Chitosan-Covered Pd@Pt Core-Shell Nanocubes for Direct Electron Transfer in Electrochemical Enzymatic Glucose Biosensor

Enzymatic bioelectrodes based on ferrocene-modified metal-organic layers for electrochemical glucose detection

Metal-organic frameworks (MOFs) are often applied for enzyme immobilization, while they are limited for bioelectrochemical applications due to poor electronic conductivity. Two-dimensional (2D) metal-organic layers (MOLs) with an ultra-thin lamellar structure can effectively shorten the electron transport path and improve the electron transfer rate. In this study, ferrocene as an electron mediator is covalently bound to a 2D-MOL (Fc-NH2-Hf-BTB-MOL) to accelerate electron transfer between the electrode surface and enzyme. Glucose oxidase (GOx) is immobilized on the electrode modified with Fc-NH2-Hf-BTB-MOL with the addition of chitosan and carboxylated carbon nanotubes. Electrochemical tests such as cyclic voltammetry are carried out on the glucose biosensor, which shows linear detection ranges of 5 ~ 400 μM and 3 ~ 9 mM, with a detection limit of 3.9 μM (S/N = 3). Therefore, this strategy of construction of an enzyme electrode based on 2D-MOLs with enhanced electron transfer results in a biosensor with excellent specificity and activity for practical glucose detection.

Solid-State On-Substrate Synthesis of Size-Controlled CuPt@Cu2O Core-Shell Nanocubes and Applications for Electrochemical Sensing and Electrocatalytic Methanol Oxidation Reaction

The development of size- and shape-controlled nanomaterials is essential to tailor their properties and performance for wide-ranging applications from catalysis to sensing. Solid-state synthesis of nanostructures is attractive from a sustainability perspective, but they typically lack the desired size and shape control at small-scale dimensions. This work shows that colloidal precursors can be used in a solid-state route to form hybrid core-shell nanostructures with simultaneous size and morphology control. Encapsulation of PtNPs with a well-defined Cu2O shell produces CuPt@Cu2O core-shell nanocubes grown directly from the underlying substrate. The controlled formation of the nanostructures is facilitated by the diamine passivation layer on the Cu substrate. On-substrate growth of the nanocubes gives ease of postsynthesis processing for them to be used directly in electrochemical applications. We show that the synthesized nanostructured substrates have high sensitivity as an electrocatalyst for glucose sensing. We further demonstrate their potential for direct methanol fuel cells by assessing the methanol oxidation reaction (MOR). The mass activity is determined to be 1.656 A mgPt-1 for MOR, and initial studies indicate the substrates show high CO tolerance.

Electrochemical Glucose Sensors: Classification, Catalyst Innovation, and Sampling Mode Evolution

Glucose sensors are essential tools for monitoring blood glucose concentration in diabetic patients. In recent years, with the increasing number of individuals suffering from diabetes, blood glucose monitoring has become extremely necessary, which expedites the iteration and upgrade of glucose sensors greatly. Currently, two main types of glucose sensors are available for blood glucose testing: enzyme-based glucose sensor (EBGS) and enzyme-free glucose sensor (EFGS). For EBGS, several progresses have been made to comprehensively improve detection performance, ranging from enhancing enzyme activity, thermostability, and electron transfer properties, to introducing new materials with superior properties. For EFGS, more and more new metallic materials and their oxides are being applied to further optimize its blood glucose monitoring. Here the latest progress of electrochemical glucose sensors, their manufacturing methods, electrode materials, electrochemical parameters, and applications were summarized, the development glucose sensors with various noninvasive sampling modes were also compared.

Recent trends in core/shell nanoparticles: their enzyme-based electrochemical biosensor applications

Improving novel and efficient biosensors for determining organic/inorganic compounds is a challenge in analytical chemistry for clinical diagnosis and research in biomedical sciences. Electrochemical enzyme-based biosensors are one of the commercially successful groups of biosensors that make them highly appealing because of their low cost, high selectivity, and sensitivity. Core/shell nanoparticles have emerged as versatile platforms for developing enzyme-based electrochemical biosensors due to their unique physicochemical properties and tunable surface characteristics. This study provides a comprehensive review of recent trends and advancements in the utilization of core/shell nanoparticles for the development of enzyme-based electrochemical biosensors. Moreover, a statistical evaluation of the studies carried out in this field between 2007 and 2023 is made according to the preferred electrochemical techniques. The recent applications of core/shell nanoparticles in enzyme-based electrochemical biosensors were summarized to quantify environmental pollutants, food contaminants, and clinical biomarkers. Additionally, the review highlights recent innovations and strategies to improve the performance of enzyme-based electrochemical biosensors using core/shell nanoparticles. These include the integration of nanomaterials with specific functions such as hydrophilic character, chemical and thermal stability, conductivity, biocompatibility, and catalytic activity, as well as the development of new hybrid nanostructures and multifunctional nanocomposites.

