Multiwalled carbon nanotubes grafted chitosan nanobiocomposite: A prosperous functional nanomaterials for glucose biosensor application

Multiwalled carbon nanotubes (MWNTs) grafted chitosan (CS) nanowire (NW) was prepared by phase separation method. Glucose oxidase (GOx) was sequentially immobilized into MWNT-CS-NW to obtain MWNT-CS-NW/GOx biosensor. Field emission scanning electron microscopy (FESEM) images of MWNT-CS-NW/GOx reveals the existence of MWNT and CS. Cyclic voltammetry and amperometry were used to evaluate the electrochemical determination of glucose. The MWNT-CS-NW/GOx biosensor shows an excellent performance for glucose at +0.34 V with a high sensitivity (5.03 μA/mM) and lower response time (3 s) in a wide concentration range of 1-10 mM (correlation coefficient of 0.9988). In addition, MWNT-CS-NW/GOx biosensor possesses better reproducibility, storage stability and there is negligible interference from other electroactive components.     

A novel biosensor using entangled carbon nanotubes layer grown on an alumina substrate by CCVD of methane on FeOx–MgO

Glucose oxidase (GOx) was immobilized on entangled and high surface area carbon nanotubes (CNTs) grown on an alumina substrate, and direct electron transfer reaction between GOx and the electrode was revealed. Fe/MgO catalyst layer was spin-coated on the insulating alumina substrate and the CNT layer was grown on the catalyst by chemical vapor deposition of methane at 950 °C for 15 min. About 20–30 nm bundles of about 1 nm single-wall as well as 10 nm multiwall CNTs are formed. The redox process was surface-controlled and electron transfer coefficient and the rate constant were estimated to be 0.35 and 0.64 s⁻¹, respectively. In addition GOx immobilized on CNT layer showed a linear response range between 12 and 62 μM of glucose concentration. A detection limit and sensitivity of 0.1 μM and 635 μA mM⁻¹ cm⁻², respectively, were obtained for the biosensor.     

An amperometric glucose biosensor based on layer-by-layer GOx-SWCNT conjugate/redox polymer multilayer on a screen-printed carbon electrode

An amperometric glucose biosensor based on a multilayer made by layer-by-layer assembly of single-walled carbon nanotubes modified with glucose oxidase (GOx-SWCNT conjugates) and redox polymer (PVI-Os) on a screen-printed carbon electrode (SPCE) surface was developed. The SPCE surface was functionalized with a cationic polymer by electrodeposition of the PVI-Os, followed by alternating immersions in anionic GOx-SWCNT conjugate solutions and cationic PVI-O solutions. The purpose is to build a multilayer structure which is further stabilized through the electrodeposition of PVI-Os on the multilayer film. The electrochemistry of the layer-by-layer assembly of the GOx-SWCNT conjugate/PVI-Os bilayer was followed by cyclic voltammetry. The resultant glucose biosensor provided stable and reproducible electrocatalytic responses to glucose, and the electrocatalytic current for glucose oxidation was enhanced with an increase in the number of bilayers. The glucose biosensor displayed a wide linear range from 0.5 to 8.0 mM, a high sensitivity of 32 μA mM⁻¹ cm⁻², and a response time of less than 5 s. The glucose biosensor proved to be promising amperometric detectors for the flow injection analysis of glucose.     

Application of functionalised carbon nanotubes immobilised into chitosan films in amperometric enzyme biosensors

A new approach for building a bio-conductive interface for enzyme immobilisation is described. This strategy permits very simple preparation of the enzyme biosensor and also reveals direct electron transfer features. A graphite-epoxy resin composite (GrEC) electrode modified with functionalised multi-wall carbon nanotubes (MWCNTs) immobilised by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide together with N-hydroxysuccinimide (EDC–NHS) in a chitosan (Chit) matrix was prepared and characterised by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the presence of hexaammineruthenium (III) chloride. It was then used as a base for glucose oxidase (GOx) immobilisation by the simple method of crosslinking with glutaraldehyde (GA) with bovine serum albumin (BSA) as carrier protein. The resulting mediator-free biosensor was applied to the determination of glucose in amperometric mode at different applied potentials and the mechanism of reaction was also investigated by cyclic voltammetry, with and without dissolved oxygen in solution. Analytical parameters, as well as reproducibility, repeatability and stability were determined. Interferences were assessed using different compounds usually present in natural samples, such as wines, juices or blood, in order to evaluate the selectivity of the developed biosensor. The novel combination of carbon nanotubes immobilised with chitosan crosslinked with EDC–NHS and glucose oxidase immobilised by crosslinking with glutaraldehyde offers an excellent, easy to make biosensor for glucose determination without interferences.     

