Electrochemical H2O2 biosensor composed of myoglobin on MoS2 nanoparticle-graphene oxide hybrid structure

Recent advances in electrochemical detection of reactive oxygen species: a review

Reactive oxygen species (ROS) are mainly generated as a result of cellular metabolism in plants and animals, playing a crucial role in cellular signaling mechanisms. The excessive generation of ROS leads to oxidative stress, which is associated with numerous diseases such as cancer, diabetes, and neurodegenerative disorders. Superoxide (O2˙-), hydrogen peroxide (H2O2), and hydroxyl radicals (˙OH) are the most common ROS involved in a wide range of human diseases. Therefore, sensitive and selective detection of these ROS is of paramount importance for understanding their roles in biological systems and for disease diagnosis. Among the various detection methods, electrochemical techniques have gained significant attention due to their high sensitivity, selectivity, and real-time monitoring capabilities. Electrochemical methods incorporate both organic and inorganic molecules to detect and monitor ROS, facilitating a deeper understanding of how their levels influence diseases linked to oxidative stress. This review aims to provide a critical discussion on the recent advances in electrochemical methods for detecting O2˙-, H2O2, and ˙OH. The review also highlights the application of these electrochemical techniques in detecting ROS in living cells and discusses the challenges and future perspectives in this field.

Multi-responsive biosensor prepared based on MXene and PDEA-HRP binary architecture films for H2O2 detection and logic gate construction

The quantitative detection of H2O2 is of great significance for preventing the occurrence of diseases. In this work, an electrochemical biosensor for detecting H2O2 was constructed through a step-by-step modification method. The PDEA-HRP/MXene/PG biosensor (PDEA = poly(N,N-dimethyl acrylamide), HRP = horseradish peroxidase, PG = pyrolytic graphite) was prepared with two-dimensional metal carbide (MXene) nano materials as the inner layer and PDEA-HRP hydrogel as the outer layer for the detection of H2O2. Due to the excellent conductivity and biocompatibility of MXene materials, the prepared PDEA-HRP/MXene/PG biosensors have high sensitivity, wide linear range, and good repeatability. The results indicated that under optimal conditions, the prepared biosensor can detect H2O2 concentration within a linear range of 0.04 mM ∼ 1.80 mM, with the detection limit of 1.08 × 10-3 mM (S/N = 3). The detection effect was good in actual samples. In addition, based on the switching properties of PDEA-HRP hydrogel under different conditions, combined with the characteristics of MXene nanomaterials. This study also constructed several biomolecule electrocatalytic logic gate systems, including binary 5-Input/5-Output logic gate network, 2-to-4 decoder, and a ternary AND logic gates.

Recent advances in graphene-based electroanalytical devices for healthcare applications

Graphene, with its outstanding mechanical, electrical, and biocompatible properties, stands out as an emerging nanomaterial for healthcare applications, especially in building electroanalytical biodevices. With the rising prevalence of chronic diseases and infectious diseases, such as the COVID-19 pandemic, the demand for point-of-care testing and remote patient monitoring has never been greater. Owing to their portability, ease of manufacturing, scalability, and rapid and sensitive response, electroanalytical devices excel in these settings for improved healthcare accessibility, especially in resource-limited settings. The development of different synthesis methods yielding large-scale graphene and its derivatives with controllable properties, compatible with device manufacturing - from lithography to various printing methods - and tunable electrical, chemical, and electrochemical properties make it an attractive candidate for electroanalytical devices. This review article sheds light on how graphene-based devices can be transformative in addressing pressing healthcare needs, ranging from the fundamental understanding of biology in in vivo and ex vivo studies to early disease detection and management using in vitro assays and wearable devices. In particular, the article provides a special focus on (i) synthesis and functionalization techniques, emphasizing their suitability for scalable integration into devices, (ii) various transduction methods to design diverse electroanalytical device architectures, (iii) a myriad of applications using devices based on graphene, its derivatives, and hybrids with other nanomaterials, and (iv) emerging technologies at the intersection of device engineering and advanced data analytics. Finally, some of the major hurdles that graphene biodevices face for translation into clinical applications are discussed.

Carbon-based nanocomposites for biomedical applications

Carbon nanomaterials have attracted significant attention in the biomedical field, including for biosensing, drug delivery, and tissue engineering applications. Based on their inherent properties such as their unique structure and high conductivity, carbon nanomaterials can overcome the current limitations in biomedical research such as poor stability of biomolecules, low sensitivity and selectivity of biosensors, and difficulty in precise drug delivery. In addition, recently, several novel nanomaterials have been integrated with carbon nanomaterials to develop carbon-based nanocomposites for application in biomedical research. In this review, we discuss recent studies on carbon-based nanocomposites and their biomedical applications. First, we discuss the representative carbon nanomaterials and nanocomposites composed of carbon and other novel nanomaterials. Next, applications of carbon nanomaterials and nanocomposites in the biomedical field are discussed according to topics in the biomedical field. We have discussed the recent studies on biosensors, drug delivery, and tissue engineering. In conclusion, we believe that this review provides the potential and applicability of carbon nanomaterials and their nanocomposites and suggests future directions of the application of carbon-based nanocomposites in biomedical applications.

