Seed-mediated growth of platinum nanoparticles on carbon nanotubes for the fabrication of electrochemical biosensors

Platinum nanoparticles (PtNPs) were prepared by seed-mediated growth method with Au nanoparticles (AuNPs) playing the role of seeds. Carbon nanotubes (CNTs) and AuNPs were first dropped onto the surface of glassy carbon (GC) electrode, and then the electrode was immersed into growth solution which contains H₂PtCl₆ and ascorbic acid. PtNPs were successfully grown onto the CNT surface due to the chemical reduction of Pt(IV). The electrode modified with AuNP_seed/PtNP/CNT film displayed excellent electrochemical response to H₂O₂ at 0.45 V versus saturated calomel electrode (SCE) with sensitivity much larger than that of PtNP/CNT and AuNP_seed/PtNP modified electrodes. Glucose oxidase was selected as a model enzyme and electrodeposited onto the AuNP_seed/PtNP/CNT modified electrode in the presence of a detergent. The resulting biosensor enabled selective determination of glucose with high sensitivity of 4.49 μA mM⁻¹, quick response time about 2 s, low-detection limit of 0.5 μM and wide linear range from 1 μM to 4 mM with a correlation coefficient 0.9998. Thus, the modified electrode proved to be a nice electrochemical biosensing platform for the fabrication of oxidase-based biosensors.     

Facile direct electron transfer in glucose oxidase modified electrodes

Glucose oxidase (GOx) is widely used in the glucose biosensor industry. However, mediatorless direct electron transfer (DET) from GOx to electrode surfaces is very slow. Recently, mediatorless DET has been reported via the incorporation of nanomaterials such as carbon nanotubes and nanoparticles in the modification of electrodes. Here we report GOx electrodes showing DET without the need for any nanomaterials. The enzyme after immobilization with poly-l-lysine (PLL) and Nafion^® retains the biocatalytic activities and oxidizes glucose efficiently. The amperometric response of Nafion-PLL-GOx modified electrode is linearly proportional to the concentration of glucose up to 10 mM with a sensitivity of 0.75 μA/mM at a low detection potential (−0.460 V vs. Ag/AgCl). The methodology developed in this study will have impact on glucose biosensors and biofuel cells and may potentially simplify enzyme immobilization in other biosensing systems.     

Neodymium (III) hexacyanoferrate (II) nanoparticles induced by enzymatic reaction and their use in biosensing of glucose

The formation of neodymium (III) hexacyanoferrate (II) (NdHCF) nanoparticles (NPs) on the surface of carbon-paste electrode induced by enzymatic reaction was described and characterized. The conditions for biosensing of glucose were optimized through various experiments. Results showed that the optimized condition of the glucose oxidase (GOx)-induced NdHCF NPs for the biosensing of glucose were 2.0 mM Nd³⁺, 40.0 mM Fe(CN)₆³⁻ and 20 μg/mL GOx. The biocatalyzed generation of NdHCF NPs in the presence of O₂/glucose and GOx enabled the development of an electrochemical biosensor for glucose. Furthermore, this system avoids the interferences from other species for the biosensing of glucose.     

Amperometric glucose biosensor based on Prussian blue-multiwall carbon nanotubes composite and hollow PtCo nanochains

In this paper, a novel glucose biosensor was developed based on immobilizing glucose oxidase (GOD) on Prussian blue-multiwall carbon nanotubes (PB@MWNTs) composite and hollow PtCo (H-PtCo) nanochains modified electrode. The PB@MWNTs/H-PtCo membrane showed good biocompatibility, large surface-to-volume ratio and excellent electron-conductive ability. The successful fabrication of the PB@MWNTs composite synthesized with MWNTs as a template and Fe(III)-reducer were characterized by UV-vis absorption spectroscopy, Fourier transform infrared (FTIR) spectrometry and transmission electron microscopy (TEM). The hollow PtCo nanochains were also characterized by TEM and X-ray photoelectron spectroscopy (XPS). The response of the biosensor towards glucose under the optimized conditions, as investigated by chronoamperometry, is linear from 3.0 μM to 3.6 mM, with a low detection limit of 0.85 μM (S/N = 3) and a high sensitivity 21 mA M⁻¹ cm⁻². Moreover, the biosensor exhibits strong anti-interferent ability, good reproducibility and excellent stability.     