Carbon felt-based bioelectrocatalytic flow-through detectors: Highly sensitive amperometric determination of H2O2 based on a direct electrochemistry of covalently modified horseradish peroxidase using cyanuric chloride as a linking agent

Horseradish peroxidase (HRP) was chemically modified using cyanuric chloride (CC) as a linking agent onto a carbon felt (CF), which is a microelectrode ensemble of micro carbon fiber (>7 μm, diameter) with a random three-dimensional structure. The resulting HRP-modified CF (HRP-ccCF) exhibited well-defined redox waves based on the HRP heme Fe^III/Fe^II redox couple at −0.23 V vs. Ag/AgCl (at pH 7.0), while the HRP-adsorbed CF (HRP-CF) showed no apparent redox couple in the same potential range, indicating that the chemical modification of HRP via CC facilitated the direct electron transfer (DET) between HRP and CF. The apparent heterogeneous electron transfer rate constant k_s was estimated to be 35 s⁻¹. Cyclic voltammetry and electrochemical impedance spectroscopy revealed that the interfacial properties (i.e., structure, morphology of enzyme-layer) of covalently modified HRP (HRP-ccCF) and physically adsorbed HRP (HRP-CF) are different, resulting in the difference in the electron transfer properties. The HRP-ccCF was successfully used as a working electrode unit in bioelectrocatalytic flow-through detector for highly sensitive amperometric determination of H₂O₂. Under the optimized conditions (i.e., applied potential, 0 V vs. Ag/AgCl; carrier flow rate, 3.25 ml/min; and carrier pH 7.0), the cathodic peak current of H₂O₂ linearly increased up to 3 μM (sensitivity, 1.94 μA/μM; the detection limit, 0.08 μM [S/N = 3]) with sample through-put of ca. 90 samples/h.     

Adsorption of glucose oxidase at platinum-multiwalled carbon nanotube-alumina-coated silica nanocomposite for amperometric glucose biosensor

Glucose oxidase (GOx) has been immobilized in platinum-multiwalled carbon nanotube-alumina-coated silica (Pt-MWCNT-ACS) nanocomposite modified glassy carbon electrode by adsorption to provide a novel amperometric glucose biosensor. The morphology, nature, and performance of the resulting GOx-Pt-MWCNT-ACS nanobiocomposite modified glassy carbon electrode were characterized by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, cyclic voltammetry, and amperometry. The influence of various experimental conditions was examined for the determination of the optimum analytical performance. The optimized glucose biosensor displayed a wide linear range of up to 10.5 mM, a high sensitivity of 113.13 mA M⁻¹ cm⁻², and a response time of less than 5 s. The sensitivity for the determination of glucose at the GOx-Pt-MWCNT-ACS nanobiocomposite modified glassy carbon electrode is better than at common GOx-Pt-CNT nanobiocomposite modified electrodes. The proposed biosensor has good anti-interferent ability and long-term storage stability after coating with Nafion, and it can be used for the determination of glucose in synthetic serum.     

Electrocatalytic characteristics of electrodes based on ferritin/carbon nanotube composites for biofuel cells

A single wall carbon nanotube (SWNT)/ferritin/glucose oxidase (GOx) layer on a glassy carbon electrode acting as a biofuel cell anode was fabricated using an SWNT/ferritin composite as an electron transfer mediator from the enzyme to the electrode. In the absence of glucose, the SWNT/ferritin/GOx composite showed a higher current response than an SWNT/GOx composite, and the electrocatalytic oxidation of glucose on the anode increased linearly with increasing concentration of glucose. The highly distributed SWNT/ferritin composite as a platform for enzyme immobilization resulted in an enhanced electrocatalytic activity towards glucose. The SWNT/ferritin composite showed an enhanced electron transfer from the enzyme to the electrode; therefore, SWNT/ferritin/GOx composites can be used as an anode in biofuel cells.     

