3D Network and 2D Paper of Reduced Graphene Oxide/Cu2O Composite for Electrochemical Sensing of Hydrogen Peroxide

THP as a sensor for the electrochemical detection of H2O2

Hydrogen peroxide (H2O2) detection is paramount in biological and clinical domains due to its pivotal role in various physiological and pathological processes. This molecule is a crucial metabolite and effector in cellular redox mechanisms, influencing diverse cellular signaling pathways and bolstering the body's defense mechanisms against infection and oxidative stress. Organic molecule-based electrodes present unique advantages such as operational versatility and scalability, rendering them attractive candidates for sensor development across diverse fields encompassing food safety, healthcare, and environmental monitoring. This study explores the electrochemical properties of a tris(3-hydroxypyridin-4-one) THP, which has been unexplored in electrochemical sensing. Leveraging THP's chelating properties, we aimed to develop an electrochemical probe for hydrogen peroxide detection. Our investigations reveal promising results, with the developed sensor exhibiting a low limit of detection (LOD) of 144 nM, underscoring its potential utility in sensitive and selective H2O2 detection applications. In addition, the new sensor was also tested on fetal bovine serum (FBS) to emphasize future applications on biological matrices. This research signifies a significant stride in advancing electrochemical sensor technologies for hydrogen peroxide detection with several novelties related to the usage of THP, such as high sensitivity and selectivity, performance in biological matrices, repeatability, stability, and reproducibility, economical and practical advantages. This research opens new avenues for enhanced biomedical diagnostics and therapeutic interventions.

Transition Metal Oxide-Decorated MXenes as Drugless Nanoarchitectonics for Enriched Nanocatalytic Chemodynamic Treatment

Despite their unique characteristics, 2D MXenes with sole photothermal conversion ability are required to explore their superfluous abilities in biomedicine. The small-molecule-based chemotherapeutics suffer from various shortcomings of time-consuming and expensiveness concerning theoretical and performance (preclinical/clinical) checks. This study demonstrates the fabrication of Ti3C2 MXene nanosheets (TC-MX NSs) and subsequent decoration with transition metal oxides, that is, copper oxide (Cu2O/MX, CO-MX NCs) as drugless nanoarchitectonics for synergistic photothermal (PTT)-chemodynamic therapeutic (CDT) efficacies. Initially, the monolayer/few-layered TC-MX NSs are prepared using the chemical etching-assisted ultrasonic exfoliation method and then deposited with Cu2O nanoconstructs using the in situ reduction method. Further, the photothermal ablation under near-infrared (NIR)-II laser irradiation shows PTT effects of CO-MX NCs. The deposited Cu2O on TC-MX NSs facilitates the release of copper (Cu+) ions in the acidic microenvironment intracellularly for Fenton-like reaction-assisted CDT effects and enriched PTT effects synergistically. Mechanistically, these deadly free radicals intracellularly imbalance the glutathione (GSH) levels and result in mitochondrial dysfunction, inducing apoptosis of 4T1 cells. Finally, the in vivo investigations in BALB/c mice confirm the substantial ablation of breast carcinoma. Together, these findings demonstrate the potential synergistic PTT-CDT effects of the designed CO-MX NCs as drugless nanoarchitectonics against breast carcinoma.

Nonenzymatic Sweat Wearable Uric Acid Sensor Based on N-Doped Reduced Graphene Oxide/Au Dual Aerogels

Sweat wearable sensors enable noninvasive and real-time metabolite monitoring in human health management but lack accuracy and wearable applicability. The rational design of sensing electrode materials will be critical yet challenging. Herein, we report a dual aerogel-based nonenzymatic wearable sensor for the sensitive and selective detection of uric acid (UA) in human sweat. The three-dimensional porous dual-structural aerogels composed of Au nanowires and N-doped graphene nanosheets (noted as N-rGO/Au DAs) provide a large active surface, abundant access to the target, rapid electron transfer pathways, and a high intrinsic activity. Thus, a direct UA electro-oxidation is demonstrated at the N-rGO/Au DAs with a much higher activity than those at the individual gels (i.e., Au and N-rGO). Moreover, the resulting sensing chip displays high performance with a good anti-interfering ability, long-term stability, and excellent flexibility toward the UA detection. With the assistance of a wireless circuit, a wearable sensor is successfully applied in the real-time UA monitoring on human skin. The obtained result is comparable to that evaluated by high-performance liquid chromatography. This dual aerogel-based nonenzymatic biosensing platform not only holds considerable promise for the reliable sweat metabolite monitoring but also opens an avenue for metal-based aerogels as flexible electrodes in wearable sensing.

