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Multifunctional materials based on carbon xerogel (CX) with embedded bismuth (Bi) and iron (Fe) nanoparticles are tested for ultrasensitive amperometric detection of lead cation (Pb2+) and hydrogen peroxide (H2O2). The prepared CXBiFe-T nanocomposites were annealed at different pyrolysis temperatures (T, between 600 and 1050 °C) and characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption, dynamic light scattering (DLS), and electron microscopies (SEM/EDX and TEM). Electrochemical impedance spectroscopy (EIS) and square wave anodic stripping voltammetry (SWV) performed at glassy carbon (GC) electrodes modified with chitosan (Chi)-CXBiFe-T evidenced that GC/Chi-CXBiFe-1050 electrodes exhibit excellent analytical behavior for Pb2+ and H2O2 amperometric detection: high sensitivity for Pb2+ (9.2·105 µA/µM) and outstanding limits of detection (97 fM, signal-to-noise ratio 3) for Pb2+, and remarkable for H2O2 (2.51 µM). The notable improvements were found to be favored by the increase in pyrolysis temperature. Multi-scale parameters such as (i) graphitization, densification of carbon support, and oxide nanoparticle reduction and purification were considered key aspects in the correlation between material properties and electrochemical response, followed by other effects such as (ii) average nanoparticle and Voronoi domain dimensions and (iii) average CXBiFe-T aggregate dimension. [ABSTRACT FROM AUTHOR]

Nanocomposite enzymes are attracting intensive attention worldwide. In the present study, a novel colorimetric H2O2 paper sensor was developed based on a new type of nanocomposites composed of Pd−Pt nanoparticles, hemin functionalized reduced graphene oxide (hemin‐rGO) and carboxylated carbon nanotubes (CNTs‐COOH). The proposed nanocomposites show a high peroxidase‐like activity. It provides a sensitive platform showing a linear response toward H2O2 in the range of 0.05–500 μM with a determination limit of 0.01 μM. Based on this, the composites were applied to construct a paper sensor for H2O2 detection in real samples. The cost‐effectiveness, simplicity and efficiency of this paper sensor could be developed for "point‐of‐care" analysis and other related areas. [ABSTRACT FROM AUTHOR]

[Display omitted] • An enzyme-free H 2 O 2 amperometric sensor was proposed based on PtPd/IL-CDs/ACF microelectrode. • PtPd/IL-CDs/ACF exhibit higher peak current and lower potential toward H 2 O 2 reduction. • The detection limit of H 2 O 2 was low down to 0.29 μM. • Such amperometric sensor was used for H 2 O 2 detection in living cancer cells successfully. Given the pivotal role of hydrogen peroxide (H 2 O 2) in numerous biological progresses, there has been a recent surge in the development of highly effective electrochemical sensors for H 2 O 2 detection. In this article, we propose an enzyme-free amperometric system for the sensitive and selective recognition of H 2 O 2 , leveraging ultrafine PtPd alloy/ionic liquid-carbon dots (IL-CDs) nanocomposites modified flexible carbon fiber. The IL-CDs were synthesized through the direct electrodeposition of ionic liquid [BMIM][PF 6 ] using Pt sheets as electrodes. Subsequently, a sequential electrodeposition of IL-CDs, H 2 PtCl 6 , and PdCl 2 onto the activated carbon fiber (ACF) yielded the PtPd/IL-CDs/ACF microelectrode. This microelectrode serves as an enzyme-free amperometric sensor for H 2 O 2 detection, exhibiting an improved response with a significantly lower detection limit of 0.29 μM and a relatively broad linear range spanning from 2 to 6561 μM. Furthermore, this enzyme-free amperometric H 2 O 2 sensor demonstrates remarkable stability over extended periods and exceptional performance in practical applications, such as the analysis of commercially available milk, human serum, human urine, and living cancer cells analysis. This study offers a fresh perspective on amperometric sensors based on metal alloys and CDs electrode, highlighting the potential of enzyme-independent detection for hydrogen peroxide in biological systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel microcapsule system was constructed for sensitive detection of H 2 O 2 at high temperature. • The microcapsules were based on PCM core, electroactive layer, and surface-immobilized catalase. • The microcapsules show a high latent heat capacity for thermal regulation of H 2 O 2 biosensor. • The biosensor exhibits an enhanced ability for H 2 O 2 determination due to in-situ thermal management. • The biosensor finds great potential for detecting the H 2 O 2 level over a broad working temperature range. To address the deterioration in electrochemical biosensing detection of hydrogen peroxide (H 2 O 2) caused by enzymatic inactivation in high-temperature environments, we have developed a novel type of catalase-immobilized electroactive phase-change microcapsules based on a phase change material (PCM) core, an SiO 2 shell, and a poly(3,4 -ethylenedioxythiophene)/Au nanocomposite layer with the surface-immobilized catalase. The microcapsules not only show a well-defined core–shell microstructure with the desired chemical compositions, but also present a high latent heat capacity of over 130 J/g for thermal regulation. An electrochemical biosensor was established using the microcapsule-modified working electrode to obtain a high electrochemical response to H 2 O 2 through combining the highly electroactive layer with covalently bonded catalase. The developed biosensor achieved an enhanced electrochemical biosensing response to H 2 O 2 through regulating the microenvironmental temperature surrounding the working electrode by the latent heat release of its PCM core to prevent enzymatic inactivation at high temperature. Compared to conventional H 2 O 2 biosensors without thermal management by PCMs, the developed biosensor exhibits a higher sensitivity of 42.85 µA·mM−1·cm−2 and a lower detection limit of 3.56 µM at a high working temperature of 50 °C. The developed biosensor has found practical applications for sensitive detection and accurate determination of H 2 O 2 level in real food and biological samples over a wide temperature range. [ABSTRACT FROM AUTHOR]

