Glucose oxidase electrodes of polyaniline,poly(<Emphasis Type="Italic">o</Emphasis>-anisidine) and their co-polymer as a biosensor: a comparative study

Polyaniline (PA), poly(o-anisidine) (POA) and their co-polymer poly(aniline-co-o-anisidine) (PA-co-POA) thin films were electropolymerized in solution containing 0.1 M monomer(s) and 1 M H₂SO₄ as a electrolyte by applying sequential linear potential scan rate 50 mV/s between −0.2 and 1.0 V vs. Ag/AgCl electrode on platinum electrode. A simple technique is described for constructing a glucose sensor by the entrapment of glucose oxidase (GOD) in PA, POA and their co-polymer PA-co-POA thin films, which were electrochemically deposited on a platinum plate in phosphate and acetate buffer. The maximum current response was observed for PA, POA, and PA-co-POA GOD electrodes at pH 5.5 and potential 0.60 V (vs. Ag/AgCl). The phosphate buffer gives fast response as compared to acetate buffer in amperometric measurements. PA GOD electrode shows fast response (means time taken for sense the glucose is lees) followed by PA-co-POA and POA GOD electrodes.     

GOD/PPy/GC电极的电化学性能研究

采用电沉积法在玻碳(GC)电极表面合成纳米级聚吡咯(PPy),通过扫描电镜得到PPy的形貌。以PPy为载体,通过吸附法固定葡萄糖氧化酶(GOD),得到GOD/PPy/GC电极。利用循环伏安法对GOD/PPy/GC电极的电化学行为进行分析,结果表明,以PPy为载体可以很好地固定GOD并保持其生物活性。在0.1mol/L磷酸盐缓冲溶液中,无任何电子媒介体存在时,GOD/PPy/GC电极显示了很好的电催化性能。     

Layer-by-layer assemblies of chitosan/multi-wall carbon nanotubes and glucose oxidase for amperometric glucose biosensor applications

A novel amperometric glucose biosensor based on multilayer films containing chitosan, multi-wall carbon nanotubes (MWCNTs) and glucose oxidase (GOD) was developed. MWCNTs were solubilized in chitosan (Chit-MWCNTs) used to interact with GOD. Poly (allylamine) (PAA) and polyvinylsulfuric acid potassium salt (PVS) were alternately deposited on the cleaned Pt electrode surface ((PVS/PAA)₃/Pt). The (PVS/PAA)₃/Pt electrode was alternately immersed in Chit-MWCNTs and GOD to assemble different layers of multilayer films. PBS washing was applied at the end of each assembly deposition for dissociating the weak adsorption. Micrographs of MWCNTs were obtained by scanning electron microscope, and properties of the resulting biosensors were measured by electrochemical measurements. Among the resulting biosensors, the biosensor based on eight layers of multilayer films was best. The resulting biosensor was able to efficiently monitor glucose, with the response time within 8 s, a detection limit of 21 μM estimated at a signal-to-noise ratio of 3, a linear range of 1–10 mM, the sensitivity of 0.45 μA/mM, and well stability. The study can provide a feasible simple approach on developing a new immobilization matrix for biosensors and surface functionalization.     

A graphene-laminated electrode with high glucose oxidase loading for highly-sensitive glucose detection

Graphene oxide(GO) has received considerable attention for glucose detection because of high surface area, abundant functional groups, and good biocompatibility. Defects and functional groups of the GO are beneficial to immobilization of glucose oxidase(GOD), but sacrificing electron-transfer capability for highly-sensitive detection. In order to obtain high GOD loading and highly-sensitive detection of biosensors, we first designed and fabricated a graphene-laminated electrode by combining GO and edgefunctionalized graphene(FG) layers together onto glassy-carbon electrode. The graphene-laminated electrodes exhibited faster electron transfer rate, higher GOD loading of 3.80 × 10^-9 mol·cm^-2, and higher detection sensitivity of 46.71 μA·mM^-1·cm^-2 than other graphene-based biosensors reported in literature. Such high performance is mainly attributed to the abundant functional groups of GO, high electrical conductivity of FG, and strong interactions between components in the graphene-laminated electrodes.By virtue of their high enzyme loading and highly-sensitive detection, the graphene-laminated electrodes show great potential to be widely used as high-performance biosensors in the field of medical diagnosis.     

