A novel enzyme-free amperometric sensor for hydrogen peroxide based on Nafion/exfoliated graphene oxide–Co3O4 nanocomposite

Co3O4/fluoro-copolymer nanocomposite modified boron-doped diamond electrode non-enzymatic sensor for the determination of skeletal muscle relaxant drug cyclobenzaprine in biological fluids

Electrochemical sensors have revolutionized pharmaceutical analysis by providing enhanced speed, selectivity, and cost-effectiveness. This study presents the development of a highly sensitive, non-enzymatic electrochemical sensor for Cyclobenzaprine (CBZ) determination. The sensor features a boron-doped diamond electrode (BDDE) modified with a novel Cobalt Oxide/Nafion-based nanocomposite (Co₃O₄/Nafion), synthesized and optimized for superior performance. The electroactive surface was fabricated by drop-casting a Co₃O₄/Nafion suspension onto the BDDE. Characterization techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), confirmed the crystallinity, morphology, and functional groups of the nanocomposite. Electrochemical analyses, comprising electrochemical impedance spectroscopy (EIS), square wave voltammetry (SWV), and cyclic voltammetry (CV), demonstrated enhanced charge transfer properties and a one-electron/proton oxidation mechanism for Cyclobenzaprine (CBZ) detection. The sensor demonstrated optimal performance in BR buffer at pH 5.6, with a linear response to CBZ concentrations ranging from 2.49 μg/L to 19.61 μg/L, achieving a LOD of 2.08 μg/L and LOQ of 6.96 μg/L. Practical applicability was established by successfully quantifying CBZ in various biological matrices, including human blood serum (37.8 %), artificial blood serum (35.6 %), artificial sweat (-28.9 %), and urine (-8.9 %), with excellent recovery rates in pharmaceutical formulations (99.75 %) and human blood serum (100.16 %). The sensor exhibited high specificity, unaffected by common interferents such as ions, carbohydrates, and heavy metals. This work introduces, for the first time, a Co₃O₄/Nafion-modified BDDE sensor for CBZ determination, offering rapid, selective, and interference-free analysis with potential applications in therapeutic drug monitoring and pharmaceutical quality control.

Impact of Initial Cyclic Loading on Mechanical Properties and Performance of Nafion

Nafion possesses many interesting properties such as a high ion-conductivity, hydrophilicity, and thermal and chemical stability that make this material highly suitable for many applications including fuel cells and various (bio-)chemical and physical sensors. However, the mechanical properties of a Nafion membrane that are known to be affected by the viscoplastic characteristics of the material itself have a strong impact on the performance of Nafion-based sensors. In this study, the mechanical properties of Nafion under the cyclic loading have been investigated in detail. After cyclic tensile loading (i.e., maximum elongation about 25% at a room temperature and relative humidity about 40%) a time-dependent recovery comes into play. This recovery process is also shown being strain-rate dependent. Our results reveal that the recovery behavior weakens after performing several stress-strain cycles. Present findings can be of a great importance in future design of various chemical and biological microsensors and nanosensors such as hydrogen or glucose ones.

Recent Advances in Electrochemical Sensing of Hydrogen Peroxide (H2O2) Released from Cancer Cells

Cancer is by far the most common cause of death worldwide. There are more than 200 types of cancer known hitherto depending upon the origin and type. Early diagnosis of cancer provides better disease prognosis and the best chance for a cure. This fact prompts world-leading scientists and clinicians to develop techniques for the early detection of cancer. Thus, less morbidity and lower mortality rates are envisioned. The latest advancements in the diagnosis of cancer utilizing nanotechnology have manifested encouraging results. Cancerous cells are well known for their substantial amounts of hydrogen peroxide (H₂O₂). The common methods for the detection of H₂O₂ include colorimetry, titration, chromatography, spectrophotometry, fluorimetry, and chemiluminescence. These methods commonly lack selectivity, sensitivity, and reproducibility and have prolonged analytical time. New biosensors are reported to circumvent these obstacles. The production of detectable amounts of H₂O₂ by cancerous cells has promoted the use of bio- and electrochemical sensors because of their high sensitivity, selectivity, robustness, and miniaturized point-of-care cancer diagnostics. Thus, this review will emphasize the principles, analytical parameters, advantages, and disadvantages of the latest electrochemical biosensors in the detection of H₂O₂. It will provide a summary of the latest technological advancements of biosensors based on potentiometric, impedimetric, amperometric, and voltammetric H₂O₂ detection. Moreover, it will critically describe the classification of biosensors based on the material, nature, conjugation, and carbon-nanocomposite electrodes for rapid and effective detection of H₂O₂, which can be useful in the early detection of cancerous cells.

