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Continuous and non‐invasive glucose monitoring and imaging is important for disease diagnosis, treatment, and management. However, glucose monitoring remains a technical challenge owing to the dearth of tissue‐transparent glucose sensors. In this study, we present the development of near‐infrared fluorescent single‐walled carbon nanotube (SWCNT) based nanosensors directly functionalized with glucose oxidase (GOx) capable of immediate and reversible glucose imaging in biological fluids and tissues. We prepared GOx‐SWCNT nanosensors by facile sonication of SWCNT with GOx in a manner that—surprisingly—does not compromise the ability of GOx to detect glucose. Importantly, we find by using denatured GOx that the fluorescence modulation of GOx‐SWCNT is not associated with the catalytic oxidation of glucose but rather triggered by glucose‐GOx binding. Leveraging the unique response mechanism of GOx‐SWCNT nanosensors, we developed catalytically inactive apo‐GOx‐SWCNT that enables both sensitive and reversible glucose imaging, exhibiting a ΔF/F0 of up to 40 % within 1 s of exposure to glucose without consuming the glucose analyte. We finally demonstrate the potential applicability of apo‐GOx‐SWCNT in biomedical applications by glucose quantification in human plasma and glucose imaging in mouse brain slices. [ABSTRACT FROM AUTHOR]

In this work, we investigated the effect of multi-walled carbon nanotubes (MWCNTs) and bio-graphene (bG) on the structure and activity of glucose oxidase (GOx), as well as on the performance of the respective electrochemical glucose biosensors. Various spectroscopic techniques were applied to evaluate conformational changes in GOx molecules induced by the presence of MWCNTs and bG. The results showed that MWCNTs induced changes in the flavin adenine dinucleotide (FAD) prosthetic group of GOx, and the tryptophan residues were exposed to a more hydrophobic environment. Moreover, MWCNTs caused protein unfolding and conversion of α-helix to β-sheet structure, whereas bG did not affect the secondary and tertiary structure of GOx. The effect of the structural changes was mirrored by a decrease in the activity of GOx (7%) in the presence of MWCNTs, whereas the enzyme preserved its activity in the presence of bG. The beneficial properties of bG over MWCNTs on GOx activity were further supported by electrochemical data at two glucose biosensors based on GOx entrapped in chitosan gel in the presence of bG or MWCNTs. bG-based biosensors exhibited a 1.33-fold increased sensitivity and improved reproducibility for determining glucose over the sweat-relevant concentration range of glucose. [ABSTRACT FROM AUTHOR]

We investigated the versatility of a monolayer of organo‐modified single‐walled carbon nanotubes (SWCNTs) on a water surface as a template to maintain activity by adsorbing various biomolecules from the subphase. Organo‐modified SWCNTs with amphiphilic properties formed a Langmuir film on the subphase containing biomolecules, and adsorbed and immobilized biomolecules via electrostatic interactions. In this study, the interactions of trypsin, lysozyme, cytochrome C protein, glucose oxidase sugar chain polymer, deoxyribonucleic acid, and chitosan with SWCNTs at the air/water interface were investigated. The uniqueness of this study is that it shows the possibility of wide‐ranging applications by utilizing an organo‐modified SWCNT interfacial film as an adsorption template for various biomolecules. The expansion behavior of the surface pressure‐area isotherms indicated the existence of interactions between the organo‐modified SWCNTs monolayer on the water surface and the biomolecules. The morphology and spectroscopic properties of the films transferred onto solid substrates clearly indicate the adsorption and immobilization of biomolecular groups. DNA and chitosan were not immobilized on the organo‐modified SWCNTs film template; however, the other four enzyme/protein molecules were adsorbed onto the solid substrate and maintained their fine second‐order structures, even under harsh conditions. [ABSTRACT FROM AUTHOR]

The electron signals in the cell can be rapidly and accurately transmitted by the spatially confined and adjacently distributed enzyme pairs anchored in the cytomembrane. As inspiration, by leverage of tannic acid‐3‐aminopropyltriethoxysilane‐Fe (TA‐APTES‐Fe) ternary coating, for the first time, a mesoporous biosensing membrane is developed by orderly assembly and targeted confinement of Prussian blue (PB) and glucose oxidase (GOx) with neighborhood nanostructure in the 3D mesoporous carbon nanotubes (CNTs) membrane electrode. The mesoporous biosensing membrane extends the triple‐phase boundary from conventional 2D contact to 3D contact, promotes the transfer rates of the cascade reactants, enhances the proximity of PB, GOx, and the electrode, and achieves in–situ removal of interferents, thereby elevating the utilization of PB, enhancing the cascade reaction efficiency, increasing the availability of the electroactive hydrogen peroxide (H2O2), and improving its stability. It exhibits superior sensitivity (31.2 µA mM−1) and long‐term stability in continuous glucose monitoring with a negligible response drift for up to 8 h. In addition, the multienzyme mimic functions of PB are employed to imitate the "loosening‐degradation" membrane cleaning process via bubble scrubbing and Fenton oxidation, thereby fully regenerating the fouled biosensing membrane. This work provides a novel design strategy for biosensors toward efficient, reliable, and stable sensing. [ABSTRACT FROM AUTHOR]

With the emerging demand of implantable microelectronics, it essentially requires the fully integrated and reliable power supplies. The study reports a stretchable and flexible electrospinning‐based glucose/O2 biofuel cell with glucose oxidase bioanode, Pt/C cathode and thermoplastic polyurethane substrate, which is capable for adapting to the various stresses and strains caused by individual movement. The rigid benzene rings and elastic chain segments of thermoplastic polyurethane ensure its superior tensile property. Furthermore, the stable covalent connections between the activated carbon nanotubes (CNTs‐COOH) and glucose oxidase inside 3D thermoplastic polyurethane network are established by amide reaction to ensure the rapid direct electron transfer of bioanode and stable power output of device in flexible environments. The biofuel cell exhibits an open circuit voltage of 0.575 V, and high‐power density of 57 µW cm−2 in 5 mM glucose. Moreover, the power‐generation properties of implantable biofuel cell keep steady, and its power density exhibits limited fluctuations on the dorsum of rat when bending, stretching, and twisting in 28 days. There is no obvious local inflammation or systemic abnormalities in rats. It satisfies the impressive biocompatible requirement, demonstrating the promising potential of electrospinning‐based biofuel cell as a robust self‐sustained power source for implantable electronics. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx)-based electrodes are important for bioelectronics, such as glucose sensors. It is challenging to effectively link GOx with nanomaterial-modified electrodes while preserving enzyme activity in a biocompatible environment. To date, no reports have used biocompatible food-based materials, such as egg white proteins, combined with GOx, redox molecules, and nanoparticles to create the biorecognition layer for biosensors and biofuel cells. This article demonstrates the interface of GOx integrated with egg white proteins on a 5 nm gold nanoparticle (AuNP) functionalized with a 1,4-naphthoquinone (NQ) and conjugated with a screen-printed flexible conductive carbon nanotube (CNT)-modified electrode. Egg white proteins containing ovalbumin can form three-dimensional scaffolds to accommodate immobilized enzymes and adjust the analytical performance. The structure of this biointerface prevents the escape of enzymes and provides a suitable microenvironment for the effective reaction. The bioelectrode's performance and kinetics were evaluated. Using redox-mediated molecules with the AuNPs and the three-dimensional matrix made of egg white proteins improves the transfer of electrons between the electrode and the redox center. By engineering the layer of egg white proteins on the GOx-NQ-AuNPs-mediated CNT-functionalized electrodes, we can modulate analytical performances such as sensitivity and linear range. The bioelectrodes demonstrate high sensitivity and can prolong the stability by more than 85% after 6 h of continuous operation. The use of food-based proteins with redox molecule-modified AuNPs and printed electrodes demonstrates advantages for biosensors and energy devices due to their small size, large surface area, and ease of modification. This concept holds a promise for creating biocompatible electrodes for biosensors and self-sustaining energy devices. [ABSTRACT FROM AUTHOR]