Highly efficient electrochemical detection of H2O2 utilizing an innovative copper porphyrinic nanosheet decorated bismuth metal-organic framework modified electrode

The ability to detect hydrogen peroxide is important due to the presence in biological systems. Researchers are highly interested in developing efficient electrochemical hydrogen peroxide sensors. Metal-organic frameworks (MOFs) with their composites, an emerging class of porous materials, are ideal candidates for heterogeneous catalysts because of their versatile functionalities. Using a facile solvothermal reaction, we fabricated a 2D Cu-TCPP nanosheet uniformly grown on a 3D Bi-MOF. The process takes advantage of the large surface area and pore volume of the Bi-MOF while maintaining the crystallinity of Bi-BTC when Cu-TCPP is added to the surface. The sensor was fabricated by depositing the Bi-BTC-Cu-TCPP nanocomposites on a glassy carbon electrode to conduct electrochemical measurements such as cyclic voltammetry and electrochemical impedance spectroscopy. Finally, differential pulse voltammetry was utilized to investigate the effect of hydrogen peroxide on the electrochemical activity of Bi-BTC-Cu-TCPP deposited on a glassy carbon electrode. This electrode showed high electrochemical performance activity for the reduction of hydrogen peroxide. The sensor showed a linear response to H2O2 in the 10-120 μM concentration range, with a detection limit of 0.20 μM. The sensor was also stable and selective for H2O2 in the presence of other interfering species. This work demonstrates the potential of nanocomposite-based electrochemical sensors for sensitive and selective detection of H2O2. Besides, the modified electrode has many advantages, including remarkable catalytic activity, long-term stability, good reproducibility, and a good signal response during H2O2 reduction.

Interlayer charge transfer in supported and suspended MoS2/Graphene/MoS2 vertical heterostructures

In this letter, we report on the optical and structural properties of supported and suspended MoS2/Graphene/MoS2 vertical heterostructures using Raman and photoluminescence (PL) spectroscopies. Vertical heterostructures (VH) are formed by multiple wet transfers on micro-sized holes in SiO2/Si substrates, resulting in VH with different configurations. The strong interlayer coupling is confirmed by Raman spectroscopy. Additionally, we observe an enhancement of the PL emission in the three-layer VH (either support or suspended) compared with bare MoS2 or MoS2/Graphene. This suggests the formation of a spatial type-II band alignment assisted by the graphene layer and thus, the operation of the VH as a n++/metal/n junction.

Enzymatic Electrochemical/Fluorescent Nanobiosensor for Detection of Small Chemicals

The detection of small molecules has attracted enormous interest in various fields, including the chemical, biological, and healthcare fields. In order to achieve such detection with high accuracy, up to now, various types of biosensors have been developed. Among those biosensors, enzymatic biosensors have shown excellent sensing performances via their highly specific enzymatic reactions with small chemical molecules. As techniques used to implement the sensing function of such enzymatic biosensors, electrochemical and fluorescence techniques have been mostly used for the detection of small molecules because of their advantages. In addition, through the incorporation of nanotechnologies, the detection property of each technique-based enzymatic nanobiosensors can be improved to measure harmful or important small molecules accurately. This review provides interdisciplinary information related to developing enzymatic nanobiosensors for small molecule detection, such as widely used enzymes, target small molecules, and electrochemical/fluorescence techniques. We expect that this review will provide a broad perspective and well-organized roadmap to develop novel electrochemical and fluorescent enzymatic nanobiosensors.

Atomic layer deposition (ALD)-constructed TaS2nanoflakes for cancer-related nucleolin detection

Sensitive detection of nucleolin (NCL) is of great significance for the early diagnosis of cancer. In this work, as a new type of two-dimensional (2D) transition metal dichalcogenides (TMDCs), TaS₂nanoflakes (NFs) were precisely constructed by atomic layer deposition (ALD) on carbon fiber paper (CFP) with high specific surface area.In situobservation showed that the nucleation and growth of TaS₂nanoflakes were precisely controlled by the number of ALD cycles, thereby regulating their electrochemical properties. The electrochemical performance of TaS₂NFs was observed in depth, and compared with that of traditional 2D TMDCs. Due to the high surface area and conductivity, anodic/cathodic current of ∼1570μA of TaS₂NFs/CFP can be obtained. Subsequently, an electrochemical biosensor based on ALD-constructed TaS₂NFs/CFP for cancer-related NCL detection was fabricated. Due to the excellent electrochemical performance of TaS₂NFs/CFP, ultrasensitive detection of NCL in the linear range of 0.1 pM-10 nM with a detection limit of 0.034 pM was achieved.

Direct fabrication of NbS2 nanoflakes on carbon fibers by atomic layer deposition for ultrasensitive cardiac troponin I detection

The sensitive detection of cardiac troponin I (cTnI) is of great significance for the early diagnosis of acute myocardial infarction (AMI). Herein, in order to fabricate an electrochemical biosensor for ultrasensitive cTnI detection, atomic layer deposition (ALD) was employed to directly deposit NbS₂ nanoflakes (NFs) on carbon fiber paper (CFP). Due to the self-limiting reaction of ALD, NbS₂NFs were deposited uniformly and accurately on the surface of carbon fibers by controlling the number of ALD cycles, which ensured ultrasensitive detection. Precise regulation of the nanoscale morphology and electrochemical performance of NbS₂ nanoflakes via ALD cycles was observed in depth. Owing to the high surface area and conductivity, an anodic/cathodic current of ∼3.01 mA of NbS₂NFs/CFP can be obtained. Subsequently, an electrochemical biosensor based on the excellent performance of NbS₂NFs/CFP was fabricated. The ultrasensitive detection of cTnI in a linear range of 1 fM to 0.1 nM with a detection limit of 0.32 fM was achieved.

Recent progress in nanomaterial-based bioelectronic devices for biocomputing system

Bioelectronic devices have received the massive attention because of their huge potential to develop the core electronic components for biocomputing system. Up to now, numerous bioelectronic devices have been reported such as biomemory and biologic gate by employment of biomolecules including metalloproteins and nucleic acids. However, the intrinsic limitations of biomolecules such as instability and low signal production hinder the development of novel bioelectronic devices capable of performing various novel computing functions. As a way to overcome these limitations, nanomaterials have the great potential and wide applicability to grant and extend the electronic functions, and improve the inherent properties from biomolecules. Accordingly, lots of nanomaterials including the conductive metal, graphene, and transition metal dichalcogenide nanomaterials are being used to develop the remarkable functional bioelectronic devices like the multi-bit biomemory and resistive random-access biomemory. This review discusses the nanomaterial-based superb bioelectronic devices including the biomemory, biologic gates, and bioprocessors. In conclusion, this review will provide the interdisciplinary information about utilization of various novel nanomaterials applicable for biocomputing system.