A novel amperometric biosensor for oxalate determination using multi-walled carbon nanotube-gold nanoparticle composite

An amperometric oxalate biosensor using nanohybrid film of multi-walled carbon nanotubes (MWCNTs) and gold colloidal nanoparticles (GNPs) via carbodiimide chemistry by forming amide linkages between carboxylic acid groups on the CNTs and amine residues of cysteamine self-assembled monolayer (SAM) has been prepared. The c-MWCNTs were immobilized on the gold (Au) electrode and characterized by FTIR. The morphologies of the c-MWCNT/Au and GNPs/MWCNT/Au electrodes were investigated by scanning electron microscopy (SEM) and the electrochemical performance of the Au, c-MWCNT/Au and GNPs/c-MWCNT/Au electrodes were also studied amperometrically. The Cl⁻ and NO₃⁻ insensitive oxalate oxidase from grain sorghum was finally immobilized on this electrode. The influence of pH, temperature and oxalate concentration on electrode activity was studied. The electrode showed optimum response within 7 s. The electrocatalytic response showed a linear dependence on the oxalic acid concentration ranging from 1 to 800 μM with a detection limit of 1 μM. The K_m value for the oxalic acid sensor was 444.44 μM. The enzyme electrode retained 30% of its initial activity after 5 months, when stored at 4 °C. The electrode was employed for measurement of oxalic acid in serum, urine and foodstuffs.     

Amperometric glucose biosensor based on integration of glucose oxidase with platinum nanoparticles/ordered mesoporous carbon nanocomposite

This article reports a new amperometric glucose biosensor based on ordered mesoporous carbon (OMC) supported platinum nanoparticles (Pt/OMC) modified electrode. The Pt/OMC nanocomposite modified electrode exhibited excellent electrocatalytic activities towards the reduction and oxidation of H₂O₂ as well. This feature allowed us to use it as bioplatform on which glucose oxidase (GOD) was immobilized by entrapment in electropolymerized pyrrole film for the construction of the glucose biosensor. The biosensor showed good analytical performances in terms of low detection (0.05 mM), high sensitivity (0.38 μA/mM) and wide linear range (0.05-3.70 mM). In addition, the effects of pH value, applied potential, electroactive interference and the stability of the biosensor were discussed. The applicability to blood analysis was also evaluated.     

Development of a dehydrogenase-based glucose anode using a molecular assembly composed of nile blue and functionalized SWCNTs and its applications to a glucose sensor and glucose/O2 biofuel cell

A simple and new way to immobilize glucose dehydrogenase (GDH) enzyme onto nile blue (NB) covalently assembled on the surface of functionalized single-walled carbon nanotubes (f-SWCNTs) modified glassy carbon (GC) electrode (GDH/NB/f-SWCNTs/GC electrode) was described. The GDH/NB/f-SWCNTs/GC electrode possesses promising characteristics as glucose sensor; a wide linear dynamic range of 100-1700 μM, low detection limit of 0.3 μM, fast response time (1-2 s), high sensitivity (14 μA cm⁻² mM⁻¹), anti-interference ability and anti-fouling. Moreover, the performance of the GDH/NB/f-SWCNTs/GC bioanode was successfully tested in a glucose/O₂ biofuel cell. The maximum power density delivered by the assembled glucose/O₂ biofuel cell could reach 32.0 μW cm⁻² at a cell voltage of 0.35 V with 40 mM glucose. The present procedure can be applied for preparing a potential platform to immobilize different enzymes for various bioelectrochemical applications.     

