In Situ Growth of Surfactant-Free Gold Nanoparticles on Nitrogen-Doped Graphene Quantum Dots for Electrochemical Detection of Hydrogen Peroxide in Biological Environments

Application of the Electrospinning Technique in Electrochemical Biosensors: An Overview

Electrospinning is a cost-effective and flexible technology for producing nanofibers with large specific surface areas, functionalized surfaces, and stable structures. In recent years, electrospun nanofibers have attracted more and more attention in electrochemical biosensors due to their excellent morphological and structural properties. This review outlines the principle of electrospinning technology. The strategies of producing nanofibers with different diameters, morphologies, and structures are discussed to understand the regulation rules of nanofiber morphology and structure. The application of electrospun nanofibers in electrochemical biosensors is reviewed in detail. In addition, we look towards the future prospects of electrospinning technology and the challenge of scale production.

Multifunctional N, Fe-doped carbon dots with peroxidase-like activity for the determination of H2O2 and ascorbic acid and cell protection against oxidation

Multifunctional N, Fe-doped carbon dots (N, Fe-CDs) were synthesized by the one-step hydrothermal method using ferric ammonium citrate and dicyandiamide as raw materials. The N, Fe-CDs exhibited peroxidase-like (POD) activity by catalyzing the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) to the green oxidation state ox-TMB in the presence of hydrogen peroxide (H2O2). Subsequently, based on the POD activity of N, Fe-CDs, an efficient and sensitive colorimetric method for the detection of H2O2 and ascorbic acid (AA) was established with a limit of detection of 0.40 µM and 2.05 µM. The proposed detection method has been successfully applied to detect AA in fruit juice, vitamin C tablets, and human serum samples and has exhibited excellent application prospects in biotechnology and food fields. Furthermore, N, Fe-CDs also showed a protective effect on the cell damage caused by H2O2 and could be used as an antioxidant agent.

Macromolecule-Nanoparticle-Based Hybrid Materials for Biosensor Applications

Biosensors function as sophisticated devices, converting biochemical reactions into electrical signals. Contemporary emphasis on developing biosensor devices with refined sensitivity and selectivity is critical due to their extensive functional capabilities. However, a significant challenge lies in the binding affinity of biosensors to biomolecules, requiring adept conversion and amplification of interactions into various signal modalities like electrical, optical, gravimetric, and electrochemical outputs. Overcoming challenges associated with sensitivity, detection limits, response time, reproducibility, and stability is essential for efficient biosensor creation. The central aspect of the fabrication of any biosensor is focused towards forming an effective interface between the analyte electrode which significantly influences the overall biosensor quality. Polymers and macromolecular systems are favored for their distinct properties and versatile applications. Enhancing the properties and conductivity of these systems can be achieved through incorporating nanoparticles or carbonaceous moieties. Hybrid composite materials, possessing a unique combination of attributes like advanced sensitivity, selectivity, thermal stability, mechanical flexibility, biocompatibility, and tunable electrical properties, emerge as promising candidates for biosensor applications. In addition, this approach enhances the electrochemical response, signal amplification, and stability of fabricated biosensors, contributing to their effectiveness. This review predominantly explores recent advancements in utilizing macrocyclic and macromolecular conjugated systems, such as phthalocyanines, porphyrins, polymers, etc. and their hybrids, with a specific focus on signal amplification in biosensors. It comprehensively covers synthetic strategies, properties, working mechanisms, and the potential of these systems for detecting biomolecules like glucose, hydrogen peroxide, uric acid, ascorbic acid, dopamine, cholesterol, amino acids, and cancer cells. Furthermore, this review delves into the progress made, elucidating the mechanisms responsible for signal amplification. The Conclusion addresses the challenges and future directions of macromolecule-based hybrids in biosensor applications, providing a concise overview of this evolving field. The narrative emphasizes the importance of biosensor technology advancement, illustrating the role of smart design and material enhancement in improving performance across various domains.

A dual-mode sensing platform coupling two-signal ratiometric and colorimetric methods for detecting Au3+ based on surface state-regulated carbon nanodot

The considerable risk posed by Au3+ residues to the environment and human health has sparked interest in researching Au3+ monitoring techniques. The detection results in the usual ratio mode are more reliable. In this work, we develop a dual-mode strategy based on reducing carbon dots coupling with two-signal ratiometric and colorimetric methods for high-sensitivity, good-selectivity, and wide-range detection of Au3+. Cyan carbon dots (C-CDs) were synthesized by a simple and efficient one-step hydrothermal method. The C-CDs with rich amino group used m-phenylenediamine as carbon source, which made it have the potential as a reducing agent. After the addition of Au3+, Au3+ was reduced to Au0, generating stable gold nanoparticles (AuNPs). The fluorescence signal (F490) of C-CDs decreased. At the same time, the large size of AuNPs enhances the second-order scattering signal (S770) and produces the UV-visible absorption peak of AuNPs. Therefore, the dual-mode sensing strategy combining S770/F490 ratiometric and colorimetric detection of Au3+ is realized with high accuracy and sensitivity. Au3+ was determined in real samples and a good recovery was obtained. The dual-mode method has good performance and practicality, so it shows great potential for environment testing in a simple and reliable way.