Flexible electrochemical biosensors based on O2 plasma functionalized MWCNT

A flexible glucose sensor is fabricated using O₂ plasma-functionalized multiwalled carbon nanotube (MWCNT) films on polydimethylsiloxane (PDMS) substrates and its performance is electrochemically characterized. After enzyme immobilization, the GOD/ MWCNT/Au/PDMS electrode exhibits a sensitivity of 18.15 μA mm^− 2mM^− 1 and a detection limit of 0.01 mM (signal to noise ratio was about 3). This high sensitivity may be attributed to a large enzyme loading and a higher electrocatalytic activity and electron transfer exhibited by O₂ plasma-functionalized CNTs than the pristine CNT, due to some oxygen-contained groups present on the O₂ plasma-functionalized CNT surface, which has been verified by XPS spectrum.     

Electrochemical biosensing based on polypyrrole/titania nanotube hybrid

The glucose oxidase (GOD) modified polypyrrole/titania nanotube enzyme electrode is fabricated for electrochemical biosensing application. The titania nanotube array is grown directly on a titanium substrate through an anodic oxidation process. A thin film of polypyrrole is coated onto titania nanotube array to form polypyrrole/titania nanotube hybrid through a normal pulse voltammetry process. GOD-polypyrrole/titania nanotube enzyme electrode is prepared by the covalent immobilization of GOD onto polypyrrole/titania nanotube hybrid via the cross-linker of glutaraldehyde. The morphology and microstructure of nanotube electrodes are characterized by field emission scanning electron microscopy and Fourier transform infrared analysis. The biosensing properties of this nanotube enzyme electrode have been investigated by means of cyclic voltammetry and chronoamperometry. The hydrophilic polypyrrole/titania nanotube hybrid provides highly accessible nanochannels for GOD encapsulation, presenting good enzymatic affinity. As-formed GOD-polypyrrole/titania nanotube enzyme electrode well conducts bioelectrocatalytic oxidation of glucose, exhibiting a good biosensing performance with a high sensitivity, low detection limit and wide linear detection range.     

An electrochemical biosensor constructed by nanosized silver particles doped sol–gel film

The nanosized silver particles are used to dope into the sol–gel film to prepare a biosensor. The horseradish peroxidase (HRP), mediator methylene blue (MB), nanosized silver particles and sol–gel solution are mixed and coated on the surface of glass carbon (GC) electrode to get the biosensor. The silver nanoparticles in the sol–gel film can adsorb the enzyme molecules and improve the sol–gel film conductivity. The biosensor has a high sensitivity, quickly response to H₂O₂ and good stability. The biosensor responds to H₂O₂ in the linear range from 1 μM to 1 mM. The detection limit was down to 0.4 μM when the signal to noise ratio is 3. The apparent Michaelis-Menten constant of the biosensor to H₂O₂ was estimated to be 1.2 mM, showing a high affinity.     

Characterization of copper manganite oxide-polypyrrole composite electrodes cathodically polarized in acidic medium

We have studied the electrochemical behaviour induced by polarization in sandwich-type composite electrodes with the structure GC/PPy/PPy(Ox)/PPy where GC stands for glassy carbon, PPy for polypyrrole and Ox for Cu_1.4Mn_1.6O₄ nanoparticles. The electrodes were polarized at ?0.45 V/SCE in 0.15 M KCl aqueous solution at pH 2.2 either saturated in Ar or O₂ at 25 °C. The changes occurring on these electrodes were studied using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (EXAFS and XANES) techniques. In previous work we have shown that when the oxide particles are incorporated into the PPy matrix the Cu⁺ present in the initial oxide suffers dismutation to give Cu²⁺ and metallic Cu. In this work we show that the polarized electrodes also reveal the presence of metallic Cu and Cu²⁺. The data also show that the oxide particles embedded in the polarized electrodes contain Mn³⁺ and Mn⁴⁺, although the Mn³⁺/Mn⁴⁺ ratio is different from that found in the fresh electrodes. The Cl 2p XPS data show that in the electrode polarized in O₂ there is an enhancement of the Cl covalent contribution that appears at 200.8 eV (which is already present in the fresh electrode although with a very small intensity). This result suggests that the oxygen reduction reaction leads to an increase of the OH^? concentration inside the composite electrode that explains the charge transport in PPy at negative potentials.     

