A poly(3-acetylthiophene) modified glassy carbon electrode for selective voltammetric measurement of uric acid in urine sample

A reliable and reproducible method for the determination of uric acid in urine samples has been developed. The method is based on the modification of a glassy carbon electrode by 3-acetylthiophene using cyclic voltammetry. The poly(3-acetylthiophene) modified glassy carbon electrode showed an excellent electrocatalytic effect towards the oxidation of uric acid in 0.1 m phosphate buffer solution (PBS) at pH 7.2. Compared with a bare glassy carbon electrode (GCE), an obvious shift of the oxidation peak potential in the cathodic direction and a marked enhancement of the anodic current response for uric acid were observed. The poly(3-acetylthiophene)/GCE was used for the determination of uric acid using square wave voltammetry. The peak current increased linearly with the concentration of uric acid in the range of 1.25 x 10(-5)-1.75 x 10(-4) M. The detection limit was 5.27 x 10(-7) M by square wave voltammetry. The poly(3-acetylthiophene)/GCE was also effective to determine uric acid and ascorbic acid in a mixture and resolved the overlapping anodic peaks of these two species into two well-defined voltammetric peaks in cyclic voltammetry at 0.030 V and 0.320 V (vs. Ag/AgCl) for ascorbic acid and uric acid, respectively. The modified electrode exhibited stable and sensitive current responses toward uric acid and ascorbic acid. The method has successfully been applied for determination of uric acid in urine samples.     

Improved voltammetric peak separation and sensitivity of uric acid and ascorbic acid at nanoplatelets of graphitic oxide

In this study, much improved voltammetric peak separation and sensitivity of uric acid and ascorbic acid was observed at a screen-printed carbon electrode modified with nanoplatelets of graphitic oxide (GO). Electrochemical sensing of uric acid and ascorbic acid was further used to explore the role of oxygen functionalities and edge plane sites on electrocatalysis at GO. We successfully apply a microwave-assisted hydrothermal elimination method to remove the oxygen-containing functional groups from the GO surface. The edge plane on GO can be retained and the density of oxygen-containing functional groups can be easily controlled by varying the microwave treatment temperature. Using this platform, such discrimination to peak separation is attributed to the very distinct behavior of uric acid and ascorbic acid to form hydrogen bonds with oxo-surface groups (especially COOH group) at GO.     

DNA/Poly(p-aminobenzensulfonic acid) composite bi-layer modified glassy carbon electrode for determination of dopamine and uric acid under coexistence of ascorbic acid

A nano-composite of DNA/poly(p-aminobenzensulfonic acid) bi-layer modified glassy carbon electrode as a biosensor was fabricated by electro-deposition method. The DNA layer was electrochemically deposited on the top of electropolymerized layer of poly(p-aminobenzensulfonic acid) (Pp-ABSA). Scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical impedance spectrum were used for characterization. It demonstrated that the deposited Pp-ABSA formed a 2-D fractal patterned nano-structure on the electrode surface, and which was further covered by a uniform thin DNA layer. Cyclic voltammetry and electrochemical impedance spectrum were used to characterize the deposition, and demonstrated the conductivity of the Pp-ABSA layer. The biosensor was applied to the detection of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). In comparison with DNA and Pp-ABSA single layer modified electrodes, the composite bi-layer modification provided superior electrocatalytic actively towards the oxidation of DA, UA and AA, and separated the originally overlapped differential pulse voltammetric signals of UA, DA and AA oxidation at the bare electrode into three well-defined peaks at pH 7 solution. The peak separation between AA and DA, AA and UA was 176 mV and 312 mV, respectively. In the presence of 1.0 mM AA, the anodic peak current was a linear function of the concentration of DA in the range 0.19-13 microM. The detection limit was 88 nM DA (s/n=3). The anodic peak current of UA was also a linear function of concentration in the range 0.4-23 microM with a detection limit of 0.19 microM in the presence of 0.5 mM AA. The superior sensing ability was attributed to the composite nano-structure. An interaction mechanism was proposed.     

