Nano nickel oxide modified non-enzymatic glucose sensors with enhanced sensitivity through an electrochemical process strategy at high potential

Development of fast and sensitive sensors for glucose determination is important in food industry, clinic diagnostics, biotechnology and many other areas. In these years, considerable attention has been paid to develop non-enzymatic electrodes to solve the disadvantages of the enzyme-modified electrodes, such as instability, high cost, complicated immobilization procedure and critical operating situation et al. Nano nickel oxide (NiO) modified non-enzymatic glucose sensors with enhanced sensitivity were investigated. Potential scanning nano NiO modified carbon paste electrodes up to high potential in alkaline solution greatly increases the amount of redox couple Ni(OH)(2)/NiOOH derived from NiO, and thus improves their electrochemical properties and electrocatalytical performance toward the oxidation of glucose. The non-enzymatic sensors response quickly to glucose and the response time is less than 5s, demonstrating excellent electrocatalytical activity and assay performance. The calibration plot is linear over the wide concentration range of 1-110 μM with a sensitivity of 43.9 nA/μM and a correlation coefficient of 0.998. The detection limit of the electrode was found to be 0.16 μM at a signal-to-noise ratio of 3. The proposed non-enzymatic sensors can be used for the assay of glucose in real sample.     

Hemoglobin niobate composite based biosensor for efficient determination of hydrogen peroxide in a broad pH range

Inorganic layered niobates (HCa2Nb3O10) were used as immobilization matrices of hemoglobin (Hb) because of their tunable interlayer spaces, large surface areas and good biocompatibilities. A pair of well-defined, quasi-reversible cycle voltammertric peaks were obtained at the Hb-HCa2Nb3O10 modified pyrolytic graphite electrode, suggesting that the layered niobates facilitate the electron transfer between the proteins and the electrode. Hb-HCa2Nb3O10 modified electrode exhibited electrocatalytic response for monitoring H2O2 with a large linear detection range from 25 microM to 3.0 mM and a relatively high sensitivity of 172 microA mM-1 cm-2. Based on the stabilizing effect of the layered niobates, Hb-HCa2Nb3O10 modified electrode can detect H2O2 in strongly acidic and basic solutions with pH of 1-12, which greatly expands the application fields of biosensors.     

Direct electrochemistry and electrocatalytic activity of catalase immobilized onto electrodeposited nano-scale islands of nickel oxide

Cyclic voltammetry was used for simultaneous formation and immobilization of nickel oxide nano-scale islands and catalase on glassy carbon electrode. Electrodeposited nickel oxide may be a promising material for enzyme immobilization owing to its high biocompatibility and large surface. The catalase films assembled on nickel oxide exhibited a pair of well defined, stable and nearly reversible CV peaks at about -0.05 V vs. SCE at pH 7, characteristic of the heme Fe (III)/Fe (II) redox couple. The formal potential of catalase in nickel oxide film were linearly varied in the range 1-12 with slope of 58.426 mV/pH, indicating that the electron transfer is accompanied by single proton transportation. The electron transfer between catalase and electrode surface, (k(s)) of 3.7(+/-0.1) s(-1) was greatly facilitated in the microenvironment of nickel oxide film. The electrocatalytic reduction of hydrogen peroxide at glassy carbon electrode modified with nickel oxide nano-scale islands and catalase enzyme has been studied. The embedded catalase in NiO nanoparticles showed excellent electrocatalytic activity toward hydrogen peroxide reduction. Also the modified rotating disk electrode shows good analytical performance for amperometric determination of hydrogen peroxide. The resultant catalase/nickel oxide modified glassy carbon electrodes exhibited fast amperometric response (within 2 s) to hydrogen peroxide reduction (with a linear range from 1 microM to 1 mM), excellent stability, long term life and good reproducibility. The apparent Michaelis-Menten constant is calculated to be 0.96(+/-0.05)mM, which shows a large catalytic activity of catalase in the nickel oxide film toward hydrogen peroxide. The excellent electrochemical reversibility of redox couple, high stability, technical simplicity, lake of need for mediators and short preparations times are advantages of this electrode. Finally the activity of biosensor for nitrite reduction was also investigated.     