Oxygen Plasma Induced Nanochannels for Creating Bimetallic Hollow Nanocrystals

Platinum-based metal catalysts are considered excellent converters in various catalytic reactions, particularly in fuel cell applications. The atomic structure at the nanocrystal surface and the metal interface both influence the catalytic performance, controlling the efficiency of the electrochemical reactions. Here we report the synthesis of Ag/Pt and Ag/Pd core/shell nanocrystals and insight into the formation mechanism of these bimetallic core/shell nanocrystals when undergoing oxygen plasma treatment. We carefully designed the oxidation treatment that determines the structural and compositional evolution. The accelerated oxidation-triggered diffusion of Ag toward the outer metal shell leads to the Kirkendall effect. After prolonged oxygen plasma treatment, most core/shell nanocrystals evolve into hollow spheres. At the same time, a minor fraction of the metal remains unchanged with a well-protected Ag core and a monocrystalline Pt or Pd shell. We hypothesize that the O2 plasma disturbs the Pt or Pd shell surface and introduces active O species that react with the diffused Ag from the inside out. Based on EDX elemental mapping, combined with several electron microscopic techniques, we deduced the formation mechanism of the hollow structures to be as follows: (I) the oxidation of Ag within the Pt or Pd lattice causes a disrupted crystal lattice of Pt or Pd; (II) nanochannels arise at the defect locations on the Pt or Pd shell; (III) the remaining Ag atoms pass through these nanochannels and leave a hollow crystal behind. Our findings deepen the understanding of interface dynamics of bimetallic nanostructured catalysts under an oxidative environment and unveil an alternative approach for catalyst pretreatment.

Smartphone-Assisted Flexible Electrochemical Sensor Platform by a Homology DNA Nanomanager Tailored for Multiple Cancer Markers Field Inspection

In this work, an ingenious sensor technology was established by integrating the EBFCs on a flexible paper strip carrier (PE) that was used for simultaneous detection of tumor markers in complex samples. Adopting high performance ultrathin graphdiyne (U-GDY) as the substrate can increase the enzyme load, accelerate the electron transfer rate, and significantly enhance the detection sensitivity. A homologous DNA nanomanager strategy cleverly uses signal switches to recycle and amplify target miRNAs, while the smartphone receives real-time instantaneous current values to realize multivariate detection. Electrochemical data show that the detection limits (LODs) of miRNA-21 and miRNA-155 are 0.09 and 0.15 fM in the wide concentration range. The results confirm that the tailored sensor platform provides a strategy for the early cancer diagnosis and lays the foundation for the construction of a flexible wearable platform.

Bioelectrocatalysis for CO2 reduction: recent advances and challenges to develop a sustainable system for CO2 utilization

Activation and turning CO₂ into value added products is a promising orientation to address environmental issues caused by CO₂ emission. Currently, electrocatalysis has a potent well-established role for CO₂ reduction with fast electron transfer rate; but it is challenged by the poor selectivity and low faradic efficiency. On the other side, biocatalysis, including enzymes and microbes, has been also employed for CO₂ conversion to target C_n products with remarkably high selectivity; however, low solubility of CO₂ in the liquid reaction phase seriously affects the catalytic efficiency. Therefore, a new synergistic role in bioelectrocatalysis for CO₂ reduction is emerging thanks to its outstanding selectivity, high faradic efficiency, and desirable valuable C_n products under mild condition that are surveyed in this review. Herein, we comprehensively discuss the results already obtained for the integration craft of enzymatic-electrocatalysis and microbial-electrocatalysis technologies. In addition, the intrinsic nature of the combination is highly dependent on the electron transfer. Thus, both direct electron transfer and mediated electron transfer routes are modeled and concluded. We also explore the biocompatibility and synergistic effects of electrode materials, which emerge in combination with tuned enzymes and microbes to improve catalytic performance. The system by integrating solar energy driven photo-electrochemical technics with bio-catalysis is further discussed. We finally highlight the significant findings and perspectives that have provided strong foundations for the remarkable development of green and sustainable bioelectrocatalysis for CO₂ reduction, and that offer a blueprint for C_n valuable products originate from CO₂ under efficient and mild conditions.