Carbon nanotube-chitosan system for electrochemical sensing based on dehydrogenase enzymes

Multiwalled carbon nanotubes (CNT) were solubilized in aqueous solutions of a biopolymer chitosan (CHIT). The CHIT-induced solubilization of CNT facilitated their manipulations, including the modification of electrode surfaces for sensor and biosensor development. The colloidal solutions of CNT-CHIT were placed on the surface of glassy carbon (GC) electrodes to form robust CNT-CHIT films, which facilitated the electrooxidation of NADH. The GC/CNT-CHIT sensor for NADH required approximately 0.3 V less overpotential than the GC electrode. The susceptibility of CHIT to chemical modifications was explored in order to covalently immobilize glucose dehydrogenase (GDH) in the CNT-CHIT films using glutaric dialdehyde (GDI). The stability and sensitivity of the GC/CNT-CHIT-GDI-GDH biosensor allowed for the interference-free determination of glucose in the physiological matrix (urine). In pH 7.40 phosphate buffer solutions, linear least-squares calibration plots over the range 5-300 microM glucose (10 points) had slopes 80 mA M(-1) cm(-2) and a correlation coefficient 0.996. The detection limit was 3 microM glucose (S/N = 3). The CNT-CHIT system represents a simple and functional approach to the integration of dehydrogenases and electrodes, which can provide analytical access to a large group of enzymes for wide range of bioelectrochemical applications including biosensors and biofuel cells.     

Ionic liquid modified carbon paste electrode and investigation of its electrocatalytic activity to hydrogen peroxide

. This paper reports on the preparation and advantages of novel amperometric biosensors in the presence of hydrophobic ionic liquid (IL), 1-methyl-3-butylimidazolium bromide ([MBIB]). Carbon paste biosensor has been constructed by entrapping horseradish peroxidase in graphite and IL mixed with paraffin oil as a binder. The resulting IL/graphite material brings new capabilities for electrochemical devices by combining the advantages of ILs composite electrodes. Amounts of H₂O₂ were amperometrically detected by monitoring current values at reduction potential (–0·15 V) of K₃Fe(CN)₆. Decrease in biosensor responses were linearly related to H₂O₂ concentrations between 10 and 100 μM with 2 s response time. Limit of detection of the biosensor were calculated to be 3·98 μM for H₂O₂. In the optimization studies of the biosensor some parameters such as optimum pH, optimum temperature, enzyme amount, interference effects of some substances on the biosensor response, reproducibility and storage stability were carried out. The promising results are ascribed to the use of an ionic liquid, which forms an excellent charge-transfer bridge and wide electrochemical windows in the bulk of carbon paste electrode.     

用单壁纳米碳管制备葡萄糖生物传感器的研究

以单壁纳米碳管为代表材料,对利用纳米碳管制备葡萄糖生物传感器中纳米碳管的作用和纳米碳管修饰电极的方法、酶的固定化方法及电极种类等因素对传感器性能的影响进行了研究.研究结果表明,纳米碳管的加入能有效地改善传感器的电化学性能,利用二茂铁和单壁纳米碳管共同修饰电极所制得的传感器的性能要好于仅用单壁纳米碳管修饰电极制得的传感器.在酶的固定化方法中,戊二醛交联法要略好于明胶包埋法;而利用铂电极制备出的生物传感器对葡萄糖的响应电流要明显高于利用金电极和玻碳电极制备出的生物传感器.这些结论对于开发纳米碳管在生物传感领域及生命科学相关领域的应用有参考价值.     