Carbon Materials in Electroanalysis of Preservatives: A Review

Electrochemical sensors in electroanalysis are a particularly useful and relatively simple way to identify electroactive substances. Among the materials used to design sensors, there is a growing interest in different types of carbon. This is mainly due to its non-toxic properties, low cost, good electrical conductivity, wide potential range, and the possibility of using it in both aqueous and nonaqueous media. The electrodes made of carbon, and especially of carbon modified with different materials, are currently most often used in the voltammetric analysis of various compounds, including preservatives. The objective of this paper is to present the characteristics and suitability of different carbon materials for the construction of working electrodes used in the voltammetric analysis. Various carbon materials were considered and briefly discussed. Their analytical application was presented on the example of the preservatives commonly used in food, cosmetic, and pharmaceutical preparations. It was shown that for the electroanalysis of preservatives, mainly carbon electrodes modified with various modifiers are used. These modifications ensure appropriate selectivity, high sensitivity, low limits of detection and quantification, as well as a wide linearity range of voltammetric methods of their identification and determination.

Direct Growth of Polycrystalline GaN Porous Layer with Rich Nitrogen Vacancies: Application to Catalyst-Free Electrochemical Detection

It has been demonstrated that defect engineering is an effective strategy to enhance the activity of materials. Herein, a polycrystalline GaN porous layer (PGP) with high catalytic activity was grown by self-assembly on GaN-coated sapphire substrate by using low-temperature (LT) MOCVD growth. Without doping, LT growth can significantly improve the activity and electrical conductivity of PGP, owing to the presence of rich N-vacancies (∼10²⁰ cm^-3). Identification of rich N-vacancies in the PGP material was realized by using atomically resolved STEM (AR-STEM) characterization. The optimized PGP was applied to catalyst-free electrochemical detection of H₂O₂ with a limit of detection (LOD) of 50 nM, a fast response speed of 3 s, a wide linear detection range (50 nM to 12 mM), and a high stability. The LOD is exceeding 40 fold lower than that of reported metal-catalyst decorated GaN. Moreover, a quantitative relationship between the sensing performances and N-vacancy of PGP was established. To our knowledge, it is the first time that intrinsic GaN materials can exhibit high catalytic activity.

Electrochemical sensing of hydrogen peroxide using a glassy carbon electrode modified with multiwalled carbon nanotubes and zein nanoparticle composites: application to HepG2 cancer cell detection

A nanobiocomposite was prepared from multiwalled carbon nanotubes and zein nanoparticles. It was dispersed in water/ethanol and drop cast onto a glassy carbon electrode. The modified electrode can be used for electroreduction of H₂O₂ (typically at a working potential of -0.71 V vs. Ag/AgCl). The electrochemical properties of the electrode were investigated by cyclic voltammetry, linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Response to H₂O₂ is linear in the 0.049 to 22 μM concentration range, and the detection limit is 35 nM at pH 7.0. The sensor was successfully utilized for the measurement of H₂O₂ in a synthetic urine sample, and for monitoring the release of H₂O₂ from human dermal fibroblasts and human hepatocellular carcinoma cells. Graphical abstractSchematic representation of a novel metal- and enzyme-free electrochemical nanosensor. A glassy carbon electrode was modified with a nanocomposite prepared from multiwalled carbon nanotubes and zein nanoparticles. It was applied to the identification of liver cancer cells via sensing of H2O2 and has a very low detection limit.