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.

A Core–Shell Au@TiO2 and Multi-Walled Carbon Nanotube-Based Sensor for the Electroanalytical Determination of H2O2 in Human Blood Serum and Saliva

A hydrogen peroxide (H₂O₂) sensor was developed based on core–shell gold@titanium dioxide nanoparticles and multi-walled carbon nanotubes modified glassy carbon electrode (Au@TiO₂/MWCNTs/GCE). Core–shell Au@TiO₂ material was prepared and characterized using a scanning electron microscopy and energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman spectroscopy, X-ray diffraction (XRD) and Zeta-potential analyzer. The proposed sensor (Au@TiO₂/MWCNTs/GCE) was investigated electrochemically using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The analytical performance of the sensor was evaluated towards H₂O₂ using differential pulse voltammetry (DPV). The proposed sensor exhibited excellent stability and sensitivity with a linear concentration range from 5 to 200 µM (R² = 0.9973) and 200 to 6000 µM (R² = 0.9994), and a limit of detection (LOD) of 1.4 µM achieved under physiological pH conditions. The practicality of the proposed sensor was further tested by measuring H₂O₂ in human serum and saliva samples. The observed response and recovery results demonstrate its potential for real-world H₂O₂ monitoring. Additionally, the proposed sensor and detection strategy can offer potential prospects in electrochemical sensors development, indicative oxidative stress monitoring, clinical diagnostics, general cancer biomarker measurements, paper bleaching, etc.

Microelectrode glucose biosensor based on nanoporous platinum/graphene oxide nanostructure for rapid glucose detection of tomato and cucumber fruits

Microelectrode glucose biosensor based on three-dimensional hybrid nanoporous platinum/graphene oxide nanostructure was developed for rapid glucose detection of tomato and cucumber fruits. The nanostructure was fabricated by a two-step modification method on microelectrode for loading a larger amount of glucose oxidase. The nanoporous structure was prepared on the surface of the platinum microelectrode by electrochemical etching, and then graphene oxide was deposited on the prepared nanoporous electrode by electrochemical deposition. The nanoprorous platinum/graphene oxide nanostructure had the advantage of improving the effective surface area of the electrode and the loading quantity of glucose oxidase. As a result, the biosensor achieved a wide range of 0.1-20.0 mM in glucose detection, which had the ability to accurately detect the glucose content. It was found that the three-dimensional hybrid nanostructure on the electrode surface realized the rapid direct electrochemistry of glucose oxidase. Therefore, the biosensor achieved high glucose detection sensitivity (11.64 μA mM -1cm -2), low detection limit (13 μM) and rapid response time (reaching 95% steady-state response within 3 seconds), when calibrating in glucose standard solution. In agricultural application, the as-prepared biosensor was employed to detect the glucose concentration of tomato and cucumber samples. The results showed that the relative deviation of this method was less than 5% when compared with that of HPLC, implying high accuracy of the presented biosensor in glucose detection in plants.

Electrochemical sensor based on a chitosan-molybdenum vanadate nanocomposite for detection of hydroxychloroquine in biological samples

In this study, we firstly introduce an ultra-high sensitive V_3.6Mo_2.4O₁₆-chitosan (MV-CHT) nanocomposite for electrochemical hydroxychloroquine sulfate (HCQ) monitoring toward paracetamol (PCM) and pantoprazole (PPZ) in environmental and clinical diagnostics. The single-phase MV nanostructures are prepared via the sol-gel pechini route, followed by engineering maleic acid as a structure-directing agent. The stabilization of the MV electro-catalysts is adopted by varying critical factors such as calcination temperature, different chelating ligands, chelating molality and cross-linker concentration. The structural and morphological characterizations, namely, ordered active sites, structural integrity, porous network and dispersibility on the cationic polymer are confirmed by physicochemical analyses. Also, analytical nature of the MV-CHT modified carbon paste electrode (MV-CHT/CPE) is constructed via electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) techniques. As a result, the nano-MV-CHT/CPE platforms with 10% of polymeric matrixes delivered the boosted analytical performance in terms of linear ranges (0.0019-194.0 µM), lower detection limit (LOD = 0.224 nM), together with excellent sensitivity and selectivity. The novel combination of MV nanoparticles and CHT provide the fluent channels for rapid charge transport and effective surface area. Such results illustrate the synergistic and interaction capability of MV-CHT-based sensing catalysts with bioactive molecules, which make them as superior drug monitoring devices.

Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing

The detection of glucose is crucial in the management of diabetes and other medical conditions but also crucial in a wide range of industries such as food and beverages. The development of glucose sensors in the past century has allowed diabetic patients to effectively manage their disease and has saved lives. First-generation glucose sensors have considerable limitations in sensitivity and selectivity which has spurred the development of more advanced approaches for both the medical and industrial sectors. The wide range of application areas has resulted in a range of materials and fabrication techniques to produce novel glucose sensors that have higher sensitivity and selectivity, lower cost, and are simpler to use. A major focus has been on the development of enzymatic electrochemical sensors, typically using glucose oxidase. However, non-enzymatic approaches using direct electrochemistry of glucose on noble metals are now a viable approach in glucose biosensor design. This review discusses the mechanisms of electrochemical glucose sensing with a focus on the different generations of enzymatic-based sensors, their recent advances, and provides an overview of the next generation of non-enzymatic sensors. Advancements in manufacturing techniques and materials are key in propelling the field of glucose sensing, however, significant limitations remain which are highlighted in this review and requires addressing to obtain a more stable, sensitive, selective, cost efficient, and real-time glucose sensor.

Analytical Parameters of a Novel Glucose Biosensor Based on Grafted PFM as a Covalent Immobilization Technique

Bioanalytical methods, in particular electrochemical biosensors, are increasingly used in different industrial sectors due to their simplicity, low cost, and fast response. However, to be able to reliably use this type of device, it is necessary to undertake in-depth evaluation of their fundamental analytical parameters. In this work, analytical parameters of an amperometric biosensor based on covalent immobilization of glucose oxidase (GOx) were evaluated. GOx was immobilized using plasma-grafted pentafluorophenyl methacrylate (pgPFM) as an anchor onto a tailored HEMA-co-EGDA hydrogel that coats a titanium dioxide nanotubes array (TiO2NTAs). Finally, chitosan was used to protect the enzyme molecules. The biosensor offered outstanding analytical parameters: repeatability (RSD = 1.7%), reproducibility (RSD = 1.3%), accuracy (deviation = 4.8%), and robustness (RSD = 2.4%). In addition, the Ti/TiO2NTAs/ppHEMA-co-EGDA/pgPFM/GOx/Chitosan biosensor showed good long-term stability; after 20 days, it retained 89% of its initial sensitivity. Finally, glucose concentrations of different food samples were measured and compared using an official standard method (HPLC). Deviation was lower than 10% in all measured samples. Therefore, the developed biosensor can be considered to be a reliable analytical tool for quantification measurements.

Recent Progress of the Practical Applications of the Platinum Nanoparticle-Based Electrochemistry Biosensors

The detection of biomolecules using various biosensors with excellent sensitivity, selectivity, stability, and reproducibility, is of great significance in the analytical and biomedical fields toward achieving their practical applications. Noble metal nanoparticles are favorable candidates due to their unique optical, surface electrical effect, and catalytic properties. Among these noble metal nanoparticles, platinum nanoparticles (Pt NPs) have been widely employed for the detection of bioactive substances such as glucose, glutamic acid, and hormones. However, there is still a long way to go before the potential challenges in the practical applications of biomolecules are fully overcome. Bearing this in mind, combined with our research experience, we summarized the recent progress of the Pt NP-based biosensors and highlighted the current problems that exist in their practical applications. The current review would provide fundamental guidance for future applications using the Pt NP-based biosensors in food, agricultural, and medical fields.