Carbon dots for staining bacterial dead cells and distinguishing dead/alive bacteria

The small molecular dyes such as propidium iodide (PI) always suffer from photo-bleaching and potential toxicity. To tackle the problems, a type of nontoxic carbon dots (CDs) was obtained for dead/alive bacterial distinguishing. This kind of carbon dots has an average size of 1.91 nm and owns carboxyl groups, emerging as excellent candidates for imaging bacterial cells. The negative charges of carboxyl groups lead their avoidance of alive cells while their small size facilitates penetration of dead cells. This kind of nontoxic CDs has effectively differentiated between and alive ones, presenting a highly promising green dye comparing with traditional small molecular dyes.

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.

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.

Red Emission Carbon Nanoparticles Which Can Simultaneously Responding to Hypochlorite and pH

Multi-targets detection has obtained much attention because this sensing mode can realize the detection of multi-targets simultaneously, which is helpful for biomedical analysis. Carbon nanoparticles have attracted extensive attention due to their superior optical and chemical properties, but there are few reports about red emission carbon nanoparticles for simultaneous detection of multi-targets. In this paper, a red emission fluorescent carbon nanoparticles were prepared by 1, 2, 4-triaminobenzene dihydrochloride at room temperature. The as-prepared red emission fluorescent carbon nanoparticles exhibited strong emission peak located at 635 nm with an absolute quantum yield up to 24%. They showed excellent solubility, high photostability and good biocompatibility. Furthermore, it could sensitively and selectively response to hypochlorite and pH, thus simultaneous detection of hypochlorite and pH was achieved by combining the red emission fluorescent carbon nanoparticles with computational chemistry. The formation mechanisms of red emission fluorescent carbon nanoparticles and their response to hypochlorite and pH were investigated, respectively.

Flexible electrode-based voltammetric detection of Y (III) ions in real water samples using an efficient CyDTA complexing strategy

The rapid detection of rare earth elements is crucial in various fields, such as materials science, biomedicine, and water quality assessment. However, no studies have reported on the detection of yttrium (Y) using electrochemical sensor-based devices. In this study, we present an innovative method for detecting Y(III) ions in aquatic environments using an electroanalytical detection platform. We have developed a complexation catalytic method that integrates trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA) and silver nanoparticles (Ag NPs), thereby enhancing the adsorption and electrochemical response of Y(III) ions. The modified electrode demonstrates an 18-fold increase in the response signal of the Y(III) reduction peak compared to the bare LIG electrode. To elucidate the electrocatalytic mechanism, we conducted various interface characterization methods and DFT simulations. The Ag-CyDTA/LIG electrode exhibits excellent detection performance, with a broad linear dynamic range of 1 × 10-6 to 0.01 g/L and an exceptionally low detection limit of 0.02 μg/L. Significantly, we successfully employed the electrochemical sensing platform to analyze real water samples from rare earth ore, marking the first report on the voltammetric detection of Y(III) ions in real water samples using a flexible electrode. These findings offer a promising technical solution for the practical detection of Y(III) ions.

High-efficiency upconversion process in cobalt and neodymium doped graphene QDs for biomedical applications

Multiphoton absorbing upconversion nanoparticles are emerging as bioimaging materials but are limited by the low quantum yield of their visible fluorescence. This article contains colloids of graphene quantum dots (GQDs), Neodymium, and Cobalt doped Graphene Quantum dots (Co-GQDs and Nd-GQDs) surrounded by carboxylic acids are synthesized which especially are suitable for bio applications; in this way, carboxylic acid groups exchanged by Amoxicillin as an antibiotic with bactericidal activity. The XRD diffraction method, TEM microscope, UV-Vis, and photoluminescence spectroscopies characterize the synthesized materials. The synthesized Quantum dots (QDs) exhibit upconversion properties and their emission is centered at 480 nm, but a red shift was observed with the increase of the excitation wavelength. In the emission spectra of synthesized QDs that can be related to the defect levels introduced by passivation of the QDs in the structure, the results show that with the interaction of the surface QDs with more carboxylic groups, the redshift is not observed. As the results indicate an increase in the intensity of upconversion emission is recorded for Co-GQDs and Nd-GQDs. The absolute quantum efficiency (QY) for Co-GQDs and Nd-GQDs were determined to be 41% and 100% more than GQDs respectively. DFT calculations indicate a strong bond between graphene and cobalt and Neodymium atoms. In doped materials, there are trap levels between the band gap of the GQDs which are responsible for increasing the intensity of the upconversion phenomenon.

