Horseradish peroxidase supported on porous graphene as a novel sensing platform for detection of hydrogen peroxide in living cells sensitively

Highly sensitive detection of environmental toxic fenitrothion in fruits and water using a porous graphene oxide nanosheets based disposable sensor

Monitoring fenitrothion (FNT) residues in food and the environment is crucial due to its high environmental toxicity. In this study, we developed a sensitive, reliable electrochemical method for detecting FNT by using screen-printed carbon electrodes (SPCE) modified with porous graphene oxide (PGO) nanosheets. PGO surface properties have been meticulously characterized using advanced spectroscopic techniques. Electrochemical impedance spectroscopy and cyclic voltammetry were used to test the electrochemical properties of the PGO-modified sensor. The PGO-modified sensor exhibited remarkable sensitivity, achieving a detection limit as low as 0.061 μM and a broad linear range of 0.02-250 μM. Enhanced performance is due to PGO's high surface area and excellent electrocatalytic properties, which greatly improved electron transfer. Square wave voltammetry was used to demonstrate the sensor's efficacy as a real-time, on-site monitoring tool for FNT residues in fruit and water. The outstanding performance of the PGO/SPCE sensor underscores its applicability in ensuring food safety and environmental protection.

Cyanobacterial Phycocyanin-Based Electrochemical Biosensor for the Detection of the Free Radical Hydrogen Peroxide

Cyanobacteria are photosynthetic prokaryotes that inhabit extreme environments by modifying their photosensitive chemoreceptors called cyanobacteriochromes (CBCRs) which are linear tetrapyrrole-linked phycobilin molecules. These light-sensitive phycobilin from Spirulina platensis is recognized as a potential photoreceptor tool in optogenetics for monitoring cellular morphogenesis. We prepared and extracted highly fluorescent cyanobacterial phycocyanin (C-PC) by irradiating the culture with ambient red light. The crude phycocyanin was subjected to ion exchange chromatography, and its purity was monitored using UV-visible, fluorescence, and FT-IR spectroscopy methods. In the conventional method, red light-induced C-PC exhibited strong antioxidant activity against H2O2, with 88.7% in vitro scavenging activity without requiring any other preservatives. Interestingly, this red light-acclimated phycocyanin was applied as a biosensing material for the detection of the free radical hydrogen peroxide (H2O2) using the enzyme horseradish peroxidase (HRP) as a mediator. The modified C-PC-HRP glassy carbon electrode (GCE) can detect H2O2 from 0.1 to 1600 µM. The lowest possible detection limit of the electrode for H2O2 was 19 nM. This electrode was used to detect free radical H2O2 in blood serum samples. The microstructure of the lyophilized PC under SEM showed a flat crystal pattern, which enabled the immobilization of HRP on the electrode surface and electron transfer.

Voltammetric determination of hydrogen peroxide at decorated palladium nanoparticles/poly 1,5-diaminonaphthalene modified carbon-paste electrode

In this work, palladium nanoparticles (PdNPs)/p1,5-DAN/ carbon paste electrode (CPE) and p1,5-DAN/CPE sensors have been developed for determination of hydrogen peroxide. Both sensors showed a highly sensitive and selective electrochemical behaviour, which were derived from a large specific area of poly 1,5 DAN and super excellent electroconductibility of PdNPs. PdNPs/p1,5-DAN/CPE exhibited excellent performance over p1,5-DAN/CPE. Thus, it was used for detecting hydrogen peroxide (H2O2) with linear ranges of 0.1 to 250 µM and 0.2 to 300 µM as well as detection limits (S/N = 3) of 1.0 and 5.0 nM for square wave voltammetry (SWV) and cyclic voltammetry (C.V) techniques, respectively. The modified CPE has good reproducibility, adequate catalytic activity, simple synthesis and stability of peak response during H2O2 oxidation on long run that exceeds many probes. Both reproducibility and stability for H2O2 detection are attributable to the PdNPs immobilized on the surface of p1,5-DAN/CPE. The modified CPE was used for determining H2O2 in real specimens with good stability, sensitivity, and reproducibility.

In situ monitoring of ROS secretion from single cells with a dual-nanopore biosensor

We report here a dual-nanopore biosensor based on modulation of surface charge density coupled with a microwell array chip for in situ monitoring of ROS secretion from single MCF-7 cells.