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.

Binary MoS2 nanostructures as nanocarriers for amplification in multiplexed electrochemical immunosensing: simultaneous determination of B cell activation factor and proliferation-induced signal immunity-related cytokines

A dual immunosensor is reported for the simultaneous determination of two important immunity-related cytokines: BAFF (B cell activation factor) and APRIL (a proliferation-induced signal). Sandwich-type immunoassays with specific antibodies (cAbs) and a strategy for signal amplification based on labelling the detection antibodies (dAbs) with binary MoS₂/MWCNTs nanostructures and using horseradish peroxidase (HRP) were implemented. Amperometric detection was carried out at screen-printed dual carbon electrodes (SPdCEs) through the hydroquinone HQ/H₂O₂ system. The developed dual immunosensor provided limit of detection (LOD) of 0.08 and 0.06 ng mL⁻¹ for BAFF and APRIL, respectively, and proved to be useful for the determination of both cytokines in cancer cell lysates and serum samples from patients diagnosed with autoimmune diseases and cancer. The obtained results agreed with those found using ELISA methodologies.

Fabrication of MERS-nanovesicle biosensor composed of multi-functional DNA aptamer/graphene-MoS2 nanocomposite based on electrochemical and surface-enhanced Raman spectroscopy

Middle East respiratory syndrome coronavirus (MERS-CoV) is one of the most harmful viruses for humans in nowadays. To prevent the spread of MERS-CoV, a valid detection method is highly needed. For the first time, a MERS-nanovesicle (NV) biosensor composed of multi-functional DNA aptamer and graphene oxide encapsulated molybdenum disulfide (GO-MoS₂) hybrid nanocomposite was fabricated based on electrochemical (EC) and surface-enhanced Raman spectroscopy (SERS) techniques. The MERS-NV aptamer was designed for specifically binding to the spike protein on MERS-NVs and it is prepared using the systematic evolution of ligands by exponential enrichment (SELEX) technique. For constructing a multi-functional MERS aptamer (MF-aptamer), the prepared aptamer was connected to the DNA 3-way junction (3WJ) structure. DNA 3WJ has the three arms that can connect the three individual functional groups including MERS aptamer (bioprobe), methylene blue (signal reporter) and thiol group (linker) Then, GO-MoS₂ hybrid nanocomposite was prepared for the substrate of EC/SERS-based MERS-NV biosensor construction. Then, the assembled multifunctional (MF) DNA aptamer was immobilized on GO-MoS₂. The proposed biosensor can detect MERS-NVs not only in a phosphate-buffered saline (PBS) solution (SERS LOD: 0.176 pg/ml, EIS LOD: 0.405 pg/ml) but also in diluted 10% saliva (SERS LOD: 0.525 pg/ml, EIS LOD: 0.645 pg/ml).

Photoelectrochemical sensing and mechanism investigation of hydrogen peroxide using a pristine hematite nanoarrays

In this paper, a facile hydrothermal combined with subsequent two-step post-calcination method was used to fabricate hematite (α-Fe₂O₃) nanoarrays on fluorine-doped SnO₂ glass (FTO). The morphology, crystalline phase, optical property and surface chemical states of the fabricated α-Fe₂O₃ photoelectrode were characterized by scanning electron microscopy, X-ray diffraction, ultraviolet visible spectroscopy and X-ray photoelectron spectroscopy correspondingly. The α-Fe₂O₃ photoelectrode exhibits excellent photoelectrochemical (PEC) response toward hydrogen peroxide (H₂O₂) in aqueous solutions, with a low detection limit of 20 μM (S/N = 3) and wide linear range (0.01-0.09, 0.3-4, and 6-16 mM). Additionally, the α-Fe₂O₃ photoelectrode shows satisfying reproducibility, stability, selectivity and good feasibility for real samples. Mechanism analysis indicates, comparing with H₂O, H₂O₂ possesses much more fast reaction kinetics over α-Fe₂O₃ surface, thus the recombination of photogenerated charges are reduced, followed by much more photogenerated electrons are migrated to the counter electrode via external circuit. The insight on the enhanced photocurrent, which is corelative to the concentration of H₂O₂ in aqueous solution, will stimulate us to further optimize the surface structure of α-Fe₂O₃ to gain highly efficient α-Fe₂O₃ based sensors.

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.

Anti-EpCAM functionalized graphene oxide vector for tumor targeted siRNA delivery and cancer therapy

Graphene oxide (GO) has emerged as a potential drug delivery vector. For siRNA delivery, GO should be modified to endow it with gene delivery ability and targeting effect. However, the cationic materials used previously usually had greater toxicity. In this study, GO was modified with a non-toxicity cationic material (chitosan) and a tumor specific monoclonal antibody (anti-EpCAM) for the delivery of survivin-siRNA (GCE/siRNA). And the vector (GCE) prepared was proved with excellent biosafety and tumor targeting effect. The GCE exhibited superior performance in loading siRNA, maintained stability in different solutions and showed excellent protection effect for survivin-siRNA in vitro. The gene silencing results in vitro showed that the mRNA level and protein level were down-regulated by 48.24% ± 2.50% and 44.12% ± 3.03%, respectively, which was equal with positive control (P > 0.05). It was also demonstrated that GCE/siRNA had a strong antitumor effect in vitro, which was attributed to the efficient antiproliferation, and migration and invasion inhibition effect of GCE/siRNA. The results in vivo indicated that GCE could accumulate siRNA in tumor tissues. The tumor inhibition rate of GCE/siRNA 54.74% ± 5.51% was significantly higher than control 4.87% ± 8.49%. Moreover, GCE/siRNA showed no toxicity for blood and main organs, suggesting that it is a biosafety carrier for gene delivery. Taken together, this study provides a novel design strategy for gene delivery system and siRNA formulation.