Novel amperometric glucose biosensor based on an ether-linked cobalt(II) phthalocyanine-cobalt(II) tetraphenylporphyrin pentamer as a redox mediator

The development of cobalt(II) phthalocyanine-cobalt(II) tetra(5-phenoxy-10,15,20-triphenylporphyrin), (CoPc-(CoTPP)₄) pentamer as a novel redox mediator for amperometric enzyme electrode sensitive to glucose is described. A glassy carbon electrode (GCE) was first modified with the pentamer, then followed by the immobilization onto the GCE-CoPc-(CoTPP)₄ with glucose oxidase (GOx) through cross-linking with glutaraldehyde in the presence of bovine serum albumin (BSA) and Nafion^® cation-exchange polymer. The proposed biosensor displayed good amperometric respose charateristics to glucose in pH 7.0 PBS solution; such as low overpotentials (+400 mV versus Ag|AgCl), very fast amperometric response time (∼5 s), linear concentration range extended up to 11 mM, with 10 μM detection limit. The biosensor exhibited electrochemical Michaelis-Menten kinetics and showed an average apparent Michaelis-Menten constant (K^′M) of 14.91 ± 0.46 mM over a storage period of 2 weeks.     

Low potential detection of glucose at carbon nanotube modified glassy carbon electrode with electropolymerized poly(toluidine blue O) film

A mediator glucose biosensor has been constructed by immobilizing glucose oxidase at electropolymerized poly(toluidine blue O) film on carbon nanotube modified glass carbon electrode. The toluidine blue O moieties served as redox mediators for enzymatic glucose oxidation and as polymeric network to maintain the biosensor activity. Great enhancement in current response was observed for the glucose biosensor. The detection potential could be decreased to −0.1 V (versus Ag|AgCl), where common interferences such as ascorbic acid, uric acid and acetamidophenol were not oxidized to cause interferences. The amperometric glucose biosensor offered a sensitivity of 14.5 mA M⁻¹ cm⁻² for the linear range of 1-7 mM.     

Glucose biosensor based on multiwalled carbon nanotubes grown directly on Si

An amperometric biosensor based on covalent immobilization of glucose oxidase (GOx) on multiwalled carbon nanotubes (MWCNTs) with potassium ferricyanide as the redox mediator was developed. The MWCNTs were grown directly on a layered structure of Co/Ti/Cr on a SiO₂/Si substrate by microwave-heated chemical vapor deposition. The mediator helps to shuttle the electrons between the immobilized GOx and the MWCNT electrode, therefore operating at a potential of 0.25 V vs. the saturated calomel electrode. This potential precludes the interfering compounds from oxidization. The sensitivity of biosensors to glucose was found to depend on the acid pretreatment and GOx reaction times. The steady-state response of the optimized biosensor exhibits a sensitivity of 20.6 μA mM⁻¹ cm⁻², a linear range of up to 8 mM, and a response time of <5 s.     

Amperometric glucose biosensor prepared with biocompatible material and carbon nanotube by layer-by-layer self-assembly technique

Prussian Blue (PB) based glucose biosensor was prepared by immobilizing glucose oxidase (GOD) in layer-by-layer (LBL) films with chitosan (Chi) and multi-walled carbon nanotubes (MWNTs). With the increasing of Chi/MWNTs/GOD layers, the response current to glucose was changed regularly and reached a maximum value when the number of layer was six. At the optimized condition, the biosensor exhibits excellent response performance to glucose with a linear range from 1 to 7 mM and a low detection limit of 0.05 mM. The biosensor also shows a high sensitivity of 8.017 μA mM⁻¹ cm⁻², which is attributed to the biocompatible nature of the LBL films. Furthermore, the biosensor shows rapid response, good reproducibility, long-term stability and freedom of interference from other co-existing electroactive species such as ascorbic acid and acetaminophen.     