Nonenzymatic glucose sensor based on over-oxidized polypyrrole modified Pd/Si microchannel plate electrode

A silicon microchannel plate (MCP) array electrode modified with over-oxidized polypyrrole (OPPy) has been fabricated to detect glucose. The morphology and structure of the electrode are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The OPPy modified silicon MCP array electrode exhibits high electrocatalytic activity as well as excellent selectivity to the electrochemical oxidation of glucose. At a potential of +0.08 V, good sensitivity of 0.37 mA mM(-1) cm(-2) and detection limit of 2.06 μM are attained. The linear range is up to 24 mM with a linear correlation coefficient of 0.997. Furthermore, the electrode is highly resistant to interfering substances because the effects of common coexisting substances can be effectively eliminated by the OPPy film and the response in the current to interferences on the electrode surface is almost negligible. This novel electrode has high potential in nonenzymatic detection of glucose.     

Palladium hexacyanoferrate hydrogel as a novel and simple enzyme immobilization matrix for amperometric biosensors

An amperometric glucose biosensor with glucose oxidase (GOx) immobilized into palladium hexacyanoferrate (PdHCF) hydrogel has been prepared and evaluated. The sensor was based on a two-layer configuration with biocatalytic and electrocatalytic layers separately deposited onto the electrode. To reduce the overpotential for reduction of hydrogen peroxide liberated in the enzyme catalyzed oxidation of glucose, an inner thin layer of nickel hexacyanoferrate (NiHCF) electrodeposited onto the surface of graphite electrode was used as an electrocatalyst. As an outer layer, the hydrogel of palladium hexacyanoferrate with entrapped glucose oxidase was used. Under optimal operating conditions (pH 5.0 and E = -0.075 V versus calomel (3.0 M KCl) reference electrode), sensor showed high sensitivity to glucose (0.3-1.0 microA/mM) and a response time of less than 30s. The linear response to glucose was obtained in the concentration range between 0.05 and 1.0 mM in batch analysis mode and 0-7.0 mM in FIA. During the 32 days testing period, no significant decrease in the sensor sensitivity was observed. The sensor was applied for the determination of glucose concentration in fruit juice and yoghurt drink, and the results obtained showed good correlation with results obtained by reference spectrophotometric enzyme method.     

Pt-Pb nanowire array electrode for enzyme-free glucose detection

Pt-Pb nanowire array was directly synthesized by electrochemical deposition of Pt-Pb alloy into the pores of microporous polycarbonate template and subsequent chemical etching of the template. The morphology and the composition of the Pt-Pb nanowires were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. Cyclic voltammetry (CV) was used to evaluate the electrochemical performance of the Pt-Pb nanowire array electrode (Pt-PbNAE). Direct glucose oxidation on Pt-PbNAE was investigated in detail by discussing the effect of the structure and materials of the electrode on electrocatalytic oxidation of glucose. As a result, we found that the Pt-PbNAE with a three-dimensional structure exhibited high electrocatalytic activity to glucose oxidation in neutral condition and could be used for the development of nonenzymatic glucose sensor. To effectively avoid the interference coming from ascorbic acid, a negative potential of -0.20V was chosen for glucose detection, and the sensitivity of the sensor to glucose oxidation was 11.25 microAmM(-1)cm(-2) with a linearity up to 11 mM, and a detection limit of 8 microM (signal-to-noise ratio of 3).     

Glucose biosensor prepared by glucose oxidase encapsulated sol-gel and carbon-nanotube-modified basal plane pyrolytic graphite electrode

A new glucose biosensor has been fabricated by immobilizing glucose oxidase into a sol-gel composite at the surface of a basal plane pyrolytic graphite (bppg) electrode modified with multiwall carbon nanotube. First, the bppg electrode is subjected to abrasive immobilization of carbon nanotubes by gently rubbing the electrode surface on a filter paper supporting the carbon nanotubes. Second, the electrode surface is covered with a thin film of a sol-gel composite containing encapsulated glucose oxidase. The carbon nanotubes offer excellent electrocatalytic activity toward reduction and oxidation of hydrogen peroxide liberated in the enzymatic reaction between glucose oxidase and glucose, enabling sensitive determination of glucose. The amperometric detection of glucose is carried out at 0.3 V (vs saturated calomel electrode) in 0.05 M phosphate buffer solution (pH 7.4) with linear response range of 0.2-20 mM glucose, sensitivity of 196 nA/mM, and detection limit of 50 microM (S/N=3). The response time of the electrode is < 5s when it is stored dried at 4 degrees C, the sensor showed almost no change in the analytical performance after operation for 3 weeks. The present carbon nanotube sol-gel biocomposite glucose oxidase sensor showed excellent properties for the sensitive determination of glucose with good reproducibility, remarkable stability, and rapid response and in comparison to bulk modified composite biosensors the amounts of enzyme and carbon nanotube needed for electrode fabrication are dramatically decreased.     

