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Developing electrochemical sensors for ascorbic acid, uric acid and glucose detection provides advantages of rapid, precise and economical monitoring of disease condition, and they have the potential to transform healthcare by enabling point-of-care diagnostic and personalised treatment. Facile and cost-effective potentiometric sensors have been developed in this work for selective and sensitive detection of ascorbic acid, uric acid and glucose, based on molecularly imprinted polymer (MIP). The imprinted polymeric matrix of para-aminobenzoic (pPABA) was developed on the surface of electrochemically reduced graphene oxide modified paraffin impregnated graphite rod electrode (rGO/PIGE). The monomeric para-aminobenzoic acid (PABA) was electropolymerised with template, viz., ascorbic acid, uric acid and glucose individually. The molecularly imprinted electrode surface was created by removing the trapped template molecule. The surface analysis of the modified electrodes was carried out by cyclic voltammetry (CV), scanning electron microscopy (SEM), attenuated total reflection spectroscopy (ATR), Raman spectroscopy and contact angle measurements. Parameters controlling the performance of the MIP (p-PABA), viz., pH of the supporting electrolyte and number of polymerisation cycle, were optimised. Under optimised conditions, the potentiometric responses of MIPs were linearly related to concentrations of ascorbic acid, uric acid and glucose in the range of 3.4 × 10−7 M–2.5 × 10−5 M, 3.3 × 10−7 M–1.3 × 10−5 M, and 3.5 × 10−7 M–2.9 × 10−5 M with a correlation coefficient, R2 of 0.99, 0.99 and 0.98 respectively. All three sensors showed high selectivity even in the presence of high concentration of similar interfering compounds. A limit of detection (LOD) for ascorbic acid, uric acid and glucose was found to be 1.1 × 10−8 M, 2.8 × 10−8 M and 1.3 × 10−8 M respectively. In addition, the developed sensors exhibited long-term stability and good reproducibility. [ABSTRACT FROM AUTHOR]

In this work, an electrochemical method for sensitive determination of creatinine has been reported based on its reaction with 2-nitrobenzaldehyde and using differential pulse voltammetry technique. A plausible mechanism of the reaction has been proposed and successful application of this method for creatinine detection in a real sample (human urine) has also been demonstrated. The mechanism is indicative of the formation of multiple electroactive species in the process. The linear range of detection being 1–25 mM, with LOD of 0.50 mM and an excellent R2 value of 0.99, was suitable enough for the detection of creatinine in human urine. Interference studies of urea, uric acid, glucose, ascorbic acid and dopamine were done and found to be within the acceptable limit. All the components except uric acid showed an interference of less than 3.2%, while uric acid showed maximum interference of 8.4%. Its robustness, high selectivity, good sensitivity, and low detection limit have projected it as a promising new tool for a point-of-care testing device. [ABSTRACT FROM AUTHOR]

A novel cobalt-doped two-dimensional molybdenum diselenide/polypyrrole hybrid-based carbon nanofiber (Co/MoSe2/PPy@CNF) was prepared using the hydrothermal method followed by electrospinning technique. The structural and morphological properties of the 2D-TMD@CNF-based hybrids were characterized through X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and transmission electron microscopy (TEM). The Co-MoSe2/PPy@CNF exhibited large surface area, porous structure, and improved active sites due to the synergistic effect of the components. The electrochemical and electrocatalytic characteristics of the 2D-TMD@CNF-modified electrodes were also investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The Co/MoSe2/PPy@CNF electrode was used as an electrochemical sensor for simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) and showed enhanced catalytic activity and sensitivity. Using DPV measurements, the Co/MoSe2/PPy@CNF demonstrated wide linear ranges of 30–3212 μM for AA, 1.2–536 μM for DA, and 10–1071 μM for UA with low detection limits of 6.32, 0.45, and 0.81 μM, respectively. The developed sensor with the Co/MoSe2/PPy@CNF-modified electrode was also applied to a human urine sample and gave recoveries ranging from 94.0 to 105.5% (n = 3) for AA, DA, and UA. Furthermore, the Co/MoSe2/PPy@CNF-based sensor exhibited good selectivity and reproducibility for the detection of AA, DA, and UA. [ABSTRACT FROM AUTHOR]