Study of the biosensor based on platinum nanoparticles supported on carbon nanotubes and sugar–lectin biospecific interactions for the determination of glucose

Highly sensitive electrochemical platform based on Pt nanoparticles supported on carbon nanotubes (Pt_nano-CNTs) and sugar–lectin biospecific interactions is developed for the direct electrochemistry of glucose oxidase (GOD). Firstly, Pt_nano-CNTs nanocomposites were prepared in the presence of carbon nanotubes (CNTs), and then the mixture was cast on a glassy carbon electrode (GCE) using chitosan as a binder. Thereafter, concanavalin A (Con A) was adsorbed onto the precursor film by the electrostatic force between positively charged chitosan and the negatively charged Con A. Finally, the multilayers of Con A/GOD films were prepared based on biospecific affinity of Con A and GOD via layer-by-layer (LBL) self-assembly technique. The electrochemical behavior of the sensor was studied using cyclic voltammetry and chronoamperometry. The electrochemical parameters of GOD in the film were calculated with the results of the electron transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (k_s) as 0.5 and 5.093 s⁻¹, respectively. Experimental results show that the biosensor responded linearly to glucose in the range from 1.2 × 10⁻⁶ to 2.0 × 10⁻³ M, with a detection limit of 4.0 × 10⁻⁷ M under optimized conditions.     

Amperometric tyrosinase biosensor based on Fe3O4 nanoparticles-coated carbon nanotubes nanocomposite for rapid detection of coliforms

A tyrosinase (Tyr) biosensor was developed based on Fe₃O₄ magnetic nanoparticles (MNPs)-coated carbon nanotubes (CNTs) nanocomposite and further applied to detect the concentration of coliforms with flow injection assay (FIA) system. Negatively charged MNPs were absorbed onto the surface of CNTs which were wrapped with cationic polyelectrolyte poly(dimethyldiallylammonium chloride) (PDDA). The Fe₃O₄ MNPs-coated CNTs nanocomposite was modified on the surface of the glassy carbon electrode (GCE), and Tyr was loaded on the modified electrode by glutaraldehyde. The immobilization matrix provided a good microenvironment for retaining the bioactivity of Tyr, and CNTs incorporated into the nanocomposite led to the improved electrochemical detection of phenol. The Tyr biosensor showed broad linear response of 1.0 × 10⁻⁸-3.9 × 10⁻⁵ M, low detection limit of 5.0 × 10⁻⁹ M and high sensitivity of 516 mA/M for the determination of phenol. Moreover, the biosensor integrated with a FIA system was used to monitor coliforms, represented by Escherichia coli (E. coli). The detection principle was based on determination of phenol which was produced by enzymatic reaction in the E. coli solution. Under the optimal conditions, the current responses obtained in the FIA system were proportional to the concentration of bacteria ranging from 20 to 1 × 10⁵ cfu/mL with detection limit of 10 cfu/mL and the overall assay time of about 4 h. The developed biosensor with the FIA system was well suited for quick and automatic clinical diagnostics and water quality analysis.     

An ECL biosensor for glucose based on carbon-nanotube/Nafion film modified glass carbon electrode

Glucose oxidase was encapsulated in carbon-nanotube/Nafion film modified glass carbon electrode and was used as electrochemiluminescence (ECL) biosensor for glucose. The glucose oxidase can be fixed firmly in the Nafion film and carbon nanotubes offer excellent electrocatalytic activity toward luminol and hydrogen peroxide liberated in enzymatic reaction between glucose oxidase and glucose, which would enable sensitive determination of glucose. Under the optimum condition, the linear response range of glucose was found to be 5.0 × 10⁻⁶ to 8.0 × 10⁻⁴ mol/L, and the detection limit (defined as the concentration that could be detected at the signal-to-noise ratio of 3) was 2.0 × 10⁻⁶ mol/L. The present carbon-nanotube/Nafion biocomposite glucose oxidase ECL biosensor showed excellent properties for sensitive determination for glucose with good reproducibility and stability, and it has been used to determine the glucose concentrations in real serum samples with the satisfactory results.     

