Catalytic and peroxidase-like activity of carbon based-AuPd bimetallic nanocomposite produced using carbon dots as the reductant

In this report, carbon-based AuPd bimetallic nanocomposite (AuPd/C NC) was synthesized using carbon dots (C-dots) as the reducing agent and stabilizer by a simple green sequential reduction strategy, without adding other agents. The as synthesized AuPd/C NC showed good catalytic activity and peroxidase-like property. The structure and morphology of these nanoparticles were clearly characterized by UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The AuPd/C NC catalyst exhibits noticeably higher catalytic activity than Pd and Au nanoparticles in catalysis reduction of 4-nitrophenol (4-NP). Moreover, based on the high peroxidase-like property of AuPd/C NC, a new colorimetric detection method for hydrogen peroxide (H₂O₂) has been designed using 3,3′,5,5′-tetramethyl-benzidine (TMB) as the substrate, which provides a simple and sensitive means to detect H₂O₂ in wide linear range of 5 μM–500 μM and 500 μM–4 mM with low detection limit of 1.6 μM (S/N = 3). Therefore, the facile synthesis strategy for bimetallic nanoparticles by the mild reductant of carbon dot will provide some new thoughts for preparing of carbon-based metal nanomaterials and expand their application in catalysis and analytical chemistry areas.     

Enhanced peroxidase‐like activity of MMT‐supported cuprous oxide nanocomposites toward rapid colorimetric estimation of H2O2

Nanocomposites based on Cu₂O and Ca‐montmorillonite (Ca⁺‐MMT) with different composition were successfully prepared via a simple hydrothermal method. The as‐prepared Cu₂O‐MMT nanocomposites can rapidly catalytically oxidize the colorless chromogenic substrate, 3,3′,5,5′‐tetramethylbenzydine (TMB) into blue oxTMB with the aid of the H₂O₂ only in 30 s, which were observed by the naked eye. The reaction catalyzed by the Cu₂O‐MMT nanocomposites followed the Michaelis–Menten kinetics. Compared to the MMT or Cu₂O alone, Cu₂O‐MMT with different mass ratio exhibited an enhanced peroxidase‐like activity. The fabricated H₂O₂ sensor exhibited a good response to H₂O₂ with a linear detection range from 3 to 80 μM as well as a detection limit of 2.395 μM. Taking the advantages of the Cu₂O‐MMT nanocomposites, including outstanding peroxidase‐like activity and high sensitivity for colorimetric detection of H₂O₂, a colorimetric sensor based on the Cu₂O‐MMT nanocomposites was designed and used to rapidly detect H₂O₂ in a short time.     

Enhanced peroxidase-like activity of hierarchical MoS_2-decorated N-doped carbon nanotubes with synergetic effect for colorimetric detection of H_2O_2 and ascorbic acid

The exploitation of multifunctional nanocomposites is highly desired in environmental monitoring,biosensors,and medical diagnosis.In this paper,a simple approach has been proposed to fabricate MoS_2 decorated N-doped carbon nanotubes(NCNTs@MoS_2) hybrid composites as efficient peroxidase-like mimics.The combination of the MoS_2 and N-doped carbon nanotubes(NCNTs) brings about an enhanced synergistic effect,leading to remarkably decent intrinsic peroxidase-mimic activities than that of the single components.Due to the high catalytic efficiency of the resultant NCNTs@MoS_2 hybrid nanotubes as peroxidase-like mimics,a co nvenient colorimetric approach for the sensitive determination of H_2 O_2 and ascorbic acid have been developed with a detection limit of about 0.14 μmol/L and 0.12 μmol/L,respectively.The work offers a new strategy for the fabrication of peroxidase-like nanomaterials with excellent catalytic activity,which indicates great promising applications in sensitive detections in real samples.     

