Preparation of a nanocomposite material consisting of cuprous oxide, polyaniline and reduced graphene oxide, and its application to the electrochemical determination of hydrogen peroxide

A robust and simple non-enzymatic electrochemical sensor based on carbon dots-metal oxide composite for the detection of metronidazole traces in food products

A facile and simple electrochemical composite sensor, CDs-Ag@Cu2O-GA, prepared from carbon dots stabilized silver nanoparticles and copper oxide, was used as an electrocatalyst and signal amplifier for the non-enzymatic detection of antibiotic traces in food products. The prepared composite demonstrated excellent stability, sensitivity, and cost-effectiveness. The sensor was constructed by modifying a glassy carbon electrode (GCE) with CDs-Ag@Cu2O-GA, and the electroanalytical response was determined for the precise determination of metronidazole (MTZ) drug traces in milk. The analytical response signified fast electron transfer and accessibility of several electroactive sites, producing an amplified response for the reduction of MTZ. The quantitative analysis by the sensor revealed a good linear range (10-110 μM), a low limit of detection (7.1 × 10-7 molL-1), and a high sensitivity (1.5 μA μM-1 cm-2). Furthermore, the sensor displayed excellent potential for practical applications, verified by the good recovery of the drug from spiked milk samples.

Polyoxometalate-based iron-organic complex nanozymes with peroxidase-like activities for colorimetric detection of hydrogen peroxide and ascorbic acid

As a new type of artificial enzyme, a nanozyme is an ideal substitute for natural enzymes and has been successfully applied in many fields. However, in the application of biomolecular detection, most nanozymes have the disadvantages of long reaction times or high detection limits, prompting researchers to search for new efficient nanozymes. In this work, the enzyme-like activities of three polyoxometalate-based iron-organic complexes ([Fe(bpp)2](Mo6O19), [Fe(bpp)2]2(Mo8O26)·2CH3OH, and [Fe(bpp)2]4H[Na(Mo8O26)]3), namely, FeMo6, Fe2Mo8, and Fe4Mo8Na, were analyzed. All three polyoxometalate-based iron-organic complexes were found to be capable of catalyzing hydrogen peroxide (H2O2) to oxidize 3,3',5,5'-tetramethylbenzidine and o-phenylenediamine, resulting in visible color changes, further exhibiting peroxidase-like activity. Results showed that Fe4Mo8Na had more active sites due to its long chain structure, endowing more prominent peroxidase-like activity compared with Fe2Mo8 and FeMo6. A colorimetric sensing platform for H2O2 and ascorbic acid detection based on Fe4Mo8Na was established. The linear response range for H2O2 detection was 0.5-100 μM, and the detection limit was 0.143 μM. The linear response for ascorbic acid detection ranges from 0 to 750 μM with a detection limit of 1.07 μM. This study provides a new perspective for developing new nanozymes and expanding the sensing and detection application of nanozymes.

Persimmon Tannin-Reduction Graphene Oxide-Platinum-Palladium Nanocomposite Decorated on Screen-Printed Carbon Electrode for Enhanced Electrocatalytic Reduction of Hydrogen Peroxide

According to studies, Hydrogen peroxide (H2O2) is a significant biomarker of physiological processes. Unnormal H2O2 levels in human body may result in diseases. Hence, there is an increasing demand for monitoring the H2O2 concentrations in biological specimen. Here, we construct a non-enzymatic H2O2 electrochemical biosensor based on persimmon tannin-reduced graphene oxide-platinum-palladium nanocomposite (PrG-Pt@Pd NPs) modified with screen-printed carbon electrode (SPE). Combined with suitable electrocatalytic mode for Pt@Pd NPs, high specific large specific volume and good electrical conductivity of RGO, well as the superior sorption capacity of PT for metal-based nano-ion, the PrGPt@Pd striped pleasing heterogeneous catalytic activity toward H2O2 reduction via the synergistic effect. In experimental conditions of optimal, this non-enzymatic electrochemical sensor exhibited excellent electrocatalytic performance for H2O2 with less negative potential (−0.5 V), fast response time (<3 s), it shows good linearity in the range of 5.0–100.0 μM, in addition to this LOD of this sensor was 0.059 μM as well as the excellent sensitivity of the sensor (13.696 μA·μM−1·cm−2). Due to excellent specificity, lower detection limit, and good recovery (98.70–99.96%) in the spiked measurements of human serum samples, this non-enzymatic electrochemical biosensor paves the way for H2O2 detection at ultra-low concentrations in physiology and diagnosis.