Direct electrochemistry of cytochrome P450 6A1 in mimic bio-membrane and its application for pesticides sensing

The direct electrochemistry of house fly cytochrome P4506A1 (CYP6A1) confined in dioctadecyl dimethyl ammonium bromide (DDAB) film was achieved. The immobilized CYP6A1 displayed a pair of redox peaks with a formal potential of −0.36 mV in pH 7.0 O₂-free phosphate buffers at scan rate of 1 V s⁻¹ and the direct electron transfer of CYP6A1 was characterized by voltammetry. The CYP6A1 in the DDAB film retained its bioactivity and could catalyze the reduction of dissolved oxygen. Upon addition of its substrate aldrin or heptachlor to the air-saturated solution, the reduction peak current of dissolved oxygen increased, which indicates the catalytic behavior of CYP6A1 to its substrates. By amperometry a calibration linear range was obtained to be 9.08 × 10⁻⁶-4.54 × 10⁻⁵ mol L⁻¹ with a sensitivity of 80 μA mM⁻¹ for aldrin or 8.91 × 10⁻⁶-4.46 × 10⁻⁵ mol L⁻¹ with a sensitivity of 66 μA mM⁻¹ for heptachlor. The apparent Michaelis-Menten constant for the electrocatalytic activity of CYP6A1 was found to be 7.468 × 10⁻⁵ mol L⁻¹ for aldrin and 4.316 × 10⁻⁵ mol L⁻¹ for heptachlor. The bioelectrocatalytic products were analysed using gas chromatography (GC) and electron ionization-mass spectrometry (EI-MS). The results confirmed that epoxidation was the main pathways of CYP6A1-mediated organochlorine pesticides oxidation.     

Correlation between cell growth rate and glucose consumption determined by electrochemical monitoring

The electrochemical monitoring of glucose consumption is relevant for cell biology studies because of its wide detection range, high sensitivity and easy implementation. Whereas the glucose consumption and cell growth rate can be tightly correlated, they should also be cell population density dependent. In this work, we fabricated high sensitive enzyme electrodes for accurate monitoring of glucose consumption of cells in different growth stages. The performance of the fabricated device was firstly evaluated by cyclic voltammetry (CV) with p-benzoquinone (PBQ) as redox mediator, showing a linear response over a wide detection range (0.3-60 mM), a high sensitivity (1.61 ± 0.10 μA mM⁻¹ mm⁻² (n = 5)) and a low detection limit (80 μM). Then, daily glucose consumptions of NIH 3T3 cells in 24-well plates were determined for a period of 7 days. The results could be compared to the cell population growth curve, showing a close correlation but different behavior. We found that the increase of the glucose consumption took place prior the cell number increase but the glucose consumption per cell decreases linearly in the exponential growth stage of cells.     

Study of an amperometric glucose sensor based on Pd-Ni/SiNW electrode

An amperometric glucose sensor based on Pd-Ni/SiNW electrode has been investigated. The silicon nanowire (SiNW) electrodes were first fabricated by chemical etching, and then nickel and palladium particles were deposited onto the surfaces of SiNWs via electroless co-plating technique followed by annealing in nitrogen atmosphere at 350 °C for 300 s. The morphology of Pd-Ni/SiNW electrode was characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The sensor performance was characterized by cyclic voltammetry (CV) and fixed potential amperometry techniques. In 0.1 M KOH alkaline medium with different glucose concentrations, the sensor shows an excellent sensitivity of 190.72 μA mM⁻¹ cm⁻² with the detection limit (S/N ratio = 3) of 2.88 μM. And it also exhibits superior anti-interference properties to the species including ascorbic acid (AA), uric acid (UA) and 4-acetamidophenol (AP). All results demonstrate that this Pd-Ni/SiNW electrode is a candidate with great potential for glucose detection.     