Sensitive detection of extracellular hydrogen peroxide using plasmon-enhanced electrochemical activity on Pd-tipped Au nanobipyramids

The fabrication of electroactive nanostructures with high electron concentration and specific electron transport is crucial for electrochemical sensing. In this study, a plasmon-enhanced electrochemical sensor has been developed for the detection of extracellular hydrogen peroxide (H2O2) from cancer cells, utilizing Pd-tipped Au nanobipyramids (PTA NBPs) as the electrocatalysts. Plasmonic PTA NBPs were synthesized by depositing Pd nanoparticles onto the tips of Au nanobipyramids (Au NBPs). Under excitation of localized surface plasmon resonance (LSPR), the PTA NBPs generate high-energy electron-hole pairs (e-/h+) on their surface. The generated electrons (e-) significantly enhance the electrochemical reduction of H2O2. Based on this, a plasmon-enhanced H2O2 electrochemical sensor is constructed with high sensitivity (986.57 μA mM-1 cm-2), low detection limit (0.02 μM), wide linear range (0.1 μM to 980 μM), and good stability and repeatability. Moreover, this sensor also enables the measurement of extracellular H2O2 derived from cancer cells (MCF-7), highlighting its potential applications in cellular biology and biomedical research.

Evolution of nanostructured skin patches towards multifunctional wearable platforms for biomedical applications

Recent advances in the field of skin patches have promoted the development of wearable and implantable bioelectronics for long-term, continuous healthcare management and targeted therapy. However, the design of electronic skin (e-skin) patches with stretchable components is still challenging and requires an in-depth understanding of the skin-attachable substrate layer, functional biomaterials and advanced self-powered electronics. In this comprehensive review, we present the evolution of skin patches from functional nanostructured materials to multi-functional and stimuli-responsive patches towards flexible substrates and emerging biomaterials for e-skin patches, including the material selection, structure design and promising applications. Stretchable sensors and self-powered e-skin patches are also discussed, ranging from electrical stimulation for clinical procedures to continuous health monitoring and integrated systems for comprehensive healthcare management. Moreover, an integrated energy harvester with bioelectronics enables the fabrication of self-powered electronic skin patches, which can effectively solve the energy supply and overcome the drawbacks induced by bulky battery-driven devices. However, to realize the full potential offered by these advancements, several challenges must be addressed for next-generation e-skin patches. Finally, future opportunities and positive outlooks are presented on the future directions of bioelectronics. It is believed that innovative material design, structure engineering, and in-depth study of fundamental principles can foster the rapid evolution of electronic skin patches, and eventually enable self-powered close-looped bioelectronic systems to benefit mankind.

Investigation of H2O2 Electrochemical Behavior on Ferricyanide-Confined Electrode Based on Ionic Liquid-Functionalized Silica-Mesostructured Cellular Foam

In this work, ionic liquid (IL) of 1-propyl-3-methyl imidazolium chloride-functionalized silica-mesostructured cellular foam (MCF) was prepared. The obtained MCF-IL was used to construct the Fe(CN)₆^3--confined electrode (MCF-IL-Fe(CN)₆^3-/PVA) and H₂O₂ electrochemical behavior on the electrode was investigated. It was found that H₂O₂ was oxidized on the freshly prepared electrode while catalytically electro-reduced on the acid pretreated one. Cyclic voltametric results revealed that the real catalyst for catalytic reduction of H₂O₂ was Prussian blue (PB) rather than Fe(CN)₆^3-. The electrocatalytic ability of the acid-pretreated MCF-IL-Fe(CN)₆^3-/PVA electrode offered a wide linear range for H₂O₂ detection. The present study on H₂O₂ electrochemical behavior on an MCF-IL-Fe(CN)₆^3-/PVA electrode might provide useful information for further developing integrated Fe(CN)₆^3--mediated biosensors as H₂O₂ is extensively involved in the classic reaction containing oxidase enzymes.

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.