Electrocatalytically active cuprous oxide nanocubes anchored onto macroporous carbon composite for hydrazine detection

Cuprous oxide (Cu₂O) is a p-type semiconductor with excellent catalytic activity and stability that has gained much attention because it is non-toxic, abundant, and inexpensive. Porous carbon materials have large specific surface areas, which offer abundant electroactive sites, enhance the electrical conductivity of materials, and prevent the aggregation of Cu₂O nanocubes. In this study, a composite with high electrocatalytic activity was prepared based on Cu₂O nanocubes anchored onto three-dimensional macroporous carbon (MPC) by a simple, eco-friendly, and cheap method for hydrazine detection. Due to the synergistic effect of MPC and Cu₂O, the sensor exhibited high electrocatalytic activity, sensitivity, better selectivity, and low limit of detection. The resulting sensor could be a sensitive and effective platform for detecting hydrazine and promising practical applications.

Impedimetric cardiac biomarker determination in serum mediated by epoxy and hydroxyl of reduced graphene oxide on gold array microelectrodes

A label-free chemical bonding strategy mediated by reduced graphene oxide (rGO) basal plane functional groups has been developed for cardiac Troponin I (cTnI) detection. Four different chemical strategies on respective electrode sensing surface were precedingly examined using electrochemical impedance spectroscopy. The impedimetric assessment was carried out by sweeping frequency at the range 0.1-500 kHz perturbated at a small amplitude of AC voltage (25 mV). The chemical strategy-4 denoted as S-4 shows a significant analytical performance on cTnI detection in spiked buffer and human serum, whereby the pre-mixture of rGO and (3-Aminopropyl)triethoxysilane (APTES) creates a large number of amine sites (-NH₂), which significantly enhanced the antibody immobilization without excessive functionalization. The as-fabricated immunosensor exhibited an ultra-low limit of detection of 6.3 ag mL^-1 and the lowest antigen concentration measured was at 10 ag mL^-1. The immunosensor showed a linear and wide range of cTnI detection (10 ag mL^-1-100 ng mL^-1) in human serum with a regression coefficient of 0.9716, rapid detection (5 min of binding time), and stable and highly reproducible bioelectrode response with RSD < 5%. Hence, the demonstrated S-4 strategy is highly recommended for other downstream biosensors applications.

Peroxidase-Like Metal-Based Nanozymes: Synthesis, Catalytic Properties, and Analytical Application

Nanozymes (NZs) are nanostructured artificial enzymes that mimic catalytic properties of natural enzymes. The NZs have essential advantages over natural enzymes, namely low preparation costs, stability, high surface area, self-assembling capability, size and composition-dependent activities, broad possibility for modification, and biocompatibility. NZs have wide potential practical applications as catalysts in biosensorics, fuel-cell technology, environmental biotechnology, and medicine. Most known NZs are mimetics of oxidoreductases or hydrolases. The present work aimed to obtain effective artificial peroxidase (PO)-like NZs (nanoPOs), to characterize them, and to estimate the prospects of their analytical application. NanoPOs were synthesized using a number of nanoparticles (NPs) of transition and noble metals and were screened for their catalytic activity in solution and on electrodes. The most effective nanoPOs were chosen as NZs and characterized by their catalytic activity. Kinetic parameters, size, and structure of the best nanoPOs (Cu/CeS) were determined. Cu/CeS-based sensor for H2O2 determination showed high sensitivity (1890 A·M−1·m−2) and broad linear range (1.5–20,000 µM). The possibility to apply Cu/CeS-NZ as a selective layer in an amperometric sensor for hydrogen-peroxide analysis of commercial disinfectant samples was demonstrated.

Label-free electrochemical aptasensor based on reduced graphene oxide–hemin–chitosan nanocomposite for the determination of glypican-3

A GPC3 electrochemical aptasensor was constructed using an RGO–H–CS-modified SPE as a biosensing platform and GPC3 aptamer as the recognition element.

