deposition of Au NPs. In addition, the intrinsic catalase and peroxidase activities of the Au NPs were increased 2-fold after the stimulation from the built-in electric field induced through US exposure. In vivo and in vitro experiments revealed that the proposed sonosensitizer can kill cancer cells and inhibit tumor growth in mice through the enhanced piezoelectric SDT and nanozyme catalytic therapy. The piezoelectric sensitizer proposed in this work proved to be an efficient candidate that can be used for multiple therapeutic modalities in tumor therapy.

A novel label-free dual-mode aptasensor based on the mutual regulation of silver nanoclusters and MoSe2 nanosheets for reliable detection of ampicillin

Current methods for the rapid detection of trace antibiotics in the environment remains problems of low accuracy and false negative or false positive, making the development of fast, and accurate, and reliable methods for antibiotic testing a major challenge that needs to be addressed. Herein, we developed a novel label-free colorimetric and fluorescent dual-mode aptasensor assembled by the strong interaction of layered MoSe2 nanosheets (MoSe2 NSs) with ampicillin (AMP) aptamer functionalized silver nanoclusters (Apt-AgNCs) that specifically bind AMP to allow the sensitive and selective detection of AMP. Apt-AgNCs could be adsorbed on the surface of MoSe2 NSs via van der Waals force to form a nanocomposite, Apt-AgNCs/MoSe2 NSs. Interestingly, Apt-AgNCs/MoSe2 NSs act together to construct dual mode aptasensor through modulation of the intrinsic peroxidase activity of MoSe2 NSs and the fluorescence of Apt-AgNCs. In the presence of AMP, Apt-AgNCs could specifically bind AMP, triggering desorption from the MoSe2 NSs surface, leading to a decrease in the peroxidase activity of the system with the recovery in Apt-AgNCs fluorescence. The dual-signal aptasensor exhibited good linear colorimetric and fluorescence responses in the AMP concentration ranges of 0.115–2.00 μM and 6–100 nM, respectively. Furthermore, the aptasensor was successfully measured AMP levels in commercially-bought milk and lake water with satisfactory results. Unlike single-signal aptasensors, the constructed dual-signal aptasensor could not only improve the detection precision, but also reduce the false positive or false negative results. These promising results suggest that the dual-readout strategy as demonstrated is general mode for the detection of other antibiotics or compounds using various aptamers functionalized AgNCs in concert with MoSe2 NSs.

Fe(III)-incorporated porphyrin-based conjugated organic polymer as a peroxidase mimic for the sensitive determination of glucose and H2O2.

Nanozymes, i.e., nanomaterials that possess intrinsic enzyme-like behaviour, have thrived over the past few decades owing to their advantages of superior stability and effortless storage. Such artificial enzymes can be a perfect alternative to naturally occurring enzymes, which have disadvantages of high cost and limited functionality. In this work, we present the fabrication of an Fe(III)-incorporated porphyrin-based conjugated organic polymer as a nanozyme for the efficient detection of glucose through its intrinsic peroxidase activity and the amperometric detection of hydrogen peroxide. The iron-incorporated porphyrin-based conjugated organic polymer (Fe-DMP-POR) possesses a spherical morphology with high chemical and thermal stability. Exploiting the peroxidase-mimicking activity of the material for the determination of glucose, a detection limit of 4.84 μM is achieved with a linear range of 0-0.15 mM. The Fe-DMP-POR also exhibits a reasonable recovery range for the detection of human blood glucose. The as-synthesized material can also act as an H2O2 sensor, with a sensitivity of 947.67 μA cm-2 mM-1 and a limit of detection of 3.16 μM.

Boron-Doped and Ketonic Carbonyl Group-Enriched Graphdiyne as a Dual-Site Carbon Nanozyme with Enhanced Peroxidase-Like Activity.