Functionalized carbon nanotube-bienzyme biocomposite for amperometric sensing

An approach to design a biocomposite bienzyme biosensor with the aim of evaluating its suitability as an amperometric sensor using functionalized multiwalled carbon nanotubes (MWCNTs) is presented. The biosensor is based on a bienzyme-channelling configuration, employing the enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP), which were immobilized with toluidine blue (TB) functionalized MWCNTs. The proposed method demonstrates an easy electron transfer between the immobilized enzymes and the electrode via functionalized MWCNTs in a Nafion matrix. Co-immobilization of GOx and HRP was employed to establish the feasibility of fabricating highly effective bienzyme-based biosensors for low-level glucose determination. Bienzyme immobilized TB functionalized MWCNTs were attached to a glassy carbon electrode, and the electrochemical behavior of the sensor was studied using electrochemical impedance spectroscopy, cyclic voltammetry and chronoamperometry. The excellent electrocatalytic activity of the biocomposite film resulted in the detection of glucose under reduced over potential with a wider range of determination from 1.5 × 10⁻⁸ M to 1.8 × 10⁻³ M and with a detection limit of 3 × 10⁻⁹ M. The sensor showed a short response time (within 2 s), good stability and anti-interferant ability. The proposed biosensor exhibits good analytical performance in terms of repeatability, reproducibility and shelf-life stability.     

Tetracarboxylic acid cobalt phthalocyanine SAM on gold: Potential applications as amperometric sensor for H2O2 and fabrication of glucose biosensor

This report describes the applications of cobalt tetracarboxylic acid phthalocyanine (CoTCAPc) self-assembled monolayer (SAM) immobilized onto a preformed 2-mercaptoethanol (Au-ME) SAM on gold surface (Au-ME-CoTCAPc SAM) as a potential amperometric sensor for the detection of hydrogen peroxide (H₂O₂) at neutral pH conditions. The Au-ME-CoTCAPc SAM sensor showed a very fast amperometric response time of approximately 1 s, good linearity at the studied concentration range of up to 5 μM with a coefficient R² = 0.993 and a detection limit of 0.4 μM oxidatively. Also reductively, the sensor exhibited a very fast amperometric response time (∼1 s), linearity up to 5 μM with a coefficient R² = 0.986 and a detection limit of 0.2 μM. The cobalt tetracarboxylic acid phthalocyanine self-assembled monolayer was then evaluated as a mediator for glucose oxidase (GOx)-based biosensor. The GOx (enzyme) was immobilized covalently onto Au-ME-CoTCAPc SAM using coupling agents: N-ethyl-N(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS), and the results demonstrated a good catalytic behavior. Kinetic parameters associated with the enzymatic and mediator reactions were estimated using electrochemical versions of Lineweaver-Burk and Hanes equation, and the stability of the sensor was tested. The biosensor (Au-ME-CoTCAPc-GOx SAM) electrode showed good sensitivity (7.5 nA/mM) with a good detection limit of 8.4 μM at 3σ, smaller Michaelis-Menten constant (4.8 mM from Hanes plot) and very fast response time of approximately 5 s.     

Microwave-polyol synthesis of nanocrystalline ruthenium oxide nanoparticles on carbon nanotubes for electrochemical capacitors

The ruthenium oxide nanoparticles dispersed on multi-wall carbon nanotubes (CNTs) were successfully synthesized via microwave-polyol process combined with forced hydrolysis without additional thermal oxidation or electrochemical oxidation treatment. The HRTEM, Raman spectra and TGA curve indicate that CNTs were uniformly coated with crystalline and partially hydrous RuO₂·0.64H₂O nanoparticles of 2 nm diameter and the loading amount of ruthenium oxide in the composite could be controlled up to 70 wt.%. The specific capacitance was 450 Fg⁻¹ of ruthenium oxide/CNT composite electrode with 70 wt.% ruthenium oxide at the potential scan rate of 10 mV s⁻¹ and it decreased to 362 Fg⁻¹ by 18% at 500 mV s⁻¹. The specific capacitance of ruthenium oxide in the composite was 620 Fg⁻¹ of ruthenium oxide at 10 mV s⁻¹. The ruthenium oxide nanoparticles in ruthenium oxide/CNT nanocomposite electrode had a high ratio of outer charge to total charge of 0.81, which confirmed its high-rate capability of the composite through the preparation of the nano-sized ruthenium oxide particles on the external surface of CNTs.     

