Facile Synthesis of ZnMn2O4@rGO Microspheres for Ultrasensitive Electrochemical Detection of Hydrogen Peroxide from Human Breast Cancer Cells

An origami microfluidic paper device based on core-shell Cu@Cu2S@N-doped carbon hollow nanocubes

BACKGROUD

The global prevalence of diabetes mellitus, a serious chronic disease with fatal consequences for millions annually, is of utmost concern. The development of efficient and simple devices for monitoring glucose levels is of utmost significance in managing diabetes. The advancement of nanotechnology has resulted in the indispensable utilization of advanced nanomaterials in high-performance glucose sensors. Modulating the morphology and intricate composition of transition metals represents a viable approach to exploit their structure/function correlation, thereby achieving optimal electrocatalytic performance of the synthesized catalysts.

RESULTS

Herein, a sensitive and rapid Cu-encapsulated Cu2S@nitrogen-doped carbon (Cu@Cu2S@N-C) hollow nanocubes-functionalized microfluidic paper-based analytical device (μ-PAD) was fabricated. Through a delicate sacrificial template/interface technique and thermal decomposition, inter-connected hollow networks were formed to boost the active sites, and the carbon shell was coated to protect Cu from being oxidation. For application, the constructed μ-PAD is used for glucose sensing utilizing an origami automated sample pretreatment system enabled by a simple application of strong alkaline solution on wax paper. Under optimal circumstances, the Cu@Cu2S@N-C electrochemical biosensor exhibits broad detection range of 2-7500 μM (R2 = 0.996) with low detection limit of 0.16 μM (S/N = 3) and high sensitivity of 1996 μA mM-1 cm-2. Additionally, the constructed μ-PAD also exhibited excellent selectivity, stability, and reproducibility.

SIGNIFICANCE

By rationally designing the double-shell hollow nanostructure and introducing Cu-encapsulated inner layer, the synthesized Cu@Cu2S@N-C hollow nanocubes show large specific surface area, short diffusion channels, and high stability. The proposed origami μ-PAD has been successfully applied to serum samples without any additional sample preparation steps for glucose determination, offering a new perspective for early nonenzymatic glucose diagnosis.

Designing Nanocomposite-Based Electrochemical Biosensors for Diabetes Mellitus Detection: A Review

This review will unveil the development of a new generation of electrochemical sensors utilizing a transition-metal-oxide-based nanocomposite with varying morphology. There has been considerable discussion on the role of transition metal oxide-based nanocomposite, including iron, nickel, copper, cobalt, zinc, platinum, manganese, conducting polymers, and their composites, in electrochemical and biosensing applications. Utilizing these materials to detect glucose and hydrogen peroxide selectively and sensitively with the correct chemical functionalization is possible. These transition metals and their oxide nanoparticles offer a potential method for electrode modification in sensors. Nanotechnology has made it feasible to develop nanostructured materials for glucose and H2O2 biosensor applications. Highly sensitive and selective biosensors with a low detection limit can detect biomolecules at nanomolar to picomolar (10-9 to 10-12 molar) concentrations to assess physiological and metabolic parameters. By mixing carbon-based materials (graphene oxide) with inorganic nanoparticles, nanocomposite biosensor devices with increased sensitivity can be made using semiconducting nanoparticles, quantum dots, organic polymers, and biomolecules.

Facile and Affordable Design of MXene-Co3 O4 -Based Nanocomposites for Detection of Hydrogen Peroxide in Cancer Cells: Toward Portable Tool for Cancer Management

Hydrogen peroxide (H2 O2 ) is a primary reactive oxygen species (ROS) that can act as a chemical signal in developing and progressing serious and life-threatening diseases like cancer. Due to the stressful nature of H2 O2 , there is an urgent need to develop sensitive analytical approaches to be applied to various biological matrices. Herein, a portable point-of-care electrochemical system based on MXene-Co3 O4 nanocomposites to detect H2 O2 in different cancer cell-lines is presented. The developed sensor is affordable, disposable, and highly selective for H2 O2 detection. This approach achieves a dynamic linear range of 75 µm with a LOD of 0.5 µm and a LOQ of 1.6 µm. To improve the practical application, the level of ROS is evaluated both in cancer cell lines MDA-MB-231 and DU145, respectively, to breast and prostate cancers, and in healthy HaCat cells. Moreover, the same cancer cells are treated with transforming growth factor-β1, and MXene-Co3 O4 modified strip is capable to monitorROS variation. The results are satisfactory compared with the cellular ROS fluorescent assay based on DCFH/DCFH-DA. These results open new perspectives for real-time monitoring of cancer progression and the efficacy of the therapy.