A hybrid borotungstate-coated metal-organic framework with supercapacitance, photocatalytic dye degradation and H2O2 sensing properties

The compounding of polyoxometalates (POMs) with structurally well-defined and porous metal-organic frameworks (MOFs) has become a hot research topic. Here, a core-shell type hybrid, {Ag₅BW₁₂O₄₀}@[Ag₃(μ-Hbtc)(μ-H₂btc)]_n (called {Ag₅BW₁₂O₄₀}@Ag-BTC-2, where BTC = 1,3,5-benzyl carboxylic acid), was successfully prepared via a simple grinding method. IR, XRD, SEM, TEM, and XPS analysis was used to confirm the structure. The specific capacitance is 179.1 F g^-1 when the current density is 1 A g^-1, using nickel foam as the collector, and the capacitance retention is 97.4% after 5000 cycles. The resulting aqueous-based symmetric supercapacitor has a power density of 496 W kg^-1 and an energy density of 12.4 W h kg^-1. In addition, the degradation rates using {Ag₅BW₁₂O₄₀}@Ag-BTC-2 toward methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) exceeded 90% in 140 min and remained essentially unchanged over five replicate experiments, showing high photocatalytic activity. Meanwhile, when {Ag₅BW₁₂O₄₀}@Ag-BTC-2 acts as a H₂O₂ biosensor, it has a low detection limit (0.19 μM), a wide linear range (0.4 μM-0.27 mM) and high anti-interference properties. This shows that the synthesis of POMOFs via a grinding method is an effective strategy to improve the performance.

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.

Utilizing dual carriers assisted by enzyme digestion chemiluminescence signal enhancement strategy simultaneously detect tumor markers CEA and AFP

To measure two tumor biomarkers, alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA), a dual-carrier CL sensor with restriction enzyme digestion (Exo I) and aptamer technology utilizing gold nanoparticles (hydroxylamine amplification) and horseradish peroxidase (HRP) as the CL signal enhancement in the sensing strategy was formed. These nanoparticles and nano-enzyme were precisely detected and tagged to the appropriate position attributable to the particular recognition of biotin and streptavidin. In this sensing strategy, target markers were further enriched and recognized sensitively by CL following enrichment, and matching strong chemical signals were collected under luminol catalysis, allowing for marker identification. For CEA (0.1-80 ng/mL) and AFP (2-500 ng/mL), the proposed method has a large linear range, with detection limits of 36.6 pg/mL and 0.94 ng/mL, respectively.

Specifically triggered dissociation based ratiometric electrochemical sensor for H2O2 measurement in food samples

A novel ratiometric strategy based electrochemical sensor was developed to quantitative assay of H₂O₂ in different food samples. 4-aminophenylboronic acid pinacol ester (ABAPE) dissociation was specifically triggered by H₂O₂ to generate electro-active 4-aminophenol (4-AP), which not only can be oxidized to indirectly indicate the concentration of H₂O₂, but also endowed the sensor with high selectivity. Meanwhile, a reference probe of poly(thionine) (TH) was modified with ketjen black (KB) and gold nanoparticles (AuNPs) on electrode surface. KB and AuNPs displayed high electrocatalytic activity to 4-AP. A current ratio between 4-AP and TH (i/i_TH) showed a good linear relationship with the concentration of H₂O₂ in a range of 3.0 × 10^-7 - 1.0 × 10^-4 mol/L (0.010 ppm - 3.40 ppm) with a limit of detection of 2.6 × 10^-7 mol/L (0.009 ppm) (S/N = 3). Moreover, the ratiometric strategy based sensor possessed good accuracy, reliability, and stability, and successfully determined H₂O₂ in food samples with satisfactory results.

Comparison of Hydrogen Peroxide Secretion From Living Cells Cultured in Different Formats Using Hydrogel-Based LSPR Substrates

Reactive oxygen species (ROS), a number of reactive molecules and free radicals derived from molecular oxygen, are generated as by-products during mitochondrial electron transport within cells. Physiologically, cells are capable of metabolizing the ROS exploiting specific mechanisms. However, if excessive ROS accumulate inside the cells, it will cause the cells apoptosis or necrosis. Hydrogen peroxide (H₂O₂) is one of the essential ROS often participating in chemical reactions in organisms and regulating homeostasis in the body. Therefore, rapid and sensitive detection of H₂O₂ is a significant task in cell biology research. Furthermore, it has been found that cells cultured in different formats can result in different cellular responses and biological activities. In order to investigate the H₂O₂ secretion from the cells cultured in different formats, a hydrogel-based substrate is exploited to separate relatively large molecular (e.g., proteins) for direct measurement of H₂O₂ secreted from living cells in complete cell culture medium containing serum. The substrate takes advantage of the localized surface plasmon resonance (LSPR) method based on enzyme immunoprecipitation. In addition, the H₂O₂ secreted from the cells cultured in different dimensions (suspension of single cells and three-dimensional cell spheroids) treated with identical drugs is measured and compared. The spheroid samples can be prepared with ample amount using a designed microfluidic device with precise control of size. The results show that the H₂O₂ secretion from the cells are great affected by their culture formats.