Electrochemical Biosensors for Whole Blood Analysis: Recent Progress, Challenges, and Future Perspectives

Whole blood, as one of the most significant biological fluids, provides critical information for health management and disease monitoring. Over the past 10 years, advances in nanotechnology, microfluidics, and biomarker research have spurred the development of powerful miniaturized diagnostic systems for whole blood testing toward the goal of disease monitoring and treatment. Among the techniques employed for whole-blood diagnostics, electrochemical biosensors, as known to be rapid, sensitive, capable of miniaturization, reagentless and washing free, become a class of emerging technology to achieve the target detection specifically and directly in complex media, e.g., whole blood or even in the living body. Here we are aiming to provide a comprehensive review to summarize advances over the past decade in the development of electrochemical sensors for whole blood analysis. Further, we address the remaining challenges and opportunities to integrate electrochemical sensing platforms.

Microwave prepared nitrogen and sulfur co-doped carbon quantum dots for rapid determination of ascorbic acid through a turn off-on strategy

A simple and eco-friendly microwave method was applied for the preparation of highly fluorescent nitrogen and sulfur co-doped carbon quantum dots (NS-CQDs) and used for the determination of ascorbic acid (ASC) in pharmaceutical dosage forms. The prepared NS-CQDs had bright blue fluorescence at a maximum emission wavelength of 440 nm, after excitation with 350 nm, with a quantum yield of 62.5 %. The developed NS-CQDs were prepared from citric acid and l-cysteine in one minute. The native fluorescence of NS-CQDs was quenched by ferric ions due to the formation of non-fluorescent CQDs/ Fe³⁺ complex. The quenched fluorescence could be restored by the addition of ASC due to the reducing properties of ASC which converts Fe³⁺ to Fe²⁺. The method was found linear over the concentration range of 2.0-100 μg/mL, with a limit of detection was 0.6 μg/mL and a coefficient of determination of 0.9965. The proposed method was cross-validated and statistically compared with a reported HPLC method. The results indicated that the developed method was greener, according to the analytical eco-scale and the green analytical procedure index (GAPI). The prepared NS-CQDs were used for spectrofluorometric determination of ASC in pharmaceutical dosage forms, with percentage recoveries ranging between 98 and 102 %, and relative standard deviations less than 2 %. The method was easy, rapid, reliable, and sensitive and did not require expensive reagents or sophisticated equipment.

Upconversion nanoparticles anchored MnO2 nanosheets for luminescence "turn on" detecting hydrogen peroxide

The sensitively and reliably detecting hydrogen peroxide (H₂O₂) is of significant for biology and environment protection fields. Herein, we reported a high sensitive H₂O₂ nanoprobe based on upconversion nanoparticles (UCNPs) anchored MnO₂ nanosheets. In which, DNA modified NaYF₄@NaYF₄:Yb,Tm core-shell nanoparticles were anchored onto the MnO₂ nanosheets surface via π-π stacking. Owing to the luminescence resonance energy transfer, the blue luminescence of UCNPs was effectively quenched by MnO₂ nanosheets, then the luminescence could be restored by adding H₂O₂ for reducing MnO₂ to Mn²⁺, and achieving a H₂O₂ concentration-dependent luminescence change, the detection limit could reach to 0.23 nM (S/N = 3). The proposed method could detect H₂O₂ in serum, lake water and real samples. Thus, a desired upconversion luminescence sensing strategy for detection H₂O₂ in life and environmental analysis was successfully constructed. It may be provide a potential tool in disease diagnosis and environmental monitoring fields.

A non-enzymatic, biocompatible electrochemical sensor based on N-doped graphene quantum dot-incorporated SnS2 nanosheets for in situ monitoring of hydrogen peroxide in breast cancer cells

The current study reports the design and construction of enzyme-free sensor using N-doped graphene quantum dots (N-GQDs)-decorated tin sulfide nanosheets (SnS₂) for in situ monitoring of H₂O₂ secreted by human breast cancer cells. N-GQDs nanoparticles having a size of less than 1 nm were incorporated into SnS₂ nanosheets to form an N-GQDs@SnS₂ nanocomposite using a simple hydrothermal approach. The resulting hybrid material was an excellent electrocatalyst for the reduction of H₂O₂, owing to the combined properties of highly conductive N-GQDs and SnS₂ nanosheets. The N-GQDs@SnS₂-based sensing platform demonstrated substantial sensing ability, with a detection range of 0.0125-1128 µM and a limit of detection of 0.009 µM (S/N = 3). The sensing performance of N-GQDs@SnS₂ was highly stable, selective, and reproducible. The practical application of the N-GQDs@SnS₂ sensor was successfully demonstrated by quantifying H₂O₂ in lens cleaner, human urine, and saliva samples. Finally, the N-GQDs@SnS₂ electrode was successfully applied for the real-time monitoring of H₂O₂ released from breast cancer cells and mouse fibroblasts. This study paves the way to designing efficient non-enzymatic electrochemical sensors for various biomolecule detection using a simple method.