Glucose biosensor from covalent immobilization of chitosan-coupled carbon nanotubes on polyaniline-modified gold electrode

An amperometric glucose biosensor was prepared using polyaniline (PANI) and chitosan-coupled carbon nanotubes (CS-CNTs) as the signal amplifiers and glucose oxidase (GOD) as the glucose detector on a gold electrode (the Au-g-PANI-c-(CS-CNTs)-GOD biosensor). The PANI layer was prepared via oxidative graft polymerization of aniline from the gold electrode surface premodified by self-assembled monolayer of 4-aminothiophenol. CS-CNTs were covalently coupled to the PANI-modified gold substrate using glutaradehyde as a bifunctional linker. GOD was then covalently bonded to the pendant hydroxyl groups of chitosan using 1,4-carbonyldiimidazole as the bifunctional linker. The surface functionalization processes were ascertained by X-ray photoelectron spectroscopy (XPS) analyses. The field emission scanning electron microscopy (FESEM) images of the Au-g-PANI-c-(CS-CNTs) electrode revealed the formation of a three-dimensional surface network structure. The electrode could thus provide a more spatially biocompatible microenvironment to enhance the amount and biocatalytic activity of the immobilized enzyme and to better mediate the electron transfer. The resulting Au-g-PANI-c-(CS-CNTs)-GOD biosensor exhibited a linear response to glucose in the concentration range of 1-20 mM, good sensitivity (21 μA/(mM·cm(2))), good reproducibility, and retention of >80% of the initial response current after 2 months of storage.     

Optimization of Conditions for Preparation of Carbon Origin Solid Electrodes Modified with Carbon Nanotubes

A multi-walled carbon nanotubes (MWCNTs) were used for modification of two solid electrode types, glassy carbon electrode (GC), which is widely used for modification in electroanalysis, and, for the first time, paraffin impregnated graphite electrode (PIGE). The optimization of MWCNT/PIGE and MWCNT/GC electrodes was carried out by altering ultrasonication parameters (ultrasonication time, ultrasound generator performance, and dispersing agent). The preparation of modified electrodes was investigated. The most electrochemically sensitive MWCNT/GC electrode was prepared with nanotubes sonicated for 30 min and the most sensitive MWCNT/PIGE for 20 min, both using ethanol/water solution as dispersing agent and 500 W ultrasound generator performance. Both electrodes were successfully used for analysis of lead performed by DC voltammetry. Current responses were measured for the concentration of lead (II) in range from 1 × 10^?5 to 5 × 10^?5 mol dm^?3 for MWCNT/PIGE and also MWCNT/GC electrode.     

Direct electron transfer and biosensing of glucose oxidase immobilized at multiwalled carbon nanotube-alumina-coated silica modified electrode

Investigations are reported regarding the direct electrochemical performance of glucose oxidase (GOD) immobilized on a film of multiwalled carbon nanotube-alumina-coated silica (MWCNT-ACS). The surface morphology of the GOD/MWCNT-ACS nanobiocomposite is characterized by scanning electron microscopy. In cyclic voltammetric response, the immobilized GOD displays a pair of well-defined redox peaks, with a formal potential (E°′) of ? 0.466 V versus Ag/AgCl in a 0.1 M phosphate buffer solution (pH 7.5) at a scan rate of 0.05 V s^? 1; also the electrochemical response indicates a surface-controlled electrode process. The dependence of formal potential on solution pH indicates that the direct electron transfer reaction of GOD is a reversible two-electron coupled with a two-proton electrochemical reaction process. The glucose biosensor based on the GOD/MWCNT-ACS nanobiocomposite shows a sensitivity of 0.127 A M^? 1 cm^? 2 and an apparent Michaelis–Menten constant of 0.5 mM. Furthermore, the prepared biosensor exhibits excellent anti-interference ability to the commonly co-existed uric acid and ascorbic acid.     