Multifunctional hybrid skin patch for wearable smart healthcare applications

Recent advances in wearable patches have included various sensors to monitor either physiological signs, such as the heart rate and respiration rate, or metabolites. Nevertheless, most of these have focused only on a single physiological measurement at a time, which significantly inhibits the calibration of various biological signals and diagnostic facilities. In this study, a novel multifunctional hybrid skin patch was developed for the electrochemical analysis of sweat glucose levels and simultaneous monitoring of electrocardiograms (ECGs). Furthermore, pH and temperature sensors were co-integrated onto the same patch for the calibration of the glucose biosensor to prevent inevitable inhibition and weakening of enzyme activity due to changes in the sweat pH and temperature levels. The fabricated electrochemical glucose biosensor exhibited excellent linearity (R² = 0.9986) and sensitivity (29.10 μA mM^-1 cm^-2), covering the normal range of human sweat. The potentiometric pH sensor displayed a good response with an excellent sensitivity of -77.81 mV/pH and high linearity (R² = 0.991), indicating that it can distinguish variations in the typical pH range for human sweat. Furthermore, the P, QRS complex, and T peaks in the measured ECG waveforms could be clearly distinguished, indicating the reliability of the fabricated flexible dry electrodes for continuous monitoring. The fabricated skin patch overcomes the inconvenience of the mandatory attachment of multiple patches on the human body by fully integrating all the electrochemical and electrophysiological sensors on a single patch, thus facilitating advanced glycemic control and continuous ECG monitoring for smart management of chronic diseases and healthcare applications.

Application of an electrochemical sensor using copper oxide nanoparticles/polyalizarin yellow R nanocomposite for hydrogen peroxide

In this study, copper oxide nanoparticles (CuONPs) were prepared by a simple chemical method and then characterized by scanning electron microscope (SEM). A novel electrochemical sensor for hydrogen peroxide (H₂O₂) analysis was prepared by immobilizing copper oxide nanoparticles and polyalizarin yellow R (PYAR) on bare glassy carbon electrode (PAYR/CuONPs/GCE). The electrocatalytical behavior of the proposed electrochemical sensor was also studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Based on the results, the PAYR/CuONP nanocomposite had significant electrocatalytic oxidation and reduction properties for the detection and determination of H₂O₂. Some parameters such as linear range, sensitivity, and detection limit for reduction peak were obtained as 0.1-140 μM, 1.4154 μA cm^-2 μM^-1, and 0.03 μM, respectively, by the DPV technique. Some advantages of this electrode were having widespread linear range, low detection limit, and, most importantly, ability in simultaneous oxidation and reduction of H₂O₂ at two applied potentials.

A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

Plasma membrane anchored nanosensor for quantifying endogenous production of H2O2 in living cells

Hydrogen peroxide (H₂O₂) is one of the main second messengers involved in signaling pathways controlling cell metabolism. During tumorigenesis H₂O₂ is generated on the extracellular space by membrane-associated NADPH oxidases and superoxide dismutase to stimulate cell proliferation and preservation of the transformed state. Accordingly, a characteristic feature of malignant cells is overproduction of H₂O₂ in the extracellular milieu and the subsequent absorption in the cytosol. Since the most significant gradients of endogenous extracellular H₂O₂ can be observed only in a very shallow region of the fluid in contact with the plasma membrane, we show here the use of a newly designed nanosensor anchored to the outer cell surface and capable of quantifying H₂O₂ at nanometer distance from the membrane proteins responsible for its production. This biosensor is built upon gold nanoparticles functionalized with a H₂O₂-sensitive boronate compound that is probed using surface enhanced Raman spectroscopy (SERS). The highly localized information obtained on the cell surface by SERS analysis is combined with analytical methods of redox biology to estimate the associated levels of intracellular H₂O₂ responsible for cell signaling. The results obtained from A549 lung cancer cell line show localized spots on the cell surface at concentration up to 12 μM, associated to intracellular concentration up to 5.1 nM.