Electrochemical Quantification of H2O2 Released by Airway Cells Growing in Different Culture Media

Quantification of oxidative stress is a challenging task that can help in monitoring chronic inflammatory respiratory airway diseases. Different studies can be found in the literature regarding the development of electrochemical sensors for H2O2 in cell culture medium to quantify oxidative stress. However, there are very limited data regarding the impact of the cell culture medium on the electrochemical quantification of H2O2. In this work, we studied the effect of different media (RPMI, MEM, DMEM, Ham's F12 and BEGM/DMEM) on the electrochemical quantification of H2O2. The used electrode is based on reduced graphene oxide (rGO) and gold nanoparticles (AuNPs) and was obtained by co-electrodeposition. To reduce the electrode fouling by the medium, the effect of dilution was investigated using diluted (50% v/v in PBS) and undiluted media. With the same aim, two electrochemical techniques were employed, chronoamperometry (CH) and linear scan voltammetry (LSV). The influence of different interfering species and the effect of the operating temperature of 37 °C were also studied in order to simulate the operation of the sensor in the culture plate. The LSV technique made the sensor adaptable to undiluted media because the test time is short, compared with the CH technique, reducing the electrode fouling. The long-term stability of the sensors was also evaluated by testing different storage conditions. By storing the electrode at 4 °C, the sensor performance was not reduced for up to 21 days. The sensors were validated measuring H2O2 released by two different human bronchial epithelial cell lines (A549, 16HBE) and human primary bronchial epithelial cells (PBEC) grown in RPMI, MEM and BEGM/DMEM media. To confirm the results obtained with the sensor, the release of reactive oxygen species was also evaluated with a standard flow cytometry technique. The results obtained with the two techniques were very similar. Thus, the LSV technique permits using the proposed sensor for an effective oxidative stress quantification in different culture media and without dilution.

Highly Dispersion Cu2O QDs Decorated Bi2WO6 S-Scheme Heterojunction for Enhanced Photocatalytic Water Oxidation

Developing suitable photocatalysts for the oxygen evolution reaction (OER) is still a challenging issue for efficient water splitting due to the high requirements to create a significant impact on water splitting reaction kinetics. Herein, n-type Bi₂WO₆ with flower-like hierarchical structure and p-type Cu₂O quantum dots (QDs) are coupled together to construct an efficient S-scheme heterojunction, which could enhance the migration efficiency of photogenerated charge carriers. The electrochemical properties are investigated to explore the transportation features and donor density of charge carriers in the S-scheme heterojunction system. Meanwhile, the as-prepared S-scheme heterojunction presents improved photocatalytic activity towards water oxidation in comparison with the sole Bi₂WO₆ and Cu₂O QDs systems under simulated solar light irradiation. Moreover, the initial O₂ evolution rate of the Cu₂O QDs/Bi₂WO₆ heterojunction system is 2.3 and 9.7 fold that of sole Bi₂WO₆ and Cu₂O QDs systems, respectively.

Pt–Pd Bimetallic Aerogel as High-Performance Electrocatalyst for Nonenzymatic Detection of Hydrogen Peroxide

Hydrogen peroxide (H2O2) plays an indispensable role in the biological, medical, and chemical fields. The development of an effective H2O2 detecting method is of great importance. In the present work, a series of PtxPdy bimetallic aerogels and Pt, Pd monometallic aerogels were controllably synthesized by one-step gelation method. Their morphologies and compositions were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and so forth. These aerogels were used as nonenzyme electrocatalysts for the detection of H2O2. The cyclic voltammetric and amperometric results demonstrated that the performance of the metal aerogels showed volcano-type behavior, with the Pt50Pd50 aerogel sitting on top. The Pt50Pd50 aerogel-based electrochemical sensor exhibited excellent comprehensive performance, with a low overpotential of −0.023 V vs. Ag/AgCl, a broad linear range from 5.1 to 3190 μM (R2 = 0.9980), and a high sensitivity of 0.19 mA mM−1 cm−2, in combination with good anti-interference ability and stability. A comprehensive study indicated that the superior sensing performance of the Pt50Pd50 aerogel is closely related to its optimized d-band center and larger cumulative pore volume. This work first applied Pt–Pd bimetallic aerogels into the detection of H2O2 and shows the promising application of noble metal aerogels in the electrochemical sensing area.

