An Electrochemical Biosensor with Uricase Immobilized on Functionalized Gold Coated Copper Wire Electrode for Urinary Uric Acid Assay

A new second generation uricase electrode for urinary uric acid determination has been developed by chemically binding both uricase and redox mediator to inexpensive copper wire through simple electrodeposition of gold on copper surface and subsequent functionalization of the gold with L‐methionine. During a 209‐day testing period, the overall electrode performance exhibits in average a low oxidation potential of 0.33 V, a response time of 5 s, a widest linear calibration concentration range (0–2.38 mM, r²>0.9952), a sensitivity of 50 μA mM^?1, and a detection limit of 2.4 μM. The measurement accuracy and precision for the determination of uric acid in human urine specimens were 85.6–95.5 % and 0.3–2.4 %, respectively. The developed uricase electrode is potential for clinical applications.     

Determination of Ascorbic Acid in the Presence of Uric Acid and Folic Acid by a Nanostructured Electrochemical Sensor Based on a TiO2 Nanoparticle Carbon Paste Electrode

A carbon paste electrode (CPE), modified with novel hydroquinone/TiO₂ nanoparticles, was designed and used for simultaneous determination of ascorbic acid (AA), uric acid (UA) and folic acid (FA). The magnitude of the peak current for modified TiO₂-nanoparticle CPE (MTNCPE) increased sharply in the presence of ascorbic acid and was proportional to its concentration. A dynamic range of 1.0–1400.0 μM, with the detection limit of 6.4 × 10^?7 M for AA, was obtained using the DPV technique (pH = 7.0). The prepared electrode was successfully applied for the determination of AA, UA, and FA in real samples.     

Electrochemical Behavior and Determination of Uric Acid at Single-Walled Carbon Nanotube Modified Gold Electrodes

The voltammetric behavior of uric acid was studied at a single-walled carbon nanotube (SWNT) modified gold electrode. Uric acid can effectively accumulate at this electrode and produce an anodic peak at about 0.45 V (vs. SCE) in pH 5.0 sodium acetate buffer solutions (HAc-NaAc). The experimental parameters, such as solution pH, accumulation time, and amount of SWNT, were optimized for determination. Under the optimum conditions, the anodic peak current is linear to the uric acid concentration over the range of 1.0×10⁻⁷ M to 2.5×10⁻⁵ M with a correlation coefficient of 0.998. The detection limit was 5.0×10⁻⁸ M for 60 s accumulation. The electrode could be easily regenerated and exhibited good stability. A 5.0×10⁻⁶ M uric acid solution was measured ten times using the same electrode, and the relative standard deviation of the peak current was 1.3%. This method was successfully applied to the determination of uric acid in human urine samples, and the recovery was 97–99%. The feasibility for simultaneous determination of xanthine, ascorbic acid and uric acid was discussed. These species did not interfere with each other in a certain concentration range. The influence of some surfactants on the anodic peak was also examined.     

聚钙羧酸修饰玻碳电极差分脉冲伏安法同时测定多巴胺和尿酸

采用电化学方法将钙羧酸(CCA)聚合修饰在玻碳电极(GCE)表面制备了聚钙羧酸指示剂修饰玻碳电极(PCCA/GCE),并用循环伏安法和交流阻抗法研究了电极的电化学性能。结果表明:在pH 6.0的磷酸盐缓冲溶液中,多巴胺(DA)和尿酸(UA)在聚钙羧酸修饰电极上的氧化峰得以分开,峰电位差为0.14V,据此提出了聚钙羧酸修饰电极差分脉冲伏安法同时测定多巴胺和尿酸的方法。DA和UA的浓度分别在5.0～43.8μmol.L-1和5.0～50.0μmol.L-1范围内与其氧化峰电流呈线性关系,检出限(3S/N)分别为0.2μmol.L-1和0.5μmol.L-1。方法可用于多巴胺注射液样品中DA和UA的测定,测定值的相对标准偏差(n=5)依次为2.43%和2.35%。     

Electrochemical Detection of Uric Acid in Mixed and Clinical Samples: A Review

The present review has sought to explore the technological advances that have been made in recent years towards the selective analysis of uric acid and critically evaluate how they could, in fact, be exploited as a basis for a multi analyte sensor incorporating uric acid detection. Numerous strategies have evolved in recent years but these have invariably focused on the manufacture and response characterization of discrete sensors. Various methods of obtaining selective detection such as use of uricase enzymes, nanoparticles, carbon nanotubes, polymers, conducting polymers and MIPs are also discussed along with the clinical relevance of UA determination.     