Synthesis, Catalytic Properties and Application in Biosensorics of Nanozymes and Electronanocatalysts: A Review

The current review is devoted to nanozymes, i.e., nanostructured artificial enzymes which mimic the catalytic properties of natural enzymes. Use of the term "nanozyme" in the literature as indicating an enzyme is not always justified. For example, it is used inappropriately for nanomaterials bound with electrodes that possess catalytic activity only when applying an electric potential. If the enzyme-like activity of such a material is not proven in solution (without applying the potential), such a catalyst should be named an "electronanocatalyst", not a nanozyme. This paper presents a review of the classification of the nanozymes, their advantages vs. natural enzymes, and potential practical applications. Special attention is paid to nanozyme synthesis methods (hydrothermal and solvothermal, chemical reduction, sol-gel method, co-precipitation, polymerization/polycondensation, electrochemical deposition). The catalytic performance of nanozymes is characterized, a critical point of view on catalytic parameters of nanozymes described in scientific papers is presented and typical mistakes are analyzed. The central part of the review relates to characterization of nanozymes which mimic natural enzymes with analytical importance ("nanoperoxidase", "nanooxidases", "nanolaccase") and their use in the construction of electro-chemical (bio)sensors ("nanosensors").

Recent developments in carbon-based two-dimensional materials: synthesis and modification aspects for electrochemical sensors

This review (162 references) focuses on two-dimensional carbon materials, which include graphene as well as its allotropes varying in size, number of layers, and defects, for their application in electrochemical sensors. Many preparation methods are known to yield two-dimensional carbon materials which are often simply addressed as graphene, but which show huge variations in their physical and chemical properties and therefore on their sensing performance. The first section briefly reviews the most promising as well as the latest achievements in graphene synthesis based on growth and delamination techniques, such as chemical vapor deposition, liquid phase exfoliation via sonication or mechanical forces, as well as oxidative procedures ranging from chemical to electrochemical exfoliation. Two-dimensional carbon materials are highly attractive to be integrated in a wide field of sensing applications. Here, graphene is examined as recognition layer in electrochemical sensors like field-effect transistors, chemiresistors, impedance-based devices as well as voltammetric and amperometric sensors. The sensor performance is evaluated from the material's perspective of view and revealed the impact of structure and defects of the 2D carbon materials in different transducing technologies. It is concluded that the performance of 2D carbon-based sensors is strongly related to the preparation method in combination with the electrical transduction technique. Future perspectives address challenges to transfer 2D carbon-based sensors from the lab to the market. Graphical abstract Schematic overview from synthesis and modification of two-dimensional carbon materials to sensor application.

A glassy carbon electrode modified with a nanocomposite prepared from Pd/Al layered double hydroxide and carboxymethyl cellulose for voltammetric sensing of hydrogen peroxide

A Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated using carboxymethyl cellulose as a green substrate via co-precipitation method. The synthesized nanocomposite was characterized using different methods such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy, and electrochemical techniques. A glassy carbon electrode (GCE) was then modified with the suspended composite to obtain an electrochemical sensor for hydrogen peroxide (H₂O₂). The voltammetric (cathodic) current of the modified GCE was measured at -380 mV (vs. Ag/AgCl), at the scan rate of 50 mV.s^-1. Results show a linear dynamic range of 1 to 120 μM, and a 0.3 µM limit of detection (at S/N = 3). Intraday and interday relative standard deviations are in the ranges of 4.9-5.4% and 6.8-7.3%, respectively. The sensor was applied for the determination of H₂O₂ in basil extracts, milk, and spiked river water samples. The recoveries are between 96.60 and 102.30%. Graphical abstractA Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated via co-precipitation method and was characterized using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy and electrochemical techniques. CMC@Pd/Al-LDH was used to fabricate H₂O₂ electrochemical sensor.

Facile Fabrication of Hierarchical rGO/PANI@PtNi Nanocomposite via Microwave-Assisted Treatment for Non-Enzymatic Detection of Hydrogen Peroxide

A hierarchical composite based on the modified reduced graphene oxide with platinum-nickel decorated polyaniline nano-spheres (rGO/PANI@PtNi) was facilely prepared via microwave-assisted self-reduction for an application in nonenzymatic hydrogen peroxide (H₂O₂) detection. Compared to the pristine rGO, the composite exhibited a much tougher surface due to the stacking of conductive PANI nano-spheres on rGO sheets, leading to good dispersion of PtNi nanoparticles and a large active area. Furthermore, the multi-valance Ni^2+/3+ in the PtNi particles effectively promoted the catalytic property of Pt sites and facilitated a superior electrochemical performance of PtNi alloy than that of neat Pt. Owing to the synergistic effect of the improved electrical conductivity and the promoted electrocatalytical property, the modified glassy carbon electrode (GCE) with rGO/PANI@PtNi nanocomposite displayed an outstanding electrochemical sensitivity towards H₂O₂ with a fast response time (<2 s), a wide linear range (0.1–126.4 mM), a low detection limit (0.5 µM), as well as a long-life stability for one week without obvious degradation. This novel strategy opens a novel and promising approach to design high performance sensors for H₂O₂ detection.