Electrodes and electrocatalysts for electrochemical hydrogen peroxide sensors: a review of design strategies

H₂O₂ sensing is required in various biological and industrial applications, for which electrochemical sensing is a promising choice among various sensing technologies. Electrodes and electrocatalysts strongly influence the performance of electrochemical H₂O₂ sensors. Significant efforts have been devoted to electrode nanostructural designs and nanomaterial-based electrocatalysts. Here, we review the design strategies for electrodes and electrocatalysts used in electrochemical H₂O₂ sensors. We first summarize electrodes in different structures, including rotation disc electrodes, freestanding electrodes, all-in-one electrodes, and representative commercial H₂O₂ probes. Next, we discuss the design strategies used in recent studies to increase the number of active sites and intrinsic activities of electrocatalysts for H₂O₂ redox reactions, including nanoscale pore structuring, conductive supports, reducing the catalyst size, alloying, doping, and tuning the crystal facets. Finally, we provide our perspectives on the future research directions in creating nanoscale structures and nanomaterials to enable advanced electrochemical H₂O₂ sensors in practical applications.

In situ electrochemical reductive construction of metal oxide/metal-organic framework heterojunction nanoarrays for hydrogen peroxide sensing

Transition metal oxide/metal-organic framework heterojunctions (TMO@MOF) that combine the large specific surface area of MOFs with TMOs' high catalytic activity and multifunctionality, show excellent performances in various catalytic reactions. Nevertheless, the present preparation approaches of TMO@MOF heterojunctions are too complex to control, stimulating interests in developing simple and highly controllable methods for preparing such heterojunction. In this study, we propose an in situ electrochemical reduction approach to fabricating Cu₂O nanoparticle (NP)@CuHHTP heterojunction nanoarrays with a graphene-like conductive MOF CuHHTP (HHTP is 2,3,6,7,10,11-hexahydroxytriphenylene). We have discovered that size-controlled Cu₂O nanoparticles could be in situ grown on CuHHTP by applying different electrochemical reduction potentials. Also, the obtained Cu₂O NP@CuHHTP heterojunction nanoarrays show high H₂O₂ sensitivity of 8150.6 μA·mM^-1·cm² and satisfactory detection performances in application of measuring H₂O₂ concentrations in urine and serum samples. This study offers promising guidance for the synthesis of MOF-based heterojunctions for early cancer diagnosis.

Electrochemical Microfluidic Multiplexed Bioanalysis by a Highly Active Bottlebrush-like Nanocarbon Microelectrode

We present a highly efficient multichannel microfluidic electrochemical sensor integrated with an electroactive nanocarbon microelectrode for sensitive and selective detection of multiple biomarkers in different biological samples. Our results have shown that ionic liquid-assisted wet spinning followed by tailored growth of metal-organic frameworks and pyrolysis treatment led to structural and molecular engineering of mechanically robust all-carbon microfibers for excellent electrochemical activities. The flexible bottlebrush-like nanocarbon microelectrode features a "stem" of freestanding N, B-codoped graphene fiber and high-density "bristles" of Co, N-codoped carbon nanotube arrays, leading to promoted electrocatalytic mechanism that has been substantiated by density functional theory calculations. The structural characteristics, high catalytic activities, and favorable biocompatibility of the bottlebrush nanocarbon electrodes provide opportunities for multichannel, microfluidic detection of redox-active biomolecules, including hydrogen sulfide (H₂S), dopamine (DA), uric acid (UA), and ascorbic acid (AA), and have been applied to on-chip monitoring of H₂S and DA released from live cancer cells or neuroblastoma cells and DA, UA, and AA in trace amounts of body fluids such as sweat, finger blood, tears, saliva, and urine, which is of great significance for clinical diagnosis and prognosis in point-of-care testing.