Sensorization of microfluidic brain-on-a-chip devices: Towards a new generation of integrated drug screening systems

Brain-on-a-chip (BoC) devices show typical characteristics of brain complexity, including the presence of different cell types, separation in different compartments, tissue-like three-dimensionality, and inclusion of the extracellular matrix components. Moreover, the incorporation of a vascular system mimicking the blood-brain barrier (BBB) makes BoC particularly attractive, since they can be exploited to test the brain delivery of different drugs and nanoformulations. In this review, we introduce the main innovations in BoC and BBB-on-a-chip models, especially focusing sensorization: electrical, electrochemical, and optical biosensors permit the real-time monitoring of different biological phenomena and markers, such as the release of growth factors, the expression of specific receptors/biomarkers, the activation of immune cells, cell viability, cell-cell interactions, and BBB crossing of drugs and nanoparticles. The recent improvements in signal amplification, miniaturization, and multiplication of the sensors are discussed in an effort to highlight their benefits versus limitations and delineate future challenges in this field.

A Flexible and Transparent PtNP/SWCNT/PET Electrochemical Sensor for Nonenzymatic Detection of Hydrogen Peroxide Released from Living Cells with Real-Time Monitoring Capability

We developed a transparent and flexible electrochemical sensor using a platform based on a network of single-walled carbon nanotubes (SWCNTs) for the non-enzymatic detection of hydrogen peroxide (H₂O₂) released from living cells. We decorated the SWCNT network on a poly(ethylene terephthalate) (PET) substrate with platinum nanoparticles (PtNPs) using a potentiodynamic method. The PtNP/SWCNT/PET sensor synergized the advantages of a flexible PET substrate, a conducting SWCNT network, and a catalytic PtNP and demonstrated good biocompatibility and flexibility, enabling cell adhesion. The PtNP/SWCNT/PET-based sensor demonstrated enhanced electrocatalytic activity towards H₂O₂, as well as excellent selectivity, stability, and reproducibility. The sensor exhibited a wide dynamic range of 500 nM to 1 M, with a low detection limit of 228 nM. Furthermore, the PtNP/SWCNT/PET sensor remained operationally stable, even after bending at various angles (15°, 30°, 60°, and 90°), with no noticeable loss of current signal. These outstanding characteristics enabled the PtNP/SWCNT/PET sensor to be practically applied for the direct culture of HeLa cells and the real-time monitoring of H₂O₂ release by the HeLa cells under drug stimulation.

Hybridizing Ti3C2Tx Layers with Layered Double Hydroxide Nanosheets at the Molecular Level: A Smart Electrode Material for H2O2 Monitoring in Cancer Cells

Vertically stacked artificial 2D superlattice hybrids fabricated through molecular-level hybridization in a controlled fashion play a vital role in scientific and technological fields, but developing an alternate assembly of 2D atomic layers with strong electrostatic interactions could be much more challenging. In this study, we have constructed an alternately stacked self-assembled superlattice composite through integration of CuMgAl layered double hydroxide (LDH) nanosheets having positive charge with negatively charged Ti₃C₂T_x layers using well-controlled liquid-phase co-feeding protocol and electrostatic attraction and investigated its electrochemical performance in sensing early cancer biomarkers, i.e., hydrogen peroxide (H₂O₂). The molecular-level CuMgAl LDH/Ti₃C₂T_x superlattice self-assembly possesses superb conductivity and electrocatalytic properties, which are significant for obtaining a high electrochemical sensing aptitude. Electron penetration in Ti₃C₂T_x layers and rapid ion diffusion along 2D galleries have shortened the diffusion path and enhanced the charge transferring efficacy. The electrode modified with the CuMgAl LDH/Ti₃C₂T_x superlattice has demonstrated admirable electrocatalytic abilities in H₂O₂ detection with a wide linear concentration range and low real-time limit of detection (LOD) of 0.1 nM with signal/noise ratio (S/N) = 3. Practically, an electrochemical sensing podium based on the CuMgAl LDH/Ti₃C₂T_x superlattice has been effectively applied in real-time in vitro tracking of H₂O₂ effluxes excreted from different live cancer cells and normal cells after being encouraged by stimulation. The results exhibit that molecular-level heteroassembly holds great potential in electrochemical sensors to detect promising biomarkers.

One-Step Microwave-Assisted Hydrothermal Preparation of Zn-ZnO(Nw)-rGO Electrodes for Supercapacitor Applications