Synthesis of NiCo2O4 Nanostructures and Their Electrochemial Properties for Glucose Detection

In this work, we prepared spinel-type NiCo2O4 (NCO) nanopowders as a low-cost and sensitive electrochemical sensor for nonenzymatic glucose detection. A facile and simple chemical bath method to synthesize the NCO nanopowders is demonstrated. The effect of pH and annealing temperature on the formation mechanism of NCO nanoparticles was systematically investigated. Our studies show that different pHs of the precursor solution during synthesis result in different intermediate phases and relating chemical reactions for the formation of NCO nanoparticles. Different morphologies of the NCO depending on pHs are also discussed based on the mechanism of growth. Electrochemical performance of the prepared NCO was characterized towards glucose, which reveals that sensitivity and selectivity of the NCO are significantly related with the final microstructure combined with constituent species with multiple oxidation states in the spinel structure.

Nanostructured materials for harnessing the power of horseradish peroxidase for tailored environmental applications

High catalytic efficiency, stereoselectivity, and sustainability outcomes of enzymes entice chemists for considering biocatalytic transformations to supplant conventional synthetic routes. As a green and versatile enzyme, horseradish peroxidase (HRP)-based enzymatic catalysis has been widely employed in a range of biological and chemical transformation processes. Nevertheless, like many other enzymes, HRP is likely to denature or destabilize in harsh realistic conditions due to its intrinsic fragile nature, which results in inevitably shortened lifespan and immensely high bioprocess cost. Enzyme immobilization has proven as a prospective strategy for improving their biocatalytic performance in continuous industrial processes. Nanostructured materials with huge accessible surface area, abundant porous structures, exceptional functionalities, and high chemical and mechanical stability have recently garnered intriguing research interests as novel kinds of supporting matrices for HRP immobilization. Many reported immobilized biocatalytic systems have demonstrated high catalytic performances than that to the free form of enzymes, such as enhanced enzyme efficiency, selectivity, stability, and repeatability due to the protective microenvironments provided by nanostructures. This review delineates an updated overview of HRP immobilization using an array of nanostructured materials. Furthermore, the general physicochemical aspects, improved catalytic attributes, and the robust practical implementations of engineered HRP-based catalytic cues are also discussed with suitable examples. To end, concluding remarks, challenges, and worthy suggestions/perspectives for future enzyme immobilization are also given.

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.

Applications of advanced materials in bio-sensing in live cells: Methods and applications

A wide variety of species, such as different ions, reactive oxygen species, and biomolecules play critical roles in many cell functions. These species are responsible for a range of cellular functions such as signaling, and disturbed levels could be involved in many diseases, such as diabetes, cancer, neurodegeneration etc. Thus, sensitive and specific detection methods for these biomarkers could be helpful for early disease detection and mechanistic investigations. New ultrasensitive sensors for detection of markers within living cells are a growing field of research. The present review provides updates in live cell-based biosensing, which have been published within the last decade. These sensors are mainly based on carbon, gold and other metals, and their physicochemical advantages and limitations are discussed. Advanced materials can be incorporated into probes for the detection of various analytes in living cells. The sensitivity is strongly influenced by the intrinsic properties of the nanomaterials as well their shape and size. The mechanisms of action and future challenges in the developments of new methods for live cell based biosensing are discussed.

Nanostructured materials as a host matrix to develop robust peroxidases-based nanobiocatalytic systems

Nanostructured materials constitute an interesting and novel class of support matrices for the immobilization of peroxidase enzymes. Owing to the high surface area, robust mechanical stability, outstanding optical, thermal, and electrical properties, nanomaterials have been rightly perceived as immobilization matrices for enzyme immobilization with applications in diverse areas such as nano-biocatalysis, biosensing, drug delivery, antimicrobial activities, solar cells, and environmental protection. Many nano-scale materials have been employed as support matrices for the immobilization of different classes of enzymes. Nanobiocatalysts, enzymes immobilized on nano-size materials, are more stable, catalytically robust, and could be reused and recycled in multiple reaction cycles. In this review, we illustrate the unique structural/functional features and potentialities of nanomaterials-immobilized peroxidase enzymes in different biotechnological applications. After a comprehensive introduction to the immobilized enzymes and nanocarriers, the first section reviewed carbonaceous nanomaterials (carbon nanotube, graphene, and its derivatives) as a host matrix to constitute robust peroxidases-based nanobiocatalytic systems. The second half covers metallic nanomaterials (metals, and metal oxides) and some other novel materials as host carriers for peroxidases immobilization. The next section vetted the potential biotechnological applications of the resulted nanomaterials-immobilized robust peroxidases-based nanobiocatalytic systems. Concluding remarks, trends, and future recommendations for nanomaterial immobilized enzymes are also given.