We demonstrate the preparation of a dual-site carbon nanozyme, boron-doped and ketonic carbonyl (-C=O) group-enriched graphdiyne (B-GDY), with an enhanced peroxidase-like activity. Taking advantage of acidic oxidation treatment, GDY oxide (GDYO) with abundant surface oxygen-containing groups is obtained from pristine bulk GDY. Upon further thermal annealing of GDYO with H3BO3 under an inert atmosphere, B is introduced into GDY, while the loading of -C=O groups is increased onto B-GDY. We discover that boron-doped and ketonic carbonyl group-enriched graphdiyne as a dual-site carbon nanozyme endows it with an enhanced peroxidase-like activity, which is nearly 4.2-fold higher than that of GDY without B atoms and 6.6-fold higher than that of GDYO without B atoms and with low loading of -C=O groups. The high peroxidase-like activity of B-GDY is ascribed to the dual active sites (-C=O group and B atom) within it, which facilitates the adsorption and decomposition of H2O2 into hydroxyl radicals revealed by experimental and theoretical studies. Moreover, B-GDY is successfully employed to develop a colorimetric method for the detection of glucose with good sensitivity and selectivity. This work probes into the intrinsic peroxidase activity and structure-reactivity correlation, creating effective strategies for the preparation of GDY-based nanozymes.

Tumor Microenvironment-Activable Manganese-Boosted Catalytic Immunotherapy Combined with PD-1 Checkpoint Blockade.

Immune checkpoint blockade (ICB) therapy has attracted widespread attention in cancer treatment. Due to the low immunogenicity and immune suppression state in the tumor microenvironment (TME), the therapeutic effects are only moderate. Herein, a TME-activable manganese-boosted catalytic immunotherapy is designed for synergism with ICB therapy to kill tumors efficiently. The tumor cell membrane (CM)-wrapping multienzyme-mimic manganese oxide (MnOx) nanozyme termed CM@Mn showed intrinsic peroxidase and oxidase-like activities in an acidic TME. These activities can generate toxic hydroxyl (•OH) and superoxide radicals (•O2-) for tumor cell killing and evoking immunogenic cell death (ICD). Furthermore, the TME-responsive release of Mn2+ directly promotes dendritic cell maturation and macrophage M1 repolarization, resulting in the reversal of an immunosuppressive TME into an immune-activating environment. Additionally, tumor hypoxia relief caused by catalase-like activity also contributes to the process of TME reversal. Finally, a robust tumor-specific T cell-mediated antitumor response occurs with the support of the PD-1 checkpoint blockade. The proliferation of primary and metastatic tumors was inhibited, and a long-term immune memory effect was induced. The therapeutic strategy outlined here may serve as a promising candidate for tumor-integrated treatment.

Colorimetric detection of H2O2 with Fe3O4@Chi nanozyme modified µPADs using artificial intelligence.

Peroxidase mimicking Fe3O4@Chitosan (Fe3O4@Chi) nanozyme was synthesized and used for high-sensitive enzyme-free colorimetric detection of H2O2. The nanozyme was characterized in comparison with Fe3O4 nanoparticles (NPs) using X-ray diffraction,Fourier-transform infrared spectroscopy,dynamic light scattering, and thermogravimetric analysis. The catalytic performance of Fe3O4@Chi nanozyme was first evaluated by UV-Vis spectroscopy using 3,3',5,5'-tetramethylbenzidine. Unlike Fe3O4NPs, Fe3O4@Chi nanozyme exhibited an intrinsic peroxidase activity with a detectionlimit of 69nM. Next, the nanozyme was applied to a microfluidic paper-based analytical device (µPAD) and colorimetric analysis was performed at varying concentrations of H2O2 using a machine learning-based smartphone app called "Hi-perox Sens++ ." The app with machine learning classifiers made the system user-friendly as well as more robust and adaptive against variation in illumination and camera optics. In order to train various machine learning classifiers, the images of the µPADs were taken at 30s and 10min by four smartphone brands under seven different illuminations. According to the results, linear discriminant analysis exhibited the highest classification accuracy (98.7%) with phone-independent repeatability at t = 30s and the accuracy was preserved for 10min. The proposed system also showed excellent selectivity in the presence of various interfering molecules and good detection performance in tap water.

Enhanced Catalytic Activity of a New Nanobiocatalytic System Formed by the Adsorption of Cytochrome c on Pluronic Triblock Copolymer Stabilized MoS2 Nanosheets.