The design of the electrode materials for electrochemical sensors is crucial for the simultaneous fast detection of ascorbic acid (AA) and uric acid (UA). A hierarchical porous carbon material (KACM) was prepared via high-temperature calcination and KOH activation using azalea (a species of rhododendron) biomass as the carbon source. KACM and thionine (Thi) were simultaneously assembled on a glassy carbon electrode (GCE) to construct a porous carbon/thionine ratiometric electrochemical biosensor for the detection of ascorbic acid and uric acid. Electrochemical evaluation showed that the Thi/KACM/GCE has good electrochemical performance, strong catalytic activity toward AA and UA oxidation, and good separation of the two oxidation peaks. Under the optimized conditions, Thi/KACM/GCE has a wide linear range (0.05–9 mM) and low detection limit (6.4 μM for AA and 10 μM for UA). Additionally, the biosensor exhibited good selectivity, stability, and reproducibility. Thi/KACM/GCE was used for the simultaneous detection of AA and UA in human urine with 99.4–101.0% recovery of the compounds. This study reports for the first time the use of azaleas in electrochemical biosensors, and the results show that small changes in the structural properties of biomass materials can affect their electrochemical properties. [ABSTRACT FROM AUTHOR]

Novel films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold nanoparticles (AuNPs) possessing diameter of 14.0 nm. Electron optical microscopy analysis reveals that decoration of N-MWCNTs with AuNPs does not have any influence on their bamboo-shaped configuration. The electrochemical response of fabricated composite films, further denoted as N-MWCNTs/AuNPs, towards oxidation of dopamine (DA) to dopamine-o-quinone (DAQ) in the presence of ascorbic acid (AA) and uric acid (UA) was probed in real pig serum by means of cyclic voltammetry (CV) and square wave voltammetry (SWV). The findings demonstrate that N-MWCNTs/AuNPs exhibit slightly greater electrochemical response and sensitivity towards DA/DAQ compared to unmodified N-MWCNTs. It is, consequently, obvious that AuNPs improve significantly the electrochemical response and detection ability of N-MWCNTs. The electrochemical response of N-MWCNTs/AuNPs towards DA/DAQ seems to be significantly greater compared to that of conventional electrodes, such as platinum and glassy carbon. The findings reveal that N-MWCNTs/AuNPs could serve as powerful analytical sensor enabling analysis of DA in real serum samples. [ABSTRACT FROM AUTHOR]

Uric acid, the end product of purine metabolism in humans, is crucial because of its anti-oxidant activity and a causal relationship with hyperuricemia and gout. Several physiologically important urate transporters regulate this water-soluble metabolite in the human body; however, the existence of latent transporters has been suggested in the literature. We focused on the Escherichia coli urate transporter YgfU, a nucleobase-ascorbate transporter (NAT) family member, to address this issue. Only SLC23A proteins are members of the NAT family in humans. Based on the amino acid sequence similarity to YgfU, we hypothesized that SLC23A1, also known as sodium-dependent vitamin C transporter 1 (SVCT1), might be a urate transporter. First, we identified human SVCT1 and mouse Svct1 as sodium-dependent low-affinity/high-capacity urate transporters using mammalian cell-based transport assays. Next, using the CRISPR-Cas9 system followed by the crossing of mice, we generated Svct1 knockout mice lacking both urate transporter 1 and uricase. In the hyperuricemic mice model, serum urate levels were lower than controls, suggesting that Svct1 disruption could reduce serum urate. Given that Svct1 physiologically functions as a renal vitamin C re-absorber, it could also be involved in urate re-uptake from urine, though additional studies are required to obtain deeper insights into the underlying mechanisms. Our findings regarding the dual-substrate specificity of SVCT1 expand the understanding of urate handling systems and functional evolutionary changes in NAT family proteins. [ABSTRACT FROM AUTHOR]