Controlled multilayer films of sulfonate-capped gold nanoparticles/thionine used for construction of a reagentless bienzymatic glucose biosensor

A novel reagentless bienzymatic sensor for the determination of glucose in the low working potentials without interference is proposed. The bienzymatic sensor was fabricated by covalently attachment of periodate-oxidized glucose oxidase (IO₄⁻-GOx) and horseradish peroxidase (HRP) on controlled multilayer films of sulfonate-capped gold nanoparticles/thionine (SCGNPs/TH). Using the layer-by-layer method (LBL), SCGNPs and TH were deposited alternately on the gold electrode through the electrostatic and covalent interactions. SCGNPs could greatly enhance the amount of immobilized TH and ensure the good conductivity of the whole structure. UV-vis absorption spectroscopy and electrochemical methods showed that the resulting multilayer films were tridimensional conductive and porous, and TH incorporated in LBL configuration had well electroactive performance. Such superstructures can thus provide an ideal matrix for the construction of bienzymatic sensor, where TH molecules acted as a mediator for electron transfer. After IO₄⁻-GOx and HRP were covalently attached to the multilayer precursor film, the resulting biosensor exhibited good electrocatalytical response toward glucose and that the electrocatalytical response increased with the number of TH layers. This suggested that the analytical performance such as sensitivity and detection limit of the bienzymatic sensors could be tuned to the desired level by adjusting the number of deposited SCGNPs/TH bilayers. Furthermore, because of the low working potentials, the interference from other electro-oxidizable compounds (such as uric acid, ascorbic acid and acetaminophen) was avoided, which improved the selectivity of the biosensors. The biosensor constructed with six bilayers of SCGNPs/TH showed a good performance of glucose detection with a fast response less than 20 s, acceptable sensitivity of 3.8 μA mM⁻¹ cm⁻² and the detection limit of 3.5 × 10⁻⁵ M.     

Development of highly sensitive non-enzymatic sensor for the selective determination of glucose and fabrication of a working model

Copper oxide (CuO)/copper oxalate (CuOx) modified non-enzymatic electrochemical sensor for the detection of glucose in alkaline medium was fabricated by electrochemical anodisation of copper electrodes in potassium oxalate solution. Morphology of the modified copper electrode was studied by Scanning Electron Microscopy (SEM) and its electrochemical behaviour by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The formation of CuOx on the copper electrode was confirmed by the Infra-red Reflection Absorption Spectrum (IRRAS). The modified electrodes were found to be microporous and rough. Linear Sweep Voltammetry (LSV) and amperometry were adopted to investigate the direct electrocatalytic oxidation of glucose on CuO/CuOx modified electrode in alkaline medium which showed excellent catalytic activity. The best performance of the sensor was obtained at 0.7 V and in 0.1 M sodium hydroxide (NaOH). At this optimum potential, the sensor was highly selective to glucose in the presence of ascorbic acid (AA) and uric acid (UA) which are common interfering species in biological fluids. The sensitivity was found to be very high (1890 μA mM⁻¹ cm⁻²) with excellent linearity (R = 0.9999) up to 15 mM having a low detection limit of 0.05 μM (S/N = 3). The modified electrode was tested for glucose level in blood serum. Based on the optimised conditions, a working model of the sensor was made and successfully tested for glucose.     

Dual oxygen and Ir oxide regeneration of glucose oxidase in nanostructured thin film glucose sensors

A nanoparticulate iridium oxide (IrOx) thin film has been developed as a redox-active matrix material for an advanced generation glucose biosensor, in which IrOx serves as the non-physiological mediator, replacing oxygen in the enzymatic re-oxidation of glucose oxidase (GOx). Ethanolic solutions of Nafion and an Ir sol were mixed with an aqueous GOx solution and then deposited on a Au support. The Ir nanoparticles were then oxidized electrochemically to IrOx and the resulting films (IrOx-GOx-Nafion) were tested for their glucose response in both oxygen- and argon-saturated solutions, with the oxygen content in both solutions monitored by a Pt electrode. The sensors that are regenerated largely by O₂ are characterized by a Michaelis-Menten K^′m value of ∼30 mM or more and i_max values of at least 20 μA cm⁻². Under fully deareated conditions, the sensors lose only ∼50% of their response to glucose, clearly indicating that a dual oxygen-regeneration and IrOx mediation mechanism is operative for the biosensor under these conditions. Under optimized conditions, involving a controlled GOx:Ir ratio, only the Ir oxide sites in the film serve to mediate GOx regeneration, giving K^′m (10-15 mM) and i_max values that are independent of the O₂ content of the solution.     