Electrophoretic Deposition of Co3O4 Particles/Reduced Graphene Oxide Composites for Efficient Non-Enzymatic H2O2 Sensing

In this work, the facile fabrication of Co₃O₄ particles/reduced graphene oxide (Co₃O₄/rGO) composites on Indium tin oxide (ITO) slide was achieved by an electrophoretic deposition and annealing process. The deposition time and ratio of the precursors were optimized. Structural characterization and chemical composition investigation indicated successful loading of Co₃O₄ particles on graphene sheets. When applied as a non-enzymatic H₂O₂ sensor, Co₃O₄/rGO showed significant electrocatalytic activity, with a wide linear range (0.1-19.5 mM) and high sensitivity (0.2247 mA mM^-1 cm^-2). The good anti-interference ability, reproducibility, and long-term stability of the constructed sensor were also presented. The application of Co₃O₄/rGO in real sample analysis was evaluated in human urine sample with satisfactory results, indicating the feasibility of the sensor in physiological and medical applications.

Innovations in the synthesis of graphene nanostructures for bio and gas sensors

Sensors play a significant role in modern technologies and devices used in industries, hospitals, healthcare, nanotechnology, astronomy, and meteorology. Sensors based upon nanostructured materials have gained special attention due to their high sensitivity, precision accuracy, and feasibility. This review discusses the fabrication of graphene-based biosensors and gas sensors, which have highly efficient performance. Significant developments in the synthesis routes to fabricate graphene-based materials with improved structural and surface properties have boosted their utilization in sensing applications. The higher surface area, better conductivity, tunable structure, and atom-thick morphology of these hybrid materials have made them highly desirable for the fabrication of flexible and stable sensors. Many publications have reported various modification approaches to improve the selectivity of these materials. In the current work, a compact and informative review focusing on the most recent developments in graphene-based biosensors and gas sensors has been designed and delivered. The research community has provided a complete critical analysis of the most robust case studies from the latest fabrication routes to the most complex challenges. Some significant ideas and solutions have been proposed to overcome the limitations regarding the field of biosensors and hazardous gas sensors.

Nanotechnology‐based electrochemical biosensors for monitoring breast cancer biomarkers

Breast cancer is categorized as the most widespread cancer type among women globally. On-time diagnosis can decrease the mortality rate by making the right decision in the therapy procedure. These features lead to a reduction in medication time and socioeconomic burden. The current review article provides a comprehensive assessment for breast cancer diagnosis using nanomaterials and related technologies. Growing use of the nano/biotechnology domain in terms of electrochemical nanobiosensor designing was discussed in detail. In this regard, recent advances in nanomaterial applied for amplified biosensing methodologies were assessed for breast cancer diagnosis by focusing on the advantages and disadvantages of these approaches. We also monitored designing methods, advantages, and the necessity of suitable (nano) materials from a statistical standpoint. The main objective of this review is to classify the applicable biosensors based on breast cancer biomarkers. With numerous nano-sized platforms published for breast cancer diagnosis, this review tried to collect the most suitable methodologies for detecting biomarkers and certain breast cancer cell types.

Graphene and Its Derivatives: Synthesis and Application in the Electrochemical Detection of Analytes in Sweat

Wearable sensors and invasive devices have been studied extensively in recent years as the demand for real-time human healthcare applications and seamless human-machine interaction has risen exponentially. An explosion in sensor research throughout the globe has been ignited by the unique features such as thermal, electrical, and mechanical properties of graphene. This includes wearable sensors and implants, which can detect a wide range of data, including body temperature, pulse oxygenation, blood pressure, glucose, and the other analytes present in sweat. Graphene-based sensors for real-time human health monitoring are also being developed. This review is a comprehensive discussion about the properties of graphene, routes to its synthesis, derivatives of graphene, etc. Moreover, the basic features of a biosensor along with the chemistry of sweat are also discussed in detail. The review mainly focusses on the graphene and its derivative-based wearable sensors for the detection of analytes in sweat. Graphene-based sensors for health monitoring will be examined and explained in this study as an overview of the most current innovations in sensor designs, sensing processes, technological advancements, sensor system components, and potential hurdles. The future holds great opportunities for the development of efficient and advanced graphene-based sensors for the detection of analytes in sweat.