Natural Molybdenite- and Tyrosinase-Based Amperometric Catechol Biosensor Using Acridine Orange as a Glue, Anchor, and Stabilizer for the Adsorbed Tyrosinase

To develop a natural mineral-based electrochemical enzyme biosensor, natural molybdenite (MLN), tyrosinase (TYR), and acridine orange (AO) were coadsorbed onto a glassy carbon electrode (GCE). The developed TYR/AO/MLN-GCE-based amperometric TYR biosensor exhibited excellent performance for highly sensitive determination of catechol (linear range, 0.1-80 μM; sensitivity, 0.0315 μA/μM; LOD, 0.029 μM; response time, <4 s) with good reproducibility and good operational and storage stabilities. The electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance with dissipation (QCM-D) revealed interesting roles of AO: (1) an efficient glue for enhancing the amount of the adsorbed TYR on the MLN-GCE, (2) an anchor for efficient orientation of the adsorbed TYR on the MLN-GCE, and (3) a stabilizer providing a suitable microenvironment for the adsorbed TYR on the MLN-GCE surface. This physical adsorption-based AO-coupled enzyme-modification strategy onto natural MLN would be a versatile strategy to develop cost-effective and environment-friendly natural mineral-based electrochemical biosensors and bioelectronic devices.

Facile synthesis of a nanorod-like MoS2 nanostructure for sensitive electrochemical biosensing application

A novel nanorod-like MoS2 semiconductor nanostructure was synthesized through a simple two-step method. The nanorod-like MoS2 nanostructure was exploited as an electrode material to immobilize enzymes and for electrochemical sensing application. Characterization of the nanorod-like MoS2 nanostructure and the resultant biosensor was performed by scanning electron microscopy, Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Enzyme molecules loaded at the MoS2 nanostructure retained their native structure and bioactivity. The direct electron transfer of glucose oxidase at the MoS2 nanostructure coated glassy carbon electrode was enhanced greatly. At an optimal potential of -0.45 V, the electrochemical glucose sensor had wide linear ranges of 1.5 × 10-5-3.25 × 10-4 M and 3.25 × 10-4-1.43 × 10-3 M, and a low detection limit of 0.005 mM (S/N = 3) with a high sensitivity of 25.06 ± 0.5 mA M-1 cm-2. At the same time, the present biosensor showed excellent selectivity, reproducibility and stability for glucose. What's more, the biosensor was successfully applied to the determination of practical samples.

Molybdenum-containing polypyrrole self-supporting hollow flexible electrode for hydrogen peroxide detection in living cells

A flexible electrode based on polypyrrole-supported free-standing molybdenum oxide-molybdenum disulfide/polypyrrole nanostructure (MoO₃-MoS₂/PPy) was synthesized. The petal-like MoO₃-MoS₂ sheets grown on PPy were prepared step by step through simple electrodeposition and hydrothermal methods. The corresponding surface morphological and structural characterizations were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that the prepared petal MoO₃-MoS₂ hybrid nanomaterials were uniformly distributed on the PPy skeleton and exhibited a three-dimensional porous network structure. The flexible electrode was used for non-enzymatic detection of hydrogen peroxide (H₂O₂), and the developed MoO₃-MoS₂/PPy nanomaterials exhibited high electrochemical sensing performance in the range of 0.3-150 μM, with the detection limit of 0.18 μM (S/N = 3). The excellent detection properties enabled the MoO₃-MoS₂/PPy flexible electrode to detect H₂O₂ released by living cells. The resulting MoO₃-MoS₂/PPy flexible electrode also has the advantages of customizable shape and adjustability, which provides a potential platform for constructing clinically diagnosed in vivo portable instruments and real-time environmental monitoring.

Graphene/MoS2 Nanohybrid for Biosensors

Graphene has been studied a lot in different scientific fields because of its unique properties, including its superior conductivity, plasmonic property, and biocompatibility. More recently, transition metal dicharcogenide (TMD) nanomaterials, beyond graphene, have been widely researched due to their exceptional properties. Among the various TMD nanomaterials, molybdenum disulfide (MoS2) has attracted attention in biological fields due to its excellent biocompatibility and simple steps for synthesis. Accordingly, graphene and MoS2 have been widely studied to be applied in the development of biosensors. Moreover, nanohybrid materials developed by hybridization of graphene and MoS2 have a huge potential for developing various types of outstanding biosensors, like electrochemical-, optical-, or surface-enhanced Raman spectroscopy (SERS)-based biosensors. In this review, we will focus on materials such as graphene and MoS2. Next, their application will be discussed with regard to the development of highly sensitive biosensors based on graphene, MoS2, and nanohybrid materials composed of graphene and MoS2. In conclusion, this review will provide interdisciplinary knowledge about graphene/MoS2 nanohybrids to be applied to the biomedical field, particularly biosensors.