Zn-ZnO(Nw)-rGO hybrid electrodes for supercapacitor applications were successfully prepared in situ by a one-step microwave-assisted hydrothermal method by deposition of reduced graphene oxide (rGO) on the structure of ZnO nanowires grown on the Zn foil. During the hydrothermal treatment, two processes occur the reduction of graphene oxide (GO) and the deposition of rGO on the Zn-ZnO(Nw) support. The growth of ZnO nanowires was achieved by thermal oxidation below the melting point of the Zn foil in a controlled atmosphere. The as-obtained electrodes were assessed for structural, optical, and morphological properties by X-ray diffraction, Raman spectroscopy, ultraviolet-visible spectroscopy, SEM microscopy, and EDX analysis. The supercapacitor properties of the Zn-ZnO(Nw)-rGO hybrid electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge analysis. The CV curve reveals that the Zn-ZnO(Nw)-rGO hybrid structures work as negative electrodes and exhibit a non-ideal rectangle-like shape, suggesting that the as-synthesized structure behaves as a pseudo-capacitor. A maximum capacitance was determined to be 395.79 mF cm^-2 at a scan rate of 5 mV s^-1. Based on GCD analysis, the maximum specific capacitance of 145.59 mF cm^-2 was achieved at a low power density of 2 mA cm^-2. The cycle life assessment of the Zn-ZnO(Nw)-rGO hybrid electrode over a 250-cycle number was performed by CV and GCD analysis. The maximum retention rate of 120.86% was achieved from GCD analysis over 250 cycles for the Zn-ZnO(Nw)-rGO hybrid electrode.

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.

Graphene-Based Electrochemical Biosensors for Breast Cancer Detection

Breast cancer (BC) is the most common cancer in women, which is also the second most public cancer worldwide. When detected early, BC can be treated more easily and prevented from spreading beyond the breast. In recent years, various BC biosensor strategies have been studied, including optical, electrical, electrochemical, and mechanical biosensors. In particular, the high sensitivity and short detection time of electrochemical biosensors make them suitable for the recognition of BC biomarkers. Moreover, the sensitivity of the electrochemical biosensor can be increased by incorporating nanomaterials. In this respect, the outstanding mechanical and electrical performances of graphene have led to an increasingly intense study of graphene-based materials for BC electrochemical biosensors. Hence, the present review examines the latest advances in graphene-based electrochemical biosensors for BC biosensing. For each biosensor, the detection limit (LOD), linear range (LR), and diagnosis technique are analyzed. This is followed by a discussion of the prospects and current challenges, along with potential strategies for enhancing the performance of electrochemical biosensors.

Synthesis of Bimetallic Ni-Co Phosphide Nanosheets for Electrochemical Non-Enzymatic H2O2 Sensing

NiCoP nanosheets (NSs) were successfully synthesized using the hydrothermal and high-temperature phosphorization process. The obtained NiCoP NSs were immobilized on a glassy carbon electrode (GCE) and used to construct a novel sensing platform for electrochemical non-enzymatic H₂O₂ sensing. Physicochemical characteristics of NiCoP NSs were obtained by field-emission scanning electron microscopy (FESEM), field-emission transmission electron microscope (FETEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In addition, the electrochemical properties of NiCoP NSs were obtained by cyclic voltammetry (CV) and chronoamperometry (CA) towards the non-enzymatic detection of H₂O₂. FESEM and FETEM images provided a morphological insight (the unique nanosheets morphology of NiCoP) that could expose more active sites to promote mass/charge transport at the electrode/electrolyte interface. XRD and XPS results also confirmed the crystalline nature of the NiCoP nanosheets and the coexistence of multiple transitional metal oxidation states in NiCoP nanosheets. These unique physicochemical characteristics had a degree of contribution to ensuring enhancement in the electrochemical behavior. As a result, the synthesized NiCoP NSs composed of intercalated nanosheets, as well as the synergistic interaction between bimetallic Ni/Co and P atoms exhibited excellent electrocatalytical activity towards H₂O₂ electroreduction at neutral medium. As the results showed, the electrochemical sensing based on NiCoP NSs displayed a linear range of 0.05~4 mM, a sensitivity of 225.7 μA mM^-1 cm^-2, a limit of detection (LOD) of 1.190 μM, and good selectivity. It was concluded that NiCoP NSs-based electrochemical sensing might open new opportunities for future construction of H₂O₂ sensing platforms.

Recent Advances in Electrochemical Biosensors for Monitoring Animal Cell Function and Viability

Redox reactions in live cells are generated by involving various redox biomolecules for maintaining cell viability and functions. These qualities have been exploited in the development of clinical monitoring, diagnostic approaches, and numerous types of biosensors. Particularly, electrochemical biosensor-based live-cell detection technologies, such as electric cell-substrate impedance (ECIS), field-effect transistors (FETs), and potentiometric-based biosensors, are used for the electrochemical-based sensing of extracellular changes, genetic alterations, and redox reactions. In addition to the electrochemical biosensors for live-cell detection, cancer and stem cells may be immobilized on an electrode surface and evaluated electrochemically. Various nanomaterials and cell-friendly ligands are used to enhance the sensitivity of electrochemical biosensors. Here, we discuss recent advances in the use of electrochemical sensors for determining cell viability and function, which are essential for the practical application of these sensors as tools for pharmaceutical analysis and toxicity testing. We believe that this review will motivate researchers to enhance their efforts devoted to accelerating the development of electrochemical biosensors for future applications in the pharmaceutical industry and stem cell therapeutics.