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

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

A reusable and sensitive electrochemical sensor for determination of idarubicin in environmental and biological samples based on NiFe2O4 nanospheres anchored N-doped graphene quantum dots composite; an electrochemical and molecular docking investigation

An ultrasensitive and selective voltammetric sensor with ultra-trace level detection limit is introduced for idarubicin (IDA) determination in real samples. The as-synthesized nanocomposite was characterized by several techniques, including Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, Energy-dispersive X-ray spectroscopy (EDX), and Field emission scanning electron microscopy (FE-SEM). The electrocatalytic performance of the developed electrode was observed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and chronoamperometry. The limit of detection (LOD) of the developed sensor for idarubicin is 1.0 nM, and the response is found to be in the dynamic concentration range of 0.01-1.9 μmol/L in a Britton-Robinson buffer (B-R, pH = 6.0). Moreover, the fabricated electrode illustrated high selectivity with good repeatability and reproducibility for diagnosing idarubicin as an anthracycline antileukemic drug. Furthermore, to evaluate the validity of the recommended method, three real samples, including human plasma, urine, and water samples, were analyzed with satisfactory recovery and compared with high-performance liquid chromatography (HPLC). The minor groove-binding mode of interaction was also supported by docking simulation studies, emphasizing that IDA can bind to ds-DNA preferably and confirmed experimental results. The reduced assay time and the possibility of measuring a single sample with another anticancer drug without any interference are significant advantages compared to the HPLC. The developed and validated sensor could be a valuable point-of-care diagnostic tool for IDA quantification in patients.

Influence of Manganese Oxide on the Esthetic Efficacy and Toxicity Caused by Conventional In-office Tooth Bleaching Therapy

OBJECTIVE

This study aimed to evaluate the esthetic efficacy, cytotoxicity, and kinetics of decomposition of hydrogen peroxide (H2O2) present in a commercial bleaching gel with 35% H2O2 (BG35%) chemically activated with manganese oxide (MnO2).

METHODS AND MATERIALS

After incorporating 2 mg/mL, 6 mg/mL, and 10 mg/mL of MnO2 into BG35%, the stability of pH and temperature of the products were analyzed. To assess the esthetic efficacy (ΔE and ΔWI), the BG35%s with MnO2 were applied for 45 minutes on enamel/dentin discs (DiE/D). BG35% or no treatment were used as positive (PC) and negative (NC) controls, respectively. To analyze the cell viability (CV) and oxidative stress (OXS), the same bleaching protocols were performed on DiE/D adapted to artificial pulp chambers. The extracts (culture medium + gel components that diffused through the discs) were applied to pulp cells and submitted to H2O2 quantification. BG35% with MnO2 that showed the best results was evaluated relative to kinetic decomposition of H2O2, with consequent generation of free radicals (FR) and hydroxyl radicals (OH•). The data were submitted to the one-way analysis of variance complemented by Tukey post-test (α=0.05). Data on kinetics of H2O2 decomposition were submitted to the Student's-t test (α=0.05).

RESULTS

All the BG35%s with MnO2 showed stability of pH and temperature, and the gel with 10 mg/mL of this activator had an esthetic efficacy 31% higher than that of the PC (p<0.05). Reduction in OXS and trans-amelodentinal diffusion of H2O2 occurred when all the BG35%s with MnO2 were used. The addition of 6 and 10 mg/mL of MnO2 to BG35% increased the CV in comparison with PC, confirmed by the cell morphology analysis. An increase in FR and OH• formation was observed when 10 mg/mL of MnO2 was added to BG35%.

CONCLUSION

Catalysis of BG35% with MnO2 minimized the trans-amelodentinal diffusion of H2O2 and toxicity of the product to pulp cells. BG35% containing 10 mg/mL of MnO2 potentiated the decomposition of H2O2, enhancing the generation of FR and OH•, as well as the efficacy of the in-office tooth therapy.

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.

Metal–Organic Frameworks for Electrocatalytic Sensing of Hydrogen Peroxide

The electrochemical detection of hydrogen peroxide (H₂O₂) has become more and more important in industrial production, daily life, biological process, green energy chemistry, and other fields (especially for the detection of low concentration of H₂O_2). Metal organic frameworks (MOFs) are promising candidates to replace the established H₂O₂ sensors based on precious metals or enzymes. This review summarizes recent advances in MOF-based H₂O₂ electrochemical sensors, including conductive MOFs, MOFs with chemical modifications, MOFs-composites, and MOF derivatives. Finally, the challenges and prospects for the optimization and design of H₂O₂ electrochemical sensors with ultra-low detection limit and long-life are presented.