This paper describes a simple electrochemical sensing platform based on single-walled carbon nanotube (SWCNT) electrodes for glucose detection. The device fabrication using O2-plasma treatment allows precision and uniformity for the construction of three SWCNT electrodes on the flexible plastic substrate. Glucose assay can be simply accomplished by introducing a glucose sample into the fabricated biosensor. The marked electrocatalytic and biocompatible properties of biosensors based on SWCNT electrodes with the incorporation of ferrocenecarboxylic acid and polyethylene glycol enable effective amperometric measurement of glucose at a low oxidation potential (0.3 V) with low interferences from coexisting species. The device shows efficient electroanalytical performances with high sensitivity (5.5 μA·mM−1·cm−2), good reproducibility (CV less than 3%), and long-term stability (over a month). A linear range of response was found from 0 to 10 mM of glucose with a fast response time of 10 s. This attractive electroanalytical device based on GOx/FCA/PEG/SWCNT electrodes offers a promising system to facilitate a new approach for diverse biosensors and electrochemical devices. [ABSTRACT FROM AUTHOR]

A highly sensitive electrochemical sensor is reported for glucose detection using carbon nanotubes grown in situ at low temperatures on photolithographically defined gold microelectrode arrays printed on a glass substrate (CNTs/Au MEA). One of the main advantages of the present design is its potential to monitor 64 samples individually for the detection of glucose. The selectivity of the fabricated MEA towards glucose detection is achieved via modification of CNTs/Au MEA by immobilizing glucose oxidase (GOx) enzyme in the matrix of poly (paraphenylenediamine) (GOx/poly (p-PDA)/CNTs/Au MEA). The electrocatalytic and electrochemical responses of the proposed sensing platform towards glucose determination were examined via cyclic voltammetry and electrochemical impedance spectroscopy. The developed impedimetric biosensor exhibits a good linear response towards glucose detection, i.e., 0.2–27.5 µM concentration range with sensitivity and detection limits of 168.03 kΩ−1 M−1 and 0.2 ± 0.0014 μM, respectively. The proposed glucose biosensor shows excellent reproducibility, good anti-interference property, and was successfully tested in blood serum samples. Further, the applicability of the proposed sensor was successfully validated through HPLC. These results supported the viability of using such devices for the simultaneous detection of multiple electroactive biomolecules of physiological relevance. [ABSTRACT FROM AUTHOR]

Diabetes remains a great threat to human beings' health and its world prevalence is projected to reach 9.9% by 2045. At present, the detection methods used are often invasive, cumbersome and time-consuming, thus increasing the burden on patients. In this paper, we propose a novel noninvasive and low-cost biosensor capable of detecting glucose in human sweat using enzyme-based electrodes for point-of-care uses. Specifically, an electrochemical method is applied for detection and the electrodes are covered with multilayered films including ferrocene-polyaniline (F-P), multi-walled carbon nanotubes (MWCNTs) and glucose oxidase (GOx) on Cu substrates (GOx/MWCNTs/F-P/Cu). The coated layers enhance the immobilization of GOx, increase the conductivity of the anode and improve the electrochemical properties of the electrode. Compared with the Cu electrode and the F-P/Cu electrode, a maximum peak current is obtained when the MWCNTs/F-P/Cu electrode is applied. We also study its current response by cyclic voltammetry (CV) at different concentrations (0–2.0 mM) of glucose solution. The best current response is obtained at 0.25 V using chronoamperometry. The effective working lifetime of an electrode is up to 8 days. Finally, to demonstrate the capability of the electrode, a portable, miniaturized and integrated detection device based on the GOx/MWCNTs/F-P/Cu electrode is developed. The results exhibit a short response time of 5 s and a correlation coefficient R2 of 0.9847 between the response current of sweat with blood glucose concentration. The LOD is of 0.081 mM and the reproducibility achieved in terms of RSD is 3.55%. The sweat glucose sensor is noninvasive and point-of-care, which shows great development potential in the health examination and monitoring field. [ABSTRACT FROM AUTHOR]

In this study, multi-walled carbon nanotubes/polythiophene composite (MWCNTs/PTh) modified glassy carbon electrode was used for the amperometric detection of glucose. Glucose oxidase (GOx) was entrapped by a crosslinking agent on the MWCNTs/PTh composite film synthesized by electrochemical polymerization of thiophene onto MWCNTs. Characterization of composite film was achieved by cyclic voltammetry (CV), fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques. The amperometric measurements of electrode was performed at +0.70V vs. SCE, which was the electrooxidation potential of enzymatically produced H2O2. The effects of thiophene amount in the composite, pH, temperature and substrate concentration were investigated on the response of enzyme electrode. Optimum pH was 7.0 at room temperature and the response time of enzyme electrode was 25 s. The upper limit of the linear working range was 4.85 mM glucose concentration. The limit of detection of sensor was calculated as 148 µM. The sensitivity of glucose biosensor was determined as 4.39 µA mM-1 cm-2 . The value of apparent Michaelis-Menten constant (KMapp) was 1.68 mM according to the Lineweaver-Burk equation. The activation energy of this immobilized enzyme system was 88.92 kJ mol-1 . [ABSTRACT FROM AUTHOR]

We proposed a specially designed sequential injection (SI) amperometric system coupling with a bioreactor for in-line glucose monitoring in cell culture. The system is composed of three main parts which are the bioreactor, SI system, and electrochemical detection unit. The bioreactor accommodates six individual cell culture units which can be operated separately under different conditions. The SI system enables automatic in-line sampling and in-line sample dilution, with a specially designed mixing unit; therefore, it has the benefits of fast analysis time and less contamination risk. The use of 3D-printed microfluidic components, a mixing channel, and a flow cell helped to reduce operational time and sample volume. A disposable screen-printed electrode (SPE), modified with glucose oxidase (GOD), carbon nanotube, and gold nanoparticle, was used for detection. The developed system provided a linear range up to 3.8 mM glucose in cell culture media. In order to work with cell culture in higher glucose media, the in-line sample dilution can be applied. The developed SI system was demonstrated with mouse fibroblast (L929) cell culture. The results show that glucose concentration obtained from the SI system is comparable with that obtained from the conventional colorimetric method. This work can be further developed and applied for in vitro cell-based experiments in biomedical research. [ABSTRACT FROM AUTHOR]

Effective wound management has the potential to reduce both the duration and cost of wound healing. However, traditional methods often rely on direct observation or complex and expensive biological testing to monitor and evaluate the invasive damage caused by wound healing, which can be time-consuming. Biosensors offer the advantage of precise and real-time monitoring, but existing devices are not suitable for integration with sensitive wound tissue due to their external dimensions. Here, we have designed a self-powered biosensing suture (SPBS) based on biofuel cells to accurately monitor glucose concentration at the wound site and promote wound healing. The anode of the SPBS consists of carbon nanotubes-modified carbon fibers, tetrathiafulvalene (TTF), and glucose oxidase (GOx), while the cathode is composed of Ag 2 O and carbon nanotubes modified nanotubes modified carbon fibers. It was observed that SPBS exhibited excellent physical and chemical stability in vitro. Regardless of different bending degrees or pH values, the maximum power density of SPBS remained above 92%, which is conducive to long-term dynamic evaluation. Furthermore, the voltage generated by SPBS reflects blood glucose concentration, and measurements at wound sites are consistent with those obtained using a commercially available blood glucose meter. SPBS achieves the healing effect of traditional medical sutures after complete healing within 14 days. It offers valuable insights for intelligent devices dedicated to real-time wound monitoring. [ABSTRACT FROM AUTHOR]