A novel glucose biosensor based on the nanoscaled cobalt phthalocyanine-glucose oxidase biocomposite

We report on the utilization of a novel nanoscaled cobalt phthalocyanine (NanoCoPc)-glucose oxidase (GOD) biocomposite colloid to create a highly responsive glucose biosensor. The biocomposite colloid is constructed under enzyme-friendly conditions by adsorbing GOD molecules on CoPc nanoparticles via electrostatic interactions. The glucose biosensor can be easily achieved by casting the biocomposite colloid on a pyrolytic graphite electrode (PGE) without any auxiliary matter. It has been found that GOD can be firmly immobilized on PGE surface and maintain its bioactivity after conjugating with NanoCoPc. NanoCoPc displays intrinsic electrocatalytic ability to the oxidation of the product of enzymatic reaction H2O2 and shows a higher catalytic activity than that of bulk CoPc. Under optimal conditions, the biosensor shows a wide linear response to glucose in the range of 0.02-18 mM, with a fast response (5s), high sensitivity (7.71 microA cm(-2) mM(-1)), as well as good thermostability and long-term life. The detection limit was 5 microM at 3 sigma. The general interferences coexisted in blood except ascorbic acid and L-cysteine do not affect glucose determination, and further coating Nafion film on the surface of the biosensor can effectively eliminate the interference from ascorbic acid and L-cysteine. The biosensor with Nafion film has been used for the determination of glucose in serum with an acceptable accuracy.     

Glucose biosensor based on electrodeposition of platinum nanoparticles onto carbon nanotubes and immobilizing enzyme with chitosan-SiO(2) sol-gel

A novel amperometric biosensor, based on electrodeposition of platinum nanoparticles onto multi-walled carbon nanotube (MWNTs) and immobilizing enzyme with chitosan-SiO(2) sol-gel, is presented in this article. MWNTs were cast on the glass carbon (GC) substrate directly. An extra Nafion coating was used to eliminate common interferents such as acetaminophen and ascorbic acids. The morphologies and electrochemical performance of the modified electrodes have been investigated by scanning electron microscopy (SEM) and amperometric methods, respectively. The synergistic action of Pt and MWNTs and the biocompatibility of chitosan-SiO(2) sol-gel made the biosensor have excellent electrocatalytic activity and high stability. The resulting biosensor exhibits good response performance to glucose with a wide linear range from 1 microM to 23 mM and a low detection limit 1 microM. The biosensor also shows a short response time (within 5s), and a high sensitivity (58.9 microAm M(-1)cm(-2)). In addition, effects of pH value, applied potential, rotating rate, electrode construction and electroactive interferents on the amperometric response of the sensor were investigated and discussed in detail.     

Immobilization of hemoglobin on zirconium dioxide nanoparticles for preparation of a novel hydrogen peroxide biosensor

Direct electrochemistry and thermal stability of hemoglobin (Hb) immobilized on a nanometer-sized zirconium dioxide (ZrO2) modified pyrolytic graphite (PG) electrode were studied. The immobilized Hb displayed a couple of stable and well-defined redox peaks with an electron transfer rate constant of (7.90 +/- 0.93)s(-1) and a formal potential of -0.361 V (-0.12 V versus NHE) in 0.1M pH 7.0 PBS. Both nanometer-sized ZrO2 and dimethyl sulfoxide (DMSO) could accelerate the electron transfer between Hb and the electrode. Spectroscopy analysis of the Hb/ZrO2/DMSO film showed that the immobilized Hb could retain its natural structure. This modified electrode showed a high thermal stability up to 74 degrees C and an electrocatalytic activity to the reduction of hydrogen peroxide (H2O2) without the aid of an electron mediator. The electrocatalytic response showed a linear dependence on the H2O2 concentration ranging from 1.5 to 30.2 microM with a detection limit of 0.14 microM at 3sigma. The apparent Michaelis-Menten constant KMapp for H2O2 sensor was estimated to be (0.31 +/- 0.02) mM, showing a high affinity.     