Enzyme-free electrocatalytic sensing of hydrogen peroxide using a glassy carbon electrode modified with cobalt nanoparticle-decorated tungsten carbide

An efficient non-enzymatic electrochemical sensor for hydrogen peroxide (H₂O₂) was constructed by modifying a glassy carbon electrode (GCE) with a nanocomposite prepared from cobalt nanoparticle (CoNP) and tungsten carbide (WC). The nanocomposite was prepared at low temperature through a simple technique. Its crystal structure, surface morphology and elemental composition were investigated via X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed the composite to be uniformly distributed and that the CoNP are well attached to the surface of the flake-like WC. Electrochemical studies show that the modified GCE has an improved electrocatalytic activity toward the reduction of H₂O₂. H₂O₂ can be selectively detected, best at a working voltage of -0.4 V (vs. Ag/AgCl), with a 6.3 nM detection limit over the wide linear range from 50 nM to 1.0 mM. This surpasses previously reported non-enzymatic H₂O₂ sensors. The sensor was successfully applied to the determination of H₂O₂ in contact lens solutions and in spiked serum samples. Graphical abstract Schematic presentation of a method for electrochemical sensing of hydrogen peroxide in real samples using cobalt nanoparticle decorated tungsten carbide (WCC) modified glassy carbon electrode (GCE).

Carbon-dot wrapped ZnO nanoparticle-based photoelectrochemical sensor for selective monitoring of H2O2 released from cancer cells

This study reports on a simple approach for the fabrication of an electrode modified with biocompatible C-dot wrapped ZnO nanoparticles for selective photoelectrochemical monitoring of H₂O₂ released from living cells. The biocompatibility of the ZnO nanoparticles was confirmed through in-vitro cellular testing using the MTT assay on Huh7 cell lines. The ZnO nanoparticles wrapped with dopamine-derived C-dots possess numerous catalytically active sites, excessive surface defects, good electrical conductivity, and efficient separation ability of photo-induced electrons and holes. These properties offer highly sensitive and selective non-enzymatic photo-electrochemical monitoring of H₂O₂ released from HeLa cells after stimulation with N-formylmethionyl-leucyl-phenylalanine. The sensor has a wide linear range (20-800 nM), low detection limit (2.4 nM), and reliable reproducibility, this implying its suitability for biological and biomedical applications. Graphical abstract Schematic of the fabrication of ZnO nanoparticles by using a plant extract as a reducing agent. Wrapping of ZnO with C-dots enhances the photoelectrocatalytic efficacy. Sensitive and selective photoelectrochemical monitoring of H₂O₂ released from cancer cells is demonstrated.

A novel hydrogen peroxide sensor based on electrodeposited copper/cuprous oxide nanocomposites

Copper/cuprous oxide nanocomposites were electrodeposited on a fluorine doped tin oxide (FTO) glass substrate for sensitive determination of hydrogen peroxide.

Nitrogen-rich core-shell structured particles consisting of carbonized zeolitic imidazolate frameworks and reduced graphene oxide for amperometric determination of hydrogen peroxide

Core-shell structured particles were prepared from carbonized zeolitic imidazolate frameworks (ZIFs) and reduced graphene oxide (rGO). The particles possess a nitrogen content of up to 10.6%. The loss of nitrogen from the ZIF is avoided by utilizing the reduction and agglomeration of graphene oxide with suitable size (>2 μm) during pyrolysis. The resulting carbonized ZIF@rGO particles were deposited on a glassy carbon electrode to give an amperometric sensor for H₂O₂, typically operated at a voltage of -0.4 V (vs. Ag/AgCl). The sensor has a wide detection range (from 5 × 10^-6 to 2 × 10^-2 M), a 3.3 μM (S/N = 3) detection limit and a 0.272 μA·μM^-1·cm^-2 sensitivity, much higher than that of directly carbonized ZIFs. The sensor material was also deposited on a screen-printed electrode to explore the possibility of application. Graphical abstract Nitrogen doped carbon (NC) derived from carbonized zeolitic imidazolate frameworks is limited because of low nitrogen content. Here, nitrogen-rich NC@reduced graphene oxide (rGO) core-shell structured particles are described. The NC@rGO particles show distinctly better H₂O₂ detection performance than NC.