AuPt/MOF-Graphene: A Synergistic Catalyst with Surprisingly High Peroxidase-Like Activity and Its Application for H2O2 Detection

Ag-doped Fe-metal–organic framework nanozymes for efficient antibacterial application

Illustration of an Fe-MOF-Ag nanozyme for antibacterial application.

Co nanoparticles decorated with N-doped carbon nanotubes as high-efficiency catalysts with intrinsic oxidase-like property for colorimetric sensing

Artificial nanozymes are designed for pursuing the functions of splendid catalytic efficiency and prominent selectivity of natural enzymes, meanwhile obtaining higher stability than that of natural enzymes. This emerging technology shows widespread application in the crossing field between nanotechnology and biomedicine. In this work, we employed a universal approach to fabricate a Co@N-CNTs hybrid nanocomposite as an oxidase mimic, in which fine Co nanoparticles were wrapped in N-doped carbon nanotubes, stacking on a hollow dodecahedron carbon skeleton. The synergistic effects of nanostructure engineering, N-doping and carbon coating, as well as the derived interfacial effect contribute to the glorious oxidase-like activity, stability and reusability. It can catalytically oxidize the colorless substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue oxidation product (ox-TMB). As a result, a colorimetric technique with excellent selectivity and sensitivity for detecting ascorbic acid (AA) with naked eyes was established, in view of specific inhibitory effects towards oxidation of TMB. Under optimal detection conditions, this method exhibits a good linearity ranging from 0.1 to 160 μM with a low limit of detection (LOD) of 0.076 μM. For practical applications, Co@N-CNTs hybrid catalyst as a mimic oxidase was used for the determination of AA in human serum, which yielded satisfactory results. This work may serve as a new research thought to guide the design of high-performance nanozymes and establish a sensing platform for the detection of AA.

In this work, we designed a Co@N-CNTs hybrid nanocomposite as an oxidase mimic for the colorimetric detection of ascorbic acid with the naked eye.

A novel dual signal and label-free electrochemical aptasensor for mucin 1 based on hemin/graphene@PdPtNPs

A dual signal and label-free electrochemical aptasensor for mucin 1 was constructed based on hemin/graphene@PdPtNPs nanocomposite (H-Gr@PdPtNPs). Hemin attached on the graphene surface not only improves the solubility of graphene and acts as an in-situ electrochemical probe but also exhibits excellent peroxidase-like properties to electrocatalyze the reduction of H2O2. PdPtNPs also show outstanding catalytic capacity to the reduction of H2O2 and provide numerous binding sites for loading dDNA (mucin 1 aptamer and cDNA) to form the sensing interface. In the presence of mucin 1, due to the specific affinity between aptamer and mucin 1, double helix would be induced dissociation and the aptamer would be pulled off from the electrode. As a result, the electrochemical signals of hemin and H2O2 were recovered. Based on these properties, the label-free and sensitive dual signal electrochemical biosensor for mucin 1 detection has been developed. The one is differential pulse voltammetry (DPV) signal of hemin and the other is chronoamperometry signal arisen from the catalytic reduction of H2O2. The linear ranges for mucin 1 were 8.0 pg mL-1 to 80 ng mL-1 and 0.8 pg mL-1 to 80 ng mL-1 with the limit of detection 2.5 pg mL-1 and 0.25 pg mL-1 by DPV and chronoamperometry, respectively. The recovery of mucin 1 in human blood serum samples was from 95.0% to 104.2%. The detection platform does not need signal labeling which greatly reduced the sophisticated and expensive procedures. The aptasensor provide a promising strategy for the determination of mucin 1 in clinical diagnostics.

In Situ Generation of Regularly Ordered 2D Ultrathin Covalent Organic Framework Films for Highly Sensitive Photoelectrochemical Bioanalysis

Developing new photoactive materials and electrode preparation technology with high stability, repeatability, easy fabrication, and a low electron-hole recombination rate is promising for ideal photoelectrochemical (PEC) biosensors, but it remains a great challenge. Here, a porous and crystalline oriented two-dimensional (2D) ultrathin covalent organic framework film (D-TA COF film) was formed in situ on indium-doped tin oxide (ITO) substrates under very mild conditions. The structure and morphology of D-TA COF film were characterized by means of Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and powder X-ray diffraction. Compared with the randomly oriented D-TA COF powder drop-coated on ITO, the photocurrent of the D-TA COF film grown on the ITO surface in situ achieved as high as ∼333-fold increase. This photocurrent can be further amplified by O₂ (acting as electron acceptors). Benefiting from the fabrication in situ, D-TA COF film also exhibited tough adhesion, assuring the film was difficult to separate from the electrode. Accordingly, D-TA COF film was applied as the photoactive material to build a PEC biosensor for H₂O₂ detection based on coupling with large amounts of catalase (CAT) through simple adsorption. The introduced CAT catalyzed the decomposition of H₂O₂ to O₂, leading to an enhancement of the photocurrent response. As a result, a "signal-on" PEC biosensor was fabricated with good sensitivity, rapid response, and high stability, and it can also detect H₂O₂ released from living cells. Taking into account these advantages, the D-TA COF film is expected to be an ideal photoactive material to construct various PEC biosensors, which as far as we know have not been reported.