The formation of nanobiohybrids through the immobilization of enzymes on functional nanomaterials has opened up exciting research opportunities at the nanobiointerfaces. These systems hold great promise for a wide range of applications in biosensing, biocatalytic, and biomedical fields. Here, we report the formation of a hybrid nanobiocatalytic system through the adsorption of cytochrome c (Cyt c) on pluronic triblock copolymer, P123 (PEO-b-PPO-b-PEO), stabilized MoS2 nanosheets. The use of pluronic polymer has helped not only to greatly stabilize the exfoliated MoS2 nanosheets but also to allow easy adsorption of Cyt c on the nanosheets without major structural changes due to its excellent biocompatibility and soft protein-binding property. By comparing the catalytic activity of the Cyt c–MoS2 nanobiohybrid with that of the free Cyt c and as-prepared MoS2 nanosheets, we have demonstrated the active role of the nanobiointeractions in enhancing the catalytic activity of the hybrid. Slight structural perturbation at the active site of the Cyt c upon adsorption on MoS2 has primarily facilitated the peroxidase activity of the Cyt c. As the MoS2 nanosheets and the native Cyt c individually exhibit weaker intrinsic peroxidase activities, their mutual modulation at the nanobiointerface has made the Cyt c–MoS2 a novel nanobiocatalyst with superior activity.

Effect on intrinsic peroxidase activity of substituting coevolved residues from Ω-loop C of human cytochrome c into yeast iso-1-cytochrome c

Naturally-occurring variants of human cytochrome c (Cytc) that induce thrombocytopenia IV occur within Ω-loop C (residues 40–57). These variants enhance the peroxidase activity of human Cytc apparently by facilitating access to the heme by destabilizing Ω-loops C and D (residues 70–85). Given the importance of peroxidase activity in the early stages of apoptosis, we identified three sites with the EVmutation algorithm in or near Ω-loop C that coevolve and differ between yeast iso-1-Cytc and human Cytc. We prepared iso-1-Cytc variants with all possible combinations of the S40T, V57I and N63T substitutions to determine if these residues decrease the peroxidase activity of iso-1-Cytc to that of human Cytc producing an effective off state for a peroxidase signaling switch. At pH 6 and above, all variants significantly decreased peroxidase activity. However, the correlation of peroxidase activity with local and global stability, expected if cooperative unfolding of Ω-loops C and D is required for peroxidase activity, was generally poor. The m-values derived from the guanidine hydrochloride dependence of the kinetics of imidazole binding to horse Cytc, which is well-characterized by native-state hydrogen exchange methods, and K72A/K73A/K79A iso-1-Cytc show that local structural fluctuations and not subglobal cooperative unfolding of Ω-loops C and D are sufficient to permit binding of a small molecule like peroxide to the heme. A 2.46 Å structure of N63T iso-1-Cytc identifies a change to a hydrogen bond network linking Ω-loops C and D that could modulate the local fluctuations needed for the intrinsic peroxidase activity of Cytc.

Naturally Occurring I81N Mutation in Human Cytochrome c Regulates Both Inherent Peroxidase Activity and Interactions with Neuroglobin.

Human cytochrome c (hCyt c) is a crucial heme protein and plays an indispensable role in energy conversion and intrinsic apoptosis pathways. The sequence and structure of Cyt c were evolutionarily conserved and only a few naturally occurring mutants were detected in humans. Among those variable sites, position 81 was proposed to act as a peroxidase switch in the initiation stages of apoptosis. In this study, we show that Ile81 not only suppresses the intrinsic peroxidase activity but also is essential for Cyt c to interact with neuroglobin (Ngb), a potential protein partner. The kinetic assays showed that the peroxidase activity of the naturally occurring variant I81N was enhanced up to threefold under pH 5. The local stability of the Ω-loop D (residues 70–85) in the I81N variant was decreased. Moreover, the Alphafold2 program predicted that Ile81 forms stable contact with human Ngb. Meanwhile, the Ile81 to Asn81 missense mutation abolishes the interaction interface, resulting in a ∼40-fold decrease in binding affinity. These observations provide an insight into the structure–function relationship of the conserved Ile81 in vertebrate Cyt c.

Insight into peroxidase and polyphenol oxidase mimic activity of spinel ferrite nanoparticles and their GO composites