A novel electrochemical glucose biosensor was fabricated using the casting technique of multi-walled carbon nanotubes (MWCNT)/polyaniline (PANI)/carboxymethyl chitosan (CCs) as an appropriate matrix for glucose oxidase (GOx) immobilization. The differential pulse voltammetry (DPV) study results demonstrated a wide linear range of glucose concentrations from 10 nM to 10 μM, with a limit of detection (LOD) of 1.41 μM and a sensitivity of 1791 μA mM−1 cm−2. Additionally, cyclic voltammetry (CV) data analysis yielded a heterogeneous rate constant (ks) of 0.3 s−1 and an apparent Michaelis-Menten constant (k m app) of 18 nM. Over a 30-day period, the biosensor exhibited exceptional repeatability and stability, maintaining approximately 84.58 % of its initial performance for storage stability at 4 °C and 82.13 % for functional stability. Moreover, the reproducibility, interference resistance, and overall performance of the biosensor were assessed, demonstrating its capability to accurately measure glucose levels in human serum with a relative standard deviation (RSD) of <5 %. [Display omitted] • Utilization of a Novel Nanocomposite (MWCNT/PANI/CCs): This composite stabilizes glucose oxidase enzyme effectively. • Comprehensive Result Presentation: Results are thoroughly presented using various techniques such as FT-IR, XRD, EIS, FE-SEM, CV, and DPV. • High Sensitivity (1791 μAmM-1cm-2) and Remarkable Stability (84.58%): The biosensor exhibits excellent selectivity and accuracy in glucose measurement. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx) was immobilized between aligned carbon nanotube films (ACNTFs) using a cross-stacking method without any purification and functionalization processes. Direct electron transfer of GOx was achieved on the ACNTFs with reversible redox peaks observed at the formal potential of –0.448 V. When applied to the determination of glucose by cyclic voltammetry, the prepared enzymatic electrode exhibited a linear range from 1 to 5 mM under mediator-free physiological conditions, which makes it a promising candidate for the development of third-generation glucose biosensors. A new strategy was developed to immobilize glucose oxidase (GOx) between aligned carbon nanotube films, which achieved direct electron transfer of GOx for the electrocatalytic determination of glucose under mediator-free physiological conditions. [ABSTRACT FROM AUTHOR]

In this study we report the development of an amperometric cholesterol biosensor based on cholesterol oxidase from Pseudomonas sp. and catalase immobilized in carbon paste electrode (CPE) modified with multiwall carbon nanotubes (MWCNT) and ionic liquid (IL). The working electrode (CPE/MWCNT-IL/Microorganism (MO)-Catalase) was characterized by impedance spectroscopy and cyclic voltammetry at different stages of its construction. This proposed cholesterol biosensor performed linear relationship in the range of 5-600 μM with a low detection limit of 1.52 μM. The biosensor showed good sensitivity and high selectivity and it was successfully applied for the measurement of cholesterol levels in lyophilized serum samples. [ABSTRACT FROM AUTHOR]

Wearable skin sensors is a promising technology for real-time health care monitoring. They are of particular interest for monitoring glucose in diabetic patients. The concentration of glucose in sweat can be more than two orders of magnitude lower than in blood. In consequence, the scientific and technological efforts are focused in developing new concepts to enhance the sensitivity, decrease the limit of detection (LOD) and reduce the response time (RT) of glucose skin sensors. This work explores the effect of adsorbed superparamagnetic magnetite nanoparticles (MNPs) and conductive nanoparticles (CNPs) on carbon nanotube substrates (CNTs) used to immobilize glucose oxidase enzyme in the working electrode of skin sensors. MNPs and CNPs are made of magnetite and gold, respectively. The performance of the sensors was tested in standard buffer solution, artificial sweat, fresh sweat and on the skin of a healthy volunteer during an exercise session. In the case of artificial sweat, the presence of MNPs accelerated the RT from 7 to 5 s at the expense of increasing the LOD from 0.017 to 0.022 mM with slight increase of the sensitivity from 4.90 to 5.09 μAm M−1 cm−2. The presence of CNPs greatly accelerated the RT from 7 to 2 s and lowered the LOD from 0.017 to 0.014 mM at the expense of a great diminution of the sensitivity from 4.90 to 4.09 μAm M−1 cm−2. These effects were explained mechanistically by analyzing the changes in the concentration of free oxygen and electrons promoted by MNPs and CNPs in the CNTs and its consequences on the the glucose oxidation process. [ABSTRACT FROM AUTHOR]

Polyaniline was electrochemically polymerized onto the platinum electrode modified with a mixture of Nafion and multiwalled carbon nanotube (PANI/MWCNT/Nf/Pt) to detect ammonium ion. The nanobiosensor (ASNase/PANI/MWCNT/Nf/Pt) was then prepared by immobilizing L-asparaginase (L-ASNase) on the PANI/MWCNT/Nf nanocomposite. The prepared nanobiosensor was used for the rapid and sensitive detection of serum concentration of the anticancer agent L-asparagine (L-Asp) during chemotherapy. The nanobiosensor has dynamic ranges of zero to 180 μM. The sensitivity of the nanobiosensor was 0.829 μA μM−1 cm−2, and the response time was less than 30 s. The detection limit was 140 nM of L-Asp. The Michaelis–Menten constant ( K m ) was measured to be 36.2 mM. The nanobiosensor was successfully applied for the determination of L-Asp in the blood samples of leukemia patients. [ABSTRACT FROM AUTHOR]

In this study, a new biosensor based on modified glucose oxidase (mGOx) and carbon nanotubes was designed. Firstly, the glucose oxidase(GOx) was chemically modified by ionic liquid to obtain a new enzyme mGOx. Secondly, ß cyclodextrin (ß-CD) was combined with multi-wall carbon nanotubes (MWCNTs) to prepare ß-CD/MWCNTs composite carrier. Finally, mGOx was loaded on the ß-CD/MWCNTs composite material to construct a new biosensor mGOx/ß-CD/MWCNTs/GCE. And it was used for the determination of glucose in honey. The prepared enzyme biosensor could sensitively detect glucose, the detection range was between 50 µM ~ 1.15 mM, the sensitivity was 35.44 µA·mM-1cm-2, and the detection limit was as low as 0.27 µM. The biosensor had good stability (95.8% current retention within two weeks), reproducibility (n = 10, relative standard deviation (RSD) = 1.6%) and anti-interference. More importantly, actual samples test showed that the glucose biosensor could be successfully applied to the detection of glucose in honey. [ABSTRACT FROM AUTHOR]

The short lifetime and low sensitivity of the current glucose electrochemical sensors are two major issues for implementing continuous real-time monitoring of glucose in vivo. Here we show that a unique microneedle-based glucose monitoring skin patch (termed here MGMSP) can continuously measure glucose in real time in live animals with micromolar sensitivity and over 14 days of service life. This MGMSP employs a glucose oxidase (GOD) and carbon nanotube (CNT) modified hollow syringe as electrochemical sensor for glucose monitoring, an integrated circuit for signal processing and transmission, and the real-time glucose levels are displayed on smartphone via Bluetooth. The designed microneedle device protects the stability of the sensing molecules immobilized within the inner surface of hollow syringe and simultaneously the interior space of hollow syringe substantially increases the amount of immobilized sensing molecules. This microneedle design thus extends the lifetime as well as improves the detection sensitivity. The final MGMSP enables the continuous real-time monitoring of glucose in the interstitial fluid of live rats. This innovative microneedle-based MGMSP could potentially provide the public with high-accuracy continual glucose monitoring. [ABSTRACT FROM AUTHOR]

