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.     

Determination of catechol derivatives on pretreatment and copolymer coated glassy carbon electrode

A glassy carbon electrode was pretreated electrochemically and was coated with a copolymer of maleic acid anhydride attached with Eastman-AQ55D (MA/AQ). The voltammetric behavior of a series of biologically important compounds, such as dopamine, L-DOPA, DOPAC, ascorbic acid and uric acid were examined at both pretreated and coated electrodes. Electrochemical pretreatment increased peak current of dopamine and L-DOPA while decreased that of ascorbic acid, uric acid and DOPAC. The copolymer coating caused a decrease of peak currents, but effectively hindered the anionic species (ascorbic acid, uric acid and DOPAC) access to the electrode surface. In flow injection and liquid chromatographic analysis. The dopamine and L-DOPA yielded the better selectivity response at MA/AQ electrode than at bare and AQ electrodes.     

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.     

A highly selective and sensitive dopamine and uric acid biosensor fabricated with functionalized ordered mesoporous carbon and hydrophobic ionic liquid

An ordered mesoporous carbon material functionalized with carboxylic acid groups was synthesized. It was characterized by powder X-ray diffraction, transmission electron microscopy, Fourier transform IR spectroscopy and N₂ adsorption/desorption. Furthermore, this material was used to modify an electrode surface combined with a hydrophobic ionic liquid. The functionalized ordered mesoporous carbon/ionic liquid gel modified electrode shows excellent electrocatalytic performances for the oxidation of dopamine, uric acid and ascorbic acid. The presence of the ionic liquid promotes the electron transfer. Linear responses for dopamine and uric acid were obtained in the ranges of 0.1 to 500 μM and from 0.1 to 100 μM with detection limits of 4.1 and 2.5 nM (signal-to-noise ratio of 3), respectively, under optimum conditions. A quick and sensitive biosensor based on functionalized ordered mesoporous carbon and an ionic liquid has been developed for the first time for the detection of dopamine and uric acid in the presence of a large amount of ascorbic acid.     

Activity of SiDbCl in the Electrooxidation of Ascorbic Acid,Dopamine, and Uric Acid

Selective electroanalytical responses for ascorbic acid, dopamine and uric acid at a carbon modified electrode based on 3‐n‐propyl‐1‐azonia‐4‐azabicyclo[2.2.2]octane silsesquioxane chloride (SiDbCl) is reported. The overlapped peaks observed at an unmodified electrode are resolved into three well defined voltammetric peaks allowing the simultaneous determination of the three species. Detection limits of 37, 0.3 and 0.1 μmo L⁻¹ of ascorbic acid, dopamine and uric acid, respectively, were calculated from calibration curves based on differential pulse voltammetric experiments performed in Britton ‐ Robinson buffer solution at pH 7.04.     

Fabrication and characterization of poly 2-napthol orange film modified electrode and its application to selective detection of dopamine

The present work is based on the use of a redox mediator containing an azo group for the selective determination of dopamine in the presence of uric acid and ascorbic acid by electrochemical method. A modified electrode was prepared by electrochemical polymerization of the poly 2-napthol orange film (P2NO) on the paraffin wax-impregnated graphite electrode (PIGE) by applying potential between ?0.6 and 0.8 V at scan rate of 50 mV s^?1 for 30 segments. The modified P2NO film electrode was characterized by ATR-IR spectroscopy, FE-SEM, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), hydrodynamic voltammetry (HDV), and chronoamperometry (CA). The P2NO film modified electrode exhibited selective determination of dopamine in the presence of uric acid and ascorbic acid, and the electrocatalytic activity for oxidation of dopamine was excellent. The linear range for the determination of dopamine was 0.6 to 250 μM with a limit of detection of 0.13 μM. The modified P2NO electrode showed good stability and reproducibility. The modified electrode was used for real sample analysis such as human blood serum, rat blood serum, and pharmaceutical samples (dopamine hydrochloride injection). The results obtained were found to be satisfactory.     

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.     

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.     

Highly selective dopamine quantification using a glassy carbon electrode modified with a melanin-type polymer

A highly selective dopamine quantification at a new polymer-modified electrode in the presence of large excess of ascorbic acid and 3,4-dihydroxyphenyl acetic acid (dopac) is described. The electrochemical detection was performed at a glassy carbon electrode modified with a melanin-type polymer obtained by polymerization of 3.0×10⁻³ M -dopa in 0.050 M phosphate buffer solution pH 7.40 by applying 1.00 V for 60 min. The polymeric film exhibits attractive permselectivity excluding anionic species such as potassium ferricyanide, ascorbic acid, dopac and uric acid. Cationic species such as epinephrine, norepinephrine and dopamine and neutral ones such as catechol and hydrogen peroxide can be oxidized at the polymer-modified electrode. The use of ascorbic acid in the measurement solution allows the amplification of dopamine oxidation signal due to the reduction of the electrochemically generated dopaminequinone. By using 1.0×10⁻³ M ascorbic acid, the detection limit for dopamine is 5.0 nM. The interference for the maximum physiological concentrations of ascorbic acid and dopac in nervous centers, i.e. 500 μM ascorbic acid and 50 μM dopac is 8.1 and 1.4%, respectively.     