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

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

Multifunctional flexible contact lens for eye health monitoring using inorganic magnetic oxide nanosheets

As a non-invasive innovative diagnosis platform, advanced flexible contact lenses can dynamically monitor vital ocular indicators, spot abnormalities and provide biofeedback guidance for real-time diagnosis and rehabilitation tracking of chronic eye diseases. However, most of the state-of-the-art reported contact lenses either can only monitor a single indicator at a time or realize multifunctional integration based on multiple materials. Herein, we developed a flexible multifunctional contact lens based on inorganic γ-Fe₂O₃@NiO magnetic oxide nanosheets, which can be attached conformally and seamlessly to the eyeball to simultaneously monitor glucose level in tears, eyeball movement, and intraocular pressure. The optimized contact lens has a reliable glucose detection limit (0.43 μmol), superior eye movement measurement accuracy (95.27%) and high intraocular pressure sensitivity (0.17 MHz mmHg^− 1). This work presents a concept in the biochemical and biophysical integrated sensing of ocular signals using contact lens via an innovative material, and provides a personalized and efficient way for health management.

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.

In-situ preparation of lactate-sensing membrane for the noninvasive and wearable analysis of sweat

In the wearable electrochemical biosensors, sensing signal duration is significantly dependent on the long-term stability of functional materials modified on the flexible substrate, the effect of pH changes of sweat on the sensing device and signal fluctuation caused by the bending of sensor. Here, we proposed a wearable biosensor based on the lactate-sensing membrane mainly constituted by Prussian blue (PB), reduced graphene oxide (rGO), Au nanoparticles and lactate oxidase (LOx). Based on the in-situ layer-by-layer spin-coating preparation method, the electrode surface was covered with an extensive and uniform PB/GO membrane with a high stability. After the electro-reduction of GO to rGO and the combination of urchin-like Au particles with sufficient tentacles to LOx, the sensing membrane showed the improved electron transport from the enzyme active center to the electrode. Therefore, the wearable biosensor achieved a high sensitivity of 40.6 μA mM^-1 cm^-2 in a range of 1-222 μM and a low sensitivity of 1.9 μA mM^-1 cm^-2 in a wide range of 0.222-25 mM, satisfying the requirement of the typical test. In addition, with the excellent running and mechanical stability, the lactate biosensor was successfully applied on volunteers' skin for real-time monitoring of perspiration in vivo. The results were comparable with ex vivo measurements achieved by a commercial lactate sensor. The wearable electrochemical biosensor provides a good candidate in the future for the evaluation of human sweat in sports and biomedical fields.

Atomistic Simulations of Dopamine Diffusion Dynamics on a Pristine Graphene Surface

Carbon microelectrodes enable in vivo detection of neurotransmitters, and new electrodes aim to optimize the carbon surface. However, atomistic detail on the diffusion and orientation of neurotransmitters near these surfaces is lacking. Here, we employ molecular dynamics simulations to investigate the surface diffusion of dopamine (DA), its oxidation product dopamine-o-quinone (DOQ), and their protonated forms on the pristine basal plane of flat graphene. We find that all DA species rapidly adsorb to the surface and remain adsorbed, even without a holding potential or graphene surface defects. We also find that the diffusivities of the adsorbed and the fully solvated DA are similar and that the protonated species diffuse more slowly on the surface than their corresponding neutral forms, while the oxidized species diffuse more rapidly. Structurally, we find that the underlying graphene lattice has little influence over the molecular adsorbate's lateral position, and the vertical placement of the amine group on dopamine is highly dependent upon its charge. Finally, we find that solvation has a large effect on surface diffusivities. These first results from molecular dynamics simulations of dopamine at the aqueous-graphene interface show that dopamine diffuses rapidly on the surface, even without an applied potential, and provide a basis for future simulations of neurotransmitter structure and dynamics on advanced carbon materials electrodes.

Bioactive Graphene Quantum Dots Based Polymer Composite for Biomedical Applications

Today, nanomedicine seeks to develop new polymer composites to overcome current problems in diagnosing and treating common diseases, especially cancer. To achieve this goal, research on polymer composites has expanded so that, in recent years, interdisciplinary collaborations between scientists have been expanding day by day. The synthesis and applications of bioactive GQD-based polymer composites have been investigated in medicine and biomedicine. Bioactive GQD-based polymer composites have a special role as drug delivery carriers. Bioactive GQDs are one of the newcomers to the list of carbon-based nanomaterials. In addition, the antibacterial and anti-diabetic potentials of bioactive GQDs are already known. Due to their highly specific surface properties, π-π aggregation, and hydrophobic interactions, bioactive GQD-based polymer composites have a high drug loading capacity, and, in case of proper correction, can be used as an excellent option for the release of anticancer drugs, gene carriers, biosensors, bioimaging, antibacterial applications, cell culture, and tissue engineering. In this paper, we summarize recent advances in using bioactive GQD-based polymer composites in drug delivery, gene delivery, thermal therapy, thermodynamic therapy, bioimaging, tissue engineering, bioactive GQD synthesis, and GQD green resuscitation, in addition to examining GQD-based polymer composites.