The expression level of glucose transporter 1 (GLUT-1) is highly correlated with tumor malignancy, making it a promising therapeutic target for cancer treatment. The detection of GLUT-1 expression level is significant for cancer discovery and valuating the efficacy of drug treatments. However, current methods for GLUT-1 detection primarily rely on traditional techniques. Therefore, the development of anon-destructive in vivo monitoring system would be invaluable for assessing GLUT-1 expression and tumor responses to various drugs. In this study, an electrochemical platform for detection of GLUT-1 on living cells was established using reduced graphene oxide-multi-wall carbon nanotube composite (rGO-MWCNT) as a conductive coating and toluidine blue O (TBO)-graphene-gold nanoparticle-GLUT-1 antibody as the electrochemical probe. The sensor demonstrated excellent performance in detecting GLUT-1 on cells with a linear range of 10 - 105 cells/mL, good stability and selectivity. The sensor successfully detected GLUT-1 expressions in multiple tumor cell types, including those treated with siRNA or drugs, and the results were consistent with those obtained from traditional methods such as flow cytometry, western blotting, and immunofluorescence. The sensor is promising in evaluating the malignant level of tumor cells, distinguishing glucose uptake pathways in tumor cells, reducing medical costs, and facilitating the translation of electrochemical sensing technology to the clinical settings. • Our biosensor specifically recognizes GLUT-1 protein expressed on the surface of living cancer cells. • The electrical signal produced by the biosensor exhibits changes corresponding to changes in cell number. • Our biosensor is quick and easy to implement and paves the way for in situ evaluation of GLUT-1 and related drug. • The design features of the sensor allow simultaneous detection of multiple cells and clinical samples. [ABSTRACT FROM AUTHOR]

We used conducting redox-active polymers based on chitosan and bovine serum albumin (BSA), covalently bound to mediators ferrocene or Neutral Red, or thionine, modified by carbon nanotubes, as a base of an amperometric biosensor for determining glucose. The structure of the obtained polymers was studied by IR spectroscopy and scanning electron microscopy. Their electrochemical characteristics were studied by cyclic voltammetry. The redox-active polymer based on BSA covalently bound to ferrocene and modified by carboxylated carbon nanotubes demonstrated the most promising characteristics. The biosensor based on the selected hybrid polymer is characterized by high sensitivity, a lower limit of determined concentrations of 0.05 mM, and a high correlation coefficient (R = 0.9919) with the results of determination of glucose in human blood by an alternative method. [ABSTRACT FROM AUTHOR]

Biosensing has capitalized on the excellent characteristics and properties of nanostructures for detecting glucose levels in diabetic patients. In glucose sensing systems, the fabrication of a suitable matrix for immobilizing glucose oxidase (GOx) has become more interesting for the application of nanofibers in enzymatic electrochemical biosensors. These nanofiber based electrochemical biosensors are superior in manufacturability and performance due to low cost, diversity of materials, ease of miniaturization, response time, durability, and structure versatility. This perspective highlights the latest material integration of various nanofibrous composite membranes of carbon nanotubes, carbon nanofibers, conductive nanoparticles and conductive polymers, that provide large matrix-like, porous surfaces to enhance the immobilization of enzymes, for the fabrication of glucose biosensors. [ABSTRACT FROM AUTHOR]

We report the development of a dual-enzyme electrochemical biosensor based on microfabricated gold band array electrodes which were first modified by gold foam (Au-foam) in order to dramatically increase the active surface area. The resulting nanostructured Au-foam deposits then served as a highly porous 3D matrix for the electrodeposition of a nanocomposite film consisting of multi walled carbon nanotubes embedded in a chitosan matrix (CS:MWCNT) designed to provide a conducting, biocompatible and chemically versatile surface suitable for the attachment of a wide range of chemically or biologically active agents. Finally, a dual enzyme mixture of glucose oxidase (GOx) and horseradish peroxidase (HRP) was immobilised onto the CS:MWCNT nanocomposite film surface. It is shown that the resulting sensing platform developed demonstrates excellent analytical performance in terms of glucose detection with a sensitivity of 261.8 μA mM−1 cm−2 and a reproducibility standard deviation (RSD) of 3.30% as determined over 7 measurements. Furthermore, long term stability studies showed that the electrodes exhibited an effectively unchanged response to glucose detection after some 45 days. The example of glucose detection presented here illustrates the fact that the particular combination of nanostructured materials employed represents a very flexible platform for the attachment of enzymes or indeed any other bioactive agent and as such may form the basis of the fabrication of a wide range of biosensors. Finally, since the platform used is based on lithographically-deposited gold electrodes on silicon, we note that it is also very suitable for further miniaturisation, mass production and packaging- all of which would serve to reduce production costs. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotubes coated with cobalt(II) sulfide nanoparticles were prepared and used for immobilization of glucose oxidase (GOx) to obtain an electrochemical glucose biosensor. The nanocomposite was synthesized through an in-situ hydrothermal method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electrochemical impedance spectroscopy. The results show that the nanocomposite possesses a large specific surface area and apparently enhances the direct electron transfer between GOx and the surface of the electrode, best at a potential near −0.43 V (vs. SCE). The immobilized GOx retains its good bioactivity even at a high surface coverage of 30 pmol cm−2. Under the optimum conditions. The biosensor exhibits a wide linear range (from 8 μM to 1.5 mM), a high sensitivity (15 mA M −1 cm−2), and a 5 μM detection limit (at S/N = 3). The sensor is selective, acceptably repeatable, specific and stable. [ABSTRACT FROM AUTHOR]

Bioanode stability with glucose oxidase was enhanced significantly by covalent crosslinking without substantial enzymatic activity and affinity loss. Initially, glucose oxidase was immobilized by aldehyde groups on the electrode that was developed using ferrocenecarboxaldehyde, polyethyleneimine, multiwall carbon nanotubes, and carbon cloth for biofuel cell applications. The glucose oxidase half-life was extended by more than 4 times, from 27.2 to 124.7 h, after the electrode was crosslinked. Enzymatic kinetic parameters were determined for the crosslinked enzyme and they were compared to the noncrosslinked immobilized enzyme parameters on the electrode. The apparent substrate affinity of the crosslinked enzyme electrode was decreased (i.e. kM was increased) by 16%, while the maximum reaction rate was decreased by only 3%, by the crosslinking process. Moreover, effects of the electrolyte type (i.e. buffer type) and concentration on the performance of the crosslinked enzyme electrode were evaluated and appropriate conditions were determined. [ABSTRACT FROM AUTHOR]

We report an innovative supramolecular architecture for bienzymatic glucose biosensing based on the non‐covalently functionalization of multi‐walled carbon nanotubes (MWCNTs) with two proteins, glucose oxidase (GOx) (to recognize glucose) and avidin (to allow the specific anchoring of biotinylated horseradish peroxidase (b‐HRP)). The optimum functionalization was obtained by sonicating for 10 min 0.50 mg mL−1 MWCNTs in a solution of 2.00 mg mL−1 GOx+1.00 mg mL−1avidin prepared in 50 : 50 v/v ethanol/water. The sensitivity to glucose for glassy carbon electrodes (GCE) modified with MWCNTs‐GOx‐avidin dispersion and b‐HRP (GCE/MWCNTs‐GOx‐avidin/b‐HRP), obtained from amperometric experiments performed at −0.100 V in the presence of 5.0×10−4 M hydroquinone, was (4.8±0.3) μA mM−1 (r2=0.9986) and the detection limit was 1.2 μM. The reproducibility for 5 electrodes using the same MWCNTs/GOx‐avidin dispersion was 4.0 %, while the reproducibility for 3 different dispersions and 9 electrodes was 6.0 %. The GCE/MWCNT‐GOx‐avidin/b‐HRP was successfully used for the quantification of glucose in a pharmaceutical product and milk. [ABSTRACT FROM AUTHOR]