Plasmonic Hot-Electron-Painted Au@Pt Nanoparticles as Efficient Electrocatalysts for Detection of H2O2

Plasmon-driven catalysis of metal nanostructures has garnered wide interest. Here, a photogenerated plasmonic hot-electron painting strategy was reported to form Au@Pt composite nanoparticles (Au@Pt NPs) with high catalytic reactivity without using reducing agents. Au nanoparticles, including Au nanospheres (Au NSs), Au nanorods (Au NRs), and Au nanobipyramids (Au NBPs), generated hot electrons under localized surface plasmon resonance (LSPR) excitation, which made the platinum precursor reduced as a consequence that Pt(0) atoms were painted on the surface of Au NPs to form an asymmetric Pt shell outside the plasmonic Au core. Compared with bare Au NPs, Au@Pt NPs exhibited significantly enhanced electrocatalytic activity toward reduction of H₂O₂ due to the bimetallic synergistic effect and great dispersion of Au@Pt NP-modified indium tin oxide (Au@Pt NPs/ITO). It exhibited a linear detection of H₂O₂ in a wide concentration range from 0.5 to 1000 μM with a low detection limit of 0.11 μM (S/N = 3). Therefore, the plasmonic hot-electron-painted Au@Pt NPs represent a novel and simple method for the design of advanced noble asymmetric metal nanomaterials.

Graphene frameworks-confined synthesis of 2D-layered NiCoP for the electrochemical sensing of H2O2 at lower overpotential

A new 2D-layered nickel cobalt phosphide nanosheet confined by 3D graphene frameworks (denoted as NiCoP/GFs) is in situ controllably synthesized as a highly efficient and durable electrocatalyst, which is obtained from the transformation of corresponding NiCo layer double hydroxides and GFs. Hydrogen peroxide (H₂O₂) is selected as a demonstration to study the electrochemical sensing performance of the NiCoP/GFs. Benefiting from 2D morphology of NiCoP and network structure of GFs, NiCoP/GFs exhibits remarkable electroactivity toward H₂O₂ at a relatively low overpotential of approximately - 0.3 V (vs sat. Ag/AgCl) in 0.01 M phosphate-buffered saline solution (PBS, pH = 7.4). The NiCoP/GFs-based H₂O₂ electrochemical sensor achieves a high sensitivity of ∼4398 μA mM^-1 cm^-2, a low detection limit of 0.028 ± 0.006 μM, and desirable selectivity. In addition, the sensor can sensitively detect H₂O₂ from living cancer cells. This study not merely broadens the synthesis methods of transition metal phosphide-based nanocrystals but the NiCoP/GFs also has broad prospects in diverse electrochemistry fields. We have reported a controllable synthesis of 2D nickel cobalt phosphide nanosheet confined by graphene frameworks (denoted as NiCoP/GFs) as a greatly efficient and durable electrocatalyst. The NiCoP/GFs exhibits remarkable electroactivity toward detection of H₂O₂ at a relatively low overpotential of approximately -0.3 V. Density functional theory (DFT) calculations further prove that regulation of the electronic structure of NiCoP by GFs lowers the adsorption free energy of *OOH intermediates, and thus contributes to the greatly improved the electrocatalytic performance of NiCoP/GFs toward H₂O₂ reduction. The developed NiCoP/GFs can be applied as excellent electrode materials for efficient electrochemical sensing of H₂O₂.

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

Tailored construction of one-dimensional TiO2/Au nanofibers: Validation of an analytical assay for detection of diphenylamine in food samples

We report a one-dimensional titanium dioxide encapsulated with gold heterojunction nanofibers (TiO₂/Au NFs) as robust electrocatalysts for electrochemical detection of diphenylamine (DPA). A TiO₂/Au NFs were successfully synthesized by a coaxial electrospinning method. The formation of TiO₂/Au NFs was confirmed by various analytical and spectroscopic approaches. The fabricated TiO₂/Au NFs modified screen-printed carbon electrodes (SPCE) exhibit a well-enhanced detection activity towards DPA sensing as compared to other electrodes. Under the experimental conditions, the proposed electrode leading to the sensing range from 0.05 to 60 µM with a detection limit of 0.009 µM was obtained for the DPA detection. Moreover, the TiO₂/Au NFs/SPCE showed good selectivity towards the electrochemical oxidation of DPA. Interestingly, the TiO₂/Au NFs modified electrode was then applied to detect the effect of DPA on spiked content in the food samples.

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.

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.