Simultaneous determination of aminothiols, ascorbic acid and uric acid in biological samples by capillary electrophoresis with electrochemical detection

A method based on capillary electrophoresis with electrochemical detection has been employed for the separation and determination of homocysteine, cysteine, reduced glutathione, ascorbic acid and uric acid. Effects of several important factors such as the acidity and concentration of the running buffer, separation voltage, injection time and detection potential were investigated to acquire the optimum conditions. The detection electrode was a 500 microm diameter platinum disk electrode at a working potential of +1.05 V (vs saturated calomel electrode). The five analytes were well separated within 10 min in a 50 cm long fused silica capillary at a separation voltage of 18 kV in a 100 mm phosphate buffer (pH 7.8). The relation between peak current and analyte concentration was linear over about 3 orders of magnitude with the detection limits (S/N = 3) ranging from 0.83 to 2.58 microm. The proposed method was successfully applied to determine cysteine, reduced glutathione, ascorbic acid and uric acid in human whole blood and rat brain tissues with satisfactory assay results and should find a wide range of bioanalytical applications.     

Simultaneous detection of epinephrine,uric acid,and ascorbic acid with graphene-modified electrode

A graphene-modified glassy carbon electrode was obtained via drop-casting method and applied to the simultaneous detection of epinephrine, uric acid, and ascorbic acid by cyclic voltammetry in a phosphate buffer solution (pH 3.0). The oxidation potentials of epinephrine, uric acid, and ascorbic acid were 0.484, 0.650, and 0.184 V at the graphene-modified glassy carbon electrode, respectively. The peak separation between epinephrine Pand uric acid, epinephrine and ascorbic acid, and uric acid and ascorbic acid was about 166, 300, and 466 mV, respectively. So, this graphene-modified electrode can be used for simultaneous determination of each component in a mixture.     

Determination of Uric Acid in the Presence of Ascorbic Acid Using Poly(3,4‐ethylenedioxythiophene)‐Modified Electrodes

A poly(3,4‐ethylenedioxythiophene) (PEDOT) modified glassy carbon electrode (GCE) was used to determine uric acid in the presence of ascorbic acid at physiological pH facilitating a peak potential separation of ascorbic acid and uric acid oxidation (ca. 365 mV), which is the largest value reported so far in the literature. Also, an analytical protocol involving differential pulse voltammetry has been developed using a microchip electrode for the determination of uric acid in the concentration range of 1 to 20 μM in presence of excess of ascorbic acid.     

Polycation coating poly(dimethylsiloxane) capillary electrophoresis microchip for rapid separation of ascorbic acid and uric acid

A novel method for rapid separation and determination of ascorbic acid and uric acid has been developed with a polycation-modified poly(dimethylsiloxane) (PDMS) microchip under a negative-separation electric field. Just by flushing the microchip with aqueous solutions of the polycations, poly(allylamine) hydrochloride, poly(diallyldimethylammonium chloride) or chitosan could be stably coated on the PDMS microchannel surface, which resulted in a reversed electroosmotic flow and thus the rapid and efficient separation of the two substrates. Factors influencing the separation, including polycation category, buffer solution, detection potential and separation voltage, were investigated and optimized. The cheapness, rapid analysis speed and the successful analysis of human urine make this microsystem attractive for application in clinics. Figure The electropherograms of 100 μ/mL AA and UA in (1) PAH, (2) PDDA, (3) Chitosan modified PDMS microchannels and native PDMS microchip (4).     

Simultaneous determination of ascorbic acid, uric acid and neurotransmitters with a carbon ceramic electrode prepared by sol-gel technique

A sol-gel carbon composite electrode (CCE) has been prepared by mixing a sol-gel precursor (e.g. methyltrimethoxysilane) and carbon powder without adding any electron transfer mediator or specific reagents. It was demonstrated that this sensor can be used for simultaneous determination ascorbic acid, neurotransmitters (dopamine and adrenaline) and uric acid. Direct electrochemical oxidation of ascorbic acid, uric acid and catecholamines at a carbon composite electrode was investigated. The experimental results were compared with other common carbon based electrodes, specifically, boron doped diamond, glassy carbon, graphite and carbon paste electrodes. It was found that the CCE shows a significantly higher of reversibility for dopamine. In addition, in comparison to the other electrodes used, for CCE the oxidation peaks of uric acid, ascorbic acid and catecholamines in cyclic and square wave voltammetry were well resolved at the low positive potential with good sensitivity. The advantages of this sensor were high sensitivity, inherent stability and simplicity and ability for simultaneous determination of uric acid, catecholamines and ascorbic acid without using any chromatography or separation systems. The analytical performance of this sensor has been evaluated for detection of biological molecules in urine and serum as real samples.     