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L^?1 for uric acid and 10.0 to 400.0 µmol L^?1 for dopamine in the presence of 500 µmol L^?1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L^?1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.     

Electropolymerisation of L-arginine at carbon paste electrode and its application to the detection of dopamine, ascorbic and uric acid

L-arginine was electropolymerised on a carbon paste electrode (CPE) to form the biopolymer by free radical formation in the electro oxidation process of the amino and carboxylic group containing compound by cyclic voltammetric technique. The modified electrode shows an excellent electrocatalytic activity towards the oxidation of both dopamine (DA) and ascorbic acid (AA). It was demonstrated that the deposited biopolymer has positive charges over the bare carbon electrode surface, which leads to the formation of electrical double layer made the fast electron transfer process could leads to the diffusion of dopamine, ascorbic acid and uric acid on their charge gradient by cyclic voltammetric technique. The response of the sensor was tested towards the different dopamine concentration. The catalytic peak current obtained was linearly related to DA concentrations in the ranges of 5×10(-5) to 1×10(-4)M L(-1) with correlation co-efficient of 0.9924 which reveals the adsorption controlled process. The detection limit for dopamine was 5×10(-7)M L(-1). The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid (AA) and response is fast stable, reliable, resistant to biofouling and can be applied for the real sample analysis in medical, pharmaceutical and biotechnological sectors. The adsorption-controlled process and kinetic parameters of the poly(L-arginine) were determined using electrochemical approaches.     

Amperometric Determination of Ascorbic Acid at an Electrodeposited Redox Polymer Film Modified Gold Electrode

A sensitive and selective electrochemical method for the determination of ascorbic acid was developed. It was shown that a hydrated osmium complex‐containing redox polymer film can be electrodeposited at the gold electrode and it exhibits excellent electrocatalytic activity towards the oxidation of ascorbic acid. In contrast to a bare gold electrode, the oxidation current of ascorbic acid increased greatly and the oxidation peak potential shifted negatively to about 0.01 V (vs. SCE) at the modified electrode. Amperometric measurements were performed at an applied potential of 0.01 V and a linear response was obtained in the range of 2–400 μM with a limit of detection (LOD) of 0.6 μM (S/N=3). The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of uric acid and dopamine. The proposed procedure was successfully applied to the determination of ascorbic acid in human urine samples.     

Facile low-temperature growth of carbon nanosheets toward simultaneous determination of dopamine, ascorbic acid and uric acid

The bare Pt electrode modified directly and simply by carbon nanosheets, which were synthesized by microwave plasma enhanced chemical vapor deposition at relatively low temperature, can be used to simultaneously and effectively detect dopamine, ascorbic acid and uric acid.     

Highly Sensitive Enzyme-free Sensor Based on a Carbon Paste Electrode Modified with Binary Zinc Oxide/Polyaniline Nanocomposites for Dopamine,Ascorbic Acid and Uric Acid Sensing

Hybrid composites ZnO/PANI were facily synthesized by a sonication process at room temperature. This procedure is non-expensive, time/energy saving and environmentally safe. The as-prepared ZnO/PANI were characterized by FTIR, UV-vis spectroscopies and SEM in order to investigate the structure and morphology of the studied composites. The samples were used to modify carbon paste electrode (CPE) in order to develop electrochemical biosensors (ZnO/PANI/CPE). The sensing properties of the nanoparticles were evaluated for dopamine, ascorbic acid and uric acid non-enzymatic detection. The effect of percentage of polyaniline in the composites and the effect of calcination on the biosensor's response were also examined in the present study. It was revealed that the existence of PANI in ZnO/PANI/CPE largely enhanced the electroactive surface area and therefore the sensitivity for electrochemical sensing. A good electrochemical behavior was noted for ZnO/40 wt% PANI-cal/CPE modified electrode toward DA, AA and UA oxidation. The electroactive surface area of the previously mentioned modified electrode (0.235 cm²) was two times higher than that of the bare electrode (0.117 cm²). The liner relationships between current intensities and concentrations were found to be 0.01–1.4 mM, 0.1–1.3 mM and 0.01–0.12 mM, with detection limit of 0.029 mM, 0.063 mM and 0.007 mM, for DA, AA and UA respectively. In the mixtures of ascorbic acid (AA), dopamine (DA) uric acid (UA) and glucose (Glu) the sensor showed high selectivity of DA with low interference of ascorbic acid by a current change of 14 %. The as-prepared ZnO/PANI/CPE biosensor displayed a good reproducibility and stability.     