2D materials in electrochemical sensors for in vitro or in vivo use

Individual cells and cell populations are at the present time investigated with a myriad of analytical tools. While most of them are commercially available, some of these analytical tools are just emerging from research laboratories and are in the developmental phase. Electrochemical sensors which allow the monitoring of low molecular weight compounds released (and / or uptaken) by cells are among these emerging tools. Such sensors are increasingly built using 2D materials (e.g. graphene-based materials, transition metal dichalcogenides, etc.) with the aim of conferring better analytical performances to these devices. The present work critically reviews studies published during the last 10 years describing electrochemical sensors made with 2D materials and exploited to monitor small compounds (e.g. H₂O₂, ·NO, glucose, etc.) in living biological systems. It also discusses the very few 2D material-based electrochemical sensors which are wearable or usable in vivo. Finally, the present work includes a specific section about 2D material biocompatibility, a fundamental requirement for 2D material-based sensor applications in vitro and in vivo. As such, the review provides a critical view on the state of the art of electrochemical sensors made with 2D materials and used at cellular level and it evaluates the possibility that such sensors will be used on / in the human body on a wider scale.

"Turn-on" ratiometric electrochemical detection of H2O2 in one drop of whole blood sample via a novel microelectrode sensor

Oxidative stress plays an important role in the pathogenesis of many diseases, while the exact mechanism that hydrogen peroxide (H₂O₂) as one of the most abundant reactive oxygen species (ROS) exerts its influence on oxidative stress remains unclear. We developed a novel turn-on ratiometric electrochemical sensor for the detection of H₂O₂ in blood samples. The electrochemical probe 5-(1,2-dithiolan-3-yl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pent-anamide (BA) was designed and synthesized for the selective detection of H₂O₂ via a one-step amide reaction. Meanwhile, Nile Blue A (NB) was optimized as an internal reference molecule, thus enabling accurate quantification of H₂O₂ in a complex environment. BA and NB were then co-assembled onto a carbon fiber microelectrode (CFME) coated with Au cones. The oxidation peak current ratio between BA and NB demonstrated good linearity with the logarithm of the H₂O₂ concentration values ranging from 0.5 μM to 400 μM with a low detection limit of 0.02 μM. The developed sensor showed remarkable selectivity against potential interferences in whole blood samples, especially for ascorbic acid, uric acid, and dopamine. In combination with the unique characteristics of CFME, such as a small size and good biocompatibility, the microsensor was used for rapid analysis of one drop of whole blood sample. This sensor not only creates a new platform for the detection of H₂O₂ in whole blood samples, but also provides a new design strategy of other ROS analysis for early diagnosis of ROS-related diseases, drug discovery processes, and pathological mechanisms.

A robust Mn@FeNi-S/graphene oxide nanocomposite as a high-efficiency catalyst for the non-enzymatic electrochemical detection of hydrogen peroxide

Exploring high-efficiency, stable, and cost-effective electrocatalysts for electrochemical activities is greatly desirable and challenging. Herein, a newly designed hybrid catalyst with manganese-doped FeNi-S encapsulated into graphene oxide (Mn@FeNi-S/GO) with unprecedented electrocatalytic activity was developed by simple one-step heat treatment followed by sonication. X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and N₂ sorption isotherm demonstrated the successful formation of Mn@FeNi-S/GO. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) further confirmed the kinetic-favourable adsorption of hydrogen peroxide (H₂O₂) onto the surface sites of Mn@FeNi-S/GO. Additionally, the synergetic effects between Mn@FeNi-S and GO are regarded as significant contributors to an efficient electron transfer path, and they promote the capture of H₂O₂ in hybrid catalysts. Under an optimal condition, a biosensor-based Mn@FeNi-S/GO electrode exhibits a high sensitivity of 8.929 μA μM^-1 cm^-2 and a detection limit of 8.84 nM with a wide detection range for H₂O₂ and excellent selectivity; also, it is capable of online monitoring H₂O₂ derived from apple juice and human blood serum.