Two-dimensional mesoporous nitrogen-rich carbon nanosheets loaded with CeO2 nanoclusters as nanozymes for the electrochemical detection of superoxide anions in HepG2 cells

Two-dimensional (2D) porous carbon-based composite nanosheets loaded with metal oxide nanoclusters are expected to be promising electrocatalysts for high-performance electrochemical sensors. However, for this complicated composite material, strict reaction conditions and complex synthesis steps limit its general application in electrochemical detection. Here we present a facile method to fabricate 2D mesoporous nitrogen-rich carbon nanosheets loaded with CeO₂ nanoclusters (2D-mNC@CeO₂), for fabricating superoxide anions (O₂^•-) electrochemical sensor. The method is based on block copolymers self-assembly and the affinity of polydopamine to metal ions to obtain organic-inorganic hybrid, which can be directly converted into 2D-mNC@CeO₂ through carbonization strategy without structural deterioration. Characterizations demonstrate that the 2D-mNC@CeO₂ owned the 2D N-doped carbon structure with an interlinked hierarchical mesoporous and the uniformly dispersed CeO₂ nanoclusters on the surface. Benefitted from the unique structure, the 2D-mNC@CeO₂ shortens electron transfer distance, enhances mass transfer efficiency, exposes numerous active sites, and obtain a high Ce³⁺/Ce⁴⁺ ratio for improving electrocatalytic performance. The 2D-mNC@CeO₂/SPCEs sensors for O₂^•- detection has a detection limit of 0.179 μM (S/N = 3) and sensitivity of 401.4 μA cm^-2 mM^-1. The sensors can be applied to capture electrochemical signals of O₂^•- released from HepG2 cells, demonstrating the application potential of the sensors to monitor O₂^•- in biological fields.

The Effect of Thin Film Fabrication Techniques on the Performance of rGO Based NO2 Gas Sensors at Room Temperature

Reduced graphene oxide (rGO) has attracted enormous interest as a promising candidate material for gas detection due to its large specific surface areas. In our work, rGO films were fabricated on a large scale using dip-coating and spin-coating methods for the detection of nitrogen dioxide (NO2) gas at room temperature. The influence of different test environments on the sensing performance, including the test atmosphere, gas flow and gas pressure was evaluated. The response time of the dip-coating method was 573 s with a long recovery period of 639 s and for the spin-coating method, the response time and recovery time was 386 s and 577 s, respectively. In addition, the spin-coated sensor exhibited high selectivity to NO2, with the response increasing by more than 20% (for 15 ppm NO2) as compared with that for HCHO, NH3, and CH4. Our results indicated that the spin coating method was more suitable for rGO-based gas sensors with higher performance.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.

ZIF-67 MOF-derived Co nanoparticles supported on N-doped carbon skeletons for the amperometric determination of hydrogen peroxide

ZIF-67-derived Co nanoparticles supported on N-doped carbon skeletons have been prepared from melamine foam (Co-NPs/NCs) for non-enzymatic electrochemical H₂O₂ detection. The synthesis of Co-NPs/NCs was demonstrated via calcination treatment using melamine foam (MF) and ZIF-67 as precursors. The experimental results show that Co-NPs/NCs composites exhibit eminent catalytic activity toward specific determination of H₂O₂ with high selectivity and sensitivity (252.43 and 203.88 μA mM^-1 cm^-2), low LOD (0.12 μM), and wide linear ranges (10-2080 and 2080-11,800 μM). The excellent performance might be ascribed to the synergetic effects of MOF and N-doped carbon skeletons. The carbon skeletons serve as a conductive bridge and provide a large specific surface area, which can facilitate electron transfer and well disperse nanoparticles. This non-enzymatic electrochemical sensor based on Co-NPs/NCs can successfully detect H₂O₂ secreted by living cells, indicating its great potential in the early diagnosis and pathological exploration of disease.

Aptamer Embedded Arch-Cruciform DNA Assemblies on 2-D VS2 Scaffolds for Sensitive Detection of Breast Cancer Cells

Arch-cruciform DNA are self-assembled on AuNPs/VS₂ scaffold as a highly sensitive and selective electrochemical biosensor for michigan cancer foundation-7 (MCF-7) breast cancer cells. In the construction, arch DNA is formed using two single-strand DNA sequences embedded with the aptamer for MCF-7 cells. In the absence of MCF-7 cells, a cruciform DNA labeled with three terminal biotin is bound to the top of arch DNA, which further combines with streptavidin-labeled horseradish peroxidase (HRP) to catalyze the hydroquinone-H₂O₂ reaction on the electrode surface. The presence of MCF-7 cells can release the cruciform DNA and reduce the amount of immobilized HRP, thus effectively inhibiting enzyme-mediated electrocatalysis. The electrochemical response of the sensor is negatively correlated with the concentration of MCF-7 cells, with a linear range of 10~1 × 10⁵ cells/mL, and a limit of detection as low as 5 cells/mL (S/N = 3). Through two-dimensional materials and enzyme-based dual signal amplification, this biosensor may pave new ways for the highly sensitive detection of tumor cells in real samples.