A highly sensitive ratiometric fluorescent sensor for copper ions and cadmium ions in scallops based on nitrogen doped graphene quantum dots cooperating with gold nanoclusters

Based on the electrostatic interaction, we constructed a ratiometric fluorescence nanomixture of graphene quantum dots-gold nanoclusters (GQDs-AuNCs) for the quantitative detection of Cu²⁺ and Cd²⁺. When Cu²⁺ or Cd²⁺ was added into the reaction system, the fluorescence of GSH-AuNCs at 565 nm can be quenched by Cu²⁺ and enhanced by Cd²⁺ while the intensity of N-GQDs at 403 nm stayed constant. Under the optimized conditions, the fluorescence intensity ratio (I₅₆₅/I₄₀₃) of the GQDs-AuNCs system was proportional to the concentration of Cu²⁺ and Cd²⁺ in the range of 8×10^-8 mol/L-6×10^-6 mol/L and 1×10^-6 mol/L-4×10^-5 mol/L, respectively, with detection limits of 4.12×10^-9 mol/L and 9.43×10^-7 mol/L, respectively. In the presence of Cu²⁺ and Cd²⁺, the paper-based vision sensor would produce visible fluorescent color changes, which can be used for rapid detection on site. The method has been successfully applied to the determination of Cu²⁺ and Cd²⁺ in scallops with satisfactory results.

A graphene-printed paper electrode for determination of H2O2 in municipal wastewater during the COVID-19 pandemic

Graphene prepared through exfoliation process was printed on paper substrate using inkjet-printer and then printed paper electrode was used as an electrochemical sensor for analysis of H2O2 in cyclic voltammetry.

Self-Terminated Electroless Deposition of Surfactant-Free and Monodispersed Pt Nanoparticles on Carbon Fiber Microelectrodes for Sensitive Detection of H2O2 Released from Living Cells

We report a self-terminated electroless deposition method to prepare surfactant-free and monodispersed Pt nanoparticle (NP)-modified carbon fiber microelectrodes (Pt NP/CFEs) for electrochemical detection of hydrogen peroxide (H₂O₂) released from living cells. The surfactant-free and monodispersed Pt NPs with a uniform size of 65 nm are spontaneously deposited on a CFE surface by immersing an exposed carbon fiber (CF) of CFE in the PtCl₄^2- solution, in which an exposed CF can be used as the reducing agent and stabilizer. A self-terminated electroless deposition method is demonstrated, in which the density and size of Pt NPs on a CFE surface do not increase when the reaction time increases from 20 to 60 min. The self-terminated electroless deposition process not only can effectively avoid any manual electrode modification and thus largely minimize person-to-person and electrode-to-electrode deviations but also can avoid the use of any extra reductant or surfactant in the fabrication process. Therefore, Pt NPs/CFEs, with good reproducibility and sensitivity, not only exhibit high electrocatalytic activity toward the oxidation of H₂O₂ but also maintain the spatial resolution of CFEs. Moreover, Pt NPs/CFEs can detect H₂O₂ with a wide linear range of 0.5-80 μM and a low detection limit of 0.17 μM and then can be successfully applied in the monitoring of H₂O₂ released from RAW 264.7 cells. The self-terminated electroless deposition method can also be extended to selectively prepare other metal NP-modified CFEs, such as Au NPs/CFEs or Ag NPs/CFEs, by choosing the metal ions with higher reduction potential as precursors. This work provides a simple, straightforward, and general method for the preparation of small, surfactant-free, and monodispersed metal NP-modified CFEs with high sensitivity, reproducibility, and spatial resolution.

Facile Fabrication of Highly Fluorescent N-Doped Carbon Quantum Dots Using an Ultrasonic-Assisted Hydrothermal Method: Optical Properties and Cell Imaging

Fluorescent N-doped carbon nanodots (CNDs) are a type of environmentally friendly nanomaterial that is promising for application in cell imaging and optoelectronics. In this paper, a natural amino acid (l-glutamic acid) was used as a precursor, and two different morphological and structured N-doped carbon quantum dots (CQDs) were synthesized via a one-step ultrasonic-assisted hydrothermal method at 230 and 250 °C. Various microscopy and spectroscopy techniques were employed to characterize the morphology, structure, optical properties, and stability of the CQDs. The results showed that N-CQDs-1 are new CNDs composed of amorphous carbon with a large amount of pyroglutamic acid, and N-CQDs-2 are composed of pure amorphous carbon. The CQDs exhibit excellent optical properties, such as 40.5% quantum yield, strong photobleaching resistance, and superior photostability. Combining the fluorescence lifetimes and radiative and non-radiative decay constants, the photoluminescence mechanism of the CQDs was qualitatively explained. The two CQDs were used for BV2 cell imaging and showed good results, implying the ultrasonic-assisted hydrothermal approach as a facile method to obtain structure- and morphology-controllable N-doped CQDs with prospect for application in cell imaging.