Immobilization of glucose oxidase on electrodeposited nickel oxide nanoparticles: direct electron transfer and electrocatalytic activity

For the first time glucose oxidase (GOx) was successfully co-deposited on nickel-oxide (NiO) nanoparticles at a glassy carbon electrode. In this paper we present a simple fabrication method of biosensor which can be easily operated without using any specific reagents. Cyclic voltammetry was used for electrodeposition of NiO nanoparticle and GOx immobilization. The direct electron transfer of immobilized GOx displays a pair of well defined and nearly reversible redox peaks with a formal potential (E(0')) of -0.420 V in pH 7 phosphate buffer solution and the response shows a surface controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant (k(s)) of GOx immobilized on NiO film glassy carbon electrode are 9.45 x 10(-13)mol cm(-2) and 25.2+/-0.5s(-1), indicating the high enzyme loading ability of the NiO nanoparticles and great facilitation of the electron transfer between GOx and NiO nanoparticles. The biosensor shows excellent electrocatalytical response to the oxidation of glucose when ferrocenmethanol was used as an artificial redox mediator. Furthermore, the apparent Michaelis-Menten constant 2.7 mM, of GOx on the nickel oxide nanoparticles exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. In addition, this glucose biosensor shows fast amperometric response (3s) with the sensitivity of 446.2nA/mM, detection limit of 24 microM and wide concentration range of 30 microM to 5mM. This biosensor also exhibits good stability, reproducibility and long life time.     

Amperometric detection of insulin at renewable sol-gel derived carbon ceramic electrode modified with nickel powder and potassium octacyanomolybdate(IV)

A renewable three-dimensional chemically modified carbon ceramic electrode (CCE) containing nickel powder and K4[Mo(CN)8] was constructed by sol-gel technique. The electrochemical properties and stability of modified electrode was evaluated by cyclic voltammetry in pH range 4-10. The redox couple of [Mo(CN)8] (4-/3-) was shown both as a solute in electrolyte solution and as a component of a carbon based conducting composite electrode. The apparent electron transfer rate constant (ks) and transfer coefficient (alpha) were determined by cyclic voltammetry and they were about 17.1 and 0.57 s(-1), respectively. The catalytic activity of the modified CCE toward insulin oxidation was investigated at pH range of 3-8 by cyclic votammetry. The modified electrode showed excellent electrocatalytic activity toward insulin electroxidation at physiological pH value. The modified electrode was used for insulin detection chronoamperometrically at pH 7. Under optimized condition in amperometry method, the concentration calibration range, detection limit and sensitivity were 0.5-500 nM, 0.45 nM and 6140 nA/microM, respectively. Flow injection amperometric determination of insulin at pH 7.4, at this modified electrode yielded a calibration curve with the following characteristics, linear dynamic range 100-500 pM; sensitivity 8.1 nA/nM and detection limit 40 pM (based on S/N = 3). The inherent stability at wide pH range, high sensitivity, low detection limit, low cost and ease of preparation are of advantageous of this insulin sensor. This sensor indicates great promise for monitory insulin in chromatographic effluents.     

A novel glucose sensor based on monodispersed Ni/Al layered double hydroxide and chitosan

A novel cheap and simple amperometric glucose biosensor, based on the electrode modified with the Ni/Al layered double hydroxide (LDH) nanoflakes and chitosan (CHT), without glucose oxidase, is presented. The glucose biosensor based on monodispersed high active Ni/Al-LDH nanoflakes and CHT exhibits an appropriate linear range of 0.01-10mM and good operational stability. The amperometric sensor shows a rapid response at the potential value 0.48V. In addition, optimization of the biosensor construction, the effects of the applied potential, the scan rate as well as common interfering compounds on the amperometric response and human serum samples analysis of the sensor were investigated and discussed.     