Electropolymerization of brilliant cresyl blue (BCB) in ethaline deep eutectic solvent (DES) has been carried out. Poly(brilliant cresyl blue) (PBCB) films were formed by electrodeposition on carbon nanotube modified glassy carbon electrodes by potential cycling in ethaline (choline chloride + ethylene glycol) with the addition of different ionic species i.e. NO 3 −, SO 4 2−, Cl−, ClO 4 −. The novel nanocomposite films were characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The composition of the polymerization solution had a large influence on the morphology as well as on the electrochemical behaviour of the electrodeposited films. The effect of scan rate on BCB polymerization was also investigated and the PBCB film synthesized at 150 mV s−1 in ethaline + NO 3 − presented a superior electrochemical performance. The PBCB Ethaline -HNO 3 /MWCNT and PBCB aqueous /MWCNT nanocomposite films were used as electrode support for the enzymes glucose oxidase and tyrosinase for the biosensing of glucose and catechol, respectively and were more sensitive than the PBCB based electrodes prepared in aqueous solution. Image 101 • Electropolymerization of brilliant cresyl blue (BCB) in ethaline DES. • Ethaline doped with various acids (HNO 3 , H 2 SO 4 , HCl, HClO 4) for BCB polymerization. • Morphology of PBCB films influenced by polymerization solution composition. • Improved electrochemical performance of PBCB DES compared with PBCB aqueous films. • Application of PBCB DES modified carbon nanotubes as enzyme biosensors. [ABSTRACT FROM AUTHOR]

• ConA successfully disperses MWCNTs and gives to them biorecognition properties. • ConA maintains the recognition properties after the drastic dispersing conditions. • GCE/MWCNTs-ConA is a versatile platform to immobilize glycobiomolecules using HRP and GOx as proof-of-concept. • GCE/MWCNT-ConA/HRP-GOx allowed the highly sensitive/selective quantification of glucose. • GCE/MWCNT-ConA/HRP-GOx was successfully used to quantify glucose in complex matrices like human serum. We propose an innovative nanoarchitecture for the development of electrochemical biosensors based on the non-covalent functionalization of multi-walled carbon nanotubes (MWCNTs) with the lectin Concanavalin A (ConA) and the site-specific supramolecular binding of glycobiomolecules. As proof-of-concept, we propose the use of two glycoenzymes, glucose oxidase (GOx) and horseradish peroxidase (HRP), for building mono and bienzymatic glucose biosensors. The selected conditions for the preparation of the dispersion were 1.5 mg MWCNTs in 1.0 mL of 2.0 mg mL−1 ConA sonicated for 5.0 min with sonicator probe. The monoenzymatic glucose biosensor was prepared by casting GCE with the MWCNTs-ConA dispersion (GCE/MWCNTs-ConA) followed by the interaction with GOx (GCE/MWCNTs-ConA/GOx), while the bienzymatic one was obtained by interaction of GCE/MWCNTs-ConA with GOx + HRP (GCE/MWCNTs-ConA/GOx-HRP). The best analytical performance was obtained with the bienzymatic biosensor from the amperometric response at -0.050 V in the presence of 1.0 × 10-4 M hydroquinone. The sensitivity was (2.22 ± 0.03) μA mM−1 (which was 5.2 times higher than the one obtained with the monoenzymatic biosensor) and a detection limit of 0.31 μM. The reproducibility was 5.4% and the biosensor was challenged with human blood serum showing an excellent correlation with the values reported by the laboratory. [ABSTRACT FROM AUTHOR]

A novel and robust enzymatic biosensing platform with high sensitivity is developed based on facile one-step assembled bio-nanocomposites with enzymes-loaded polymeric nanoparticles decorating multi-walled carbon nanotubes (MWCNTs). An amphiphilic copolymer PAVE containing photo-cross-linkable coumarin segments and carboxylic groups was co-assembled with MWCNTs in aqueous solution while encapsulating the model enzyme namely glucose oxidase (GOx) simultaneously, generating necklace-like bio-nanocomposites (GOx@PAVE-CNTs) with GOx-loading polymeric nanoparticles as nanobeads and MWCNTs as conducting micron-string. Then the GOx@PAVE-CNTs bio-nanocomposites were electro-deposited onto electrode surface and a robust biosensing complex film with porous network structure was formed after following photo-cross-linking. Consequently, an enzymatic glucose biosensor was successfully constructed. The biosensor exhibited ultrafast response (<3 s) to glucose with a considerably wide linear range (1.0 μM ∼ 5 mM) and a low detection limit (0.36 μM) for glucose detection. High sensitivity and selectivity of the biosensor toward glucose were also well demonstrated. Furthermore, the biosensor showed exceptionally good stability and reproducibility. More importantly, the glucose biosensor was practically used for glucose detection from human urine and serum samples with satisfactory results. As a proof-of-concept strategy, this facile and effective strategy for biosensor fabrication is of considerable interest because of its versatility to be generalized to many other enzymatic biosensor systems, exhibiting promising and practical potential in bio-medical and life health applications. Image 1 • Necklace-like bio-sensing nanocomposite was developed by facile one step co-assembly of GOx, copolymer and MWCNTs. • A robust enzymatic biosensor was constructed by electrophoretic deposition of the bio-nanocomposite on electrode surface. • The biosensor showed fast response, high sensitivity and stability, good reproducibility towards glucose detection. • Satisfactory analytical results were obtained from real samples, demonstrating great potential in practical applications. [ABSTRACT FROM AUTHOR]

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Electron transfer (ET) reactions in bioelectrocatalysis of enzymes at electrode surfaces require not only the efficient immobilization, but also highly conductive nanostructured platform, which allows for retaining its bioactivity and structural conformation. The novel architecture of spatially separated electrochemically reduced graphene oxide (ERGO) by multi‐walled carbon nanotubes functionalized with 4‐(pyrrole‐1‐yl) benzoic acid (MWCNT/PyBA) with the accurate porous structure could be an alternative for earlier approaches to the construction of bioelectrocatalytic systems with rapid diffusion of reagents from the solution to the enzyme molecule. The formation of ERGO/MWCNT/PyBA system was confirmed by electrochemical, spectroscopic and microscopic methods. The cyclic voltammetry experiments revealed that the presence of ERGO in the conductive material affects the electronic communication between the enzyme molecule and modified electrode surface greatly improving its ET properties resulting in a double increase of the heterogeneous ET rate constant value (ks=6.5 s−1). The fabricated glucose oxidase based biosensor sensitively detects glucose, therefore, ERGO/MWCNT/PyBA architecture could provide a novel and efficient platform for immobilization of redox enzymes. [ABSTRACT FROM AUTHOR]

The characteristics of biosensors based on screen-printed electrodes containing glucose oxidase, alcohol oxidase, lactate oxidase, and a mixture of glucose oxidase and γ-amylase are studied. The enzymes have been immobilized in a conductive hydrogel of cross-linked bovine serum albumin modified with carbon nanotubes. The developed biosensors are applicable for the quantification of glucose, ethanol, lactic acid, and starch in fermentation media. The analytical and metrological characteristics of these biosensors are determined. The developed biosensor system allows for quantification of glucose, ethanol, lactate, and starch in the concentration range of 0.1–2.7, 1–27, 0.02–73 mM, and 0.6–21 g/L, respectively. Samples of alcoholic and fermented milk products, kvass, and fermentation mass have been analyzed. Statistical analysis of the assay results shows that glucose, ethanol, lactic acid, and starch concentrations determined by biosensors insignificantly differ from those determined by the reference methods. The developed set of biosensors based on specifically selected enzymes can be used for effective monitoring of biotechnological processes as an alternative to the conventional analytical methods. [ABSTRACT FROM AUTHOR]