Present work reports the comparative evaluation of MFe2O4 (M = Mn, Co and Cu) nanoparticles (NPs), graphene oxide (GO) and their nanocomposite (NC) for their intrinsic peroxidase and polyphenol oxidase (PPO) mimic activity of followed by the catalytic sensing of H2O2. Pure and doped MFe2O4 NPs were screened initially for peroxidase and PPO mimic activity. Among the tested metal ferrite NPs, MnFe2O4 NPs showed the highest enzyme mimic activity for both the enzymes. Thus, MnFe2O4-GO NC was synthesized by the facile ultrasonication method and characterized using FT-IR and XRD techniques. TEM micrographs of NC showed that MnFe2O4 NPs were anchored on GO sheets with lesser agglomeration than bare ferrite NPs. SEM-EDX confirmed the presence of MnFe2O4 and GO in NC. The greater surface area of NC as compared to pristine NPs was confirmed from BET analysis. MnFe2O4 NPs displayed highest peroxidase and PPO mimic activity followed by NC and GO. The results were correlated with the facile inter-conversion of Mn2+-Mn3+ ions. Thus, ease of inter-conversion of oxidation state was the dominating factor of highest activity of MnFe2O4 NPs rather than the surface area. The colorimetric detection of H2O2 was also achieved in the range 0.2 mM–1.0 mM H2O2. In-situ trapping experiments confirmed that OH. radicals were major active species involved in peroxidase mimic activity. The reaction mechanisms for both the reactions were proposed. Kinetic studies were performed and data was analysed using Michaelis Menten equation. The values of Vmax and Km for both the reactions proved MnFe2O4 NPs as potential oxidase mimic for a wide range of potential applications.

Self‐assembled CoSe2 Microspheres with Intrinsic Peroxidase Mimicking Activity for Efficient Degradation of Variety of Dyes

AbstractIn this investigation, we report a new and greener self‐assembly of CoSe2 microsphere (CoSe2 MS) without assistance of harmful reducing and structure‐directing agents (SDA). Intrinsic peroxidase mimicking activity of synthesized CoSe2 MS was evaluated for 3,3,5,5′‐tetramethylbenzidine as a substrate by monitoring the absorbance of oxidized product at 653 nm. The smaller Michalis Menten constant (Km) for CoSe2 MS catalyzed reaction (0.371 mM), than the natural Horse Radish Peroxidase (HRP) enzyme, signifies the high substrate affinity of CoSe2 MS than HRP. Further, intrinsic peroxidase activity was assessed using emission intensity enhancement of terephthalic acid (TA) in presence of CoSe2 MS and H2O2 with time due to the production of .OH radicals and subsequent hydroxylation of TA. CoSe2 MS was further employed for organic dyes degradation in presence of H2O2, where cationic and anionic dyes degraded within 120 min with the highest degradation efficiency of 99.45 % for malachite green.

Stochastic Collision Electrochemistry from Single G-Quadruplex/Hemin: Electrochemical Amplification and MicroRNA Sensing.

Stochastic collision electrochemistry is a hot topic in single molecule/particle research, which provides an opportunity to investigate the details of the single molecule/particle reaction mechanism that is always masked in ensemble-averaged measurements. In this work, we develop an electrochemical amplification strategy to monitor the electrocatalytic behavior of single G-quadruplex/hemin (GQH) for the reaction between hydrogen peroxide and hydroquinone (HQ) through the collision upon a gold nanoelectrode. The intrinsic peroxidase activities of single GQH were investigated by stochastic collision electrochemical measurements, giving further insights into understanding biocatalytic processes. Based on the unique catalytic activity of GQH, we have also designed a hybridization chain reaction strategy to detect miRNA-15 with good selectivity and sensitivity. This work provided a meaningful strategy to investigate the electrochemical amplification and the broad application for nucleic acid sensing at the single molecule/particle level.

Selective and sensitive detection of cholesterol using intrinsic peroxidase-like activity of biogenic palladium nanoparticles

Abstract Biogenic palladium nanoparticles (Pd NPs) based colorimetric sensing and detection of cholesterol is being reported. Pd NPs used in this method were synthesized using gum kondagogu (GK), a biopolymer, which acted as both reducing and stabilizing agent. The GK reduced / stabilized Pd NPs (GK-Pd NPs) were directly used for the selective and colorimetric detection of cholesterol without any further modification. Cholesterol is known to be catalyzed by cholesterol oxidase (ChOx) and H2O2 produced in the reaction. The intrinsic peroxidase activity of GK-Pd NPs was coupled with catalytic oxidation of cholesterol by ChOx to colorimetric oxidation of 3, 3, 5, 5-tetramethylbenzidine (TMB) for the detection of cholesterol. Under the optimal conditions, the absorbance was proportional to the concentration of cholesterol over the range of 5–100 µM and the limit of quantification (LOQ) was recorded to be 3.7 µM. Moreover, the practicability of the assay in the detection of cholesterol in human serum was validated with promising results and has potential application in clinical diagnosis due to its selectivity and sensitivity.