Copper Oxide/Functionalized Graphene Hybrid Nanostructures for Room Temperature Gas Sensing Applications

Oxide semiconductors are conventionally used as sensing materials in gas sensors, however, there are limitations on the detection of gases at room temperature (RT). In this work, a hybrid of copper oxide (CuO) with functionalized graphene (rGO) is proposed to achieve gas sensing at RT. The combination of a high surface area and the presence of many functional groups in the CuO/rGO hybrid material makes it highly sensitive for gas absorption and desorption. To prepare the hybrid material, a copper oxide suspension synthesized using a copper acetate precursor is added to a graphene oxide solution during its reduction using ascorbic acid. Material properties of the CuO/rGO hybrid and its drop-casted thin-films are investigated using Raman, FTIR, SEM, TEM, and four-point probe measurement systems. We found that the hybrid material was enriched with oxygen functional groups (OFGs) and defective sites, along with good electrical conductivity (Sheet resistance~1.5 kΩ/□). The fabricated QCM (quartz crystal microbalance) sensor with a thin layer of the CuO/rGO hybrid demonstrated a high sensing response which was twice the response of the rGO-based sensor for CO2 gas at RT. We believe that the CuO/rGO hybrid is highly suitable for existing and future gas sensors used for domestic and industrial safety.

EDTA derived graphene supported porous cobalt hexacyanoferrate nanospheres as a highly electroactive nanocomposite for hydrogen peroxide sensing

Developed a highly electroactive graphene and porous cobalt hexacyanoferrate nanosphere (Gr/P-CoHCF-NSPs) composite for H2O2 sensing by using EDTA chelation strategy.

Long-term cell culture and electrically in situ monitoring of living cells based on a polyaniline hydrogel sensor

Accurate, in situ and long-term electrically monitoring of cell development plays an important role in cell study, which brings in challenges in terms of biocompatibility, processability, and sensing capability of electrochemical sensors. Based on biocompatible conductive polyaniline (PAni) hydrogels, we constructed a flexible sensor with flexible carbon cloth for electrical analysis of living cells. The carbon fiber substrate modified with conductive PAni hydrogels was selected as the electrode to promote the current collection of the sensor. The three dimensional nanostructured mesoporous matrix of PAni hydrogels is favorable for in situ generation of catalytic Pt nanoparticles and cell growth. With these hierarchically nanostructured features, the hydrogel electrochemical sensor was endowed with high sensitivity and selectivity in the detection of H₂O₂ (with a low detection limit of 1.6 μM in 0.01 M PBS and a wide linear range from 10 μM to 10 mM), and good biocompatibility for cell growth as long as 5 days. The accurate detection of H₂O₂ released from cells enabled us to differentiate the physiological states of cells and imitate the different stimuli-responsive behavior, which can provide real-time information on cell biological events. With outstanding biocompatibility, operability and repeatability, this strategy can be expanded to the fields of other biosensor fabrication and cell-related biomarker monitoring, which exhibits a broad application potential in bioanalysis catering to new generation sensors.

Cu-MOF/hemin: a bionic enzyme with excellent dispersity for the determination of hydrogen peroxide released from living cells

The stability, repeatability and sensitivity of an electrochemical biosensor material are closely connected with the dispersibility of metal organic frameworks (MOFs) in aqueous media. Herein, a nanocomposite based on Cu-MOF/hemin, which is not only highly water-soluble but also simple and efficient in synthesis, was used for the construction of a non-enzymatic sensor to detect hydrogen peroxide (H₂O₂). The Cu-MOF/hemin was characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS)-mapping, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA), which indicate that hemin and the Cu-MOF were successfully combined. As a H₂O₂ electrochemical biomimetic enzyme, the Cu-MOF/hemin exhibited excellent electrocatalytic performance, which was confirmed by the electrochemical experiments and chromogenic reactions, and the possible mechanism of the reactions has been deduced. The electrochemical sensor based on the biomimetic enzyme exhibited an extended linear detection range from 0.01-5.0 mM (R = 0.998), low detection limit of 4.14 μM, and high selectivity and stability under the optimized conditions. More importantly, the practical application ability of the sensor was verified by the test of H₂O₂ in human serum samples and it could be used for the real-time detection of H₂O₂ released from living cells with satisfactory results. Therefore, this novel nanocomposite has certain potential in preparing electrochemical sensing platforms for nonenzymatic biosensing and provides a new method for clinical diagnosis and real-time monitoring.