A Prussian blue-doped RGO/MXene composite aerogel with peroxidase-like activity for real-time monitoring of H2O2 secretion from living cells

Herein, we develop a novel 3D composite aerogel (3D PB/GMA) and apply it to the real-time monitoring of H₂O₂ secretion from living cells. The 3D PB/GMA shows an obvious porous structure and superior peroxidase-like activity. The electrochemical sensor based on 3D PB/GMA shows an excellent electrocatalytic performance towards H₂O₂. When applied to the real-time tracking of H₂O₂ secretion from living cells, it can satisfactorily distinguish cancer cell lines from normal cell lines, revealing a good application potential in pathological diagnosis.

Deployment of MIL-88B(Fe)/TiO2 Nanotube-Supported Ti Wires as Reusable Electrochemiluminescence Microelectrodes for Noninvasive Sensing of H2O2 from Single Cancer Cells

As one of the significant intracellular signaling molecules, hydrogen peroxide (H₂O₂) regulates some vital biological processes. However, it remains a challenge to develop noninvasive electrodes that can be used for sensing trace H₂O₂ at the cellular level. Here, we evaluated a high-performance solid-state electrochemiluminescence (ECL) H₂O₂ sensor based on MIL-88B(Fe) nanocrystal-anchored Ti microwires. Semiconducting TiO₂ nanotubes (TiNTs) vertically grown around a Ti wire via an anodization technique act as an intrinsic ECL luminophore. By integrating with MIL-88B(Fe), the synergistic effect of the TiO₂ luminophore and the remarkable peroxidase-like activity of MIL-88B(Fe) enable the resulting H₂O₂ sensor an ultrahigh sensitivity featuring a minimum detection limit of 0.1 nM (S/N = 3), long-term stability, high durativity, and wide-range linear response to a concentration of up to 10 mM. To demonstrate the concept of a MIL-88B(Fe)@TiO₂ microelectrode for single-cell sensing, the electrode was used to detect intracellular H₂O₂ in a single cell. Moreover, benefiting from the heterojunction of MIL-88B(Fe)/TiO₂, the microelectrode was found to exhibit excellent photocatalytic activity in the visible-light range, that is, the sensor surface can be self-cleaning after a short visible-light treatment. These advanced sensor characteristics involving easy reusability reveal that the MIL-88B(Fe)@TiO₂ microelectrode is a new platform for cytosensing. This study provides a new strategy to design semiconductor materials with arbitrary shape and size, allowing for profound applications in biomedical and clinical analysis.

Facile synthesis of ultrathin two-dimensional graphene-like CeO2-TiO2 mesoporous nanosheet loaded with Ag nanoparticles for non-enzymatic electrochemical detection of superoxide anions in HepG2 cells

Here we presented a new facile strategy to fabricate ultrathin two-dimensional (2D) metal oxide nanosheets, by using polydopamine-coated graphene (rGO@PDA) as a template under simply wet-chemical conditions. Based on the strategy, graphene-like CeO₂-TiO₂ mesoporous nanosheet (MNS-CeO₂-TiO₂) was prepared and was loaded with dispersive Ag nanoparticles (AgNPs) to obtain effective electrocatalysts (denoted as Ag/MNS-CeO₂-TiO₂) for electrochemical detection of superoxide anion (O₂^•-). Characterizations demonstrated that MNS-CeO₂-TiO₂ exhibited ultrathin thickness, larger specific surface area, and pore volume in comparison with its bulk counterpart. The above properties of MNS-CeO₂-TiO₂ shorten electron transmission distance, promotes mass transfer, and is conducive to the dispersion of post-modified AgNPs. Therefore, the recommended Ag/MNS-CeO₂-TiO₂ sensors (denoted as Ag/MNS-CeO₂-TiO₂/SPCE) exhibited satisfactory properties, including the sensitivity of 737.1 μA cm^-2 mM^-1, the detection limit of 0.0879 μM (S/N = 3), and good selectivity. Meanwhile, the sensors also successfully realized in the online monitoring of O₂^•- released from HepG2 cells, meaning the prepared sensors had practical application potential towards the analysis of O₂^•- in biological samples.