An Inexpensive Biosensor for Uric Acid Determination in Human Serum by Flow‐Injection Analysis

An inexpensive and easy to construct miniaturized biosensor is described for the determination of uric acid in biological fluids. The amperometric biosensor was prepared by using a carbon paste electrode prepared with uricase from Arthrobacter globiforms and tetracyanoquinodimethane as electron transfer mediator. When incorporated into a flow‐injection system it was enabled to perform 50 measurements/h of uric acid in the analytical range of 1–100 μmol dm^?3 with a relative standard deviation of 0.20% (n=14). The system was applied to human serum samples analysis providing good data correlation with those obtained by the reference spectrophotometric method. A linear relationship AM (μmol dm^?3)=1.02 (±0.05) SP (μmol dm^?3) ?0.12 (±0.13) was obtained evidencing the absence of significant error. The constructed biosensor was successfully used for at least four months (250 assays) with only a 13% of decrease in the enzymatic activity.     

Electrochemical Determination of Uric Acid,Dopamine and Tryptophan at Zinc Hexacyanoferrate Clay Modified Electrode

A Cameroonian smectite clay has been transformed into Zn²⁺ homoionic form and then used to prepare film modified glassy carbon electrodes and carbon paste electrodes. These electrodes containing Zn²⁺ were exploited to prepare a mixed valence zinc hexacyanoferrate (ZnHCF). Cyclic voltammetry has been employed to monitor the in situ growth of ZnHCF on clay modified electrodes. Although interesting electrocatalytic properties toward UA were observed with these modified electrodes, the modified carbon paste electrodes were the most suitable for dopamine, uric acid and tryptophan detection and exhibited for these analytes extended linear range, high sensitivities, selectivity and low limit.     

碳纤维微电极伏安法测定动物脑内5-羟吲哚乙酸、尿酸和高香草酸

目前,将微电极植入动物脑内,采用伏安法连续监测神经递质已被公认是最有效的在体测定方法。碳纤维电极已成为活体分析中使用的主要电极,为提高其灵敏度和分辨率,电极在使用前必须经过特殊的预处理。我们曾提出一种简单的恒电位处理方法,电极处理后     

Determination of Uric Acid and Norepinephrine by Chitosan‐Multiwall Carbon Nanotube Modified Electrode

A novel chemically modified electrode based on the chitosan‐multiwall carbon nanotube (MWNT) coated glassy carbon electrode (GCE) is described, which exhibited an attractive ability to determine uric acid (UA) and norepinephrine (NE) simultaneously. The responses of UA and NE merged into a large peak at a bare GCE, but yielded two well‐defined oxidation peaks at the chitosan‐MWNT modified GCE (MC/GCE). The experimental parameters were optimized, and a direct electrochemical method for the simultaneous determine for UA and NE is proposed. The MC/GCE showed good sensitivity, selectivity and stability.     

抗坏血酸和尿酸在甘氨酸-壳聚糖修饰玻碳电极上的电化学行为及测定

制备了甘氨酸-壳聚糖复合膜修饰玻碳电极(Gly-CTS/GCE),研究了抗坏血酸(AA)和尿酸(UA)在该修饰电极上的电化学行为。结果表明在pH=5.59的磷酸盐缓冲溶液中,AA、UA在Gly-CTS/GCE上均产生灵敏的不可逆氧化峰,其峰电流与浓度在一定范围内呈良好的线性关系。对AA和UA混合溶液平行测定7次,相对标准偏差分别为4.6%、2.9%,表明该电极重现性和稳定性良好。AA、UA在Gly-CTS/GCE电极上的氧化峰峰电位相差340mV,据此可实现对二者的同时检测,并可应用于实际样品测定。     

Selective Electrochemical Determination of Uric Acid in the Presence of Ascorbic Acid Using a Carbon Paste Electrode Modified with β‐Cyclodextrin

Uric acid (UA) was determined in the presence of ascorbic acid (AA) by using a carbon paste electrode modified superficially by a β‐cyclodextrin film (CPE/β‐CD). The surface carbon paste electrode was prepared applying a 30 cycles potential program and using a 1 M HClO₄+0.01 M β‐CD electrolytic solution. The UA and AA solutions were used to evaluate the electrode selectivity and sensitivity by cyclic voltammetric and amperometric methods. In these experiments the detection limit for UA was (4.6±0.01)×10^?6 M and the RSD calculated from the amperometric curves was 10%. From the data obtained it was possible to quantify UA in the urine and saliva samples. Selective detection of UA was improved by formation of an inclusion complex between β‐CD and UA. The results show that the CPE/β‐CD is a good candidate due to its selectivity and sensitivity in the UA determination in complex samples like the biological fluids.     