Simultaneous determination of dopamine, ascorbic acid and uric acid at poly (Evans Blue) modified glassy carbon electrode

A sensitive and selective electrochemical method for the determination of dopamine using an Evans Blue polymer film modified on glassy carbon electrode was developed. The Evans blue polymer film modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solution (pH 4.5). The linear range of 1.0 x 10(-6)-3.0 x 10(-5) M and detection limit of 2.5 x 10(-7) M were observed in pH 4.5 phosphate buffer solutions. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid and uric acid. The separation of the oxidation peak potentials for dopamine-ascorbic acid and dopamine-uric acid were about 182 mV and 180 mV, respectively. The differences are large enough to determine AA, DA and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect dopamine in the presence of ascorbic acid and uric acid in physiological samples.     

Simultaneous voltammetric determination of uric acid and ascorbic acid using carbon paste/cobalt Schiff base composite electrode

Differential pulse and cyclic voltammetry were applied for the oxidation of mixture of uric acid and ascorbic acid at the surface of carbon paste/cobalt Schiff base composite electrode. The electrooxidation of these compounds at bare electrode is sluggish, and there is no suitable peak separation between them. However, using cobalt methyl salophen as modifier, two well-defined anodic waves with a considerable enhancement in the peak current and a remarkable peak potential separation near 315 mV are obtained. It can improve the kinetics of electron transfer for both compounds remarkably. All these improvements are created because of the electrocatalytic property of cobalt Schiff base complex. The effect of some parameters such as pH and scan rates were studied. All the anodic peak currents for the oxidation of ascorbic acid and uric acid shifted toward more negative potential with an increase in pH, revealing that protons have taken part in their electrode reaction processes. The best peak separation with appropriate current was obtained for pH 4.0. A linear range of 5.0?×?10^?4 to 1.0?×?10^?8 and 1.0?×?10^?3 to 1.0?×?10^?8 M with detection limit of 8.0?×?10^?9 and 8.0?×?10^?9 M was obtained for ascorbic acid and uric acid using differential pulse voltammetry at the surface of modified electrode, respectively. Analytical utility of the modified electrode has been examined successfully using human urine samples and vitamin C commercial tablets.     

Simultaneous Sensitive Determination of Dopamine and Uric Acid in the Presence of Excess Ascorbic Acid with a Magnetic Chitosan Microsphere/Thionine Modified Electrode

Magnetic chitosan microspheres (MCMS) and thionine were incorporated in a modified electrode for the simultaneous sensitive determination of dopamine (DA) and uric acid (UA). Due to the unique properties of the MCMS and the electron mediation of thionine, this modified electrode showed excellent electrocatalytic oxidation toward dopamine and uric acid with a large separation of peak potentials and a significant enhancement of peak currents. However, the electrochemical behavior of ascorbic acid may be depressed at the modified electrode. Differential pulse voltammetry was used for the simultaneous sensitive determination of dopamine and uric acid in the presence of excess ascorbic acid at this modified electrode. The current responses showed excellent linear relationships in the range of 2–30 µM and 9–100 µM for dopamine and uric acid, respectively. The detection limits were estimated to be 0.5 µM and 2.3 µM for dopamine and uric acid, respectively. In addition, this modified electrode showed excellent repeatability, good stability, and satisfactory reliability, thus indicating potential for the practical applications.     

A selective voltammetric method for uric acid detection at beta-cyclodextrin modified electrode incorporating carbon nanotubes

A beta-cyclodextrin-coated electrode incorporating carbon nanotubes was constructed and applied to the detection of uric acid in the presence of high concentration of ascorbic acid. The major obstacle of the overlapped oxidation potential of ascorbic acid was overcome owing to the distinct ability of the carbon nanotubes-modified electrode to yield a large anodic peak difference ca. 400 mV. The sensitive detection of uric acid has been further improved by the formation of a supramolecular complex between beta-cyclodextrin and uric acid. A linear calibration curve was obtained for 5 x 10(-7) to 5 x 10(-5) M in 0.2 M HAc-NaAc buffer (pH 4.5) with correlation coefficient of 0.998 and detection limit of 0.2 microM. The practical analytical application was illustrated by a selective measurement of uric acid in human urine without any preliminary treatment.     