Vanadium/cobalt oxides–anchored flexible carbon nanofibers with tunable magnetism as recoverable peroxidase-like catalysts

High-efficiency peroxidase-like catalysts that can be easily recycled are desperately needed for the rapid and accurate detection of H₂O₂. Herein, a novel flexible membrane composed of vanadium/cobalt oxides–anchored carbon (VCoO/C) nanofibers has been purposely designed and fabricated by electrospinning and subsequent carbonization, where there are processing temperature-dependent morphology, composition, and versatile properties. As the carbonization temperature increases from 600°C to 900°C, the saturation magnetization of the as-prepared VCoO/C nanofibers rises gradually. When treated at 750°C under Ar protection, the resultant VCoO/C-750 nanofibers yield superior peroxidase-like catalytic activity toward H₂O₂ with a low limit of detection of 0.44 μM (signal-to-noise ratio = 3). The combination of magnetic behavior and flexibility enables the effective recovery of catalysts. It is believed that our results will open a new avenue for the controlled preparation of flexible nanofiber materials, which are endowed with multiple functions.     

Smartphone-based colorimetric determination of glucose in food samples based on the intrinsic peroxidase-like activity of nitrogen-doped carbon dots obtained from locusts

In this study, nitrogen-doped carbon dots (N-CDs) with excellent peroxidase-like activity were prepared using locust powder as the carbon source by a self-exothermic reaction. The obtained N-CDs could catalyze the oxidation of the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate a blue oxidized product (TMB_ox) with a maximum absorption peak at 654 nm. The catalytic reaction conditions were optimized; furthermore, steady-state kinetic analysis indicated that N-CDs exhibited high affinity toward both TMB and H₂O₂, and the Michaelis-Menten constant (k_m) values were 0.115 mM (TMB) and 0.764 mM (H₂O₂). A smartphone-based colorimetric method was developed for quantitative detection. The 1/L values (L stands for lightness in HSL color space) of the TMB_ox solution were recorded via an iPhone application Color Analyzer. Since H₂O₂ is the by-product of glucose (Glu) oxidation in the presence of glucose oxidase (GOx), a simple, sensitive, and selective smartphone-based colorimetric method was developed for the determination of Glu, and the detection limit was 1.09 μM. The smartphone-based method was successfully applied to determine Glu in different food samples with recoveries in the range of 88.5–109.0 %.     

Ratiometric two-photon excited photoluminescence of quantum dots triggered by near-infrared-light for real-time detection of nitric oxide release in situ

Probe-donor integrated nanocomposites were developed from conjugating silica-coated Mn²⁺:ZnS quantum dots (QDs) with MoS₂ QDs and photosensitive nitric oxide (NO) donors (Fe₄S₃(NO)₇⁻, RBS). Under excitation with near-infrared (NIR) light at 808 nm, the Mn²⁺:ZnS@SiO₂/MoS₂-RBS nanocomposites showed the dual-emissive two-photon excited photoluminescence (TPEPL) that induced RBS photolysis to release NO in situ. NO caused TPEPL quenching of Mn²⁺:ZnS QDs, but it produced almost no impact on the TPEPL of MoS₂ QDs. Hence, the nanocomposites were developed as a novel QDs-based ratiometric TPEPL probe for real-time detection of NO release in situ. The ratiometric TPEPL intensity is nearly linear (R² = 0.9901) with NO concentration in the range of 0.01∼0.8 μM, which corresponds to the range of NO release time (0∼15 min). The detection limit was calculated to be approximately 4 nM of NO. Experimental results confirmed that this novel ratiometric TPEPL probe possessed high selectivity and sensitivity for the detection of NO against potential competitors, and especially showed high detection performance for NIR-light triggered NO release in tumor intracellular microenvironments. These results would promote the development of versatile probe-donor integrated systems, also providing a facile and efficient strategy to real-time detect the highly controllable drug release in situ, especially in physiological microenvironments.     

Investigation on the Peroxidase-like Activity of Vitamin B6 and Its Applications in Colorimetric Detection of Hydrogen Peroxide and Total Antioxidant Capacity Evaluation