Macromolecular assembly and membrane activity of antimicrobial D,L-α-Cyclic peptides

Antimicrobial peptides are viewed as a promising alternative to conventional antibiotics, as their activity through membrane targeting makes them less prone to resistance development. Among them, antimicrobial D,L-α-cyclic peptides (CPs) have been proposed as an alternative, specially due to their cyclic nature and to the presence of D-α-amino acids that increases their resistance to proteases. In present work, second generation D,L-α-cyclic peptides with proven antimicrobial activity are shown to form complex macromolecular assemblies in the presence of membranes. We addressed the CPs:membrane interactions through a combination of experimental techniques (DSC and ATR-FTIR) with coarse-grained molecular dynamics (CG-MD) simulations, aiming at understanding their interactions, macromolecular assemblies and eventually unveil their mechanism of action. DSC shows that the interaction depends heavily on the negatively charge content of the membrane and on lipid/peptide ratio, suggesting different mechanisms for the different peptides and lipid systems. CG-MD proved that CPs can self-assemble at the lipid surface as nanotubes or micellar aggregates, depending on the peptide, in agreement with ATR-FTIR results. Finally, our results shed light into possible mechanisms of action of the peptides with pending hydrocarbon tail, namely membrane extensive segregation and/or membrane disintegration through the formation of disk-like lipid/peptide aggregates.

Postmodulation of the Metal-Organic Framework Precursor toward the Vacancy-Rich CuxO Transducer for Sensitivity Boost: Synthesis, Catalysis, and H2O2 Sensing

Metal-organic frameworks (MOFs) act as versatile coordinators for the subsequent synthesis of high-performance catalysts by providing dispersed metal-ion distribution, initial coordination condition, dopant atom ratios, and so on. In this work, a crystalline MOF trans-[Cu(NO₃)₂(Him)₄] was synthesized as the novel precursor of a redox-alternating Cu_xO electrochemical catalyst. Through simple temperature modulation, the gradual transformation toward a highly active nanocomposite was characterized to ascertain the signal enhancing mechanism in H₂O₂ reduction. Owing to the proprietary structure of the transducer material and its ensuing high activity, a proof-of-principle sensor was able to provide an amplified sensitivity of 2330 μA mM^-1 cm^-2. The facile one-pot preparation and intrinsic nonenzymatic nature also suggests its wide potentials in medical settings.

A metal-organic framework with multienzyme activity as a biosensing platform for real-time electrochemical detection of nitric oxide and hydrogen peroxide

A Metal-Organic Framework (MOFs) with large surface area, exposed active site, excellent catalytic performance and high chemical stability has been used as an artificial enzyme and designed for nonenzymatic electrochemical sensors. Here, a strategy of using an enhanced electrochemical sensing platform for the detection of nitic oxide (NO) and hydrogen peroxide (H2O2) was designed via a nano-metalloporphyrinic metal-organic framework (NporMOF(Fe)) as an electrode material. By taking advantage of the small size, high surface area and exposed Fe active site, the obtained NporMOF(Fe) displays excellent electrocatalytic activity toward NO and H2O2. The NporMOF(Fe) modified electrode shows high sensing ability toward the in situ generated NO in NO2- containing phosphate buffer (PB) solution with a wide linear detection range of 5 μM to 200 μM and a very low detection limit of 1.3 μM. Moreover, NporMOF(Fe) exhibits high electrocatalytic activity toward the reduction of H2O2 and the practical detection of H2O2 released from HeLa cells. Furthermore, the NporMOF(Fe) modified electrode shows excellent selectivity toward the detection of NO and H2O2 in the presence of other physiologically important analytes. This method shows excellent biosensing performance, implying the universal applicability of MOFs-based artificial nanozymes for biosensors and the potential application for third generation biosensors.