Electrochemical immunosensor based on binary nanoparticles decorated rGO-TEPA as magnetic capture and Au@PtNPs as probe for CEA detection

Using gold and magnetic nanoparticles co-decorated reduced graphene oxide-tetraethylenepentamine (rGO-TEPA/Au-MNPs) as the magnetic platform for capturing the primary antibody (Ab₁), separation and preconcentration of immunocomplex, a novel homogeneous electrochemical immunosensor was successfully developed. The newly prepared magnetic rGO-TEPA/Au-MNPs, compared with MNPs, exhibited better stability and enhanced electrical conductivity attributed to rGO-TEPA, and showed higher biorecognition efficiency due to AuNPs. In addition, Au@PtNPs were prepared and modified with secondary antibody (Ab₂) as an efficient signal probe for signal readout. Using carcinoembryonic antigen (CEA) as a model analyte, the prepared immunosensor demonstrated satisfactory properties like high stability, good repeatability and selectivity, wide linear range (5.0 pg mL^-1~200.0 ng mL^-1) as well as low detection limit (1.42 pg mL^-1). The homogenous electrochemical immunosensor was applied to the detection of CEA in human serum and was found to exhibit good correlation with the reference method. Thus, the proposed rGO-TEPA/Au-MNPs-based homogenous immunoassay platform might open up a new way for biomarker diagnosis. Graphical Abstract.

One-Step Electrodeposition of Silver Nanostructures on 2D/3D Metal-Organic Framework ZIF-67: Comparison and Application in Electrochemical Detection of Hydrogen Peroxide

Metal-organic frameworks (MOFs) have been widely used as supporting materials to load or encapsulate metal nanoparticles for electrochemical sensing. Herein, the influences of morphology on the electrocatalytic activity of Co-containing zeolite imidazolate framework-67 (ZIF-67) as supporting materials were studied. Three types of morphologies of MOF ZIF-67 were facilely synthesized by changing the solvent because of the influence of the polar solvent on the nucleation and preferential crystal growth. Two-dimensional (2D) ZIF-67 with microplate morphology and 2D ultrathin ZIF-67 nanosheets were obtained from pure H₂O (H-ZIF-67) and a mixed solution of dimethylformamide and H₂O (D-ZIF-67), respectively. Three-dimensional ZIF-67 with rhombic dodecahedron morphology was obtained from pure methanol (M-ZIF-67). Then, one-step electrodeposition of silver nanostructures on ZIF-67-modified glassy carbon electrode (Ag/ZIF-67/GCE) was performed for the reduction of hydrogen peroxide (H₂O₂). Cyclic voltammetry can be used to investigate the electrocatalytic activity of Ag/ZIF-67/GCE, and Ag/H-ZIF-67/GCE displayed the best electrocatalytic property than Ag/D-ZIF-67/GCE and Ag/M-ZIF-67/GCE. The electrochemical H₂O₂ sensor showed two wide linear ranges of 5 μM to 7 mM and 7 to 67 mM with the sensitivities of 421.4 and 337.7 μA mM^-1 cm^-2 and a low detection limit of 1.1 μM. In addition, the sensor exhibited good selectivity, high reproducibility, and stability. Furthermore, it has been utilized for real-time detection of H₂O₂ from HepG2 human liver cancer cells. This work provides a novel strategy for enhancing the detection performance of electrochemical sensors by changing the crystalline morphologies of supporting materials.