Recent Advances on Functional Nucleic-Acid Biosensors

In the past few decades, biosensors have been gradually developed for the rapid detection and monitoring of human diseases. Recently, functional nucleic-acid (FNA) biosensors have attracted the attention of scholars due to a series of advantages such as high stability and strong specificity, as well as the significant progress they have made in terms of biomedical applications. However, there are few reports that systematically and comprehensively summarize its working principles, classification and application. In this review, we primarily introduce functional modes of biosensors that combine functional nucleic acids with different signal output modes. In addition, the mechanisms of action of several media of the FNA biosensor are introduced. Finally, the practical application and existing problems of FNA sensors are discussed, and the future development directions and application prospects of functional nucleic acid sensors are prospected.

Fabrication strategies and surface tuning of hierarchical gold nanostructures for electrochemical detection and removal of toxic pollutants

The intensive research on the synthesis and characterization of gold (Au) nanostructures has been extensively documented over the last decades. These investigations allow the researchers to understand the relationships between the intrinsic properties of Au nanostructures such as particle size, shape, morphology, and composition to synthesize the Au nano/hybrid nanostructures with novel physicochemical properties. By tuning the properties above, these nanostructures are extensively employed to detect and remove trace amounts of toxic pollutants from the environment. This review attempts to document the achievements and current progress in Au-based nanostructures, general synthetic and fabrication strategies and their utilization in electrochemical sensing and environmental remediation applications. Additionally, the applications of Au nanostructures (e.g., as adsorbents, sensing platforms, catalysts, and electrodes) and advancements in the field of electrochemical sensing of different target analytes (e.g., proteins, nucleic acids, heavy metals, small molecules, and antigens) are summarized. The literature survey concludes the existing methods for the detection of toxic contaminants at various concentration levels. Finally, the existing challenges and future research directions on electrochemical sensing and degradation of toxic contaminants using Au nanostructures are defined.

Enzyme-Encapsulated Zeolitic Imidazolate Frameworks Formed Inside the Single Glass Nanopore: Catalytic Performance and Sensing Application

Metal-organic frameworks (MOFs) can improve the stability and activity of enzymes under the MOF encapsulation. However, it remains a challenge to explore the effects of the MOF environment on enzymatic activity in a confined space. In this work, we immobilized the enzyme inside a glass nanopore to study the catalytic activity and stability of the enzyme in the MOF environment. Horseradish peroxidase (HRP) is encapsulated in zeolitic imidazolate framework-90 (ZIF-90) and zeolitic imidazolate framework-8 (ZIF-8), which are used as the catalytic platforms. The HRP can catalyze 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS) molecules to generate ABTS⁺ ions, and the change of the transmembrane ion current will be monitored in real time. As the concentration of H₂O₂ increases, the amount of produced ABTS⁺ will increase; thus, the ionic current increases. The effects of the MOF structure on enzyme activity and stability are also investigated. The HRP encapsulated in the MOF and modified inside the nanopore provides a novel and unlabeled design for studying enzymatic catalysis in a confined environment, which should have extensive applications in chemical-/bio-sensing, electrocatalysis, and fundamental electrochemistry.

A nanostructured microfluidic device for plasmon-assisted electrochemical detection of hydrogen peroxide released from cancer cells

Non-invasive liquid biopsies offer hope for a rapid, risk-free, real-time glimpse into cancer diagnostics. Recently, hydrogen peroxide (H₂O₂) was identified as a cancer biomarker due to its continued release from cancer cells compared to normal cells. The precise monitoring and quantification of H₂O₂ are hindered by its low concentration and the limit of detection (LOD) in traditional sensing methods. Plasmon-assisted electrochemical sensors with their high sensitivity and low LOD make a suitable candidate for effective detection of H₂O₂, yet their electrical properties need to be improved. Here, we propose a new nanostructured microfluidic device for ultrasensitive, quantitative detection of H₂O₂ released from cancer cells in a portable fashion. The fluidic device features a series of self-organized gold nanocavities, enhanced with graphene nanosheets having optoelectrical properties, which facilitate the plasmon-assisted electrochemical detection of H₂O₂ released from human cells. Remarkably, the device can successfully measure the released H₂O₂ from breast cancer (MCF-7) and prostate cancer (PC3) cells in human plasma. Briefly, direct amperometric detection of H₂O₂ under simulated visible light illumination showed a superb LOD of 1 pM in a linear range of 1 pM-10 μM. We thoroughly studied the formation of self-organized plasmonic nanocavities on gold electrodes via surface and photo-electrochemical characterization techniques. In addition, the finite-difference time domain (FDTD) simulation of the electric field demonstrates the intensity of charge distribution at the nanocavity structure edges under visible light illumination. The superb LOD of the proposed electrode combining gold plasmonic nanocavities and graphene sheets paves the way for the development of non-invasive plasmon-assisted electrochemical sensors that can effectively detect low concentrations of H₂O₂ released from cancer cells.