The analysis of uric acid in urine using microchip capillary electrophoresis with electrochemical detection

Clinical studies have linked irregular concentrations of uric acid in urine to several diseases. Conventional methods for the measurement of uric acid are however temperature-dependent, expensive, and require labile reagents. The miniaturization of analytical techniques, specifically capillary electrophoresis, offers an ideal alternative for clinical analyses such as uric acid determination. The added benefits include reduced reagent and analyte consumption, decreased maintenance costs, and increased throughput and portability. A microchip capillary electrophoresis-electrochemical system for the analysis of uric acid in urine is described. The poly(dimethylsiloxane) (PDMS)/glass microchip utilizes amperometric detection via an off-chip platinum working electrode. Linear responses from 1 to 165 microM and 15 to 110 microM were found for dopamine and uric acid, respectively. The limit of detection for both compounds was 1 microM. Once characterized, the system was used to measure the concentration of uric acid in a dilute urine sample in less than 30 s. The measured uric acid concentration was verified with the uricase reaction and found to be acceptable. Six additional urine samples were evaluated with the microchip device and the uric acid concentration for each sample was found to be in the expected clinical concentration range.     

Ytterbium fluoride nanoparticles on carbon nanotubes: preparation, characterization and application for simultaneous electrochemical determination of ascorbic acid, dopamine and uric acid

A novel modified glassy carbon electrode with ytterbium fluoride nanoparticles (YFNPs)-multiwalled carbon nanotubes (MWCNTs) was fabricated and then successfully used for the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). YFNPs were successfully coated on the MWCNTs via the intermediate of noncovalent hydrophobic interactions of the MWCNTs surface with sodium dodecyl sulfate. The YFNPs and immobilization of YFNPs on MWCNTs were confirmed by transmission electron microscopy. The particle size of YFNPs was measured to be around 45 nm. The catalytic peak currents for AA, DA and UA were linearly dependent on their concentrations in the range of 2.0–600.0, 2.0–560.0 and 1.8–640.0 μM, respectively, with the corresponding detection limits of 0.77, 0.22 and 0.17 μM. The modified electrode provided good sensitivity and stability, and was successfully applied for the simultaneous determination of AA, DA and UA in human blood serum and urine samples.     

Polystyrene sulphonate wrapped multiwalled carbon nanotubes modified graphite electrode for simultaneous determination of ascorbic acid, dopamine and uric acid

Graphite electrode is modified by casting multi-walled carbon nanotubes (MWCNTs) wrapped with polystyrene sulphonate (PSS) onto the surface of the bare graphite electrode. The modified electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The behavior of the modified electrode towards the oxidation of ascorbic acid (AA), dopamine (DA) and uric acid (UA) has been determined by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA). The modified electrode showed better electrocatalytic activity towards AA, DA and UA compared to bare graphite electrode. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential difference of 222, 128 and 350 mV between AA-DA, DA-UA and AA-UA respectively in CV studies and corresponding peak potential separation in DPV are 228, 120 and 348 mV. This modified electrode was successfully used for simultaneous determination of AA, DA and UA in ternary mixture.     

Nafion-离子液体-修饰碳糊电极在抗坏血酸和尿酸存在下选择性测定多巴胺

用Nafion和亲水性离子液体溴化1-辛基-3-甲基咪唑([OMIM]Br)作修饰剂制作了Nafion-离子液体-修饰碳糊电极;在0.1 mol/L磷酸盐缓冲溶液(pH 7.40)中,用循环伏安法(CV)和方波伏安法(SWV)研究了多巴胺在该修饰电极上的电化学行为,建立了抗坏血酸和尿酸存在下选择性测定多巴胺的新方法.研究表明,该修饰电极降低了多巴胺氧化、还原反应的过电位,增大了其氧化、还原反应的峰电流,而抗坏血酸和尿酸在该修饰电极上无响应;在方波伏安曲线上,多巴胺的氧化电流与其浓度在3.0×10-8～2.0×10-6 mol/L范围内呈线性关系,检出限为1.0×10-8 mol/L.该法可用于注射液和模拟生物样品中多巴胺的测定.     