FEAST of biosensors: Food, environmental and agricultural sensing technologies (FEAST) in North America

We review the challenges and opportunities for biosensor research in North America aimed to accelerate translational research. We call for platform approaches based on: i) tools that can support interoperability between food, environment and agriculture, ii) open-source tools for analytics, iii) algorithms used for data and information arbitrage, and iv) use-inspired sensor design. We summarize select mobile devices and phone-based biosensors that couple analytical systems with biosensors for improving decision support. Over 100 biosensors developed by labs in North America were analyzed, including lab-based and portable devices. The results of this literature review show that nearly one quarter of the manuscripts focused on fundamental platform development or material characterization. Among the biosensors analyzed for food (post-harvest) or environmental applications, most devices were based on optical transduction (whether a lab assay or portable device). Most biosensors for agricultural applications were based on electrochemical transduction and few utilized a mobile platform. Presently, the FEAST of biosensors has produced a wealth of opportunity but faces a famine of actionable information without a platform for analytics.

Novel flexible bifunctional amperometric biosensor based on laser engraved porous graphene array electrodes: Highly sensitive electrochemical determination of hydrogen peroxide and glucose

Polyimide-laser-engraved porous graphene (LEPG) are hopeful electrode modification materials for flexible electrochemical sensing based on its high-efficiency preparation and low cost. Herein, a flexible, multi-patterned, and miniaturized electrode was fabricated via a simple and novel direct laser engraving. 3D LEPG with porous network structure can selective decorated with Pt nanoparticles (Pt NPs) by in situ electrochemical depositions (Pt-LEPG) as sensitively H₂O₂ sensors with a wide range of linear (0.01-29 nM) and high sensitivity (575.75 μA mM^-1 cm^-2). Subsequently, a glucose biosensor was successfully constructed through immobilized glucose oxidases (GOD) onto Pt-LEPG electrode. New-designed GOD/Pt-LEPG glucose sensor exhibited a noteworthy lower limit of detection (0.3 μM, S/N = 3) and high sensitivity (241.82 μA mM^-1 cm^-2), as much a wide-range of linear (0.01-31.5 mM) at near-neutral pH conditions, enabling detect glucose in real human serum specimens with satisfactory results. Predictably, these outstanding performance sensors have great potential in terms of flexible and wearable electronics.

Developing a CNT-SPE Sensing Platform Based on Green Synthesized AuNPs, Using Sargassum sp

Detection and quantification of diverse analytes such as molecules, cells receptor and even particles and nanoparticles, play an important role in biomedical research, particularly in electrochemical sensing platform technologies. In this study, gold nanoparticles (AuNPs) prepared by green synthesis from Sargassum sp. were characterized using ultraviolet-visible (UV-Vis) and Fourier transform-infrared (FT-IR) spectroscopies, X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS) and zeta potential (ζ) obtaining organic capped face-centered cubic 80-100 nm AuNPs with an excellent stability in a wide range of pH. The AuNPs were used to modify a carbon nanotubes-screen printed electrode (CNT-SPE), through the drop-casting method, to assemble a novel portable electrochemical sensing platform for glucose, using a novel combination of components, which together have not been employed. The ability to sense and measure glucose was demonstrated, and its electrochemical fundamentals was studied using cyclic voltammetry (CV). The limits of detection (LOD) and quantification (LOQ) to glucose were 50 μM and 98 μM, respectively, and these were compared to those of other sensing platforms.

A Critical Review of Electrochemical Glucose Sensing: Evolution of Biosensor Platforms Based on Advanced Nanosystems

The research field of glucose biosensing has shown remarkable growth and development since the first reported enzyme electrode in 1962. Extensive research on various immobilization methods and the improvement of electron transfer efficiency between the enzyme and the electrode have led to the development of various sensing platforms that have been constantly evolving with the invention of advanced nanostructures and their nano-composites. Examples of such nanomaterials or composites include gold nanoparticles, carbon nanotubes, carbon/graphene quantum dots and chitosan hydrogel composites, all of which have been exploited due to their contributions as components of a biosensor either for improving the immobilization process or for their electrocatalytic activity towards glucose. This review aims to summarize the evolution of the biosensing aspect of these glucose sensors in terms of the various generations and recent trends based on the use of applied nanostructures for glucose detection in the presence and absence of the enzyme. We describe the history of these biosensors based on commercialized systems, improvements in the understanding of the surface science for enhanced electron transfer, the various sensing platforms developed in the presence of the nanomaterials and their performances.