Direct electrochemistry of covalently immobilized hemoglobin on a naphthylimidazolium butyric acid ionic liquid/MWCNT matrix

Monitoring the concentration levels of hydrogen peroxide (H₂O₂) is significant in both clinical and industrial applications. Herein, we develop a facile biosensor for the detection of H₂O₂ based on direct electron transfer of hemoglobin (Hb), which was covalently immobilized on a hydrophobic naphthylimidazolium butyric acid ionic liquid (NIBA-IL) over a multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE) to obtain an Hb/NIBA-IL/MWCNT/GCE. Highly water-soluble Hb protein was firmly immobilized on NIBA-IL via stable amide bonding between the free NH₂ groups of Hb and COOH groups of NIBA-IL via EDC/NHS coupling. Thus fabricated biosensor showed a well resolved redox peak with a cathodic peak potential (E_pc) at -0.35 V and anodic peak potential (E_pa) at -0.29 V with a formal potential (E°') of -0.32 V, which corresponds to the deeply buried Fe^III/Fe^II redox centre of Hb, thereby direct electrochemistry of Hb was established. Further, the modified electrode demonstrated very good electrocatalytic activity towards H₂O₂ reduction and showed a wide linear range of detection from 0.01 to 6.3 mM with a limit of detection and sensitivity of 3.2 μM and 111 μA mM^-1 cm^-2, respectively. Moreover, the developed biosensor displayed high operational stability under dynamic conditions as well as during continuous potential cycles and showed reliable reproducibility. The superior performance of the fabricated biosensor is attributed to the effective covalent immobilization of Hb on the newly developed highly conducting and biocompatible NIBA-IL/MWCNT/GCE platform.

Electrochemical H2O2 biosensor based on horseradish peroxidase encapsulated protein nanoparticles with reduced graphene oxide-modified gold electrode

In this study, an electrochemical biosensor composed of a horseradish peroxidase (HRP)-encapsulated protein nanoparticles (HEPNP) was fabricated for the sensitive and selective detection of H₂O₂. The HEPNP has a three-dimensional structure that can contain a large amount of HRP; therefore, HEPNP can amplify the electrochemical signals necessary for the detection of H₂O₂. Furthermore, reduced graphene oxide (rGO) was used to increase the efficiency of electron transfer from the HEPNP to an electrode, which could enhance the electrochemical signal. This biosensor showed a sensitive electrochemical performance for detection of H₂O₂ with signals in the range from 0.01-100 μM, and it could detect low concentrations up to 0.01 μM. Furthermore, this biosensor was operated against interferences from glucose, ascorbic acid, and uric acid. In addition, this fabricated H₂O₂ biosensor showed selective detection performance in human blood serum. Therefore, the proposed biosensor could promote the sensitive and selective detection of H₂O₂ in clinical applications.

Metal Nanoparticles for Electrochemical Sensing: Progress and Challenges in the Clinical Transition of Point-of-Care Testing

With the rise in public health awareness, research on point-of-care testing (POCT) has significantly advanced. Electrochemical biosensors (ECBs) are one of the most promising candidates for the future of POCT due to their quick and accurate response, ease of operation, and cost effectiveness. This review focuses on the use of metal nanoparticles (MNPs) for fabricating ECBs that has a potential to be used for POCT. The field has expanded remarkably from its initial enzymatic and immunosensor-based setups. This review provides a concise categorization of the ECBs to allow for a better understanding of the development process. The influence of structural aspects of MNPs in biocompatibility and effective sensor design has been explored. The advances in MNP-based ECBs for the detection of some of the most prominent cancer biomarkers (carcinoembryonic antigen (CEA), cancer antigen 125 (CA125), Herceptin-2 (HER2), etc.) and small biomolecules (glucose, dopamine, hydrogen peroxide, etc.) have been discussed in detail. Additionally, the novel coronavirus (2019-nCoV) ECBs have been briefly discussed. Beyond that, the limitations and challenges that ECBs face in clinical applications are examined and possible pathways for overcoming these limitations are discussed.

Recent Advances in MXene Nanocomposite-Based Biosensors

The development of advanced biosensors with high sensitivity and selectivity is one of the most demanded concerns in the field of biosensors. To meet this requirement, up until now, numerous nanomaterials have been introduced to develop biosensors for achieving high sensitivity and selectivity. Among the latest nanomaterials attracting attention, MXene is one of the best materials for the development of biosensors because of its various superior properties. MXenes are two-dimensional inorganic compounds with few atomic layers that possess excellent characteristics including high conductivity and superior fluorescent, optical, and plasmonic properties. In this review, advanced biosensors developed on the basis of the MXene nanocomposite are discussed with the selective overview of recently reported studies. For this, introduction of the MXene including the definition, synthesis methods, and its properties are discussed. Next, MXene-based electrochemical biosensors and MXene-based fluorescent/optical biosensors are provided, which are developed on the basis of the exceptional properties of the MXene nanocomposite. This review will suggest the direction for use of the Mxene nanocomposite to develop advanced biosensors with high sensitivity and selectivity.

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.

Recent advances on TMDCs for medical diagnosis

Transition metal dichalcogenides (TMDCs), such as MoS₂ and WS₂, have attracted much attention in biosensing and bioimaging due to its excellent stability, biocompatibility, high specific surface area, and wide varieties. In this review, we overviewed the application of TMDCs in biosensing and bioimaging. Firstly, the synthesis methods and surface functionalization methods of TMDCs were summarized. Secondly, according to the working mechanism, we classified and gave a detailed account of the latest research progress of TMDC-based biosensing for the detection of the enzyme, DNA, and other biological molecules. Then, we outlined the recent progress of applying TMDCs in bio-imaging, including fluorescence, X-ray computed tomographic, magnetic response imaging, photographic and multimodal imaging, respectively. Finally, we discussed the future challenges and development direction of the application of TMDCs in medical diagnosis. Also, we put forward our view on the opportunity of TMDCs in the big data of modern medical diagnosis.