The peroxidase-like activity of vitamin B6 (VB6) was firstly demonstrated by catalyzing the peroxidase chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) at the existence of H₂O₂. The influence of different factors on the catalytic property of VB6, including pH, temperature, VB6 concentration, and incubation time, were investigated. The steady-state kinetic study results indicate that VB6 possesses higher affinity to H₂O₂ than natural horseradish peroxidase and some other peroxidase mimics. Besides, the radical quenching experiment results confirm that hydroxyl radical (•OH) accounts for the catalytic process. Based on the excellent peroxidase-like catalytic activity of VB6, the colorimetric methods for H₂O₂ and gallic acid (GA) detection were developed by measuring the absorbance variance of the catalytic system. Under the optimal conditions, the linear ranges of the methods for H₂O₂ and GA determination with good selectivity are 50.0–600.0 μM and 10.0–50.0 μM, respectively. In addition, the developed method was applied in the detection of H₂O₂ in milk samples and evaluation of total antioxidant capacity of different tea infusions. This study may broaden the application prospect of VB6 in environmental and biomedical analysis fields, contribute to profound insight of the physiological functions of VB6, as well as lay foundation for further excavation of small-molecule peroxidase mimics.     

Amelioration of human acute lymphoblastic leukemia (ALL) cells by ZnO-TiO2-Chitosan-Amygdalin nanocomposites

The present study aims to study the cytotoxicity of ZnO-TiO₂-Chitosan-Amygdalin nanocomposites (ZnO-TiO₂-Chitosan-Amygdalin) on T lymphoblast cancer cells (MOLT-4). In a study, nanocomposites containing 2.5 to 15 µg/ml MTT were screened for their anticancer activity. Its anticancer properties were significantly higher than those of other nanocomposites with an IC₅₀ value of 10.34 µg/ml. We studied the mechanism of action for cytotoxic cell death by fluorescence microscopy using Acridine Orange/EtBr (AO/EtBr) and Rhodamine 123 staining procedures. Using DCFH-DA, ZnO-TiO₂-Chitosan-Amygdalin nanocomposites were analyzed to determine ROS production. The change in apoptotic protein expression for the 24 h following treatment with MOLT-4 cells for Caspase-3, 8, and 9. Nanocomposites containing ZnO-TiO₂-Chitosan-Amygdalin increased the number of early and late apoptotic cells in MOLT-4 cells. ZnO-TiO₂-Chitosan-Amygdalin nanocomposites also enhanced mitochondrial apoptosis through Caspase cascade signaling. MOLT-4 cells phosphorylated Caspase cascade in response to ZnO-TiO₂-Chitosan-Amygdalin nanocomposites. Compared to the control group, the cancer cells treated with ZnO-TiO₂-Chitosan-Amygdalin nanocomposites significantly arrest the proliferation and induces cleavage of pro-apoptotic proteins which leads to apoptotic cell death. Accordingly, ZnO-TiO₂-Chitosan-Amygdalin nanocomposites might be effective against T lymphoblast cancer.     

Peroxidase-Like Platinum Clusters Synthesized by Ganoderma lucidum Polysaccharide for Sensitively Colorimetric Detection of Dopamine

The sensitive and selective detection of dopamine (DA) is very important for the early diagnosis of DA-related diseases. In this study, we reported the colorimetric detection of DA using Ganoderma lucidum polysaccharide (GLP) stabilized platinum nanoclusters (Pt_n-GLP NCs). When Pt₆₀₀-GLP NCs was added, 3,3’,5,5’-tetramethylbenzidine (TMB) was rapidly catalyzed and oxidized to blue oxTMB, indicating the peroxidase-like activity of Pt₆₀₀-GLP NCs. The catalytic reaction on the substrate TMB followed the Michaelis-Menton kinetics with the ping-pong mechanism. The mechanism of the colorimetric reaction was mainly due to the formation of hydroxyl radical (•OH). Furthermore, the catalytic reaction of Pt₆₀₀-GLP NCs was used in the colorimetric detection of DA. The linear range for DA was 1–100 μM and the detection limit was 0.66 μM. The sensitive detection of DA using Pt-GLP NCs with peroxidase-like activity offers a simple and practical method that may have great potential applications in the biotechnology field.     