尿酸在有序介孔碳-壳聚糖修饰电极上的电化学行为及其测定

用硬模板法合成了有序介孔碳(OMC),并以壳聚糖(Chitosan)作为分散剂制备了有序介孔碳-壳聚糖复合膜(OMC-Chitosan)修饰电极.应用该电极研究了尿酸(UA)的电化学行为以及实际样品的分析检测.在0.1 mol/L(pH 6.5)的磷酸盐(PBS)缓冲溶液中,UA在OMC-Chitosan修饰电极上于0.334 V处产生一灵敏的不可逆氧化峰,氧化峰电流(ipa)与UA的浓度在4.0×10-6～2.0×10-4 mol/L范围内呈良好的线性关系,相关系数为0.9997,检出限为2.0×10-6 mol/L.对0.2 mmol/L UA平行测定10次,相对标准偏差为3.8%,表明该电极重现性和稳定性良好.     

Electrochemical Study of Gold Microelectrodes Modified with PEDOT to Quantify Uric Acid in Milk Samples

A gold microelectrode (10 μm diameter) with an electropolymerized layer of poly(3,4‐ethylenedioxythiophene) (PEDOT) was used to quantify uric acid and investigate the antioxidant profile of milk and flavored milks. Comparisons were made with a bare gold microelectrode and a PEDOT‐glassy carbon macroelectrode (3 mm diameter). Two different electropolymerization processes were undertaken in an aqueous and an organic solution, and superior polymer growth was observed for PEDOT polymerized in lithium perchlorate/propylene carbonate. In the presence of a ferri/ferrocyanide redox couple, diffusion‐controlled redox peaks were observed with the PEDOT‐gold microelectrode rather than the plateau current typical of a bare microelectrode. Likewise, an anodic peak for uric acid was observed at the high surface‐area PEDOT‐gold microelectrode, with evidence for pre‐adsorption of uric acid at the electrode. The linear concentration range for uric acid standards was from 6 to 200 μM, and the limit of detection, limit of quantification, and sensitivity were determined to be 7 μM, 24 μM, and 397 μAμM^?1cm², respectively. Cyclic voltammograms of chocolate and espresso flavored milks exhibited significant contributions from the phenolic compounds present. Peak separation was more clearly defined using the PEDOT‐microelectrode compared to a PEDOT‐glassy carbon macroelectrode.     

Electrochemical Determination of Tyrosine in the Presence of Dopamine and Uric Acid at the Surface of Gold Nanoparticles Modified Carbon Paste Electrode

A gold nanoparticles modified carbon paste electrode (GN‐CPE) was used as a highly sensitive electrochemical sensor for determination of tyrosine (Tyr), dopamine (DA) and uric acid (UA) in phosphate buffer solution (PBS). The study and measurements were carried out by using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry methods. In DPV, the GN‐CPE could separate the oxidation peak potentials of DA and UA present in the same solution, though at the unmodified CPE the peak potentials were indistinguishable. The prepared electrode showed voltammetric responses with high sensitivity and selectivity for Tyr, DA and UA in optimal conditions, which makes it very suitable for simultaneous determination of these compounds. The calibration curves for Try, DA and UA were linear for the concentrations of each species. The proposed voltammetric approach was also applied to the determination of Tyr concentration in human serum as a real sample.     

基于含有活性铜的碳点电化学传感器选择性检测尿酸

采用水热法制备了含有活性铜的碳点,利用荧光光谱和紫外可见吸收光谱对其光学性质进行了表征.通过电沉积法将其修饰于玻碳电极表面, 构建了电化学生物传感器,采用循环伏安法、交流阻抗法和差分脉冲伏安法对电极的电化学行为进行了考察, 并对其电化学反应机理进行了探讨.结果表明,此传感器对尿酸具有良好的电催化效果,可有效消除抗坏血酸和多巴胺等物质的干扰.在最佳条件下,氧化峰电流与尿酸的浓度在1.00~300 μmol/L范围内呈良好的线性关系, 检出限为0.30 μmol/L(S/N=3).此传感器具有制作简单、选择性好、灵敏度高和线性范围宽等优点,有望应用于实际样品的检测.     