A Surface Plasmon Resonance Biosensor Based on Directly Immobilized Hemoglobin and Myoglobin

Immobilization of proteins on a surface plasmon resonance (SPR) transducer is a delicate procedure since loss of protein bioactivity can occur upon contact with the untreated metal surface. Solution to the problem is the use of an immobilization matrix having a complex structure. However, this is at the expense of biosensor selectivity and sensitivity. It has been shown that the matrix-assisted pulsed laser evaporation (MAPLE) method has been successfully applied for direct immobilization (without a built-in matrix) of proteins, preserving their bioactivity. So far, MAPLE deposition has not been performed on a gold surface as required for SPR biosensors. In this paper we study the impact of direct immobilization of heme proteins (hemoglobin (Hb) and myoglobin (Mb)) on their bioactivity. For the purpose, Hb and Mb were directly immobilized by MAPLE technique on a SPR transducer. The bioactivity of the ligands immobilized in the above-mentioned way was assessed by SPR registration of the molecular reactions of various Hb/Mb functional groups. By SPR we studied the reaction between the beta chain of the Hb molecule and glucose, which shows the structural integrity of the immobilized Hb. A supplementary study of films deposited by FTIR and AFM was provided. The experimental facts showed that direct immobilization of an intact molecule was achieved.

Modulating physicochemical properties in Gd3+@Yb2O3 nanospheres for efficient electrochemical monitoring of H2O2

Herein, a uniform spherical shaped Gd(III) doped Yb₂O₃ (Gd@Yb₂O₃) nanoparticles (NPs) was successfully synthesized via hydrothermal method for electrochemical detection of H₂O₂. The calcination effect and porosity of the materials well elaborated in the present work. The optical properties, size, morphological, thermal, sensing, surface and crystalline properties of synthesized materials were examined by several techniques. The enhanced electrocatalytic performance of Gd@Yb₂O₃ make the present sensor excellent towards the determination of H₂O₂.The anodic and cathodic peak current increased regularly with addition of H₂O₂ solution. The electrode coating surface was stable even after a number of electrochemical cycles and have high limit of detection (51 nM). Moreover, the present sensor was successfully employed for detection of H₂O₂ in real samples.

Carbon Nitride Nanosheet and Myoglobin Modified Electrode for Electrochemical Sensing Investigations

Background:

Carbon-based nanomaterials, especially carbon nitride (C3N4) has attracted tremendous interest in biosensor applications. Meanwhile, the mechanism of redox protein sensing and related electrocatalytic reactions can provide a valid basis for understanding the process of biological redox reaction.

Objective:

The aim of this paper is to construct a new electrochemical enzyme sensor to achieve direct electron transfer of myoglobin (Mb) on CILE surface and display electrocatalytic reduction activity to catalyze trichloroacetic acid (TCA) and H2O2.

Methods:

The working electrode was fabricated based on ionic liquid modified Carbon Paste Electrode (CILE) and C3N4 nanosheets were modified on the CILE surface, then Mb solution was fixed on C3N4/CILE surface and immobilized by using Nafion film. The as-prepared biosensor displayed satisfactory electrocatalytic ability towards the reduction of TCA and H2O2 in an optimum pH 7.0 buffer solution.

Results:

The results indicated that C3N4 modified electrode retained the activity of the enzyme and displayed quasi-reversible redox behavior in an optimum pH 7.0 buffer solution. The electrochemical parameters of the immobilized Mb on the electrode surface were further calculated with the results of the electron transfer number (n) as 1.27, the charge transfer coefficient (α) as 0.53 and the electrontransfer rate constant (ks) as 3.32 s-1, respectively. The Nafion/Mb/C3N4/CILE displayed outstanding electrocatalytic reduction activity to catalyze trichloroacetic acid and H2O2.

Conclusion:

The Nafion/Mb/C3N4/CILE displayed outstanding electrocatalytic reduction, which demonstrated the promising applications of C3N4 nanosheet in the field electrochemical biosensing.

Preparation of SnS2/MWCNTs chemically modified electrode and its electrochemical detection of H2O2

Considering the importance of hydrogen peroxide (H₂O₂) rapid detection, a SnS₂/MWCNTs composite was prepared by loading tin disulfide (SnS₂) nanoparticles on a three-dimensional conductive network composed of multi-walled carbon nanotubes (MWCNTs). The obtained SnS₂/MWCNTs composite was used as the modified material to prepare a chemically modified electrode (CME), which was used for the rapid detection of H₂O₂. The morphology and structure of the obtained samples were characterized and analyzed by scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy. The electrochemical performance of the modified electrode was researched by cyclic voltammetry, amperometric i-t curves, and AC impedance techniques. The results show that SnS₂ nanoparticles with a size of about 33 nm are evenly dispersed on the surface of MWCNTs. The obtained SnS₂/MWCNTs-CME has a strong current response to H₂O₂: it has a good linear relationship during the range of 0.248 ~ 16.423 mmol L^-1, and its linear regression equation is I_pa (mA) = (-0.94 ± 0.05) × 10^-2 + (- 0.43 ± 0.06) × 10^-2c (mmol L^-1) (R² = 0.997) with a sensitivity of 87.84 μA mmol^-1 L cm^-2. The corresponding detection limit is 1.04 μmol L^-1 (S/N = 3). At the same time, the SnS₂/MWCNTs-CME has good selectivity, reproducibility, and stability. Graphical abstract Uniformly distributed SnS₂/CNTs composite is used to prepare a chemically modified electrode for H₂O₂ detection. The prepared electrode has a strong electrochemical response to H₂O₂ due to the excellent conductivity and support of CNTs. And the SnS₂/CNTs electrode shows high sensitivity and selectivity for the electrochemical detection of H₂O₂.