Core–shell magnetic Fe3O4/CNC@MOF composites with peroxidase-like activity for colorimetric detection of phenol

Rapid and accurate detection of phenolic wastewater from industries has created global concern. Herein, core–shell magnetic cellulose nanocrystal supported MOF (Fe₃O₄/CNC@ZIF-8) with robust peroxidase-like activity was synthesized with tannic acid as modifier and bridge. The peroxidase-mimic catalytic activity of as-prepared Fe₃O₄/CNC@ZIF-8 was further investigated using o-phenylenediamine (OPD) as peroxidase substrates in the presence of H₂O₂. Moreover, the experimental conditions were optimized and the kinetic analysis results showed that Fe₃O₄/CNC@ZIF-8 had higher affinity towards both the substrate OPD and H₂O₂ than horseradish peroxidase (HRP). Finally, a phenol colorimetric assay with a linear range of 2–200 µM and a detection limit of 0.316 µM was constructed. The catalytic mechanism of Fe₃O₄/CNC@ZIF-8 with phenol was further investigated by fluorescence test and the generated ·OH was proved to act a crucial role to produce quinoid radicals. Additionally, the synthesized magnetic material had excellent stability and recyclability and ease to separation. These results suggest that the Fe₃O₄/CNC@ZIF-8 may be one of the promising candidates as peroxidase mimic for colorimetric detection of phenol.

     

Nanoflower-like composites of ZnO/SiO2 synthesized using bamboo leaves ash as reusable photocatalyst

In this study, the synthesis of ZnO/SiO₂ nanocomposites using bamboo leaf ash (BLA) and tested their photocatalytic activity for rhodamine B decolorization have been conducted. The nanocomposites were prepared by the sol–gel reaction of zinc acetate dihydrate, which was used as a zinc oxide precursor, with silica gel obtained from the caustic extraction of BLA. The effect of the Zn content (5, 10, and 20 wt%) on the physicochemical characteristics and photocatalytic activity of the nanocomposites was investigated. The results of X-ray diffraction, scanning electron microscopy, gas sorption, and transmission electron microscopy characterization confirmed the mesoporous structure of the composites containing nanoflower-like ZnO (wurtzite) nanoparticles of 10–30 nm in size dispersed on the silica support. Further, the nanocomposites were confirmed to be composed of ZnO/SiO₂ by X-ray photoelectron spectroscopy analysis. Meanwhile, diffuse-reflectance UV–visible spectrophotometry analysis of the nanocomposites revealed band gap energies of 3.38–3.39 eV. Of the tested nanocomposites, that containing 10 wt% Zn exhibited the highest decolorization efficiency (99%) and fastest decolorization rate. In addition, the degradation efficiencies were not reduced significantly after five repeated runs, demonstrating the reusability of the nanocomposite catalysts. Therefore, the ZnO/SiO₂ nanocomposite obtained from BLA is a promising reusable photocatalyst for the degradation of dye-polluted water.     

Peroxidase-like catalytic activity of copper ions and its application for highly sensitive detection of glypican-3

Glypican-3 (GPC3) might be used as new biomarker of liver cancer for the development of new diagnostic methods. The most commonly used methods for protein detection are based on natural enzymes, which are easily affected by environmental conditions and suffer from the rigorous preparation conditions. Thus, the development of new enzyme mimetics with high and stable catalytic activity is of great significance in diagnostic applications. In this paper, copper ions (Cu²⁺) was found to possess the peroxidase-like catalytic activity, which can catalyze H₂O₂-mediated oxidation of peroxidase substrate and obtain the oxidation product with color change. This catalytic activity is much more stable than other nanomaterials based peroxidase mimetics, and can significantly increase by increasing the concentration of H₂O₂. It is worth mentioning that the absorbance signal induced by 5 nM Cu²⁺ can be easily detected. This Cu²⁺-catalyzed reaction can be also applied in the detection of GPC3 by using the anti-GPC3 antibody functionalized CuO NPs, which can release the Cu²⁺ by dissolved in HCl solution. This method permits detection of as low as 0.26 pg mL⁻¹ GPC3. This sensitivity is about one or several magnitudes higher than that of ELISA or other peroxidase mimetics based methods. The high catalytic activity of Cu²⁺ and the signal amplification process of CuO NPs into high amount of Cu²⁺ also make this method more simple and effective.     