Determination of Heavy Metals in Herbal Food Supplements using Bismuth/Multi-walled Carbon Nanotubes/Nafion modified Graphite Electrodes sourced from Waste Batteries

An electrochemical sensor based on graphite electrode extracted from waste zinc-carbon battery is developed. The graphite electrode was modified with bismuth nanoparticles (BiNP), multi-walled carbon nanotubes (MWCNT) and Nafion via the drop coating method. The bare and modified graphite electrodes were used as the working electrode in anodic stripping voltammetry for the determination of trace amounts of cadmium (Cd²⁺) and lead (Pb²⁺). The modified electrode exhibited excellent electroanalytical performance for heavy metal detection in comparison with the bare graphite electrode. The linear concentration range from 5 parts per billion (ppb) to 1000 ppb (R² = 0.996), as well as detection limits of 1.06 ppb for Cd²⁺ and 0.72 ppb for Pb²⁺ were obtained at optimized experimental conditions and parameters. The sensor was successfully utilized for the quantification of Cd²⁺ and Pb²⁺ in herbal food supplement samples with good agreement to the results obtained by atomic absorption spectroscopy. Thus, the BiNP/MWCNT/Nafion modified graphite electrode is a cost-effective and environment-friendly sensor for monitoring heavy metal contamination.

A Storage-Dependent Platinum Functionalization with a Commercial Pre-Polymer Useful for Hydrogen Peroxide and Ascorbic Acid Detection

A preliminary assessment of properties of the commercial product Chemiplus 2DS HB (BI-QEM Specialties SpA) is proposed. Cyclic voltammetry of this oligomer containing sulfate/sulfone groups shows a single oxidative peak at +0.866 V vs. Ag/AgCl, and its passivating process on Pt electrode suggests the formation of a non-conductive layer. Electrode modification was achieved by exploiting the constant potential amperometry setting potential at +0.900 V vs. Ag/AgCl. A substantial change in the oxidative currents from electroactive species H₂O₂ and ascorbic acid (AA) were observed on Pt/Chemiplus 2DS HB sensors compared to unmodified Pt. Furthermore, the influence of different storage conditions on modified sensors was examined. A storage solution containing AA concentration from 0.1 until 10 mM maintained effective AA rejection of Pt/Chemiplus 2DS HB after 7 days from construction; H₂O₂ oxidation capability was also retained. Sulfone and sulfonate groups of Chemiplus 2DS HB are likely responsible for the dimensionality of the film and the electrostatic interaction leading to a self-blocking/self-rejection of AA. The way Pt/Chemiplus can reveal the AA presence depends on the maintaining of AA rejection, and this peculiarity can distinguish it from other sensors or biosensors.

Fabrication of RGO-NiCo2O4 nanorods composite from deep eutectic solvents for nonenzymatic amperometric sensing of glucose

A novel reduced graphene oxide supported nickel cobaltate nanorods composite (RGO-NiCo₂O₄) was prepared by a simple ionothermal method in deep eutectic solvents for the first time. Electrochemical results demonstrated that the obtained nanocomposite modified glassy carbon electrode exhibited excellent electrocatalytic performance towards the oxidation of glucose with a wide double-linear range from 1 μM to 25 mM and a low detection limit of 0.35 μM (S/N = 3). NiCo₂O₄ nanorods with many small interconnected nanoparticles provided many electrocatalytic active sites, while RGO with large surface area offered good electrical conductivity. The synergistic effect between NiCo₂O₄ nanorods and RGO contributed to the enhanced sensing ability of the hybrid nanostructure. This sensitive glucose sensor can be also used for the practical detection of glucose in human serum.