New Reusable Solid Biosensor with Covalent Immobilization of the Horseradish Peroxidase Enzyme: In Situ Liberation Studies of Hydrogen Peroxide by Portable Chemiluminescent Determination

Herein, we reported a chemiluminescent biosensor based on the covalent immobilization of the horseradish peroxidase (HRP) enzyme on a polydimethylsiloxane (PDMS) support to quantify in situ hydrogen peroxide (H₂O₂). The chemiluminescent reaction based on the use of luminol as an oxidizable substrate, with HRP as the catalyst, has been used in order to quantify H₂O₂ as the oxidizing agent. The performance of the proposed biosensor has been demonstrated to determine H₂O₂ liberated by cells in a culture medium and for evaluating the delivery of H₂O₂ from denture cleaner tablets, as examples of application. For both analyses, the results indicated that the biosensor is cost-effective, sensitive, and selective with a detection limit of 0.02 μM and good linearity over the range 0.06-10 μM. Precision was also satisfactory (relative standard deviation, % RSD < 6). The strength of this biosensing system is the simplicity, portability, and reusability of the devices; it can be applied up to 60 times with 90% of its activity maintained.

A H2O2-free electrochemical peptide biosensor based on Au@Pt bimetallic nanorods for highly sensitive sensing of matrix metalloproteinase 2

We construct for the first time a H₂O₂-free electrochemical peptide biosensor based on Au@Pt bimetallic nanorods in neutral substrate solutions for highly sensitive detection of matrix metalloproteinase 2.

Highly monodisperse Pd-Ni nanoparticles supported on rGO as a rapid, sensitive, reusable and selective enzyme-free glucose sensor

In this work, highly monodispersed palladium-nickel (Pd-Ni) nanoparticles supported on reduced graphene oxide (rGO) were synthesized by the microwave-assisted methodology. The synthesized nanoparticles were used for modification of a glassy carbon electrode (GCE) to produce our final product as PdNi@rGO/GCE, which were utilized for non-enzymatic detecting of glucose. In the present study, electrochemical impedance spectroscopy (EIS), chronoamperometry (CA) and, cyclic voltammetry (CV) methods were implemented to investigate the sensing performance of the developed glucose electrode. The modified electrode, PdNi@rGO/GCE, exhibited very noticeable results with a linear working range of 0.05-1.1 mM. Moreover, an ultralow detection limit of 0.15 μM was achieved. According to the results of amperometric signals of the electrodes, no significant change was observed, even after 250 h of operation period. In addition, the highly monodisperse PdNi@rGO/GCE was utilized to electrochemical detection of glucose in real serum samples. In light of the results, PdNi@rGO/GCE has shown an excellent sensing performance and can be used successfully in serum samples for glucose detection and it is suitable for practical and clinical applications.

Organic Electrochemical Transistor for in Situ Detection of H2O2 Released from Adherent Cells and Its Application in Evaluating the In Vitro Cytotoxicity of Nanomaterial

Detection of hydrogen peroxide (H₂O₂) produced by living cells is very significant to fully understand its roles in cellular physiology, as well as providing reliable diagnosis of pathological conditions. However, in situ detection of H₂O₂ released from adherent cells in cellular culture medium is still insufficiently achieved. Here, we report an electrochemical platform for in situ detection of H₂O₂ produced by adherent cells in cellular culture medium. It is based on the use of organic electrochemical transistor (OECT) fabricated on a flexible poly(ethylene terephthalate) substrate and Transwell support. A screen-printed carbon paste electrode was modified with carbon nanotubes and platinum nanoparticles and served as the gate of the device. Under optimal conditions, this device exhibits good modulation and sensitivity. It works in the 0.5 μM to 0.1 mM H₂O₂ concentration range and has a 0.2 μM detection limit. The cells were seeded and grew on the Transwell membrane. Upon being stimulated by N-formylmethionyl-leucyl-phenylalanine peptide, H₂O₂ produced by the adherent cells diffused into the bottom chamber of the Transwell and was in situ detected by OECT. Moreover, evaluating in vitro cytotoxicity of the nanomaterial using the OECT-Transwell platform was realized. This simple electrochemical platform would be of great interest for in vitro cytotoxicity, cellular physiology study, and diagnosis of pathological conditions.