Fe3C-Assisted Single Atomic Fe Sites for Sensitive Electrochemical Biosensing

The rational construction of advanced sensing platforms to sensitively detect H₂O₂ produced by living cells is one of the challenges in both physiological and pathological fields. Owing to the extraordinary catalytic performances and similar metal coordination to natural metalloenzymes, single atomic site catalysts (SASCs) with intrinsic peroxidase (POD)-like activity have shown great promise for H₂O₂ detection. However, there still exists an obvious gap between them and natural enzymes because of the great challenge in rationally modulating the electronic and geometrical structures of central atoms. Note that the deliberate modulation of the metal-support interaction may give rise to the promising catalytic activity. In this work, an extremely sensitive electrochemical H₂O₂ biosensor based on single atomic Fe sites coupled with carbon-encapsulated Fe₃C crystals (Fe₃C@C/Fe-N-C) is proposed. Compared with the conventional Fe SASCs (Fe-N-C), Fe₃C@C/Fe-N-C exhibits superior POD-like activity and electrochemical H₂O₂ sensing performance with a high sensitivity of 1225 μA/mM·cm², fast response within 2 s, and a low detection limit of 0.26 μM. Significantly, sensitive monitoring of H₂O₂ released from living cells is also achieved. Moreover, the density functional theory calculations reveal that the incorporated Fe₃C nanocrystals donate electrons to single atomic Fe sites, endowing them with improved activation ability of H₂O₂ and further enhancing the overall activity. This work provides a new design of synergistically enhanced single atomic sites for electrochemical sensing applications.

Hydrothermally synthesized cubical zinc manganite nanostructure for electrocatalytic detection of sulfadiazine

An electrocatalyst modified electrode has been investigated to develop the rapid detection of antibiotics. The modified electrocatalyst was intended for the determination of sulfadiazine (SFZ) in biological fluids by electrochemical methods. Nanocube of zinc manganite (ZnMn₂O₄-NC) is prepared by hydrothermal method and a glassy carbon electrode (GCE) has been modified with the zinc manganite. The ZnMn₂O₄/GCE exhibit enhanced detection performances towards SFZ drug owing to their selective adsorption ability and the combination of electrostatic attraction of nanocube with SFZ. The modified electrocatalyst shows excellent electrocatalytic interactions with antibiotic drug. Besides, the modified sensors exhibit nanomolar detection limit (0.0021 μM) in 0.05 M phosphate buffer (pH = 7.0) using differential pulse voltammetric method. The working range of the modified electrode is 0.008-1264 μM, and the sensitivity of the SFZ sensor is 11.44 μA μM^-1 cm^-2. The modified sensor stability and reproducibility performances have been examined by electrochemical method. In addition, the obtained results of real sample analysis with different concentrations of SFZ in biological fluids are satisfactory with good recovery.

Nanomolar level detection of non-steroidal antiandrogen drug flutamide based on ZnMn2O4 nanoparticles decorated porous reduced graphene oxide nanocomposite electrode

Flutamide is a non-steroidal antiandrogen drug and widely used in the treatment of prostatic carcinoma. Nevertheless, the excessive intake and improper disposal could affect the living organisms. In this work, we have synthesized a new nanocomposite based on ZnMn₂O₄ nanoparticles and porous reduced graphene oxide nanosheets (ZnMn₂O₄-PGO) for the electrocatalytic detection of flutamide (FLU) drug. The crystallinity and morphological properties of ZnMn₂O₄-PGO composite examined by different characterization techniques such as X-ray diffraction, Raman spectroscopy and so on. The fabricated ZnMn₂O₄-PGO nanocomposite modified electrode exhibited superior electrocatalytic performance to FLU drug in an optimized pH electrolyte. Fascinatingly, the electrode received a wide linear range (0.05-3.5 µM) with limit of detection of 8 nM. Besides, the developed ZnMn₂O₄-PGO nanocomposite electrode showed good sensitivity 1.05 µAµM^-1 cm^-2 and excellent selectivity for FLU detection in presence of various interfering species. A developed disposable electrode was scrutinized to determine FLU level in human urine samples by spiking method and the results achieved good recoveries in real sample analysis.

Detection Technologies for Reactive Oxygen Species: Fluorescence and Electrochemical Methods and Their Applications

Reactive oxygen species (ROS) have been found in plants, mammals, and natural environmental processes. The presence of ROS in mammals has been linked to the development of severe diseases, such as diabetes, cancer, tumors, and several neurodegenerative conditions. The most common ROS involved in human health are superoxide (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). Organic and inorganic molecules have been integrated with various methods to detect and monitor ROS for understanding the effect of their presence and concentration on diseases caused by oxidative stress. Among several techniques, fluorescence and electrochemical methods have been recently developed and employed for the detection of ROS. This literature review intends to critically discuss the development of these techniques to date, as well as their application for in vitro and in vivo ROS detection regarding free-radical-related diseases. Moreover, important insights into and further steps for using fluorescence and electrochemical methods in the detection of ROS are presented.