Natural-based Hydrogels: A Journey from Simple to Smart Networks for Medical Examination

Natural hydrogels, due to their unique biological properties, have been used extensively for various medical and clinical examinations that are performed to investigate the signs of disease. Recently, complex-crosslinking strategies improved the mechanical properties and advanced approaches have resulted in the introduction of naturally derived hydrogels that exhibit high biocompatibility, with shape memory and self-healing characteristics. Moreover, the creation of self-assembled natural hydrogels under physiological conditions has provided the opportunity to engineer fine-tuning properties. To highlight recent studies of natural-based hydrogels and their applications for medical investigation, a critical review was undertaken using published papers from the Science Direct database. This review presents different natural-based hydrogels (natural, natural-synthetic hybrid and complex-crosslinked hydrogels), their historical evolution, and recent studies of medical examination applications. The application of natural-based hydrogels in the design and fabrication of biosensors, catheters and medical electrodes, detection of cancer, targeted delivery of imaging compounds (bioimaging) and fabrication of fluorescent bioprobes is summarised here. Without doubt, in future, more useful and practical concepts will be derived to identify natural-based hydrogels for a wide range of clinical examination applications.

Synthesis, Properties, and Biological Applications of Metallic Alloy Nanoparticles

Metallic alloy nanoparticles are synthesized by combining two or more different metals. Bimetallic or trimetallic nanoparticles are considered more effective than monometallic nanoparticles because of their synergistic characteristics. In this review, we outline the structure, synthesis method, properties, and biological applications of metallic alloy nanoparticles based on their plasmonic, catalytic, and magnetic characteristics.

Exploration of Chitinous Scaffold-Based Interfaces for Glucose Sensing Assemblies

: The nanomaterial-integrated chitinous polymers have promoted the technological advancements in personal health care apparatus, particularly for enzyme-based devices like the glucometer. Chitin and chitosan, being natural biopolymers, have attracted great attention in the field of biocatalysts engineering. Their remarkable tunable properties have been explored for enhancing enzyme performance and biosensor advancements. Currently, incorporation of nanomaterials in chitin and chitosan-based biosensors are also widely exploited for enzyme stability and interference-free detection. Therefore, in this review, we focus on various innovative multi-faceted strategies used for the fabrication of biological assemblies using chitinous biomaterial interface. We aim to summarize the current development on chitin/chitosan and their nano-architecture scaffolds for interdisciplinary biosensor research, especially for analytes like glucose. This review article will be useful for understanding the overall multifunctional aspects and progress of chitin and chitosan-based polysaccharides in the food, biomedical, pharmaceutical, environmental, and other diverse applications.

Gold nanocubes embedded biocompatible hybrid hydrogels for electrochemical detection of H2O2

Smart electrochemical biosensors have emerged as a promising alternative analytical diagnostic tool in recent clinical practice. However, improvement in the biocompatibility and electrical conductivity of the biosensor matrix and the immobilization of various bioactive molecules such as enzymes still remain challenging. The present research reports the synthesis of a biocompatible hydrogel network and its integration with gold nanocubes (AuNCs) for developing a novel biosensor with improved functionality. The interpenetrating hydrogel network consist of biopolymers developed using graft co-polymerization of β-cyclodextrin (β-CD) and chitosan (CS). The novelty of this work is in integrating the CS-g-β-CD hydrogel network with conductive AuNCs for improving hydrogel conductivity, biosensor sensitivity and use of the material for a biocompatible sensor. The present protocol advances the state of the art for the utilization of biopolymeric hydrogels system in synergy with an enzymatic biosensing protocol for exclusively detecting hydrogen peroxide (H₂O₂). Immobilization of the mitochondrial protein, cytochrome c (cyt c) into the hydrogel nanocomposite matrix was performed via thiol cross-linking. This organic-inorganic hybrid nanocomposite hydrogel matrix exhibited high biocompatibility (RAW 264.7 and N2a cell lines), improved electrical conductivity to attain high sensitivity (1.2 mA mM^-1 cm^-2) and a low detection limit (15 × 10^-9 M) for H₂O₂.