Third-generation biosensors based on TiO2 nanostructured films

The functionalisation of solid electrodes with thin films of biocompatible materials revealed very attractive for the development of biosensors on miniaturized platforms, since this configuration could provide a rapid translation of the biological processes occurring on the surface to electronic outputs. In this study, the realization of functionalised TiO₂ thin films on Si substrates for the immobilization of several enzymes and biological molecules is reported. Deposition parameters were found to affect the chemical and microstructural features of the films, which influenced the protein immobilization. Glucose oxidase and horseradish peroxidase immobilized onto TiO₂-based nanostructured surfaces exhibited a pair of well-defined and quasi-reversible voltammetric peaks. The electron exchange between the enzyme and the electrodes was greatly enhanced in the TiO₂ nanostructured environment. The electrocatalytic activity of HRP and GOD embedded in TiO₂ electrodes toward H₂O₂ and glucose, respectively, may have a potential perspective in the fabrication of third-generation biosensors based on direct electrochemistry of enzymes.     

Preparation, characterization, and application of electrochemically functional graphene nanocomposites by one-step liquid-phase exfoliation of natural flake graphite with methylene blue

Electrochemically functional graphene nanocomposites have been directly prepared by one-step liquid-phase exfoliation of natural flake graphite with methylene blue (MB). UV-visible spectra of the obtained aqueous dispersions of graphene-methylene blue (G-MB) nanocomposite at different exfoliation time indicate that the concentration of graphene dispersion increased markedly with increasing exfoliation time. Atomic force microscopy (AFM) and Raman spectroscopy verified that the graphene was exfoliated into single-layer or bilayer states. FT-IR spectroscopy of G-MB suggests that a ??-?? stacking interaction is involved in the structure-associated interactions between graphene and adsorbed MB molecules. A G-MB nanocomposite modified glassy carbon (GC) electrode exhibits excellent electrochemical properties and good electrochemical stability. Additionally, the G-MB/GC modified electrode shows more favorable electron transfer kinetics for potassium ferricyanide and potassium ferrocyanide probe molecules, which are important electroactive compounds, compared with reduced graphene oxide (RGO)-MB/GC, RGO/GC, bare GC and graphite/GC electrodes. Furthermore, the G-MB/GC modified electrode exhibits good electrocatalytic activity toward hydrogen peroxide (H₂O₂) and ??-nicotinamide adenine dinucleotide (NADH). The excellent electroactivity, electrochemical stability and electrocatalytic activity of the G-MB nanocomposites prepared in this work are potentially very useful for basic electrochemical studies and for the practical development of electronic devices such as biosensors and photovoltaic cells.      

A non-enzymatic amperometric sensor for glucose based on cobalt oxide nanoparticles

A cobalt oxide nanoparticle-modified glassy carbon (CONM/GC) electrode was prepared by potential cycling in a pH-controlled solution containing tartrate. The electrocatalytic oxidation of glucose on CONM/GC electrode in alkaline solution was investigated and the kinetics was developed. In cyclic voltammograms, the peak current of the oxidation of low valence cobalt oxide in the presence of glucose is increased and it was followed by a decrease in the corresponding cathodic current. This suggested that glucose oxidation was being catalysed on the redox mediator with an electrocatalytic mechanism. Using cyclic voltammetry, chronoamperometry, steady-state polarisation measurements and impedance spectroscopy, the kinetic parameters of the glucose electrooxidation such as charge-transfer coefficient, the catalytic reaction rate constant and the diffusion coefficient were determined. Based on the results, an efficient enzyme-less sensing procedure for determination of glucose was developed. The resulting sensor exhibited excellent performance for the glucose determination and a sensitive and time-saving amperometric procedure was successfully applied for the quantification of glucose in both batch and flow systems. Glucose was determined with a linear range of 0.7–60?µM, a limit of detection of 0.15?µM and a sensitivity of 2515.35?µA?mM^?1?cm^?2 in batch system and with a linear range of 1.3–50?µM, a limit of detection of 0.14?µM and a sensitivity of 3240.25?µA?mM^?1?cm^?2 in the flow system.     