Sensitive determination of dopamine in the presence of uric acid and ascorbic acid using TiO2 nanotubes modified with Pd, Pt and Au nanoparticles

A simple modified TiO(2) nanotubes electrode was fabricated by electrodeposition of Pd, Pt and Au nanoparticles. The TiO(2) nanotubes electrode was prepared using the anodizing method, followed by modifying Pd nanoparticles onto the tubes surface, offering a uniform conductive surface for electrodeposition of Pt and Au. The performance of the modified electrode was characterized by cyclic voltammetry and differential pulse voltammetry methods. The Au/Pt/Pd/TiO(2) NTs modified electrode represented a high sensitivity towards individual detection of dopamine as well as simultaneous detection of dopamine and uric acid using 0.1 M phosphate buffer solution (pH 7.00) as the base solution. In both case, electro-oxidation peak currents of dopamine were linearly related to accumulated concentration over a wide concentration range of 5.0 × 10(-8) to 3.0 × 10(-5) M. However in the same range of dopamine concentration, the sensitivity had a significant loss at Pt/Pd/TiO(2) NTs electrode, suggesting the necessity for Au nanoparticles in modified electrode. The limit of the detection was determined as 3 × 10(-8) M for dopamine at signal-to-noise ratio equal to 3. Furthermore, the Au/Pt/Pd/TiO(2) NTs modified electrode was able to distinguish the oxidation response of dopamine, uric acid and ascorbic acid in mixture solution of different acidity. It was shown that the modified electrode possessed a very good reproducibility and long-term stability. The method was also successfully applied for determination of DA in human urine samples with satisfactory results.     

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.     

Poly(3,4-ethylenedioxythiophene-co-(5-amino-2-naphthalenesulfonic acid)) (PEDOT-PANS) film modified glassy carbon electrode for selective detection of dopamine in the presence of ascorbic acid and uric acid

Poly(3,4-ethylenedioxythiophene-co-(5-amino-2-naphthalenesulfonic acid)) (PEDOT-PANS) film modified glassy carbon electrode was prepared by electrochemical polymerization technique. The properties of modified electrode was studied. It was found that the electrochemical properties of modified electrode was very much dependent on the experimental conditions, such as monomer oxidation potential and pH. The modified electrode surface was characterized by scanning electron microscopy (SEM). The PEDOT-PANS film modified electrode shows electrocatalytic activity toward oxidation of dopamine (DA) in acetate buffer solution (pH 5.0) and results in a marked enhancement of the current response. The linear sweep voltammetric (LSV) peak heights are linear with DA concentration from 2 × 10⁻⁶ to 1 × 10⁻⁵ M. The detection limit is 5 × 10⁻⁷ M. More over, the interferences of ascorbic acid (AA) and uric acid (UA) were effectively diminished. This work provides a simple and easy approach for selective determination of dopamine in the presence of ascorbic acid and uric acid.     

Gold nanoparticles on a thiol-functionalized silica network for ascorbic acid electrochemical detection in presence of dopamine and uric acid

A simple preparation methodology able to stabilize gold nanoparticles and to obtain an electrode which detects ascorbic acid, uric acid, and dopamine by different techniques is presented. A 3-mercaptopropyl-functionalized silica network was synthesized using the sol–gel method. Gold nanoparticles (nAu) were immobilized on the material at synthesis by adding a sol of these previously prepared particles to the reaction mixture. The electrochemical behavior of the SiO₂/MPTS/Au carbon paste electrode was studied using cyclic voltammetry in the presence of a hexacyanoferrate probe molecule. The presence of nAu in the functionalized silica network changes the electrochemical characteristics of the material, favoring the electron transfer process of this complex ion. The SiO₂/MPTS/Au electrode was proven to be an efficient tool in the simultaneous determination of ascorbic acid (H₂AA), dopamine (DA), and uric acid (UA) using square wave voltammetry techniques. With the nAu on the electrode, an increase in the peak current related to the redox process of the H₂AA, DA, and UA was observed. The separations of the anodic peak potentials between DA/H₂AA and UA/H₂AA were 310 and 442?mV, respectively. The results obtained show that the SiO₂/MPTS/Au electrode can be used in the simultaneous determination of H₂AA, DA, and UA.     

Carbon nanotubes paste electrode

The performance of carbon nanotubes paste electrodes (CNTPE) prepared by dispersion of multi-wall carbon nanotubes (MWNT) within mineral oil is described. The resulting electrode shows an excellent electrocatalytic activity toward ascorbic acid, uric acid, dopamine, 3,4-dihydroxyphenylacetic acid (dopac) and hydrogen peroxide. These properties permit an important decrease in the overvoltage for the oxidation of ascorbic acid (230 mV), uric acid (160 mV) and hydrogen peroxide (300 mV) as well as a dramatic improvement in the reversibility of the redox behavior of dopamine and dopac, in comparison with the classical carbon (graphite) paste electrodes (CPE). The substantial decrease in the overvoltage of the hydrogen peroxide reduction (400 mV) associated with a successful incorporation of glucose oxidase (GOx) into the composite material, allow the development of a highly selective and sensitive glucose biosensor without using any metal, redox mediator or anti-interference membrane. No interference was observed at −0.100 V even for large excess of ascorbic acid, uric acid and acetaminophen. A linear response up to 30 mM (5.40 g l⁻¹) glucose with a detection limit of 0.6 mM (0.11 g l⁻¹) were obtained with the CNTPE modified with 10% w/w GOx. Such an excellent performance of CNTPE toward hydrogen peroxide, represents a very good alternative for developing other enzymatic biosensors.