High-Sensitivity Detection of the Lung Cancer Biomarker CYFRA21-1 in Serum Samples Using a Carboxyl-MoS2 Functional Film for SPR-Based Immunosensors

We constructed a novel surface plasmon resonance (SPR) detection assay using carboxyl-functionalized molybdenum disulfide (carboxyl-MoS2) nanocomposites as a signal amplification sensing film for the ultrasensitive detection of the lung cancer-associated biomarker cytokeratin 19 fragment (CYFRA21-1). The experiment succeeded in MoS2 reacted with chloroacetic acid giving carboxyl-MoS2 as the reaction product. The additional shoulder in the C 1s and O 1s peaks of carboxyl-MoS2, which were increased in X-ray photoelectron spectroscopy, confirmed the presence of O-C=O groups on the surface of the carboxyl-MoS2. Compared to MoS2, the experimental results confirmed that carboxyl-modified MoS2 had improved low impedance and low refractive index. The carboxyl-MoS2-based chip had a high affinity, with an SPR angle shift enhanced by 2.6-fold and affinity binding K A enhanced by 15-fold compared to a traditional SPR sensor. The results revealed that the carboxyl-MoS2-based chip had high sensitivity, specificity, and SPR signal affinity, while the CYFRA21-1 assay in spiked clinical serum showed a lower detection limit of 0.05 pg/mL and a wider quantitation range (0.05 pg/mL to 100 ng/mL). The carboxyl-MoS2-based chip detection value was about 104 times more sensitive than the limit of detection of an enzyme-linked immunosorbent assay (ELISA) (0.60 ng/mL). The results showed that the carboxyl-MoS2-based chip had the potential to rapidly assay complex samples including bodily fluids, whole blood, serum, plasma, urine, and saliva in SPR-based immunosensors to diagnose diseases including cancer.

Screen-printed electrochemical biosensor based on a ternary Co@MoS2/rGO functionalized electrode for high-performance non-enzymatic glucose sensing

In this study, cobalt oxides functionalized MoS₂/reduced graphene oxide was synthesized via a facile one-pot hydrothermal approach. Morphology and crystal structure of this ternary nanoarchitecture were characterized through scanning electron microscopy, transmission electron microscopy, Raman spectra and X-ray photoelectron spectroscopy. An ultrasensitive non-enzymatic glucose sensor was developed by decorating this ternary nanohybrid on the working electrode of a screen-printed electrochemical sensor. Cycle sweep voltammetry and amperometry were used to study the electro-catalytic activity of the modified working electrode, which demonstrated superior catalytic activity towards glucose oxidation with an extremely low detection limit of 30 nM. Meanwhile, this sensor showed an excellent selectivity in the presence of interfering species such as uric acid, ascorbic acid, etc. Based on the screen-printed technique, enzyme mimic nanomaterials could be easily introduced into portable devices, which opens the way to take non-enzymatic glucose electrochemical sensing towards point-of-care.

Highly Sensitive Biosensors Based on Biomolecules and Functional Nanomaterials Depending on the Types of Nanomaterials: A Perspective Review

Biosensors are very important for detecting target molecules with high accuracy, selectivity, and signal-to-noise ratio. Biosensors developed using biomolecules such as enzymes or nucleic acids which were used as the probes for detecting the target molecules were studied widely due to their advantages. For example, enzymes can react with certain molecules rapidly and selectively, and nucleic acids can bind to their complementary sequences delicately in nanoscale. In addition, biomolecules can be immobilized and conjugated with other materials by surface modification through the recombination or introduction of chemical linkers. However, these biosensors have some essential limitations because of instability and low signal strength derived from the detector biomolecules. Functional nanomaterials offer a solution to overcome these limitations of biomolecules by hybridization with or replacing the biomolecules. Functional nanomaterials can give advantages for developing biosensors including the increment of electrochemical signals, retention of activity of biomolecules for a long-term period, and extension of investigating tools by using its unique plasmonic and optical properties. Up to now, various nanomaterials were synthesized and reported, from widely used gold nanoparticles to novel nanomaterials that are either carbon-based or transition-metal dichalcogenide (TMD)-based. These nanomaterials were utilized either by themselves or by hybridization with other nanomaterials to develop highly sensitive biosensors. In this review, highly sensitive biosensors developed from excellent novel nanomaterials are discussed through a selective overview of recently reported researches. We also suggest creative breakthroughs for the development of next-generation biosensors using the novel nanomaterials for detecting harmful target molecules with high sensitivity.

Recent advances in synthesis and biosensors of two-dimensional MoS2

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted tremendous research interests due to their exciting optical properties, large surface area, intercalatable morphologies and excellent electrochemically catalytic activity. Acting as the most typical member in TMDCs family, layer-dependent molybdenum disulfide (MoS₂) with particular direct bandgap of 1.8 eV in monolayer has been widely applied in various biosensors with high sensitivity and selectivity. In this review, the preparation methods of MoS₂, together with MoS₂-based biosensors for detecting cells and biomolecules (such as glucose, DNA and antigens) would be summarized. In addition, the current challenges and future perspectives are outlined for the applications of biosensors based on 2D MoS₂.

2D Materials in Development of Electrochemical Point-of-Care Cancer Screening Devices

Effective cancer treatment requires early detection and monitoring the development progress in a simple and affordable manner. Point-of care (POC) screening can provide a portable and inexpensive tool for the end-users to conveniently operate test and screen their health conditions without the necessity of special skills. Electrochemical methods hold great potential for clinical analysis of variety of chemicals and substances as well as cancer biomarkers due to their low cost, high sensitivity, multiplex detection ability, and miniaturization aptitude. Advances in two-dimensional (2D) material-based electrochemical biosensors/sensors are accelerating the performance of conventional devices toward more practical approaches. Here, recent trends in the development of 2D material-based electrochemical biosensors/sensors, as the next generation of POC cancer screening tools, are summarized. Three cancer biomarker categories, including proteins, nucleic acids, and some small molecules, will be considered. Various 2D materials will be introduced and their biomedical applications and electrochemical properties will be given. The role of 2D materials in improving the performance of electrochemical sensing mechanisms as well as the pros and cons of current sensors as the prospective devices for POC screening will be emphasized. Finally, the future scopes of implementing 2D materials in electrochemical POC cancer diagnostics for the clinical translation will be discussed.