Recent advances in graphene-based nanomaterials for fabricating electrochemical hydrogen peroxide sensors

Due to the large specific surface area, extraordinary mechanical flexibility, chemical stability, and superior electrical and thermal conductivities, graphene (G)-based materials have recently opened up an exciting field in the science and technology of two-dimensional (2D) nanomaterials with continuously growing academic and technological impetus. In the past several years, graphene-based materials have been well designed, synthesized, and investigated for sensing applications. In this review, we discuss the synthesis and application of graphene-based 2D nanomaterials for the fabrication of hydrogen peroxide (H₂O₂) electrochemical sensors. In particular, graphene-based nanomaterials as immobilization matrix of heme proteins for the fabrication of enzymatic H₂O₂ electrochemical biosensors is first summarized. Then, the application of graphene-based electrocatalysts (metal-free, noble-metals and non-noble metals) in constructing non-enzymatic H₂O₂ electrochemical sensors is discussed in detail. We hope that this review is helpful to push forward the advancement of this academic issue (189 references).

Cobalt ferrite nanoparticles decorated on exfoliated graphene oxide, application for amperometric determination of NADH and H2O2

Here, cobalt ferrite nanohybrid decorated on exfoliated graphene oxide (CoFe2O4/EGO) was synthesized. The nanohybrid was characterized by different methods such as X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray diffraction microanalysis, transmission electron microscopy, FT-IR, Raman spectroscopy and electrochemical methods. The CoFe2O4/EGO nanohybrid was used to modify glassy carbon electrode (GCE). The voltammetric investigations showed that CoFe2O4/EGO nanohybrid has synergetic effect towards the electro-reduction of H2O2 and electro-oxidation of nicotinamide adenine dinucleotide (NADH). Rotating disk chronoamperometry was used for their quantitative analysis. The calibration curves were observed in the range of 0.50 to 100.0 μmol L(-1) NADH and 0.9 to 900.0 μmol L(-1) H2O2 with detections limit of 0.38 and 0.54 μmol L(-1), respectively. The repeatability, reproducibility and selectivity of the electrochemical sensor for analysis of the analytes were studied. The new electrochemical sensor was successfully applied for the determination of NADH and H2O2 in real samples with satisfactory results.

Graphene/nano-porous silicon and graphene/bimetallic silicon nanostructures (Pt–M, M: Pd, Ru, Rh), efficient electrocatalysts for the hydrogen evolution reaction

In this work nano-porous silicon flour (Nano-PSiF) was synthesized first and then there was an investigation into its electrocatalytic activity for the electrochemical hydrogen evolution reaction (HER).

Facile preparation of graphene nanoribbon/cobalt coordination polymer nanohybrid for non-enzymatic H2O2 sensing by dual transduction: electrochemical and fluorescence

A novel graphene nanoribbon (GNR)/cobalt coordination polymer (MCPs) composite (MCPs@GNR) is prepared by in situ reduction of graphene oxide nanoribbon (GONR) with simultaneous growth of MCPs nanoparticles on its surface demonstrating high H₂O₂ sensing.

Design synthesis of polypyrrole-Co3O4 hybrid material for the direct electrochemistry of Hemoglobin and Glucose Oxidase

We designed and synthesized a novel organic-inorganic hybrid material polypyrrole-Co3O4 (Ppy-Co3O4), then mixed it with ionic liquid (IL) to form stable composite films for the immobilization of Hemoglobin (Hb) and Glucose Oxidase (GOD). The combination of Ppy and Co3O4 as well as IL created a platform with exceptional characteristics, and the content of Ppy had an effect on the direct electron transfer (DET) of Hb/GOD. Notably, when weight percentage of pyrrole monomer was 20%, the heterogenous electron transfer rate constant (ks) for Hb and GOD was estimated to be 1.71s(-1) and 1.67s(-1), respectively. In the meantime, electrochemical and spectroscopic measurements showed that Hb/GOD remained their bioactivity, and achieved fast electron transfer on the Ppy-Co3O4/IL composite film modified electrode. Furthermore, the Ppy-Co3O4/IL/Hb composite film modified electrode was used as a biosensor, and exhibited a long linear range and lower detection limit to H2O2. The apparent Michaelis-Menten constant (Km) was found to be 0.53mM. The sensing design based on the Ppy-Co3O4 hybrid material was demonstrated to be effective and promising in developing protein and enzyme biosensors.