Self-Circulation Oxygen-Hydrogen Peroxide-Oxygen System for Ultrasensitive Cathode Photoelectrochemical Bioassay Using a Stacked Sealed Paper Device

In this work, a self-circulation oxygen-hydrogen peroxide-oxygen (O₂-H₂O₂-O₂) system with photogenerated electrons as fuel and highly active hemin monomers as operators was engineered for ultrasensitive cathode photoelectrochemical bioassay of microRNA-141 (miRNA-141) using a stacked sealed paper device. During the circulation, the photogenerated electrons from BiVO₄/Cu₂O photosensitive structures assembled on a reduced graphene oxide paper electrode first reduced the electron acceptors (dissolved O₂) to H₂O₂, which was then catalytically decomposed by hemin monomers to generate O₂ again. The regenerated O₂ continued to be reduced, which made O₂ and H₂O₂ stuck in the infinite loop of O₂-H₂O₂-O₂ accompanied by the fast consumption of photogenerated electrons, generating an amplified photocurrent signal. When a target existed, a duplex-specific nuclease-induced target recycling reaction with dual trigger DNA probes as the output was performed to initiate the assembly of bridge-like DNA nanostructures, which endowed the self-circulation system with dual destruction functions as follows. (i) Reduced fuel supply: the assembled DNA bridges acting as a negatively charged barrier prevented the photogenerated electrons from participating in the O₂ reduction to H₂O₂. (ii) Incapacitation of operators: DNA bridging induced the dimerization of hemin monomers linked on the DNA hairpins to catalytically inactive hemin dimers, leading to the abortive regeneration of O₂. These destruction functions resulted in the circulation interruption and a remarkably decreased photocurrent signal. Thus, the developed cathode photoelectrochemical biosensing platform achieved ultrasensitive miRNA-141 detection with a linear range of 0.25 fM to 1 nM and a detection limit of 83 aM, and it also exhibited high accuracy, selectivity, and practicability.

Electrochemical Biosensor Based on HRP/Ti3C2/Nafion Film for Determination of Hydrogen Peroxide in Serum Samples of Patients with Acute Myocardial Infarction

Hydrogen peroxide (H₂O₂) has been reported to mediate a variety of physiological and pathological processes in living systems. In this work, a biosensor for determination of H₂O₂ was prepared by using an HRP/Ti₃C₂/Nafion film-modified glassy carbon electrode (GCE). Ti₃C₂ nanosheets with remarkable conductivity and high specific surface area were chosen as carriers for HRP. Moreover, this biosensor modified with HRP has a specific catalytic effect on H₂O₂. The difference in peak current could reflect the quantitative change of H₂O₂. The linear range of the biosensor is 5-8000 μM, and the detection limit is 1 μM (S/N = 3). This biosensor was used to detect H₂O₂ in clinical serum samples of normal controls and patients with acute myocardial infarction (AMI) before and after percutaneous coronary intervention (PCI). The results showed that the difference between normal controls and patients is significant (P < 0.05), as well as the difference for patients before and after PCI (P < 0.01), but no significant difference existed between postoperative patients and normal controls. This biosensor has the advantages of simple preparation, high sensitivity, and quick detection, showing potential application in clinical diagnosis.

Carbon Nanomaterials: Synthesis, Functionalization and Sensing Applications

Recent advances in nanomaterial design and synthesis has resulted in robust sensing systems that display superior analytical performance. The use of nanomaterials within sensors has accelerated new routes and opportunities for the detection of analytes or target molecules. Among others, carbon-based sensors have reported biocompatibility, better sensitivity, better selectivity and lower limits of detection to reveal a wide range of organic and inorganic molecules. Carbon nanomaterials are among the most extensively studied materials because of their unique properties spanning from the high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency fostering their use in sensing applications. In this paper, a comprehensive review has been made to cover recent developments in the field of carbon-based nanomaterials for sensing applications. The review describes nanomaterials like fullerenes, carbon onions, carbon quantum dots, nanodiamonds, carbon nanotubes, and graphene. Synthesis of these nanostructures has been discussed along with their functionalization methods. The recent application of all these nanomaterials in sensing applications has been highlighted for the principal applicative field and the future prospects and possibilities have been outlined.