Highly sensitive detection of H2O2 and glucose is critical for fundamental research and disease diagnosis. A ratiometric sensor can simultaneously afford two readout signals that provide an internally normalized response to change, thereby reducing false results and improving detection accuracy. A novel ratiometric fluorescent nanosensor for ultrasensitive detection of hydrogen peroxide and glucose was constructed on the basis of the peroxidase-like properties of a hierarchical cobalt/carbon nanotube hybrid nanocomplex (Co-CNT). The as-prepared Co-CNT catalyzes the transformation of the non-fluorescent Amplex Red (AR) into a fluorescent derivative and the transformation of fluorescent scopoletin (SC) into a non-fluorescent derivative in the presence of H2O2. The sensing system changes colour from yellow to blue, which can be clearly seen with the naked eye. With the fluorescence ratio of AR to SC as readout, the detection limit of H2O2 reaches as low as 100 nM. The developed assay is further utilized for determining H2O2-related oxidase reactions with the glucose and glucose oxidase system as model. Glucose can be selectively and sensitively detected as low as 150 nM. Satisfactory recoveries are obtained for glucose detection in serum samples. The developed assay is simple in terms of preparation and operation and provides a straightforward method for cost-effective and reliable detection of H2O2 and H2O2-related reactions in clinical diagnosis and biomedical applications. Graphical abstract [ABSTRACT FROM AUTHOR]

Abstract The in situ electrodeposition of cholesterol oxidase (ChOx)-modified polydopamine (PDA) thin film on nanostructured-screen printed electrodes (SPEs) is described here. Prussian Blue (PB) and multi-wall carbon nanotubes (MWCNTs) were used for their outstanding properties in biosensing applications. Cyclic Voltammetry (CV), Constant Potential Amperometry (CPA) and Electrochemical Impedance Analysis (EIS) were used to confirm the correct electrodeposition of the enzyme-modified PDA thin film on the SPE. In addition, the assembly protocol was fully revised to optimize the biosensor response. The proposed cholesterol biosensor showed Michaelis-Menten behavior with Kapp M , V max and Hill parameter values of 1.97 mM, 7.33 μA and 1.06, respectively. Biosensor sensitivity, stability, reproducibility, repeatability and anti-interference properties were obtained and confirmed the feasibility of using this biosensor for cholesterol determination. In order to show the applicability of such an approach, the biosensor was incorporated in a Flow Injection Analysis (FIA) device and had a high sensitivity of 32.14 mA M−1 cm−2 (R2 = 0.999), a linear range over two orders of magnitude and a detection limit (S/N = 3) of 1.5 μM. The results confirmed the success of the biosensor for determining cholesterol in future applications in diagnostic laboratories. Graphical abstract Unlabelled Image Highlights • A new method for obtaining cholesterol oxidase-modified thin film is reported. • Polydopamine thin film results convenient for enzymatic immobilization. • Enzyme-modified thin film is used in biosensing applications. • The main analytical parameters and its application in FIA devices are presented. • The outstanding anti-interference properties of such biosensor are confirmed. [ABSTRACT FROM AUTHOR]

In this paper, a composite material comprised of ZnFe2O4 nanomaterial, carbon nanotubes (CNT) and glucose oxidase (GOD) was synthesized and used for glucose detection. ZnFe2O4–CNT was formed by a one-step solvothermal approach using acid-treated CNT as precursor, then GOD was linked to it by coupling reaction between –NH2 and –COOH. After addition of glucose, which is oxidized by GOD, the intermediate product (H2O2) further oxidizes the 3,3′,5,5′-tetramethylbenzidine (TMB) substrate and forms a blue product. This process was accelerated in the presence of peroxidase-mimic ZnFe2O4 nanomaterial and the detected signal intensity was correspondingly enhanced. The linear detection range of glucose was 0.8 to 250 μM, with a limit of detection of 0.58 μM. This may originate from (1) the limited diffusion of intermediate species, which resulted in enhanced local concentrations of reaction compounds; (2) enhanced electron transmission among CNT, GOD and ZnFe2O4; (3) the synergistic enhancement of catalytic activity of ZnFe2O4 compared with other metal oxides; (4) the high loading capacity of ZnFe2O4–CNT for GOD molecules, because of its high surface-to-volume ratio. Meanwhile, this method has reasonable selectivity, stability and reusability and can be used for real serum detection, which may be useful for the development of sensitive biosensors. [ABSTRACT FROM AUTHOR]

Abstract A multifunctional bioelectrocatalytic material that permits shifting the onset potential for the oxidation of glucose to the value starting below −0.2 V (vs. Ag/AgCl) is described. It includes carbon nanotubes modified with 4‑(pyrrole‑1‑yl) benzoic acid, which introduces carboxyl groups that play an important role in enzyme (glucose oxidase) immobilization and improve the stability of the system. Glucose oxidase has been immobilized by a chemical crosslinking method, where bovine serum albumin and glutaraldehyde are used as a blocking and a crosslinking agent, respectively. Here N -methylphenazonium methyl sulfate has been considered as co-catalyst and a component of the redox mediating system facilitating the effective flow of electrons from redox centers of the enzyme to the electrode surface at fairly negative potentials. The mediator has been confined to the system by the electrostatic attraction with the sulfonate groups of Nafion. Dynamics of charge propagation in the proposed hybrid bioelectrocatalytic films have been assessed from chronocoulometric measurements. The combination of carbon nanotubes, glucose oxidase and N -methylphenazonium methyl sulfate produces a system that is capable of effective oxidation of glucose in 0.1 mol dm−3 phosphate buffer solution at pH 7.0. It can be concluded on the basis of various biochemical and electroanalytical approaches that the system is well-behaved, stable, and redox facile. The Michaelis-Menten constant and the maximum current density (measured in the glucose-containing solutions) are 18 mmol dm−3 and 0.32 mA cm−2, respectively. By referring to fundamentals of electrochemical kinetic analysis, the rate constant in heterogeneous units, 5 ∗ 10−5 cm s−1, has been determined. The calibration plot has a linear response range for glucose concentrations up to ca. 10–12 mmol dm−3 (sensitivity, 12.1 μA mmol−1 dm3 cm−2). An observation of importance to the biofuel cell technology is the appearance of the glucose oxidation voltammetric peak at fairly negative potentials, namely ca. −0.05 V (vs. Ag/AgCl). Highlights • Functionalized carbon nanotubes, glucose oxidase and N -methylphenazonium methyl sulfate mediator are integrated here. • The system has is characterized by fast charge propagation and by stabilizing interactions between components. • Electrooxidation of glucose at relatively low potential and with reasonably high current densities has been observed at pH 7. • The system is redox facile and well-behaved based on data of biochemical and heterogeneous electrochemical kinetic analyses. [ABSTRACT FROM AUTHOR]

Abstract The demand of new and environmentally friendly energy sources has induced the research and development of technologies for the energy generation from organic compounds. Among these strategies of energy production by bioelectrochemical systems the enzymatic fuel cells show several potential applications including as power suppliers for non-invasive and implantable medical devices. In this work, a new membrane-less enzymatic biofuel cell based on mediated electron transfer glucose oxidase-anode and direct electron transfer laccase-cathode operated in acidic conditions has been designed and characterized. Both, glucose oxidase/hydroquinone anode and laccase cathode were obtained by enzyme covering on gold electrodes modified with single-walled carbon nanotubes. The maximal current density generated was 3.87 and 2.36 mA cm−2 for the anode and cathode, respectively. The glucose/O 2 biofuel cell showed an OCV of 0.52 V and delivered a maximum power density of 0.24 mW cm−2 at 0.27 V in acidic pH conditions. This performance is the higher reported so far without added cofactor to the electrolyte in acidic conditions. Highlights • Glucose oxidase/laccase enzymatic fuel cell efficiently works at low pH. • Immobilized hydroquinone is an effective redox mediator for anode. • The enzymatic fuel cell showed a maximal current density of 0.79 mA/cm2. • The enzymatic fuel cell showed a maximal power density of 0.24 mW/cm2. • This performance is the higher reported so far in acidic conditions. [ABSTRACT FROM AUTHOR]