Electrocatalytic determination of hydrazine by a glassy carbon electrode modified with PEDOP/MWCNTs-Pd nanoparticles

The electrocatalysis of hydrazine oxidation by poly-ethylenedioxy pyrrole (PEDOP)-coated MWCNTs-palladium nanoparticles [PEDOP/MWCNTs-Pd] was investigated as an electrochemical sensor on the surface of glassy carbon electrode (GCE) in aqueous medium. Electrochemical oxidation of hydrazine in phosphate buffer (pH 7.4) was performed using cyclic voltammetry (CV) and chronoamperometry (CA) methods. Using the proposed electrode, the catalytic oxidation peak current of hydrazine was high and the overpotential of its oxidation decreased. Based on the obtained results, a mechanism for electrooxidation of hydrazine at [PEDOP/MWCNTs-Pd/GCE] demonstrated an irreversible diffusion-controlled electrode process and a four-electron transfer involved in the overall reaction. The experimental results showed that the mediated oxidation peak currents of the hydrazine were linearly dependent on the concentration of hydrazine in the range of 1.0 × 10⁻⁷ to 5.0 × 10⁻³ M. The detection limit (S/N = 3) was found to be 4 × 10⁻⁸ M with a fast response time of 10 s.     

Targeting of multiple metabolites in neural cells monitored by using protein-based carbon nanotubes

Microdevices dedicated to monitor metabolite levels have recently enabled many applications in the field of cell analysis, to monitor cell growth and development of numerous cell lines. By combining the traditional technology used for electrochemical biosensors with nanoscale materials, it is possible to develop miniaturized metabolite biosensors with unique properties of sensitivity and detection limit. In particular, enzymes tend to adsorb onto carbon nanotubes and their optical or electrical activity can perturb the electronic properties. In the present work we propose multi-walled carbon nanotube-based biosensors to monitor a cell line highly sensitive to metabolic alterations, in order to evaluate lactate production and glucose uptake during different cell states. We achieve sensors for both lactate and glucose, with sensitivities of 40.1 μA mM⁻¹ cm⁻² and 27.7 μA mM⁻¹ cm⁻², and detection limits of 28 μM and 73 μM, respectively. This nano-biosensing technology is used to provide new information on cell line metabolism during proliferation and differentiation, which are unprecedented in cell biology.     

Sensitive electrochemical determination of acetaminophen in pharmaceutical formulations at multiwalled carbon nanotube-alumina-coated silica nanocomposite modified electrode

A highly sensitive electrochemical sensor for the determination of acetaminophen at the multiwalled carbon nanotube-alumina-coated silica (MWCNT-ACS) nanocomposite modified glassy carbon electrode is reported. The morphology of the MWCNT-ACS nanocomposite was characterized by field emission scanning electron microscopy. The electrocatalytic properties of the MWCNT-ACS nanocomposite modified glassy carbon electrode were characterized by cyclic voltammetry and square-wave voltammetry in the presence of acetaminophen. The MWCNT-ACS nanocomposite modified glassy carbon electrode exhibited the abilities to raise the current response and to decrease the electrooxidation potential. In cyclic voltammetric responses, the oxidation peak current of acetaminophen obtained at the MWCNT-ACS modified glassy carbon electrode was 100 times greater than that of bare glassy carbon electrode. The MWCNT-ACS nanocomposite modified glassy carbon electrode for the determination of acetaminophen displayed a sensitivity of 376.5 A M⁻¹ cm⁻² and a detection limit of 0.05 μM using square-wave voltammetry. The analytical applicability of the developed method was achieved by analyzing the content of acetaminophen in five commercial drugs without pretreatment.     

Poly(brilliant cresyl blue) electrogenerated on single-walled carbon nanotubes modified electrode and its application in mediated biosensing system

Single-walled carbon nanotubes (SWCNTs) functionalized with carboxylic acid groups were cast to glassy carbon electrode (GCE) to construct a three-dimensional nano-micro structured scaffold. Brilliant cresyl blue (BCB) was electropolymerized on the above-mentioned SWCNTs/GCE using continuous cycling between −0.7 and 0.9 V vs. SCE. PolyBCB yielded on SWCNTs/GCE exhibited the enhanced electrochemical redox behavior compared with that electrogenerated on bare GCE. The apparent surface coverage of PolyBCB obtained by SWCNTs/GCE was at least 10 times higher than that obtained by bare GCE, namely 4.8 × 10⁻⁹ and 3.6 × 10⁻¹⁰ mol cm⁻². The cyclic voltammograms recorded by PolyBCB/SWCNTs/GCE exhibited well-defined two peaks located at −0.25 V and −0.06 V, respectively, with a surface-controlled mechanism. In addition, morphologies of PolyBCB electrogenerated on GCE and SWCNTS/GCE were characterized by atomic force microscopy. Finally, this proposed PolyBCB/SWCNTs/GCE was used in the construction of the second-generation biosensors to hydrogen peroxide and glucose, with the enhanced analytical performance.     