Titanium dioxide-multiwalled carbon nanotube/polyimide (TiO2–MWCNT/PI) composite film modified electrodes for simultaneous detection of dopamine (DA), uric acid (UA), and ascorbic acid (AA) in clinical or biomedical applications were prepared. Firstly, TiO2–MWCNT and polyimide structures were synthesized. Then, TiO2–MWCNT/PI composites containing different ratios of MWCNT were subsequently prepared and characterized with chemical, thermal and morphological analysis techniques. Synthesized TiO2–MWCNT/PI composites were coated on the platinum electrode surface. Prepared electrodes were used to sense DA, UA, and AA with voltammetric measurements. LOD and LOQ parameters of modified electrodes for DA were observed 8.5114 μM and 25.5342 μM, respectively. The R2 value for the DA in the linear range from 175 to 325 µM was obtained 0.9967 (in the existence of AA and UA). After five repeatability results, 96.3% AA, 98.2% DA, and 88.3% UA peak currents were maintained. The modified electrode exhibited good selectivity, acceptable durability, high repeatability, and sensitivity. [ABSTRACT FROM AUTHOR]

An electrochemical approach is presented based on multiwall carbon nanotubes (MWCNTs) and neodymium(III) hydroxide (Nd(OH)3) nanoflakes for detection of bovine serum albumin (BSA). The materials were characterized morphologically (XRPD, SEM, and HR-TEM) and electrochemically (DPV, EIS). The MWCNTs@Nd(OH)3 composite was used as support for bovine serum albumin polyclonal antibody (anti-BSA). After the antibody immobilization on the electrochemical platform and antigen/antibody binding time (optimum 60 min), the proposed approach shows a linear voltammetric response toward BSA concentration in the range 0.066 to 6.010 ng mL−1 at maximum peak potential of 0.13 V (vs. Ag/AgCl). Limit of detection (LOD) and limit of quantification (LOQ) were 18 pg mL−1 and 61 pg mL−1, respectively. The precision of the method calculated as relative standard deviation (RSD) of five independent measurements was better 3%. The selectivity of the optimized method regarding structurally similar proteins (human serum albumin and human hemoglobin), ions (Na+, K+, Ca2+, and NO2−), or compounds (glucose, ascorbic acid, dopamine, uric acid, paracetamol, and glycine) was found to be satisfactory, with the current changes of less than 5% in the presence of up to 1 × 105 times higher concentrations (depending on the compound) of the listed potential interfering compounds. Practical applicability of immunosensor for BSA determination in cow whey sample, with recovery values in the range 97 to 103%, shows that the developed method has high potential for precise and accurate detection of BSA, as well as exceptional miniaturization possibilities for on-site and equipment-free sensing. [ABSTRACT FROM AUTHOR]

The selectivity and sensitivity in the detection of ascorbic acid, dopamine and uric acid is an open problem in the field of biosensing. The host-guest interactions of Cucurbit[n]uril (n=7, 8) as host and ascorbic acid (AA), dopamine (DA) and uric acid (UA) as the guest molecules has been studied using density functional theory with dispersion corrections. The energetic and thermodynamic results indicates that UA forms the most stable structure with CB7 and CB8 in gas phase. In aqueous phase, CB7 favours complexation with AA while CB8 favours DA. The non-covalent interactions that binds the supramolecular complexes are analyzed by molecular electrostatic potentials, non-covalent interactions-reduced density gradient and natural bond orbital analysis. Local energy decomposition (LED) analysis based on the non-perturbative natural orbital local domain (DLPNO)-CCSD(T) calculations is carried out for quantifying the intermolecular forces which stabilizes the complexes. The results indicate that the electrostatic interactions, van der Waals forces, intermolecular charge transfer interactions and intermolecular hydrogen bonding are responsible for the stabilization of the complexes. The study may be useful in designing Cucurbituril-based sensing device for these analytes. [ABSTRACT FROM AUTHOR]