A sputtered thin film of nanostructured Ni/Pt/Ti on Al2O3 substrate for ethanol sensing

A novel thin film ethanol sensor using sputtered Ni/Pt/Ti on an Al2O3 substrate as the working electrode in an alkaline solution was developed. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the nanostructure of nickel films. Sputtering deposition conditions for maximum catalytic efficiency, electrode selectivity, and reproducibility were discussed. The results showed that ethanol oxidation was more efficient on the sputtered Ni/Pt/Ti on an Al2O3 substrate electrode than that on the conventional nickel electrode. The optimal operating conditions to generate the sputtered Ni/Pt/Ti on the Al2O3 substrate electrode were: 45 min of Ni sputtering deposition time, and 50 W of Ni sputtering power. The results also indicated that the response time of the prepared ethanol sensor is 27 s and the best sensitivity is 3.08 microA microM(-1) cm(-2).     

Electrochemical sensor for guanine using a self-assembled monolayer of 1,8,15,22-tetraaminophthalocyanatonickel(II) on glassy carbon electrode

This article describes the selective determination of guanine (G) using the self-assembled monolayer (SAM) of 1,8,15,22-tetraaminophthalocyanatonickel(II) (4α-Ni(II)TAPc) modified glassy carbon electrode (GCE) in 0.2 M acetate buffer solution (pH 4.0). The SAM of 4α-Ni(II)TAPc was formed on GCE by spontaneous adsorption of 1 mM 4α-Ni(II)TAPc in dimethylformamide (DMF). It shows two pairs of redox waves corresponding to Ni(III)/Ni(II) and Ni(III)Pc(-1)/Ni(III)Pc(-2) in 0.2 M acetate buffer solution. The SAM modified electrode exhibits excellent electrocatalytic activity toward the oxidation of G by enhancing its oxidation current with 150 mV less positive potential shift in contrast to bare GCE. Furthermore, the SAM modified electrode selectively determines G in the presence of high concentration of adenine (A). In differential pulse voltammetry measurements, the oxidation current response of G was increased linearly in the concentration range of 10 to 100 μM, and a detection limit was found to be 3×10(-8)M (signal/noise=3).     

Rapid Prototyping of a High Sensitivity Graphene Based Glucose Sensor Strip

A rapid prototyping of an inexpensive, disposable graphene and copper nanocomposite sensor strip using polymeric flexible substrate for highly sensitive and selective nonenzymatic glucose detection has been developed and tested for direct oxidization of glucose. The CuNPs were electrochemically deposited on to the graphene sheets to improve electron transfer rates and to enhance electrocatalytic activity toward glucose. The graphene based electrode with CuNPs demonstrated a high degree of sensitivity (1101.3±56 μA/mM.cm²), excellent selectivity (without an interference with Ascorbic Acid, Uric Acid, Dopamine, and Acetaminophen), good stability with a linear response to glucose ranging from 0.1 mM to 0.6 mM concentration, and detection limits of 0.025 mM to 0.9 mM. Characterization of the electrodes was performed by scanning electron microscopy (FESEM and SEM). The electrochemical properties of the modified graphene electrodes were inspected by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry.     

Nickel(II)-baicalein complex modified multiwall carbon nanotube paste electrode and its electrocatalytic oxidation toward glycine

A modified electrode, nickel(II)-baicalein complex modified multiwall carbon nanotube paste electrode (Ni(II)-BA-MWCNT-PE), has been fabricated by electrodepositing Ni(II)-BA complex on the surface of MWCNT-PE in alkaline solution. The Ni(II)-BA-MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)-BA-carbon paste electrode (CPE). It also shows better electrocatalytic activity toward the oxidation of glycine than Ni(II)-MWCNT-PE. Kinetic parameters such as the electron transfer coefficient α, rate constant k_s of the electrode reaction, the diffusion coefficient D of glycine, and the catalytic rate constant k_cat of the catalytic reaction are determined. Moreover, the catalytic currents present linear dependence on the concentration of glycine from 20 μM to 1.0 mM by amperometry. The detection limit and sensitivity are 9.2 μM and 3.92 μA mM⁻¹, respectively. The modified electrode for glycine determination is of the property of simple preparation, fast response, and good stability.     