Functionalized-graphene modified graphite electrode for the selective determination of dopamine in presence of uric acid and ascorbic acid

Graphene is chemically synthesized by solvothermal reduction of colloidal dispersions of graphite oxide. Graphite electrode is modified with functionalized-graphene for electrochemical applications. Electrochemical characterization of functionalized-graphene modified graphite electrode (FGGE) is carried out by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The behavior of FGGE towards ascorbic acid (AA), dopamine (DA) and uric acid (UA) has been investigated by CV, differential pulse voltammetry (DPV) and chronoamperommetry (CA). The FGGE showed excellent catalytic activity towards electrochemical oxidation of AA, DA and UA compared to that of the bare graphite electrode. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 193mv, 172mv and 264mV between AA-DA, DA-UA and AA-UA respectively in CV studies and the corresponding peak potential separations in DPV mode are 204mv, 141mv and 345mv. The FGGE is successfully used for the simultaneous detection of AA, DA and UA in their ternary mixture and DA in serum and pharmaceutical samples. The excellent electrocatalytic behavior of FGGE may lead to new applications in electrochemical analysis.     

Selective determination of epinephrine in the presence of ascorbic acid and uric acid by electrocatalytic oxidation at poly(eriochrome black T) film-modified glassy carbon electrode.

An electropolymerized film of eriochrome black T (EBT) has been prepared at a glassy carbon electrode (GCE) by cyclic voltammetry (CV). The poly(EBT) membrane at GCE exhibits an excellent electrocatalytic activity towards the oxidation of epinephrine (EP), ascorbic acid (AA) and uric acid (UA) in acidic solution and reduced the overpotential for the oxidation of EP. The poly(EBT)-coated electrode could separately detect EP, AA and UA in their mixture with the potential differences of 180 and 160 mV for EP-AA and UA-EP, respectively, which are large enough to allow for determination of EP in the presence of AA and UA. Using differential pulse voltammetry, the peak current of EP recorded in pH 3.5 solution was linearly dependent on EP's concentration in the range of 2.5 - 50 microM. Due to its good selectivity and stability, the polymer-coated GCE was successfully applied to the determination of EP in real samples.     

聚茜素黄R膜修饰电极对尿酸电催化及对人尿中尿酸的检测

用电聚合的方法制备了聚茜素黄R膜修饰的玻碳电极,研究了尿酸在该电极上的电化学行为。结果表明,该修饰电极对尿酸的氧化具有良好的电催化能力。示差脉冲伏安法测定尿酸的氧化峰电流与其浓度在1.0×10-6～1.0×10-4mol/L范围内呈现良好的线性范围,检测限为8.6×10-7 mol/L(S/N=3)。本方法用于人尿液中尿酸含量的测定,结果令人满意。     

Simultaneous electrochemical sensing of ascorbic acid,dopamine and uric acid at anodized nanocrystalline graphite-like pyrolytic carbon film electrode

Nanocrystalline graphite-like pyrolytic carbon film (PCF) electrode fabricated by a non-catalytic chemical vapor deposition (CVD) process was used for the simultaneous electrochemical sensing of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electrode was studied with respect to changes in electrocatalytic activity caused by a simple and fast electrochemical pretreatment. The anodized electrode exhibited excellent performance compared to many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Differential pulse voltammetry (DPV) was used for the simultaneous determination of ternary mixtures of DA, AA, and UA. Under optimum conditions, the detection limits were 2.9 μM for AA, 0.04 μM for DA, and 0.03 μM for UA with sensitivities of 0.078, 5.345, and 6.192 A M⁻¹, respectively. The peak separation was 219 mV between AA and DA and 150 mV between DA and UA. No electrode fouling was observed and good reproducibility was obtained in all the experiments. The sensor was successfully applied for the assay of DA in an injectable drug and UA in human urine by using standard addition method.