Acylated xylan-based magnetic Fe3O4 nanocomposite hydrogels (ACX-MNP-gels) were prepared by fabricating Fe3O4 nanoctahedra in situ within a hydrogel matrix which was synthesized by the copolymerization of acylated xylan (ACX) with acrylamide and N-isopropylacrylamide under ultraviolet irradiation. The size of the Fe3O4 fabricated within the hydrogel matrix could be adjusted through controlling the crosslinking concentrations (C). The magnetic hydrogels showed desirable magnetic and mechanical properties, which were confirmed by XRD, Raman spectroscopy, physical property measurement system, SEM, TGA, and compression test. Moreover, the catalytic performance of the magnetic hydrogels was explored. The magnetic hydrogels (C = 7.5 wt %) presented excellent catalytic activity and provided a sensitive response to H2O2 detection even at a concentration level of 5 x 10-6 mol⋅L-1. This approach to preparing magnetic hydrogels loaded with Fe3O4 nanoparticles endows xylan-based hydrogels with new promising applications in biotechnology and environmental chemistry. [ABSTRACT FROM AUTHOR]

• Synthesis of silver-decorated polypyrrole-carbon black/TiO 2 nanocomposites (NCs). • Electrochemical detection of H 2 O 2 with NCs coated PEDOT:PSS/GCE. • Exhibited the highest sensitive as 8.9273 µAµM-1cm−2. • Found lowest detection limit as 0.23 ± 0.012 µM. • Safety of healthcare and environmental fields. Herein, a sensor probe based on differential pulse voltammetric (DPV) electrochemical approach was developed for an efficient detection of hydrogen peroxide (H 2 O 2) in a room conditions. In this approach, flat-polished glassy carbon electrode (GCE) was coated with silver (Ag)-decorated polypyrrole-carbon black/TiO 2 (Ag@PPy-C/TiO 2) nanocomposites (NCs) with the help of PEDOT:PSS, which functioned as conducting coating binder for active sensing substrate. The prepared Ag@PPy-C/TiO 2 NCs were totally characterized using various analyzing tools such as High-Resolution Transmission Electron Microscopy (HR-TEM), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), X-ray photo-electron spectroscopy (XPS), Fourier-Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), and powder X-ray Diffraction (XRD). The fabricated working electrode (WE) as Ag@PPy-C/TiO 2 NCs/GCE was found to respond linearly in a wide concentration range of H 2 O 2 of 0.5 ∼ 57.0 µM, which defined as a dynamic detection range (LDR). The sensor's reliability measuring parameter's including sensitivity (10.4146 µAµM-1cm−2), detection limit (LOD; 0.23 ± 0.012 µM), and limit of quantification (LOQ; 0.697 µM) were also calculated in this development. In addition, the other sensors' parameters (like, reproducibility) were measured during the electrochemical detection of H 2 O 2. Real samples were collected from the various sources, which tested to execute the validation of this H 2 O 2 sensor. It is exhibited the sensitive and reproducible responses by electrochemical approach towards H 2 O 2 at room conditions. Therefore, the developed Ag@PPy-C/TiO 2 NCs/GCE sensor probe by DPV technique based on the current-developed sensing substrate might be facile and reliable to enrich the sensor technology and for the sensitive detection of unsafe chemicals for the safety of healthcare and environmental fields in a broad scale. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report on one-pot synthesis of Ag nanoparticles/reduced graphene oxide (AgNPs/rGO) nanocomposites by heating mixed solution of graphene oxide (GO) and AgNO3 with the use of diethylenetriamine as a reducing agent at 80°C for 30min. Several analytical techniques including UV–vis spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM) have been employed to characterize the resulting nanocomposites. It was found that such nanocomposites exhibit good catalytic activity toward the reduction of H2O2. This nonenzymatic H2O2 sensor shows a fast amperometric response time of less than 2s. The linear detection range is estimated to be from 0.1 to 100mM (r =0.999), and the detection limit is estimated to be 3.6μM at a signal-to-noise ratio of 3. [Copyright &y& Elsevier]

Abstract: In this paper, we report on the one-step preparation of Ag nanoparticle (AgNP)-decorated coordination polymer nanobelts, carried out by direct mixing of an aqueous AgNO3 solution and a N,N-dimethylformamide (DMF) solution of 4,4′-bipyridine (BPD) at room temperature. The construction of an enzymeless H2O2 sensor using such nanocomposites with a detection limit of 0.9μM is also demonstrated. [Copyright &y& Elsevier]