Magnetic carbon nitride nanocomposites as enhanced peroxidase mimetics for use in colorimetric bioassays,and their application to the determination of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and glucose

Graphite-like carbon nitride ? Fe₃O₄ magnetic nanocomposites were synthesized by a chemical co-precipitation method. The nanocomposites were characterized by transmission electron microscopy, X-ray diffraction, FTIR spectroscopy, X-ray photoelectron spectroscopy and magnetization hysteresis loops. The nanocomposites exhibit enhanced peroxidase-like activity (compared to that of graphite-like carbon nitride or Fe₃O₄ NPs). More specifically, they are capable of catalyzing the oxidation of different peroxidase substrates (such as TMB, ABTS or OPD) by H₂O₂ to produce the typical color reactions (blue, green or orange). The nanocomposites retain their magnetic properties and can be separated by an external magnet. On the basis of these findings, a highly sensitive and selective method was applied to the determination of H₂O₂ and glucose (by using glucose oxidase). It was successfully applied to the determination of glucose in (spiked) human serum. Compared to other nanomaterial-based peroxidase mimetics, the one described here provides distinctly higher sensitivity for both H₂O₂ and glucose, with detection limits as low as 0.3 μM and 0.25 μM, respectively.

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Graphical abstract The magnetic carbon nitride nanocomposite exhibits enhanced peroxidase-like activity that is much larger than that of graphite-like carbon nitride or Fe₃O₄ NPs alone. This finding was applied to design a highly sensitive and selective colorimetric assay for H₂O₂ and glucose.

     

Silver nanoparticles-decorated reduced graphene oxide: A novel peroxidase-like activity nanomaterial for development of a colorimetric glucose biosensor

In this study, we present a novel approach to prepare of a colorimetric chemical sensor for H₂O₂ and a glucose biosensor basing on the use of peroxidase-like activity of silver nanoparticles decorated on reduced graphene oxide sheets (AgNPs@rGO) nanocomposite. Herein, AgNPs@rGO nanocomposite was synthesized by a one-step hydrothermal reducing method and its physico-chemical properties were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Ultraviolet–visible spectroscopy (UV–Vis), Fourier-Transform Infrared spectroscopy (FT-IR) and Energy Dispersive X-ray spectroscopy (EDX). Obtained evaluation results shown that the synthesized AgNPs/rGO nanocomposite has performed an efficient peroxidase-like activity for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB_red) by H₂O₂, leading to the oxidized form (TMB_ox) which presents a typical blue color (maximum of absorbance at λ_max = 655 nm). A colorimetric assay for H₂O₂ detection was designed and fabricated with a limit of detection of 20 μM. Moreover, we have used of AgNPs/rGO nanocomposite combining with glucose oxidase (GOx) to develop of a colorimetric glucose biosensor with a low limit of detection of 40 μM and a linear dynamic range from 125 μM to 1 mM. This glucose test was applied to the detection of glucose in human serum samples.     

A novel nonenzymatic biosensor for evaluation of oxidative stress based on nanocomposites of graphene blended with CuI

A high-sensitive nonenzymatic hydrogen peroxide (H₂O₂) biosensor based on cuprous iodide and graphene (CuI/Gr) composites has been explored for the detection of H₂O₂ released by living cells and monitoring the oxidative stress of cells under excellular stimulation. The biosensor properties were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), amperometric i-t curve, and the redox-competition mode of scanning electrochemical microscopy (SECM). Our observations demonstrate that the CuI/Gr nanocomposites modified glassy carbon electrode (GCE) exhibits excellent catalytic activity for H₂O₂ with relatively low detection limit and a wide linear range from 0.5 μM to 3 mM. Moreover, the redox-competition mode of SECM imaging study further illustrates the improved electrochemical catalytic capability for H₂O₂ reduction with CuI/Gr nanocomposites deposited on graphite electrode. Hence, the as-prepared nonenzymatic H₂O₂ biosensor could be used to detect H₂O₂ release from different kinds of living cells under stimulation while eliminating the interference of ascorbic acid.     