Facile Fabrication of Rhodium/Nanodiamond Hybrid as Advanced Catalyst toward Hydrogen Production from Ammonia–Borane

Hydrogen generation through ammonia–borane (AB) hydrolysis has been regarded as one of the most promising pathways to tap renewable green energy. The design and synthesis of highly effective catalysts toward hydrogen production from aqueous AB is of paramount significance. Here, the facile synthesis of Rh nanoparticles (NPs) immobilized on nanodiamond (nano-DA) and concomitant AB hydrolysis to produce hydrogen was successfully achieved. The in situ generated Rh/nano-DA exhibited excellent catalytic activity toward AB hydrolysis, with a high turnover frequency (TOF) value of 729.4 min−1 at 25 °C and a low activation energy of 25.6 kJ mol−1. Moreover, the catalyst could be reused four times. The unique properties of DA with abundant oxygen-containing groups enable the homogeneous distribution of small and surface-clean Rh NPs on the nano-DA surface, which can supply abundant accessible active sites for hydrogen evolution from AB hydrolysis. This study demonstrated that nano-DA can be applied as an ideal matrix to deposit efficient Rh nanocatalyst toward hydrogen evolution reaction.

Au@Pt Nanotubes within CoZn-Based Metal-Organic Framework for Highly Efficient Semi-hydrogenation of Acetylene

Designing nanocatalysts with synergetic functional component is a desirable strategy to achieve both high activity and selectivity for industrially important hydrogenation reaction. Herein, we fabricated a core-shell hollow Au@Pt NTs@ZIFs (ZIF, zeolitic imidazolate framework; NT, nanotube) nanocomposite as highly efficient catalysts for semi-hydrogenation of acetylene. Hollow Au@Pt NTs were synthesized by epitaxial growth of Pt shell on Au nanorods followed with oxidative etching of Au@Pt nanorod. The obtained hollow Au@Pt NTs were then homogeneously encapsulated within ZIFs through in situ crystallization. By combining the high activity of bimetallic nanotube and gas enrichment property of porous metal-organic frameworks, hollow Au@Pt NT@ZIF catalyst was demonstrated to show superior catalytic performance for the semi-hydrogenation of acetylene, in terms of both selectivity and activity, over those of monometallic Au and solid bimetal nanorod@ZIF counterparts. This catalysts design idea is believed to be inspirable for the development of highly efficient nanocomposite catalysts.

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Core-shell nanocomposite catalysts M@ZIFs are assembled

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The M NRs and NTs are well dispersed and fully encapsulated in ZIF-67 and ZIF-8

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Au@Pt_NT enhance the selectivity and conversion for the semi-hydrogenation of acetylene

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DFT calculations show Au@Pt_NT has lower energy barrier compared with Au@Pt_NR

Novel Graphene/In2O3 Nanocubes Preparation and Selective Electrochemical Detection for L-Lysine of Camellia nitidissima Chi

In this work, novel graphene/In₂O₃ (GR/In₂O₃) nanocubes were prepared via one-pot solvothermal treatment, reduction reaction, and successive annealing technology at 600 °C step by step. Interestingly, In₂O₃ with featured cubic morphology was observed to grow on multi-layered graphene nanosheets, forming novel GR/In₂O₃ nanocubes. The resulting nanocomposites were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), etc. Further investigations demonstrated that a selective electrochemical sensor based on the prepared GR/In₂O₃ nanocubes can be achieved. By using the prepared GR/In₂O₃-based electrochemical sensor, the enantioselective and chem-selective performance, as well as the optimal conditions for L-Lysine detection in Camellia nitidissima Chi, were evaluated. The experimental results revealed that the GR/In₂O₃ nanocube-based electrochemical sensor showed good chiral recognition features for L-lysine in Camellia nitidissima Chi with a linear range of 0.23–30 μmol·L⁻¹, together with selectivity and anti-interference properties for other different amino acids in Camellia nitidissima Chi.

An Ultrasensitive Non-Enzymatic Sensor for Quantitation of Anti-Cancer Substance Chicoric Acid Based on Bimetallic Nanoalloy with Polyetherimide-Capped Reduced Graphene Oxide

Exploiting effective therapies to fight tumor growth is an important part of modern cancer research. The anti-cancer activities of many plant-derived substances are well known, in part because the substances are often extensively distributed. Chicoric acid, a phenolic compound widely distributed in many plants, has drawn widespread attention in recent years because of its extraordinary anti-cancer activities. However, traditional methods for quantifying chicoric acid are inefficient and time-consuming. In this study, an ultrasensitive non-enzymatic sensor for the determination of chicoric acid was developed based on the use of an Au@Pt-polyetherimide-reduced graphene oxide (PEI-RGO) nanohybrid-modified glassy carbon electrode. Owing to the considerable conductivity of PEI-functionalized RGO and the efficient electrocatalytic activity of Au@Pt nanoalloys, the designed sensor exhibited a high capacity for chicoric acid measurement, with a low detection limit of 4.8 nM (signal-to-noise ratio of 3) and a broad linear range of four orders of magnitude. With the advantages provided by the synergistic effects of Au@Pt nanocomposites and PEI-RGO, the developed sensor also revealed exceptional electrochemical characteristics, including superior sensitivity, fast response, acceptable long-term stability, and favorable selectivity. This work provides a powerful new platform for the highly accurate measurement of chicoric acid quantities, facilitating further research into its potential as a cancer treatment.