Abstract: Nanocomposite of Ag nanoparticles self-supproted on Ag2V4O11 nanobelts, prepared by γ-ray irradiation treatments of Ag2V4O11 nanobelts, was used to immobilize hemoglobin on glassy carbon electrode. Detailed electrochemical analysis was performed and it was found that Ag/Ag2V4O11 nanocomposite significantly improved the direct electron transfer between hemoglobin and glassy carbon electrode, leading to the fabrication of a biosensor with a very sensitive detection of H2O2. The apparent surface concentration (Γ*) of hemoglobin and the electron transfer rate constant (k s) were calculated to be 1.6×10−10 mol/cm2 and 2.6s−1, respectively. The linear detection range of H2O2 was 1.0–120μM, with a detection limit of 0.3μM. [Copyright &y& Elsevier]

Abstract: Graphene-CdS (G-CdS) nanocomposites were successfully prepared by CdS nanocrystals (CdS NCs) formed in situ on the surface of graphene sheets, using graphene oxide (GO) sheets with rich negatively charged carboxylic acid groups as starting materials. Compared with pure CdS NCs, the presence of the graphene doped in G-CdS nanocomposites could facilitate the electrochemical redox process of CdS NCs; further, the as-prepared G-CdS nanocomposite can react with H2O2 to generate strong and stable electrochemiluminescent (ECL) emission, which not only enhances its ECL intensity by about 4.3-fold but also decreases its onset potential for about 320mV. The as-prepared solid-state ECL H2O2 sensor shows acceptable linear response from 5μM up to 1mM with a detection limit of 1.7μM (S/N=3). The ECL H2O2 sensor exhibits excellent reproducibility and long-term stability. Such a property would promote the potential application of the graphene as enhanced materials in fabricating sensors for chemical and biochemical analysis. [Copyright &y& Elsevier]

Abstract: A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5–120s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2–12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k s) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5×10−10 molcm−2, 6.12s−1, 5.9×10−10 molcm−2 and 6.58s−1, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96(±0.2)×103 M−1 s−1 and 5.5(±0.2)×103 M−1 s−1, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67μM, 4.14nAμM−1 nAμM−1 and 5μM to 20mM, and 0.36μM, 7.62nAμM−1, and 1μM to 10mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction. [Copyright &y& Elsevier]

Functional nanostructured transition metal oxides hold great promise in catalysis based sensors due to their superb catalytic activity, good stability, ease of preparation and cost-effectiveness. In this work, MnO 2 nanowires and MnO 2 /multi-walled carbon nanotubes (MWCNTs) nanocomposite were prepared via a simple hydrothermal method. The MnO 2 /MWCNTs nanocomposite was developed by deposition of MnO 2 on MWCNTs surface, which have abundant hydrophilic groups facilitating ion-adsorption and nucleation process. The MWCNTs/MnO 2 exhibited higher catalytic activity upon hydrogen peroxide (H 2 O 2) electrooxidation, with reduced overpotential by 100 mV and 220 mV in contrast to those values of MWCNTs and MnO 2 nanowires, respectively. Thus the MnO 2 /MWCNTs nanocomposite modified glass carbon electrode (GCE) enabled to detect H 2 O 2 sensitively. Moreover, by incorporation of glucose oxidase (GOx), a glucose biosensor GOx/MnO 2 /MWCNTs/GCE was prepared. The as-proposed biosensor had wide linear range (5–200 μM and 0.2–1 mM) and a low detection limit of 2 μM (S/N = 3), which could be applicable to detect real sample with satisfying accuracy and reproducibility. Due to the superb electrochemical properties, the as-developed MnO 2 /MWCNTs nanocomposite is prospected in electrochemical sensor, electrocatalysis and supercapacitor. [ABSTRACT FROM AUTHOR]

A bio-mediated route for the synthesis of silver nanoparticles (AgNPs) is an area of interest in research of many scientists, and this work aims to study the electrocatalytic activity of these particles during electrochemical sensing of H2O2 in a phosphate buffer media. The composite electrodes were fabricated using nearly spherical AgNPs and reduced graphene oxide (rGO) with the graphite (99.999% purity) support made of graphite paste. Graphene oxide (GO) was first synthesized using the modified Hummers method followed by rGO synthesis by chemical reduction of GO. rGO is consisting of about nine layers of rGO sheets of a wrinkled surface morphology with an intensity ratio of D to G band (ID/IG) of 1.17 and an interplanar d-spacing of 0.36 nm as evidenced by HRTEM micrograph. There was about 10 times increase in the cell current with the AgNPs-impregnated composite-electrode compared to without AgNPs impregnation, and an overpotential of H2O2 reduction was found to be -1.373 V with a detection limit of 19.04 μM and 95.3% electrode stability with the graphite-rGO-AgNPs composite electrode. A nafion membrane cast on the rGO-AgNPs prevented the leakage of this composite from the electrode surface. The interference of various electroactive compounds on the amperometric response of the graphite-rGO-AgNPs electrode was also investigated. [ABSTRACT FROM AUTHOR]