A new colorimetric assay for amylase based on starch-supported Cu/Au nanocluster peroxidase-like activity

In this paper, we present a new colorimetric technique as a novel assay for the easy and direct detection of α-amylase activity. This detection system utilizes the interaction of α-amylase with starch that is supporting copper/gold (Cu/Au) nanoclusters. The Cu/Au nanoclusters are synthesized using starch as a stabilizing agent at room temperature. These nanoclusters show robust peroxidase-like activity and are able to catalyze the oxidation of TMB (3,3,5,5-tetramethylbenzidine) in the presence of hydrogen peroxide (H₂O₂), leading to the generation of a blue-colored solution. The α-amylase detection mechanism is based on the digestion of the starch by α-amylase, which results in nanocluster aggregation, leading to increased nanoparticle size and thus decreased peroxidase-like activity of the Cu/Au NCs. Experiments showed that the gradual addition of α-amylase causes the peroxidase activity to decrease step by step in a linear fashion. Using this method, colorimetric sensing of α-amylase was achieved with a detection limit (LOD) of 0.04 U/mL and a linear range of 0.1–10 U/mL. This method is significantly selective for α-amylase and could be affordably and conveniently applied to the detection of α-amylase in blood serum.

Graphical Abstract

     

Application of carboxyl functionalized graphene oxide as mimetic peroxidase for sensitive voltammetric detection of H2O2 with 3,3′,5,5′-tetramethylbenzidine

A sensitive electrochemical method for H₂O₂ determination was proposed with carboxyl functionalized graphene oxide (GO-COOH) as mimetic peroxidase and 3,3′,5,5′-tetramethylbenzidine (TMB) as substrate. GO-COOH exhibited intrinsic peroxidase-like activity that could catalyze the oxidation of TMB with H₂O₂. The generated product exhibited a sensitive second order derivative linear sweep voltammetric reduction peak at − 0.93 V (vs. Ag/AgCl) in Britton–Robinson buffer. Under the optimal conditions the reduction peak current was proportional to H₂O₂ concentration in the linear range from 0.006 to 0.8 μmol L^− 1 with the detection limit of 1.0 nmol L^− 1 (3σ). This proposed method was further applied to determine H₂O₂ content in fresh milk samples with satisfactory results.     

A sensitive fluorescent assay for thiamine based on metal-organic frameworks with intrinsic peroxidase-like activity

Metal-organic frameworks (MOFs) with tunable structures and properties have recently been emerged as very interesting functional materials. However, the catalytic properties of MOFs as enzymatic mimics remain to be further investigated. In this work, we for the first time demonstrated the peroxidase-like activity of copper-based MOFs (HKUST-1) by employing thiamine (TH) as a peroxidase substrate. In the presence of H₂O₂, HKUST-1 can catalyze efficiently the conversion of non-fluorescent TH to strong fluorescent thiochrome. The catalytic activity of HKUST-1 is highly dependent on the temperature, pH and H₂O₂ concentrations. As a peroxidase mimic, HKUST-1 not only has the features of low cost, high stability and easy preparation, but also follows Michaelis–Menten behaviors and shows stronger affinity to TH than horseradish peroxidase (HRP). Based on the peroxidase-like activity of HKUST-1, a simple and sensitive fluorescent method for TH detection has been developed. As low as 1 μM TH can be detected with a linear range from 4 to 700 μM. The detection limit for TH is about 50 fold lower than that of HRP-based fluorescent assay. The proposed method was successfully applied to detect TH in tablets and urine samples and showed a satisfactory result. We believed that the present work could improve the understanding of catalytic behaviors of MOFs as enzymatic mimics and find out a wider application in bioanalysis.     

Intrinsic peroxidase-like catalytic activity of nitrogen-doped graphene quantum dots and their application in the colorimetric detection of H2O2 and glucose

In this paper, the highly intrinsic peroxidase-like catalytic activity of nitrogen-doped graphene quantum dots (N-GQDs) is revealed. This activity was greatly dependent on pH, temperature and H₂O₂ concentration. The experimental results showed that the stable N-GQDs could be used for the detection of H₂O₂ and glucose over a wide range of pH and temperature, offering a simple, highly selective and sensitive approach for their colorimetric sensing. The linearity between the analyte concentration and absorption ranged from 20 to 1170 μM for H₂O₂ and 25 to 375 μM for glucose with a detection limit of 5.3 μM for H₂O₂ and 16 μM for glucose. This assay was also successfully applied to the detection of glucose concentrations in diluted serum and fruit juice samples.