Selectivity of dopamine (DA), uric acid (UA), and ascorbic acid (AA) is an open challenge of electrochemical sensors in the field of biosensing. In this study, two selective mechanisms for detecting DA, UA, and AA biomolecules on the pristine boron nitride nanosheets (BNNS) and functionalized BNNS with tryptophan (Trp), i.e., Trp@BNNS have been illustrated through density functional density (DFT) calculation and charge population analysis. Our findings reveal that the adsorbed biomolecules on Trp@BNNS indicate the less sensitivity factor of biomolecule separation than the functionalized biomolecules with Trp (Trp@biomolecule) adsorbed on pristine BNNS. From the calculations, strong adsorption of Trp@biomolecule on the pristine substrate corresponds to enhancing of electron charge transfer and electrical dipole moment. Our analysis is in good agreement with the previous theoretical and experimental results and suggests new pathway for electrode modification for electrochemical biosensing. [ABSTRACT FROM AUTHOR]

In this study, a new amperometric biosensor for creatinine determination was developed. For this purpose, a polypyrrole-polyvinylsulfonate film was prepared by electropolymerization of pyrrole in a polyvinylsulfonate medium on a platinum plate. Creatinase and sarcosine oxidase enzymes were immobilized on polypyrrole-polyvinylsulfonate film by cross-linking with glutaraldehyde. The determination of creatinine was made based on the oxidation of hydrogen peroxide at 0.4 V formed as a result of the enzymatic reaction on the surface of the prepared biosensor. The linear working range of the biosensor obtained was found between 5.0 × 10−6 and 1.0 × 10−4 M. Using this linear graph, the Km (observed) and Imax (observed) values for the double enzyme electrode system were calculated as 5.0 × 10−3 mM and 0.34 µA/min, respectively. Optimum working pH and temperature were determined as 8.0 and 60 °C, respectively. The reusability and shelf life of the biosensor were determined. The effects of interferences in biological environments on biosensor response were investigated. For this purpose, uric acid, ascorbic acid, paracetamol, glycine, urea, and formaldehyde were used. The results have shown that the prepared biosensor has the potential to be used for creatinine determination in biological fluids. [ABSTRACT FROM AUTHOR]

In this research work, a straightforward strategy for the development of carbon-based electrodes is presented using nanoclay as a modifier, and a room temperature ionic liquid was employed as a binder for the simultaneous determination of dopamine (DP) and uric acid (UA) in the presence of ascorbic acid (AA) in real samples in the form of serum and urine. The synergistic effect between nanoclay and the ionic liquid results in an increase in the activity of the prepared carbon ionic liquid/nanoclay (NC-CILE) nanocomposites, promoting the electron transfer and electrocatalytic activity. Considerable stability, electrocatalytic properties, and large surface area make it possible to exploit low detection limit sensors for long term applications in real samples and wide linear dynamic ranges. The electrochemical behavior of the prepared NC‑CILE electrode was diagnostically studied by cyclic voltammetry and differential pulse voltammetry analyses. The response currents were linear in the DP and UA concentration ranges of 1.0–100.0 and 0.1–10.0 μM, respectively. In addition, at 50.0 µM of AA, the detection limits for DP and UA were estimated to be around 0.45 and 0.025 μM (S/N = 3), respectively. [ABSTRACT FROM AUTHOR]

The integration of the enzymes on the solid electrode surfaces is an indispensable step for the construction of the bioelectrochemical electrode. In the current work, the blend nanofibers consisting of poly (vinyl alcohol) and poly(ethyleneimine) were deposited by the electrospinning method on an H2O2-sensitive modified glassy carbon electrode. Glucose oxidase was immobilized on the glutaraldehyde-activated blend nanofibers. Bioelectrochemical electrode displayed a good linear response to the glucose concentration ranges with two separate calibration curves, from 2 to 8 mmol L−1 and from 10 to 30 mmol L−1. Besides, it showed a high anti-interference performance against ascorbic and uric acids as well as long-term storage stability over 63 days. Moreover, analysis results in a diluted human serum sample showed that the prepared bioelectrochemical electrode has the ability to measure glucose in real samples. [ABSTRACT FROM AUTHOR]