Three-dimensional graphene encapsulated Ag-ZnFe2O4 flower-like nanocomposites with enhanced photocatalytic degradation of enrofloxacin

Three-dimensional (3D) Ag–ZnFe₂O₄-reduced graphene oxide (rGO) was successfully synthesized using a hydrothermal and photo-reduction method, and the morphological differences of the materials were observed. Their photocatalytic activity was evaluated by photocatalytic degradation of enrofloxacin (ENR) under visible-light irradiation. The results indicated that Ag–ZnFe₂O₄–rGO exhibited superior photocatalytic properties and good stability. In this research, the enhancement of photocatalytic performance is mainly attributed to the electron channelization ability of rGO, which traps the photoexcited electrons of ZnFe₂O₄ on its π framework, and reduces the electron–hole recombination rate. Moreover, the high surface area of 3D pompon mum flower-like ZnFe₂O₄ provides more reactive sites. In addition, free radical capture and ESR experiments as well as pathway analysis of degradation also confirmed that superoxide radicals (˙O₂⁻) and photo-generated holes from Ag–ZnFe₂O₄–rGO were the main active species in the degradation progress of ENR.

Three-dimensional (3D) Ag–ZnFe₂O₄-reduced graphene oxide (rGO) was successfully synthesized using a hydrothermal and photo-reduction method, and the morphological differences of the materials were observed.

Tellurium doped zinc imidazole framework (Te@ZIF-8) for quantitative determination of hydrogen peroxide from serum of pancreatic cancer patients

The tellurium doped zinc imidazole framework (Te@ZIF-8) is prepared by a two-step hydrothermal strategy for the electrochemical sensing of hydrogen peroxide. Material is characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The electrochemical characterization of the MOF modified electrode is done by a three-electrode system. Electrochemical sensing of hydrogen peroxide is made by cyclic voltammetry, amperometry, and impedance measurements. Results demonstrate that Te@ZIF-8 shows a detection limit of 60 µM with linearity up to 0.98855. Material is stable to 1000 cycles with no significant change in electrochemical response. Amperometry depicts the recovery of hydrogen peroxide from human serum up to 101%. Impedance curve reveals the surface of Te@ZIF-8-GCE (glassy carbon electrode) as porous and rough and an interface is developed between analyte ions and the sensing material. Finally, the modified electrode is used for the quantitative determination of hydrogen peroxide from serum samples of pancreatic cancer patients, diagnosed with CA 19-9.

General and fast synthesis of graphene frameworks using sugars for high-performance hydrogen peroxide nonenzymatic electrochemical sensor

3D graphene frameworks (GFs) are fast and scalably synthesized via a general and facile method from the rich biomass of sugars with the aid of molten salts, using glucose as the prototype, to obtain an effective sensing platform for sensitive nonenzymatic hydrogen peroxide (H₂O₂) detection. The electroactive area of the GFs/GCE (0.1437 cm²) is obviously higher than that of bare GCE (0.0653 cm²). The GFs are found to exhibit remarkable electrocatalytic activity toward H₂O₂ reduction while avoiding enzyme loading. The electrochemical sensor for H₂O₂ based on GFs displays a low detection limit of 0.032 ± 0.005 μM (S/N = 3) at a working potential of - 0.55 V in 0.01 M N₂-saturated phosphate-buffered saline (PBS, pH = 7.4) by an amperometric method. The sensor has good selectivity over other compounds such as ascorbic acid, dopamine, uric acid, NaCl, citric acid, and glucose. Moreover, the sensor shows excellent reproducibility with a relative standard deviation of 3.7% and acceptable stability after 30 days of usage. Furthermore, it can detect H₂O₂ released from living tumorigenic cells in real time. Most importantly, it is demonstrated that such GFs can be obtained from a variety of sugars (sucrose, fructose, lactose, and maltose). This work may offer a new general avenue for the synthesis of 3D GFs and promote the development of electrochemical sensors. Graphical abstract We have reported a general and fast method to synthesize GFs from sugars (glucose, sucrose, fructose, lactose, and maltose) with the addition of molten Na₂CO₃ salt as a template. The developed GFs can be applied as excellent electrode materials for efficient electrochemical sensing of H₂O₂.

Hetero-structured MnO-Mn3O4@rGO composites: Synthesis and nonenzymatic detection of H2O2

The construction of metal-oxide heterojunction architecture has greatly widened applications in the fields of optoelectronics, energy conversions and electrochemical sensors. In this study, olive-like hetero-structured MnO-Mn₃O₄ microparticles wrapped by reduced graphene oxide (MnO-Mn₃O₄@rGO) were synthesized through a facile solvothermal-calcination treatment. The morphology and structure of MnO-Mn₃O₄@rGO were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. The as-synthesized MnO-Mn₃O₄@rGO exhibited prominent catalyzing effect on the electroreduction of H₂O₂, due to the combination of good electrical conductivity of rGO and the synergistic effect of MnO and Mn₃O₄. The MnO-Mn₃O₄@rGO modified glassy carbon electrode provided a wide linear response from 0.004 to 17 mM, a low detection limit of 0.1 μM, and high sensitivity of 274.15 μA mM^-1 cm^-2. The proposed sensor displayed noticeable selectivity and long-term stability. In addition, the biosensor has been successfully applied for detecting H₂O₂ in tomato sauce with good recovery, revealing its promising potential applications for practical electrochemical sensors.