Amperometric bienzyme glucose biosensor based on carbon nanotube modified electrode with electropolymerized poly(toluidine blue O) film

The amperometric bienzyme glucose biosensor utilizing horseradish peroxidase (HRP) and glucose oxidase (GOx) immobilized in poly(toluidine blue O) (PTBO) film was constructed on multi-walled carbon nanotube (MWNT) modified glassy carbon electrode. The HRP layer could be used to analyze hydrogen peroxide with toluidine blue O (TBO) mediators, while the bienzyme system (HRP + GOx) could be utilized for glucose determination. Glucose underwent biocatalytic oxidation by GOx in the presence of oxygen to yield H₂O₂ which was further reduced by HRP at the MWNT-modified electrode with TBO mediators. In the absence of oxygen, glucose oxidation proceeded with electron transfer between GOx and the electrode mediated by TBO moieties without H₂O₂ production. The bienzyme electrode offered high sensitivity for amperometric determination of glucose at low potential, displaying Michaelis-Menten kinetics. The bienzyme glucose biosensor displayed linear response from 0.1 to 1.2 mM with a sensitivity of 113 mA M⁻¹ cm⁻² at an applied potential of −0.10 V in air-saturated electrolytes.     

Alcohol dehydrogenase amperometric biosensor based on a colloidal gold-carbon nanotubes composite electrode

A novel ethanol biosensor based on the bulk incorporation of alcohol dehydrogenase (ADH) into a colloidal gold (Au_coll)-multiwalled carbon nanotubes (MWCNTs) composite electrode using Teflon as binding material is reported. The composite Au_coll-MWCNTs-Teflon electrode exhibited significantly improved electrooxidation of NADH when compared with other carbon composite electrodes, including those based on carbon nanotubes. Amperometric measurements for NADH at +0.3 V showed significant differences in sensitivity between Au_coll-MWCNTs-Teflon and MWCNTs-Teflon composite electrodes. Incorporation of ADH into the bulk electrode material allowed the construction of a mediatorless ethanol biosensor. Both the enzyme loading and the NAD⁺ concentration in solution were optimized. The ADH-Au_coll-MWCNTs-Teflon biosensor allowed a limit of detection for ethanol of 4.7 μmol l⁻¹, which is remarkably better than those reported for other CNTs-based ADH biosensors. The apparent Michaelis-Menten constant was 4.95 mmol l⁻¹, which is much lower than that reported by immobilization of ADH onto a gold electrode. Both repeatability of the ethanol amperometric measurements, reproducibility with different biosensors, lifetime and storage ability can be, in general, advantageously compared with other ADH-CNTs biosensors. The biosensor was applied for the rapid determination of ethanol in commercial and certified beer samples.     

HRP biosensor based on sugar-lectin biospecific interactions for the determination of phenolic compounds

A layer-by-layer self-assembly of concanavalin A (Con A) and glycoprotein horseradish peroxidase (HRP) afforded multilayer thin films on the surface of a thiol-modifed gold electrode, through biospecific complexation of Con A and sugar residues in the glycoenzymes. The performance of the HRP biosensor is reported for the amperometric detection of phenolic compounds. The concentration of hydrogen peroxide and assembly conditions of the precursor film, such as pH, the ionic strength of the polyelectrolyte solutions and the number of assembled bilayers were investigated using catechol. With optimized conditions, the biosensor presented a linear response for catechol from 6.0 to 48.0 μmol l⁻¹, with a high sensitivity of 160 μmol⁻¹ l nA and a detection limit of 0.6 μmol l⁻¹. The response time of the biosensor for phenolic compounds was very short, reaching 95% of its maximum response in about 2 s. The differences in sensitivity observed for a series of phenolic substrates were discussed in terms of the stability of the oxidized phenolic compounds and the properties of substituents.