Controlled fabrication of gold nanoparticles biomediated by glucose oxidase immobilized on chitosan layer-by-layer films

The control of size and shape of metallic nanoparticles is a fundamental goal in nanochemistry, and crucial for applications exploiting nanoscale properties of materials. We present here an approach to the synthesis of gold nanoparticles mediated by glucose oxidase (GOD) immobilized on solid substrates using the Layer-by-Layer (LbL) technique. The LbL films contained four alternated layers of chitosan and poly(styrene sulfonate) (PSS), with GOD in the uppermost bilayer adsorbed on a fifth chitosan layer: (chitosan/PSS)₄/(chitosan/GOD). The films were inserted into a solution containing gold salt and glucose, at various pHs. Optimum conditions were achieved at pH 9, producing gold nanoparticles of ca. 30 nm according to transmission electron microscopy. A comparative study with the enzyme in solution demonstrated that the synthesis of gold nanoparticles is more efficient using immobilized GOD.     

High-sensitivity non-enzymatic glucose biosensor based on Cu(OH)2 nanoflower electrode covered with boron-doped nanocrystalline diamond layer

A non-enzymatic biosensor was developed using boron-doped nanocrystalline diamond (BDND) based on a Cu electrode with Cu(OH)₂ dendritic architecture. The Cu(OH)₂ nanoflower electrode was covered with a BDND layer using an electrostatic self-assembly seeding method with nanodiamond particles and hot-filament chemical vapor deposition. X-ray diffraction and Raman spectral analysis confirmed that the BDND nanoflower electrode was synthesized onto Cu(OH)₂ nanoflowers. Field-emission scanning electron microscope images showed that the fabricated electrodes were nanoflowers possessing large surface areas. From cyclic voltammetry, the peak currents of an BDND/Cu(OH)₂/Cu electrode was about 7, 6.2, and 5.9 times higher than that of the Cu foil, Cu(OH)₂/Cu, and BDND/Cu electrodes, respectively. A biosensor based on BDND/Cu(OH)₂/Cu exhibited excellent performance for glucose detection, and it had a linear detection range of 0 to 6 mM, a correlation coefficient of 0.9994, a low detection limit of 9 μM, and a high sensitivity of 2.1592 mA mM^− 1 cm^− 1.     

Nano iron oxide (Fe2O3)/carbon black electrodes as electrode material for electrochemical capacitors: Effect of the nanoparticles dispersion quality

In the present study, nano Fe₂O₃/carbon black electrodes are proposed for electrochemical capacitors and the effect of nanoparticles dispersion quality on the surface morphology, nature and electrochemical properties of the electrodes are investigated. Mechanical pressing is accompanied by different mixing (mechanical and sonication) processes to prepare the electrode. Electrochemical properties of the produced nanocomposites are studied using cyclic voltammetry and electrochemical impedance spectroscopy tests in 2 M KCl electrolyte. Scanning electron microscopy is used to characterize the microstructure and the nature of the nanoparticles on the nanocomposites produced. Results obtained show that the sonicated and unsonicated 10:80:10 (CB:Fe₂O₃:PTFE) electrodes have specific capacitance of 22.02 and 22.35 F g⁻¹ respectively, at scan rate of 10 mV s⁻¹. Sonication process breaks the agglomerated particles and disperses them on the electrode surface, uniformly. This increases the specific surface area and the electrical resistance of the electrodes. The sonicated electrodes show a higher charge separation capability at electrolyte/electrode interfaces, lower ratio of outer to total charge (q_O*/q_T*) of 0.13 and lower current response at end potentials. Energy density was increased after the sonication process from 0.686 to 1.498 (Wh kg⁻¹). Charge/discharge cycling results confirmed that the uniform dispersion of active material on the electrode surface postpones the electrolyte decomposition and improves the electrical conductivity during cycling.