Cobalt and nitrogen co-doped mesoporous carbon for electrochemical hydrogen peroxide sensing: the effect of graphitization

In this study, a facile strategy for the scalable synthesis of cobalt and nitrogen co-doped mesoporous carbon (Co-N/C) is reported. Structural characterization demonstrated that Co and N were successfully co-doped in the highly porous carbon. Graphitization of porous carbon was achieved by the introduction of cobalt species. The degree of graphitization of Co-N/C could be further promoted by increasing the calcination temperature. By taking advantage of the excellent mass and electron transfer kinetics attributed to the high specific surface area, high porosity and high graphitization, the obtained Co-N/C exhibited good electrochemical activity towards H₂O₂ reduction and excellent sensing performance for the electrochemical detection of H₂O₂. The Co-N/C-950 catalyst obtained at 950 °C showed good electrochemical sensing performance with a detection limit of 2 μM and a wide linear response over the concentration range from 0.03 mM to 13 mM. Meanwhile, Co-N/C exhibited high selectivity toward the detection of H₂O₂ in the presence of possible interferences during the applications such as NaCl, glucose, ascorbic acid and so on. The results confirm that Co-N/C could be used as an efficient electrocatalyst to fabricate electrochemical sensing devices.

Highly sensitive non-enzymatic electrochemical glucose sensor based on dumbbell-shaped double-shelled hollow nanoporous CuO/ZnO microstructures

A high-performance non-enzymatic glucose sensor based on hybrid metal-oxides is proposed. Dumbbell-shaped double-shelled hollow nanoporous CuO/ZnO microstructures (CuO/ZnO-DSDSHNM) were prepared via the hydrothermal method using pluronic F-127 as a surfactant. This structure is studied by various physicochemical characterizations such as scanning electron microscopy, X-ray diffraction spectroscopy, inductively coupled plasma atomic emission spectroscopy, elemental mapping techniques, X-ray photoelectron spectroscopy, and transmission electron microscopy. This unique CuO/ZnO-DSDSHNM provides both a large surface area and an easy penetrable structure facilitating improved electrochemical reactivity toward glucose oxidation. The prepared CuO/ZnO-DSDSHNM was used over the glassy carbon electrode (GCE) as the active material for glucose detection and then coated by Nafion to provide the proposed Nafion/CuO/ZnO-DSDSHNM/GCE. The fabricated glucose sensor exhibits an extremely wide dynamic range from 500 nM to 100 mM, a sensitivity of 1536.80 µA mM^-1 cm^-2, a low limit of detection of 357.5 nM, and a short response time of 1.60 s. The proposed sensor also showed long-term stability, good reproducibility, favorable repeatability, excellent selectivity, and satisfactory applicability for glucose detection in human serum samples. The achieved high-performance glucose sensing based on Nafion/CuO/ZnO-DSDSHNM/GCE shows that both the material synthesis and the sensor fabrication methods have been promising and they can be used in future researches.

Novel neuron-network-like Cu-MoO2/C composite derived from bimetallic organic framework for highly efficient detection of hydrogen peroxide

Fabrication of non-enzymatic electrochemical sensors based on metal oxides with low valence-state for nanomolar detection of H₂O₂ has been a great challenge. In this work, a novel neuron-network-like Cu-MoO₂/C hierarchical structure was simply prepared by in-situ pyrolysis of 3D bimetallic-organic framework [Cu(Mo₂O₇)L]_n [L: N-(pyridin-3-ylmethyl)pyridine-2-amine] crystals. Meanwhile, the MoO₂/C nano-aggregates were also obtained by liquid phase copper etching. Subsequently, two non-enzymatic electrochemical sensors were fabricated by simple drop-coating of the above two materials on the surface of glassy carbon electrode (GCE). Electrochemical measurements indicate that the Cu-MoO₂/C/GCE possesses highly efficient electrocatalytic H₂O₂ property during wider linear range of 0.24 μM-3.27 mM. At room temperature, the Cu-MoO₂/C composite displays higher sensitivity (233.4 μA mM^-1 cm^-2) and lower limit of detection (LOD = 85 nM), which are 1 and 2.5 times larger than those of MoO₂/C material, respectively. Such excellent ability for trace H₂O₂ detection mainly originates from the synergism of neuron-network-like structure, enhanced electrical conductivity and increased active sites caused by low valence-state MoO₂ and co-doping of Cu and carbon, and even the interaction between Cu and Mo. In addition, the H₂O₂ detection in spiked human serum and commercially real samples indicates that the Cu-MoO₂/C/GCE sensor has certain potential application in the fields of environment and biology.