A review on recent advancements in electrochemical biosensing using carbonaceous nanomaterials

This review, with 201 references, describes the recent advancement in the application of carbonaceous nanomaterials as highly conductive platforms in electrochemical biosensing. The electrochemical biosensing is described in introduction by classifying biosensors into catalytic-based and affinity-based biosensors and statistically demonstrates the most recent published works in each category. The introduction is followed by sections on electrochemical biosensors configurations and common carbonaceous nanomaterials applied in electrochemical biosensing, including graphene and its derivatives, carbon nanotubes, mesoporous carbon, carbon nanofibers and carbon nanospheres. In the following sections, carbonaceous catalytic-based and affinity-based biosensors are discussed in detail. In the category of catalytic-based biosensors, a comparison between enzymatic biosensors and non-enzymatic electrochemical sensors is carried out. Regarding the affinity-based biosensors, scholarly articles related to biological elements such as antibodies, deoxyribonucleic acids (DNAs) and aptamers are discussed in separate sections. The last section discusses recent advancements in carbonaceous screen-printed electrodes as a growing field in electrochemical biosensing. Tables are presented that give an overview on the diversity of analytes, type of materials and the sensors performance. Ultimately, general considerations, challenges and future perspectives in this field of science are discussed. Recent findings suggest that interests towards 2D nanostructured electrodes based on graphene and its derivatives are still growing in the field of electrochemical biosensing. That is because of their exceptional electrical conductivity, active surface area and more convenient production methods compared to carbon nanotubes. Graphical abstract Schematic representation of carbonaceous nanomaterials used in electrochemical biosensing. The content is classified into non-enzymatic sensors and affinity/ catalytic biosensors. Recent publications are tabulated and compared, considering materials, target, limit of detection and linear range of detection.

Recent Advances of Porous Graphene: Synthesis, Functionalization, and Electrochemical Applications

Graphene is a 2D sheet of sp² bonded carbon atoms and tends to aggregate together, due to the strong π-π stacking and van der Waals attraction between different layers. Its unique properties such as a high specific surface area and a fast mass transport rate are severely blocked. To address these issues, various kinds of 2D holey graphene and 3D porous graphene are either self-assembled from graphene layers or fabricated using graphene related materials such as graphene oxide and reduced graphene oxide. Porous graphene not only possesses unique pore structures, but also introduces abundant exposed edges and accelerates mass transfer. The properties and applications of these porous graphenes and their composites/hybrids have been extensively studied in recent years. Herein, recent progress and achievements in synthesis and functionalization of various 2D holey graphene and 3D porous graphene are reviewed. Of special interest, electrochemical applications of porous graphene and its hybrids in the fields of electrochemical sensing, electrocatalysis, and electrochemical energy storage, are highlighted. As the closing remarks, the challenges and opportunities for the future research of porous graphene and its composites are discussed and outlined.

Starch-regulated copper-terephthalic acid as a pH/hydrogen peroxide simultaneous-responsive fluorescent probe for lysosome imaging

Lysosome visualization is very important for accurate diagnosis of human diseases. However, currently developed lysosome imaging probes usually have poor specificity and are easily quenched, leading to a low signal to noise ratio in lysosome labeling. To resolve this problem, herein, metal-organic framework-based probes of copper-terephthalic acid (CuBDC) are investigated, which show sensitivity to pH and hydrogen peroxide (H₂O₂), simultaneously. By self-assembling under the template effect of soluble starch, the particle size of CuBDC can be well controlled for entering into cells and locating lysosomes. Based on the Fenton-like reaction, CuBDC can catalyze the decomposition of H₂O₂ into ˙OH, which in turn reacts with CuBDC to generate a stable fluorescent substance. Meanwhile, Cu²⁺ can be released from CuBDC under acidic conditions for reacting with H₂O₂ more thoroughly. And the synthesized CuBDC has a similar attraction to the electrophilic ˙OH at different pH values owing to the residual soluble starch in the particles. The above properties cause CuBDC to have a stable fluorescence signal with low pH values and high H₂O₂ concentration, simultaneously. The fluorescence imaging experiments in HeLa cells demonstrate that CuBDC acting as a pH/H₂O₂ responsive fluorescent probe holds great promise for lysosome-specific imaging.