Electrochemical behaviors and determination of isoniazid at ordered mesoporous carbon modified electrode

In this work, an electrochemical sensor based on ordered mesoporous carbon (OMC) for the amperometric detection of isoniazid was developed. OMC was dispersed in a solution of Nafion, and the suspension was modified onto the surface of glassy carbon (GC) electrode. Cyclic voltammetry and amperometry were used to investigate the electrochemical behaviors of isoniazid on Nafion-OMC modified electrode (Nafion-OMC/GC). The results indicate that OMC can facilitate the electrochemical oxidation of isoniazid with a great decrease of overpotential in pH 7.0 phosphate buffer solution. The proposed biosensor provides excellent performance towards the determination of isoniazid with a high sensitivity of 0.031 μA/μM, a low detection limit of 8.4 × 10⁻⁸ M and wide linear range from 1.0 × 10⁻⁷ M to 3.7 × 10⁻⁴ M at +0.20 V vs. Ag/AgCl. The method was successfully applied to the determination of isoniazid tablets with satisfying results. All the results suggest that Nafion-OMC/GC electrode is a potential candidate for a stable and efficient electrochemical sensor to detect isoniazid.     

High-performance glucose sensor based on glucose oxidase encapsulated in new synthesized platinum nanoparticles supported on carbon Vulcan/Nafion composite deposited on glassy carbon

In this study we synthesized Pt nanoparticles supported on carbon Vulcan (Pt/C), a cheap and high surface area carbon. Compared to the commercialized Pt/C, which showed a moderate activity towards the oxidation of H₂O₂ and a high catalytic activity to the interferences specially AP; the synthesized Pt/C illustrated a high activity towards the oxidation of H₂O₂ and negligible response towards the oxidation of the interferences at high applied potentials (>0.6 V). This difference in the catalytic behavior was attributed to the homogenous distribution of the synthesized Pt nanoparticles in the supporting carbon Vulcan as well as, to their relatively bigger size (8-9 nm) compared to (1-2 nm) estimated for the commercialized Pt/C. This particular and interesting behavior of the synthesized Pt/C was used to encapsulate glucose oxidase along with a small amount of Nafion for the manufacturing of a glucose sensor. The resulting glucose sensor has a high sensitivity of 1.25 μA/mM mm², which compares very well with other glucose sensors based on precious metal nanoparticles and carbon nanotubes, an extended linear range up to 45 mM without using any outer polymer layer, low interference from endogenous species, short response time (<5 s), was stable for at least 1 month and, found to be dependable for glucose determination in human serum.     

Direct electrochemistry and electrocatalysis of hemoglobin immobilized into poly (lactic-co-glycolic acid)/room temperature ionic liquid composite film

A promising material of poly(lactic-co-glycolic acid) (PLGA) and, room temperature ionic liquid (ILs) (1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) was firstly used as an immobilization matrix to entrap proteins and its bioelectrochemical properties were studied. Direct electrochemistry and electrocatalytic behaviors of hemoglobin (Hb) entrapped in the PLGA/ILs composite film on the surface of glass carbon electrode were investigated. UV-vis spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the composite film. The obtained results demonstrated that the Hb molecule in the film kept its native structure and showed its good electrochemical behavior. A pair of well-defined redox peaks of Hb was obtained at the Hb/PLGA/ILs composite film-modified GC electrode through direct electron transfer between the protein and the underlying electrode. The proposed biosensor showed good reproducibility and high sensitivity to H₂O₂ with the detection limit of 2.37 × 10⁻⁷ M (S/N = 3). In the range of 5.0 × 10⁻⁶ to 8.05 × 10⁻³ M, the catalytic reduction current of H₂O₂ was proportional to its concentration. The apparent Michaelis-Menten constant of Hb in the PLGA/ILs composite film was estimated to be 0.069 mM, showing its high affinity.