Fabrication of Graphene/Molybdenum Disulfide Composites and Their Usage as Actuators for Electrochemical Sensors and Biosensors

From the rediscovery of graphene in 2004, the interest in layered graphene analogs has been exponentially growing through various fields of science. Due to their unique properties, novel two-dimensional family of materials and especially transition metal dichalcogenides are promising for development of advanced materials of unprecedented functions. Progress in 2D materials synthesis paved the way for the studies on their hybridization with other materials to create functional composites, whose electronic, physical or chemical properties can be engineered for special applications. In this review we focused on recent progress in graphene-based and MoS2 hybrid nanostructures. We summarized and discussed various fabrication approaches and mentioned different 2D and 3D structures of composite materials with emphasis on their advances for electroanalytical chemistry. The major part of this review provides a comprehensive overview of the application of graphene-based materials and MoS2 composites in the fields of electrochemical sensors and biosensors.

Fabrication of Electrochemical-Based Bioelectronic Device and Biosensor Composed of Biomaterial-Nanomaterial Hybrid

The field of bioelectronics has paved the way for the development of biochips, biomedical devices, biosensors and biocomputation devices. Various biosensors and biomedical devices have been developed to commercialize laboratory products and transform them into industry products in the clinical, pharmaceutical, environmental fields. Recently, the electrochemical bioelectronic devices that mimicked the functionality of living organisms in nature were applied to the use of bioelectronics device and biosensors. In particular, the electrochemical-based bioelectronic devices and biosensors composed of biomolecule-nanoparticle hybrids have been proposed to generate new functionality as alternatives to silicon-based electronic computation devices, such as information storage, process, computations and detection. In this chapter, we described the recent progress of bioelectronic devices and biosensors based on biomaterial-nanomaterial hybrid.

Development of Bioelectronic Devices Using Bionanohybrid Materials for Biocomputation System

Bioelectronic devices have been researched widely because of their potential applications, such as information storage devices, biosensors, diagnosis systems, organism-mimicking processing system cell chips, and neural-mimicking systems. Introducing biomolecules including proteins, DNA, and RNA on silicon-based substrates has shown the powerful potential for granting various functional properties to chips, including specific functional electronic properties. Until now, to extend and improve their properties and performance, organic and inorganic materials such as graphene and gold nanoparticles have been combined with biomolecules. In particular, bionanohybrid materials that are composed of biomolecules and other materials have been researched because they can perform core roles of information storage and signal processing in bioelectronic devices using the unique properties derived from biomolecules. This review discusses bioelectronic devices related to computation systems such as biomemory, biologic gates, and bioprocessors based on bionanohybrid materials with a selective overview of recent research. This review contains a new direction for the development of bioelectronic devices to develop biocomputation systems using biomolecules in the future.

Golf ball-like MoS2 nanosheet arrays anchored onto carbon nanofibers for electrochemical detection of dopamine

Arrays of molybdenum(IV) disulfide nanosheets resembling the shape of golf balls (MoS₂ NSBs) were deposited on carbon nanofibers (CNFs), which are shown to enable superior electrochemical detection of dopamine without any interference by uric acid. The MoS₂ NSBs have a diameter of ∼ 2 μm and are made up of numerous bent nanosheets. MoS₂ NSBs are connected by the CNFs through the center of the balls. Figures of merit for the resulting electrode include (a) a sensitivity of 6.24 μA·μM^-1·cm^-2, (b) a low working voltage (+0.17 V vs. Ag/AgCl), and (c) a low limit of detection (36 nM at S/N = 3). The electrode is selective over uric acid, reproducible and stable. It was applied to the determination of dopamine in spiked urine samples. The recoveries at levels of 10, 20 and 40 μM of DA are 101.6, 99.8 and 107.8%. Graphical abstract Schematic presentation of the golf ball-like MoS₂ nanosheet balls/carbon nanofibers (MoS₂ NSB/CNFs) by electrospining and hydrothermal process to detect dopamine (DA).

Flexible electrochemical glucose biosensor based on GOx/gold/MoS2/gold nanofilm on the polymer electrode

The need for flexible biosensors has increased because of their potential applications for point-of-care diagnosis and wearable biosensors. However, flexible biosensors have low sensitivity due to the flexibility of the electrode, and their fabrication involves complex processes. To overcome these limitations, a flexible electrochemical enzyme biosensor was developed in this study by immobilizing an enzyme on the flexible polymer electrode modified with a gold/MoS₂/gold nanofilm. The fabrication process involved sputter deposition of gold, spin coating of MoS₂, and sputter deposition of gold on the flexible polymer electrode (commercially available Kapton^® polyimide film). The flexible glucose biosensor was made by immobilization of glucose oxidase on a flexible electrode by using a chemical linker. The detection limit for glucose was estimated to be 10 nM, which indicates more sensitivity as compared with a previously reported flexible glucose sensor. This sensitivity is due to the facilitation of electron transfer by MoS₂. The flexure extension of this biosensor was estimated at 3.48 mm, which is much higher than that of the rigid sensor using a gold-coated silicon electrode (0.09 mm), according to measurements with a micro-fatigue tester. The proposed flexible biosensor composed of the enzyme/gold/MoS₂/gold nanofilm on the polymer electrode can be used as a flexible sensing platform for developing wearable biosensing systems because of its high sensitivity, high flexibility, and simple fabrication process.