Meso-Cellular Silicate Foam-Modified Reduced Graphene Oxide with a Sandwich Structure for Enzymatic Immobilization and Bioelectrocatalysis

An integrated composite of meso-cellular silicate foam (MCF)-modified reduced graphene oxide (MCF@rGO) was designed and synthesized based on polyethylene oxide-polypropylene oxide-polyethylene oxide (P123)-modified rGO (P123-rGO). As the polymeric template for the fabrication of mesoporous silicates, modified P123 greatly improved the affinity between the nanosheet and the in situ formed MCFs, resulting in the formation of thin layers of MCFs on both sides of rGO. Therefore, the MCFs@rGO formed exhibited a unique sandwich structure with an inner skeleton of rGO and two outer layers of MCFs. The outer modification by MCFs, with the presence of large mesopores, not only shifted the surface property of rGO from hydrophobic to hydrophilic but also offered immobilized enzymes a favorable microenvironment to maintain their bioactivity. Meanwhile, the inner skeleton of rGO compensated for the weak conductivity of MCFs, providing a pathway for the direct electron transfer (DET) of various redox enzymes or proteins, such as hemoglobin (Hb), horseradish peroxidase, glucose oxidase (GOD), and cholesterol oxidase. It was found that the DET signal obtained from Hb-MCFs@rGO/glassy carbon electrode (GCE) was much larger than the sum of the signals from two components-based modified electrodes of Hb-P123-rGO/GCE and Hb-MCFs/GCE. A similar improvement in DET signal was also observed using GOD-MCFs@rGO/GCE. The significant enhancement of DET signals for both protein electrodes can be ascribed to the synergistic effects generated from the integration of the two components, one of which enhances biocompatibility and the other enhances conductivity. The bioelectrocatalytic performance of Hb and GOD electrodes was further investigated. As for Hb-MCFs@rGO/GCE, the GOD electrode displayed excellent analytical performance for the detection of hydrogen peroxide (H₂O₂), including a good sensitivity of 0.25 μA μmol^-1 L cm^-2, a low detection limit of 63.6 nmol L^-1 based on S/N = 3, and a low apparent Michaelis-Menten constant (K_M^app) of 49.05 μmol L^-1. GOD-MCFs@rGO/GCE also exhibited good analytical performance for the detection of glucose, with a wide linear range of 0.25-8.0 mmol L^-1. In addition, blood glucose detection in samples of human serum was successfully achieved using GOD-MCFs@rGO/GCE with a low quantification limit.

A single nanowire sensor for intracellular glucose detection

Glucose metabolism plays an important role in cell energy supply, and quantitative detection of the intracellular glucose level is particularly important for understanding many physiological processes. Glucose electrochemical sensors are widely used for blood and extracellular glucose detection. However, intracellular glucose detection cannot be achieved by these sensors owing to their large size and consequent low spatial resolution. Herein, we developed a single nanowire glucose sensor for electrochemical detection of intracellular glucose by depositing Pt nanoparticles (Pt NPs) on a SiC@C nanowire and further immobilizing glucose oxidase (GOD) thereon. Glucose was converted by GOD to an electroactive product H2O2 which was further electro-catalyzed by Pt NPs. The glucose nanowire sensor is endowed with a high sensitivity, high spatial-temporal resolution and enzyme specificity due to its nanoscale size and enzymatic reaction. This allows the real-time monitoring of the intracellular glucose level, and the increase of the intracellular glucose level induced by a novel potential hypoglycemic agent, reinforcing its potential application in lowering the blood glucose level. This work provides a versatile method for the construction of enzyme-modified nanosensors to electrochemically detect intracellular non-electroactive molecules, which is of great benefit for physiological and pathological studies.

Electrodeposition⁻Assisted Assembled Multilayer Films of Gold Nanoparticles and Glucose Oxidase onto Polypyrrole-Reduced Graphene Oxide Matrix and Their Electrocatalytic Activity toward Glucose

The study reports a facile and eco-friendly approach for nanomaterial synthesis and enzyme immobilization. A corresponding glucose biosensor was fabricated by immobilizing the gold nanoparticles (AuNPs) and glucose oxidase (GOD) multilayer films onto the polypyrrole (PPy)/reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) via the electrodeposition and self-assembly. PPy and graphene oxide were first coated on the surface of a bare GCE by the electrodeposition. Then, AuNPs and GOD were alternately immobilized onto PPy-RGO/GCE electrode using the electrodeposition of AuNPs and self-assembly of GOD to obtain AuNPs-GOD multilayer films. The resulting PPy-RGO-(AuNPs-GOD)_n/GCE biosensors were used to characterize and assess their electrocatalytic activity toward glucose using cyclic voltammetry and amperometry. The response current increased with the increased number of AuNPs-GOD layers, and the biosensor based on four layers of AuNPs-GOD showed the best performance. The PPy-RGO-(AuNPs-GOD)₄/GCE electrode can detect glucose in a linear range from 0.2 mM to 8 mM with a good sensitivity of 0.89 μA/mM, and a detection limit of 5.6 μM (S/N = 3). This study presents a promising eco-friendly biosensor platform with advantages of electrodeposition and self-assembly, and would be helpful for the future design of more complex electrochemical detection systems.