Simultaneous Determination of Ascorbic Acid and Uric Acid by Using a PVC/TTF‐TCNQ Composite Electrode as Detector in a FIA System

A PVC/TTF‐TCNQ composite electrode has been employed as detector in a flow injection system. The proposed method allows the simultaneous detection of ascorbic acid (AA) and uric acid (UA) in mixtures by using a FIA system in a simple manner, without pre‐treatment or modified electrode. This method is based on the amperometric determination of (a) ascorbic acid at 0.15 V and (b) both analytes at 0.35 V, being the response linear in the range 1×10^?2–4×10^?4 M for both analytes with detection limits (S/N=3) of 1.2×10^?4 M and 8.1×10^?5 M for AA and UA, respectively.     

Simultaneous Determination of Ascorbic Acid,Dopamine and Uric Acid,at a Graphene Paste Electrode Modified with Functionalized Graphene Sheets

The present study reports the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) in phosphate buffer solution (pH 7.0) using graphene paste electrode modified with functionalized graphene sheets (GPE‐MFGSs). The presence of FGS inhibited the adsorption of AA owing to the electrostatic repulsion, but was favorable for the affinity adsorption of DA and UA via the ion exchange and hydrogen bonding mechanisms, respectively. This led to the decrease in the oxidation potential of AA and the significantly enhanced oxidation peak currents of DA and UA at the GPE‐MFGSs. By cyclic voltammetry and differential pulse voltammetry, the oxidation potentials of AA, DA, and UA, at the GPE‐MFGSs in a ternary mixture were found to be well resolved so that their simultaneous determination could be achieved. Furthermore, the influence of some experimental variables such as graphene paste composition, working solution pH, scan rate and pulse amplitude was studied. In addition, by differential pulse voltammetry, the linear dependence of peak current on the concentration was obtained in the ranges of 0.05–9.0, 0.03–13, and 0.03–5.5 µM with the lowest detection limits of 0.02, 0.01, and 0.01 µM for AA, DAand UA, , respectively.     

RNA Modified Electrodes for Simultaneous Determination of Dopamine and Uric Acid in the Presence of High Amounts of Ascorbic Acid

A promising electrochemical biosensor was fabricated by electrochemical grafting of ribonucleic acid (RNA) at 1.8 V (vs. SCE) on glassy carbon electrode (GCE) (denoted as RNA/GCE), for simultaneous detection of dopamine (DA) and uric acid (UA) with coexistence of excess amount of ascorbic acid (AA). The electrode was characterized by X‐ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The RNA modified layer on GCE exhibited superior catalytic ability and anionic exclusive ability in comparison with the DNA modified electrode. Three separated anodic DPV peaks were obtained at 0.312, 0.168 and ?0.016 V for UA, DA and AA, respectively, at the RNA/GCE in pH 7.0 PBS. In the presence of 2.0 mM AA, a linear range of 0.37 to 36 μM with a detection limit of 0.2 μM for DA, and in the range of 0.74 to 73 μM with a detection limit of 0.36 μM for UA were obtained. The co‐existence of 5000 fold AA did not interfere with the detection of DA or UA. The modified electrode shows excellent selectivity, good sensitivity and good stability.     

钴配合物/单壁碳纳米管修饰电极对尿酸的检测

采用滴加单壁碳纳米管(SWCNTs)悬浮液和电沉积钴配合物[Co(phen)3]2+(phen=邻菲啰啉)的方法,制备了钴配合物-单壁碳纳米管修饰玻碳电极([Co(phen)3]2+-SWCNTs/GCE),研究了尿酸(UA)在该修饰电极上的电化学行为。结果表明,修饰电极对UA具有良好的电催化作用,在1~249μmol·L-1浓度范围内,氧化峰电流与UA浓度之间存在良好的线性关系,检出限(S/N=3)为1μmol·L-1,加标回收率在98%~102%之间。该修饰电极的稳定性和重现性好,可用于UA的定量分析。     

A Novel Strategy for Simultaneous Determination of Dopamine and Uric Acid Using a Carbon Paste Electrode Modified with CdTe Quantum Dots

A novel CdTe quantum dots‐modified carbon paste electrode (QDMCPE) was fabricated and used to study the electrooxidation of dopamine and uric acid and their mixtures by electrochemical methods. Using square wave voltammetry (SWV), a highly sensitive and simultaneous determination of dopamine and uric acid was explored at the modified electrode. SWV peak currents of dopamine and uric acid increased linearly with their concentrations in the ranges of 7.5×10^?8–6.0×10^?4 M, and 7.5×10^?6–1.4×10^?3 M, respectively. Finally this new sensor was used for determination of dopamine and uric acid in some real samples.