Efficient Visual Chemosensor for Hexavalent Chromium via a Controlled Strategy for Signal Amplification in Water

Generally, 3,3',5,5'-tetramethylbenzidine (TMB) cannot react with hydrogen peroxide (H₂O₂) in neutral pH or in water at room temperature and pressure. Herein, we found that hexavalent chromium (Cr⁶⁺) can trigger TMB reacting with H₂O₂ (TMB-H₂O₂) in ultrapure water along with a weak signal output. Then, to implement signal amplification effectively, we designed a ternary nanohybrid material containing graphene oxide (GO) nanosheets, gold nanoparticles (Au NPs), and hyperbranched polyethylenimine (PEI) to form rGO/PEI/Au nanohybrids via chemical bonding. After addition of a trace amount of Cr⁶⁺, rGO/PEI/Au nanohybrids can effectively catalyze TMB-H₂O₂ in ultrapure water; thus, a visual chemosensor and electronic spectrum quantitative analysis method for Cr⁶⁺ based on chromium-stimulated peroxidase mimetic activity of rGO/PEI/Au nanohybrids were established. The visual chemosensor exhibits excellent selectivity and interference immunity against 34 other interfering substances with a detection limit as low as 2.14 nM. The visual chemosensor for Cr⁶⁺ with a low detection limit and high selectivity is expected to have a potential application in environmental analysis, monitoring, and human health maintenance.

In situ formation and immobilization of gold nanoparticles on polydimethylsiloxane (PDMS) exhibiting catalase-mimetic activity

We used needles to prepare immobilized AuNPs on the surface of PDMS in situ with catalase-mimetic activity.

Polyoxometalate-like sub-nanometer molybdenum(vi)-oxo clusters for sensitive, selective and stable H2O2 sensing

Polyoxometalate-like sub-nanometer molybdenum(vi)-oxo clusters supported on mesoporous carbon are stably deposited on glassy carbon and screen-printed electrodes suitable for selective, sensitive and stable H₂O₂ sensing.

A Non-Enzymatic Sensor Based on Trimetallic Nanoalloy with Poly (Diallyldimethylammonium Chloride)-Capped Reduced Graphene Oxide for Dynamic Monitoring Hydrogen Peroxide Production by Cancerous Cells

Catching cancer at an early stage is necessary to make it easier to treat and to save people's lives rather than just extending them. Reactive oxygen species (ROS) have sparked a huge interest owing to their vital role in various biological processes, especially in tumorigenesis, thus leading to the potential of ROS as prognostic biomarkers for cancer. Herein, a non-enzymatic biosensor for the dynamic monitoring of intracellular hydrogen peroxide (H2O2), the most important ROS, via an effective electrode composed of poly (diallyldimethylammonium chloride) (PDDA)-capped reduced graphene oxide (RGO) nanosheets with high loading trimetallic AuPtAg nanoalloy, is proposed. The designed biosensor was able to measure H2O2 released from different cancerous cells promptly and precisely owing to the impressive conductivity of RGO and PDDA and the excellent synergistic effect of the ternary alloy in boosting the electrocatalytic activity. Built upon the peroxidase-like activity of the nanoalloy, the developed sensor exhibited distinguished electrochemical performance, resulting in a low detection limit of 1.2 nM and a wide linear range from 0.05 μM to 5.5 mM. Our approach offers a significant contribution toward the further elucidation of the role of ROS in carcinogenesis and the effective screening of cancer at an early stage.

Temperature controllable electrochemical sensors based on horseradish peroxidase as electrocatalyst at heated Au disk electrode and its preliminary application for H2O2 detection

In this paper, horseradish peroxidase (HRP) was successfully immobilized on heated Au disk electrode (HAuDE) by biotin-streptavidin specific interaction through HS-ssDNA-biotin self-assembled on HAuDE for investigation the electrocatalytic activity of HRP. With elevated electrode temperature, the significant temperature effect of the electrocatalytic activity of HRP for H₂O₂ reduction was demonstrated by using this bio-sensing platform. With an electrode temperature of 40 °C, a detection limit of 1.5 × 10^-6 mol L^-1 for H₂O₂ reduction could be obtained, which was more than one magnitude lower than that with an electrode temperature of 0 °C. Because HRP can be widely used as an enzyme label for amplification detection, this sensing platform can be broadly applied to analytical chemistry such as nucleic acid detection, and aptamer-based biosensors.