Advances in Carbon Nanotubes-Hydrogel Hybrids in Nanomedicine for Therapeutics

In spite of significant advancement in hydrogel technology, low mechanical strength and lack of electrical conductivity have limited their next-level biomedical applications for skeletal muscles, cardiac and neural cells. Host-guest chemistry based hybrid nanocomposites systems have gained attention as they completely overcome these pitfalls and generate bioscaffolds with tunable electrical and mechanical characteristics. In recent years, carbon nanotube (CNT)-based hybrid hydrogels have emerged as innovative candidates with diverse applications in regenerative medicines, tissue engineering, drug delivery devices, implantable devices, biosensing, and biorobotics. This article is an attempt to recapitulate the advancement in synthesis and characterization of hybrid hydrogels and provide deep insights toward their functioning and success as biomedical devices. The improved comparative performance and biocompatibility of CNT-hydrogels hybrids systems developed for targeted biomedical applications are addressed here. Recent updates toward diverse applications and limitations of CNT hybrid hydrogels is the strength of the review. This will provide a holistic approach toward understanding of CNT-based hydrogels and their applications in nanotheranostics.

Ultrafine Pt–Ni bimetallic nanoparticles anchored on reduced graphene oxide nanocomposites for boosting electrochemical detection of dopamine in biological samples

The present report demonstrates the development of a Pt–Ni/rGO composite electrochemical sensor for the detection of dopamine.

Microwave Deposition of Palladium Catalysts on Graphite Spheres and Reduced Graphene Oxide Sheets for Electrochemical Glucose Sensing

This work outlines a synthetic strategy inducing the microwave-assisted synthesis of palladium (Pd) nanocrystals on a graphite sphere (GS) and reduced graphene oxide (rGO) supports, forming the Pd catalysts for non-enzymatic glucose oxidation reaction (GOR). The pulse microwave approach takes a short period (i.e., 10 min) to fast synthesize Pd nanocrystals onto a carbon support at 150 °C. The selection of carbon support plays a crucial role in affecting Pd particle size and dispersion uniformity. The robust design of Pd-rGO catalyst electrode displays an enhanced electrocatalytic activity and sensitivity toward GOR. The enhanced performance is mainly attributed to the synergetic effect that combines small crystalline size and two-dimensional conductive support, imparting high accessibility to non-enzymatic GOR. The rGO sheets serve as a conductive scaffold, capable of fast conducting electron. The linear plot of current response versus glucose concentration exhibits good correlations within the range of 1–12 mM. The sensitivity of the Pd-rGO catalyst is significantly enhanced by 3.7 times, as compared to the Pd-GS catalyst. Accordingly, the Pd-rGO catalyst electrode can be considered as a potential candidate for non-enzymatic glucose biosensor.

Synthesis of gold nanoparticles supported on functionalized nanosilica using deep eutectic solvent for an electrochemical enzymatic glucose biosensor

Engineering of nanoparticle (NP) surfaces offers an effective approach for the development of enzymatic biosensors or microbial fuel cells with a greatly enhanced direct electron transport process. However, lack of control over the surface functionalization process and the operational instability of the immobilized enzymes are serious issues. Herein, we demonstrate a facile and green deep eutectic solvent (DES)-mediated synthetic strategy for efficient amine-surface functionalization of silicon dioxide and to integrate small gold nanoparticles (AuNPs) for a glucose biosensor. Owing to the higher viscosity of the DES, it provides uniform surface functionalization and further coupling of the AuNPs on the SiO₂ support with improved stability and dispersion. The amine groups of the functionalized Au-SiO₂NPs were covalently linked to the FAD-center of glucose oxidase (GOx) through glutaraldehyde as a bifunctional cross-linker, which promotes formation of "electrical wiring" with the immobilized enzymes. The Au-SiO₂NP/GOx/GC electrode exhibits direct electron transfer (DET) for sensing of glucose with a sensitivity of 9.69 μA mM^-1, a wide linear range from 0.2 to 7 mM and excellent stability. The present green DES-mediated synthetic approach expands the possibilities to support different metal NPs on SiO₂ as a potential platform for biosensor applications.