Graphene and Perovskite-Based Nanocomposite for Both Electrochemical and Gas Sensor Applications: An Overview

Perovskite and graphene-based nanocomposites have attracted much attention and been proven as promising candidates for both gas (H₂S and NH₃) and electrochemical (H₂O₂, CH₃OH and glucose) sensor applications. In this review, the development of portable sensor devices on the sensitivity, selectivity, cost effectiveness, and electrode stability of chemical and electrochemical applications is summarized. The authors are mainly focused on the common analytes in gas sensors such as hydrogen sulfide, ammonia, and electrochemical sensors including non-enzymatic glucose, hydrazine, dopamine, and hydrogen peroxide. Finally, the article also addressed the stability of composite performance and outlined recent strategies for future sensor perspectives.

Cu2O-mediated assembly of electrodeposition of Au nanoparticles onto 2D metal-organic framework nanosheets for real-time monitoring of hydrogen peroxide released from living cells

The development of metal nanoparticles (MNP) combined with a metal-organic framework (MOF) has received more and more attention due to its excellent synergistic catalytic ability, which can effectively broaden the scope of catalytic reactions and enhance the catalytic ability. In this work, we developed a novel ternary nanocomposite named Cu₂O-mediated Au nanoparticle (Au NP) grown on MIL-53(Fe) for real-time monitoring of hydrogen peroxide (H₂O₂) released from living cells. First, Cu₂O-MIL-53(Fe) was prepared by redox assembly technology, which provided the growth template, and active sites for AuCl^4-. Au@Cu₂O-MIL-53(Fe)/GCE biosensor was prepared by further loading nano-Au uniformly on the surface of Cu₂O by electrochemical deposition. Compared to individual components, the hybrid nanocomposite showed superior electrochemical properties as electrode materials due to the synergistic effect between AuNPs, Cu₂O, and MIL-53(Fe). Electrochemical measurement showed that the Au@Cu₂O-MIL-53(Fe)/GCE biosensor presented a satisfactory catalytic activity towards H₂O₂ with a low detection limit of 1.01 μM and sensitivity of 351.57 μA mM^-1 cm^-2 in the linear range of 10-1520 μM. Furthermore, this biosensor was successfully used for the real-time monitoring of dynamic H₂O₂ activated by PMA released from living cells. And the great results of confocal fluorescence microscopy of the co-culture cells with PMA and Au@Cu₂O-MIL-53(Fe) verified the reliability of the biosensor, suggesting its potential application to the monitoring of critical pathological processes at the cellular level.

Co-Cr mixed spinel oxide nanodots anchored on nitrogen-doped carbon nanotubes as catalytic electrode for hydrogen peroxide sensing

Hydrogen peroxide (H₂O₂) is a significant biomarker in physiological processes. Abnormal levels of H₂O₂ are considered to be closely related to some acute diseases. Therefore, it is important to monitor the H₂O₂ levels in bio-samples. Herein, we present a novel non-enzymatic electrochemical H₂O₂ sensor based on the excellent electrocatalytic performance of a composite comprising Zn-Cr-Co ternary spinel metal oxide nanodots (ZnCrCoO₄) anchored on the surface of nitrogen-doped carbon nanotubes (NCNTs), denoted as ZnCrCoO₄/NCNTs, toward H₂O₂ reduction. ZnCrCoO₄/NCNTs were synthesized using a facile one-pot hydrothermal strategy. The enhanced electrocatalytic performance of ZnCrCoO₄ is resulted from the partial substitution of Co in spinel zinc cobaltate (ZnCo₂O₄) with Cr, which modifies the CoO electronic structure and enhances electroconductivity. The ZnCrCoO₄/NCNTs-based H₂O₂ sensor exhibited a wide quantitative detection range from 1 to 7330 μM with a detection limit of 1 μM. The sensor showed excellent reproducibility and selectivity for H₂O₂ sensing. In addition, remarkable recoveries were obtained for H₂O₂-spiked fish serum samples. These results demonstrated that the as-developed sensor has a great potential in monitoring H₂O₂ levels in practical applications.