In this study, a photoelectrochemical (PEC) biosensor was constructed by depositing supercapacitor carbon nanotubes (CNT) and Co 3 O 4 onto the anatase TiO 2 coated ITO electrodes. Herein, supercapacitor Co 3 O 4 was employed as a semiconductor with a band gap of ~2.07 eV, and the supercapacitor behavior of the PEC system was improved by introducing CNT into the electrode material. Furthermore, a self-empowering glucose biosensor operating at 0 V was constructed for the first time. Also, upon the formation of p-n junction, Co 3 O 4 was rendered electron accepting material, unlike its usual use in photocatalytic systems. Co 3 O 4 -CNT-anatase TiO 2 semiconductor hybrid was used to reduce recombination of exited electrons, and increasing the visible light absorption. Prior to enzyme immobilization, CNT containing electrode material was modified with 1-pyrene boronic acid via π-π interactions. The enzyme immobilization was carried out through covalent esterification between the boronic acid moiety and the carbohydrate part of GOx. Enzyme immobilization way enabled the close contact between FAD and electrode material, and the electron donor FADH 2 forming after the enzymatic reaction can give electrons to the photogenerated holes of Co 3 O 4 through CNT along with H 2 O 2 by enhancing the photocurrent. The obtained PEC biosensor demonstrated acceptable reproducibility and decent stability with a linear measurement range of 0–4 mM, a sensitivity of 0.3 µA mM −1 cm −2 , and lower detection limit of 0.16 µM. Thus, a self-powered biosensor was constructed by combining the PEC, and supercapacitor behavior of Co 3 O 4 for the first time, and the utilization of the present PEC material can be extended to the other analytes detection through photoelectrochemistry. The supercapacitor materials led to the high current at direct electron transfer potential range, and this phenomenon implies that the PEC electrode can also be used in biofuel cells to obtain high power. [ABSTRACT FROM AUTHOR]

SF 6 remote plasma treatment was performed to fluorinate the CNTs surface without physical damage. The fluorination of CNTs may control electronic conductivity and hydrophobicity. The hydrophobic interaction of GOx and F-CNTs increased the loading amount and activity of GOx. The sensitivity of the enzyme biosensors were improved due to the decrease in resistance and high GOx activity. [Display omitted] • Fabrication of highly-sensitive enzyme electrode via simple adsorption protocol. • Grafting of hydrophobic fluorine onto CNTs via remote plasma treatment (F-CNTs). • Increased enzyme loading owing to hydrophobic interaction between GOx and F-CNTs. • Enhanced electrochemical performance of enzyme biosensor employing GOx/F-CNTs. Remote SF 6 plasma treatment of CNTs is performed to graft hydrophobic fluorine on the surface of CNTs. Fluorinated CNTs (F-CNTs) allow for the facile adsorption of enzyme molecules via hydrophobic interaction between F-CNTs and the hydrophobic patches of enzyme molecules. The loading of glucose oxidase (GOx) on F-CNTs correlates well with plasma treatment time. Interestingly, the Rct value of GOx/F-CNTs decreases when CNTs are treated with plasma for a short time such as 1 and 5 min, which is due to weakly-bound chemisorbed fluorine molecules on F-CNTs (semi-ionic C-F). As an example, the Rct value of GOx/F-CNT electrode with 1 min plasma treatment is 0.57 times lower than that of GOx/CNTs, while increasing its sensitivity by 2.5 times. Upon extending the treatment time such as 30, 45 and 60 min, the XPS results reveal the dominance of covalently-attached fluorine, leading to marginally-increased resistance and sensitivity. It is worthy of noting this work is the first report of simple enzyme adsorption on remote-plasma treated CNT surfaces together with its detailed mechanism studies, especially for the binding of enzyme molecules semi-ionic fluorine. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient GOx/Nf-CNT/SPE electrochemical saliva glucose sensor is developed. • The ratio of Nafion and CNT is optimized for high glucose sensitivity. • The effect of plasma treatment on morphology and glucose sensing is studied. • A high sensitivity of 99.13 µA/mMcm2 in the range of 20–700 µM glucose is achieved. Due to unhealthy lifestyles, the population of diabetics is rapidly increasing, therefore, the demand of glucose meter is also increasing. However, not all the people could overcome the fear of jabbing a needle during blood glucose tests. In this regard, we report a non-invasive glucose sensing electrode composed of conductive and bio-compatible Nafion-carbon nanotubes (Nf-CNT) nanocomposite and glucose oxidase (GOx), which are sequentially coated on screen-printed electrode (SPE). The Nf-CNT nanocomposite is prepared through ultrasonication followed by drop casting it onto the SPE. Subsequently, Nf-CNT/SPEs are subjected to plasma treatment followed by drop-casting of GOx to fabricate GOx/Nf-CNT/SPE electrodes. The plasma treatment alters the hydrophobic nature of Nf-CNT/SPE, which not only exposes the surface of Nf-CNT layer, but also enables it for uniform coating of GOx. The results confirm that the mixing ratio of Nafion and CNT as well as plasma treatment time significantly affects sensing performance. The GOx/Nf-CNT/SPE subjected to 1 min of plasma treatment prior to the coating of GOx shows the best performance with a sensitivity of 99.13 μA/mMcm2 and a linear range of 20–700 μM. Moreover, the GOx/Nf-CNT/SPE electrodes are also tested under artificial saliva, which shows their high potential in the diagnosis of diabetes. [ABSTRACT FROM AUTHOR]

Abstract Glucose oxidase can catalyze the oxidization of glucose in the mild conditions, which can be used to decorate the anode of the biofuel cells. The carbon nanotube electrode can direct contact with the flavin adenine dinucleotide cofactor of glucose oxidase by automatic absorption. Our ab initio calculations reveal that proton/electron transfer from β- d -glucose to isoaloxazine ring occurs via a proton-coupled double-electron transfer mechanism according to a model including deprotonated glucose and lumiflavin with a high energy barrier of 30.5 kcal/mol. The similar result is obtained from the examination of the corresponding reaction in glucose oxidase at the ONIOM(M06–2X/6-31 + G(d,p):amber) level. When the isoalloxazine ring directly interacts with the surface of carbon nanotube in the glucose-oxidase-modified electrode, however, the reaction occurs through a π-π-driven proton-coupled double-electron transfer mechanism with a low energy barrier (0.2–12.0 kcal/mol). This is because that the π-π interaction plays a central role in promoting electron transfer from substrate to flavin. These findings indicate that the association of glucose oxidase and carbon nanotube is a potential application for the effective electrode of enzymatic biofuel cell. Highlights • Proton-coupled ET from glucose to FAD occurs with a high energy barrier. • Direct interactions of CNT with FAD greatly promote PT/ET from glucose to FAD. • Direct interaction of CNT with FAD can achieve direct ET from GOx to electrode. • CNTs hold great promise for constructing glucose-oxidase-modified electrode. [ABSTRACT FROM AUTHOR]

A versatile enzyme-functionalized carbon nanotube (CNT) platform was fabricated by covalently conjugating glucose oxidase (GOD) and/or horseradish peroxidase (HRP) on carboxyl-group-functionalized CNTs. The GOD and HRP co-conjugated CNTs were used for the detection of glucose through the chain reaction between glucose, GOD and HRP. The locally formed H2O2 originating from the oxidization of glucose by GOD is able to further oxidize the 3,3′,5,5′-tetramethylbenzidine (TMB) substrate, resulting in the production of colorimetric products. The reaction between H2O2 and Fe2+ can deplete the amount of H2O2 in solution, which in turn decreases the oxidization extent of TMB and decreases the absorbance of the solution in the presence of HRP-conjugated CNTs. The hybrid materials can increase the number of active sites, thus increasing the amount of immobilized enzyme molecules on the surface. Electron transmission between different species is also accelerated and the co-conjugated enzymes can decrease the diffusion of intermediate products, further increasing the local concentrations of reactants. By utilizing these hybrid materials, glucose and Fe2+ were successfully detected. The linear dynamic range of glucose and Fe2+ was 1–100 μM, and the limits of detection for glucose and Fe2+ were 0.3 and 0.22 μM, respectively. The selectivity of glucose and Fe2+ was also studied by adding different kinds of interferents (e.g., sugars, metallic ions and biomolecules), and satisfactory results were obtained. In particular, Fe2+ can be distinguished from Fe3+. Meanwhile, the performance of these biosensors was also validated in biological samples (human serum and human serum albumin) using standard addition methods, and good recoveries were obtained. [ABSTRACT FROM AUTHOR]