Covalent immobilization of cholesterol oxidase on self-assembled gold nanoparticles for highly sensitive amperometric detection of cholesterol in real samples

A novel scheme for the fabrication of gold nanoparticle modified cholesterol oxidase based bioelectrode is presented and its application potential for cholesterol biosensor is investigated. The fabrication procedure is based on the deposition of gold nanoparticles on the 1,6-hexanedithiol modified gold electrode, functionalization of the surface of deposited gold nanoparticles with carboxyl groups using 11-mercaptoundecanoic acid and then covalent immobilization of cholesterol oxidase on the surface of gold nanoparticle film using the N-ethyl-N'-(3-dimethylaminopropyl carbodimide) and N-hydroxysuccinimide ligand chemistry. The assembly process of the bioelectrode is investigated using atomic force microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The gold nanoparticle film on the electrode surface provided an environment for the enhanced electrocatalytic activities and thus resulted in enhanced analytical response. The resulting bioelectrode is further applied to the amperometric detection of cholesterol and exhibited a linear response to cholesterol in the range of 0.04-0.22 mM with a detection limit of 34.6 μM, apparent Michaelis-Menten constant (K(m)(app)) of 0.062 mM and a high sensitivity of 9.02 μA mM(-1). The fabricated bioelectrode is successfully used for the selective determination of cholesterol in human serum samples.     

An amperometric biosensor based on a composite of single-walled carbon nanotubes, plasma-polymerized thin film, and an enzyme

We report on an amperometric biosensor that is based on a nanocomposite of carbon nanotubes (CNT), a nano-thin plasma-polymerized film (PPF), and glucose oxidase (GOx) as an enzyme model. A mixture of the GOx and a CNT film is sandwiched with 10-nm-thick acetonitrile PPFs. Under PPF layer was deposited onto a sputtered gold electrode. To facilitate the electrochemical communication between the CNT layer and GOx, CNT was treated with nitrogen or oxygen plasma. The resulting device showed that the oxidizing current response due to enzymatic reaction was 4-16-fold larger than that with only CNT or PPF, showing that the PPF and/or plasma process is an enzyme-friendly platform for designing electrochemical communication from the reaction center of GOx to the electrode via CNTs. The optimized glucose biosensor showed high sensitivity (sensitivity of 42 microA mM(-1)cm(-2), correlation coefficient of 0.992, linear response range of 0.025-2.2 mM, and a detection limit of 6 microM at signal/noise ratio of 3, +0.8 V versus Ag/AgCl), high selectivity (almost no interference by 0.5 mM ascorbic acid) for glucose quantification, and rapid response (<4 s to reach 95% of maximum response). Additionally, the devices showed a small and stable background current (0.35+/-0.013 microA) compared with the glucose response (ca. 10 microA at 10mM glucose) and suitable reproducibility from sample-to-sample (<3%, n=4).     

Mercaptoethylpyrazine promoted electrochemistry of redox protein and amperometric biosensing of uric acid

Electrochemistry of microperoxidase-11 (MPx-11) anchored on the mixed self-assembled monolayer (SAM) of 2-(2-mercaptoethylpyrazine) (PET) and 4,4'-dithiodibutyric acid (DTB) on gold (Au) electrode and the biosensing of uric acid (UA) is described. MPx-11 has been covalently anchored on the mixed SAM of PET and DTB on Au electrode. MPx-11 on the mixed self-assembly exhibits reversible redox response characteristic of a surface confined species. The heterocyclic ring of PET promotes the electron transfer between the electrode and the redox protein. The apparent standard rate constant kapps obtained for the redox reaction of MPx-11 on the mixed monolayer is approximately 2.15 times higher than that on the single monolayer of DTB modified electrode. MPx-11 efficiently mediates the electrocatalytic reduction of H2O2. MPx-11 electrode is highly sensitive to H2O2 and it shows linear response for a wide concentration range. The electrocatalytic activity of the MPx-11 electrode is combined with the enzymatic activity of uricase (UOx) to fabricate uric acid biosensor. The bienzyme assembly is highly sensitive towards UA and it could detect UA as low as 2 microM at the potential of -0.1 V. The biosensor shows linear response with a sensitivity of 3.4+/-0.08 nA cm(-2) microM(-1). Ascorbate (AA) and paracetamol (PA) do not significantly interfere in the amperometric sensing of UA.