Abstract: Acid functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were decorated with Au and Fe2O3 nanoparticles (FeONPs) and deposited on glassy carbon electrode (GCE). The resulting hybrid Au/Fe2O3/f‐MWCNTs/GCE electrode and the one further modified by glucose oxidase were compared for detection of glucose. FeONPs and Au were deposited on the f‐MWCNTs by sonication‐assisted precipitation and deposition‐precipitation methods, respectively. The morphology and structure of the samples were characterized by transmission electron microscopy, scanning electron microscopy, X‐ray diffraction and Raman spectroscopy. A uniform distribution of FeONPs with an average size of 5 nm increased the surface area of functionalized nanotubes from 39 to 50 m2/g. The electrocatalytic glucose detection on the modified electrodes was evaluated using cyclic voltammetry and chronoamperometry in 0.1 M phosphate buffer solution at pH 7.0. The non‐enzymatic and enzymatic electrodes show sensitivity of 512.4 and 921.4 mA/mM.cm2 and detection limit of 1.7 and 0.9 mM, respectively. The enzymatic and enzymeless electrodes retained more than 70 % and 80 % of their cathodic faradic current after 70 days, respectively. The sensing mechanism of the non‐enzymatic biosensor is described through the reaction of glucose with iron (III) ions, while in the case of enzymatic electrode, glucose is oxidized by glucose oxidase. [ABSTRACT FROM AUTHOR]

Bioelectrocatalytic carbon nanotube pellets comprising glucose oxidase (GOx) at the anode and horseradish peroxidase (HRP) at the cathode were integrated in a glucose/H 2 O 2 flow-through fuel cell setup. The porous bioelectrodes, separated with a cellulose membrane, were assembled in a design allowing the fuel/electrolyte flow through the entire fuel cell with controlled direction. An air saturated 5 mmol L −1 glucose solution was directed through the anode where glucose is used for power conversion and for the enzymatic generation of hydrogen peroxide supplying the HRP biocathode with its substrate. This configuration showed an open circuit voltage (OCV) of 0.6 V and provided 0.7 ± 0.035 mW at 0.41 V. Furthermore, different charge/discharge cycles at 500 Ω and 3 kΩ were applied to show the long term stability of this setup producing 290 μW h (1.04 J) of energy after 48 h. The biofuel cell design further allows a convenient assembly of several glucose biofuel cells in reduced volumes and its connection in parallel or in series. [ABSTRACT FROM AUTHOR]

Abstract: The rational design of electrocatalysts with abundant active sites and high conductivity is the key to the development of glucose sensors. Herein, we report the preparation of a Cu2+‐doped C3N4 supported on multi‐walled carbon nanotube (MWCNT) network (Cu2+‐C3N4/MWCNT) as a highly efficient non‐enzymatic glucose sensing system. The morphologic and structural investigations using TEM, AFM, XRD, XPS, EPR, and i‐V response indicate the successful insertion of Cu2+ into the C3N4 inter‐layers via an out‐of‐plane on‐top configuration and the consequent exfoliation of C3N4 layers without forming CuO or Cu(OH)2. Such material can act as an electrocatalyst for glucose electrooxidation, and MWCNT can greatly reduce the charge transfer resistance and enhances activity. An optimised Cu2+ doping level (12 wt%) in Cu2+‐C3N4/MWCNT was established to realise high sensitivity towards glucose sensing (929 mA/M cm2), large linear range (0.5 μM∼12 mM), low detection limit (0.35 μM), and short response time (<3 s). Excellent selectivity against the interferents, such as dopamine, ascorbic acid, sucrose, and lactose, is also observed. In the blood serum tests, as‐prepared glucose sensor reports comparable and reproducible results, demonstrating its practical potentials. [ABSTRACT FROM AUTHOR]

Abstract: Graphite electrodes are modified with a redox polymer, [Os(4,4′‐dimethoxy‐2,2′‐bipyridine)2(polyvinylimidazole)10Cl]+ (E°′=−0.02 V vs Ag/AgCl (3 M KCl), crosslinked with a flavin adenine dinucleotide glucose dehydrogenase and multi‐walled carbon nanotubes for electrocatalytic oxidation of glucose. The enzyme electrodes provide 52 % higher current density, 1.22±0.10 mA cm−2 in 50 mM phosphate‐buffered saline at 37 °C containing 5 mM glucose, when component amounts are optimised using a design of experiments approach compared to one‐factor‐at‐a‐time. Current densities of 0.84±0.15 mA cm−2 were achieved in the presence of oxygen for these enzyme electrodes. Further analysis of the model allowed for altering of the electrode components while maintaining similar current densities, 0.78±0.11 mA cm−2 with 34 % less enzyme. Application of the cost‐effective anodes in membrane‐less enzymatic fuel cells is demonstrated by connection to cathodes prepared by co‐immobilisation of [Os(2,2′‐bipyridine)2(polyvinylimidazole)10Cl+] redox polymer, Myrothecium verrucaria bilirubin oxidase and multi‐walled carbon nanotubes on graphite electrodes. Power densities of up to 285 μW cm−2, 146 μW cm−2 and 60 μW cm−2 are achieved in pseudo‐physiological buffer, artificial plasma and human plasma respectively, showing promise for in vivo or ex vivo power generation under these conditions. [ABSTRACT FROM AUTHOR]

Abstract: Paper‐based analytical devices, which are suited to point‐of‐care diagnostics and on‐site detection because of cheap price and portability, have attracted increasing attention for improving global health and in other applications. Here, we constructed one carbon nanotube paper‐based electrode (CNTPE) for the detection of neurochemicals in brain microdialysate. CNTPE was directly fabricated through filter depositing CNT dispersion onto the surface of filter paper. The fabricated CNTPE have good electrochemical performance with advantage of CNT, which not only facilitate ascorbic acid (AA) oxidation, also could as a good platform to functionalize. As a proof, we demonstrate that the CNTPE act as electrode to detect AA directly and detect glucose with further modified CNTPE through electrodeposited Prussian blue (PB). The results show that the easily prepared CNTPE can be used for the selective measurement of AA without interference from dopamine and other electrochemical active substances; what's more, PB and glucose oxidase (GOx) modified CNTPE has good performance towards the specific detection of glucose. Therefore, we believe that CNTPE would have great potential application in detection of chemicals to understand the function of brain. [ABSTRACT FROM AUTHOR]

This work reports an amperometric enzyme-electrode prepared with glucose oxidase, which have been immobilized by a cross-linking step with glutaraldehyde in a mixture containing albumin and a novel carbon nanotubes-mucin composite (CNT-muc). The obtained hydrogel matrix was trapped between two polycarbonate membranes and then fixed at the surface of a Pt working electrode. The developed biosensor was optimized by evaluating different compositions and the analytical properties of an enzymatic matrix with CNT-muc. Then, the performance of the resulting enzymatic matrix was evaluated for direct glucose quantification in human blood plasma. The novel CNT-muc composite provided a sensitivity of 0.44 ± 0.01 mA M −1 and a response time of 28 ± 2 s. These values were respectively 20% higher and 40% shorter than those obtained with a sandwich-type biosensor prepared without CNT. Additionally, CNT-muc based biosensor exhibited more than 3 orders of magnitude of linear dynamic calibration range and a detection limit of 3 μM. The short-term and long-term stabilities of the biosensors were also examined and excellent results were obtained through successive experiments performed within the first 60 days from their preparation. Finally, the storage stability was remarkable during the first 300 days. [ABSTRACT FROM AUTHOR]