A simple Co3O4 modified carbon paste electrode (CPE) was developed as an electrochemical sensor for the selective detection and quantification of dopamine (DA) via fastest synthesis and fabrication methods. The solution combustion method and bulk modification techniques were sequentially used for the preparation of the sensor. The modifier was characterized using different techniques such as PXRD, FT-IR, SEM and TG-DSC. The fabricated sensor shows a wide linear dynamic range of 80 µM-300 nM, low detection limit, excellent reproducibility and high stability. The differential pulse voltammetry (DPV) and cyclic voltammetry (CV) techniques were extensively used for the electrochemical studies. The same electrode was used for detecting DA in the solution of coexisting ascorbic acid (AA) and uric acid (UA). Well resolved peaks and good current sensitivity of this electrochemical sensor extended its utility in determining DA in blood serum at physiological pH. [ABSTRACT FROM AUTHOR]

In this work, UV/Vis spectroelectrochemistry (SEC), in a thin-layer regime and parallel configuration, is selected to solve a complex mixture that contains dopamine (DA), ascorbic acid (AA) and uric acid (UA). These molecules, like many other biological compounds, are assuming a highly important place in analytical and biomedical fields due to the fundamental role that they play in human metabolism. In addition, low or high levels of these compounds are associated with diseases such as Parkinson's disease. For this reason, the quantification of these biomolecules is becoming increasingly critical. However, some drawbacks must be overcome, because the three molecules coexist in the human body, and the species are subject to mutual interference. In fact, they are all oxidized at similar potentials, and their UV/Vis absorption bands overlap, greatly complicating their quantification. For this reason, derivative SEC together with suitable chemometric tools such as PARAFAC are proposed to solve this complex matrix. This technique allows us to separate the contribution of each of these molecules present in a sample and to quantify all of them, achieving high resolution and reproducibility. Besides, detection limits at the micromolar level are achieved for DA, AA and UA in mixture solutions. This work thus demonstrates the great potential for derivative potentiodynamic SEC combined with the appropriate chemometric tools in solving complex mixtures, a field where SEC is still taking the first steps. [ABSTRACT FROM AUTHOR]

The surface of polycrystalline gold (Au (poly)) electrode was ex situ modified with self-assembled monolayer (SAM) of thiourea (TU) with a view of applying the electrode for the electrochemical oxidation of uric acid (UA) in alkaline media. UA undergoes an enhanced electrochemical oxidation at the monolayer of TU-modified Au (poly) (TU|Au (poly)) electrode at a remarkably lower potential with a higher current density as compared to the bare Au (poly) electrode. The enhanced activity of the electrode was achieved due to the effective blocking of harmful adsorption of UA that takes place strongly at the bare Au (poly) electrode surface. The TU|Au (poly) electrode was also found to be very effective towards simultaneous oxidations of UA, ascorbic acid (AA) and dopamine (DA) in their mixture with well separation of the peak current of the individual substance. This technique may be advantageously utilized for developing sensor for the purpose of detection of UA. [ABSTRACT FROM AUTHOR]

Uncontrolled oxidative stress, reported in Salmonella and HIV infections, colorectal cancer or severe acute malnutrition, has been associated with anaerobic gut microbiome alteration, impaired butyrate production, mucosal immunity dysregulation and disruption of host-bacterial mutualism. However, the role of major antioxidant molecules in the human body, such as glutathione, ascorbic acid and uric acid, has been neglected in this context. Here, we performed an in vitro metabolomics study of the 3 most odorous anaerobic microbes isolated from the human gut in our laboratory (Clostridium sporogenes, Clostridium subterminale and Romboutsia lituseburensis) when grown in anaerobiosis or in aerobiosis with these 3 antioxidant molecules via gas and liquid chromatography-mass spectrometry (GC/MS and LC/MS). There was no growth or volatile organic compound production in aerobic cultures without the 3 antioxidant molecules. In anaerobiosis, the major metabolic products of the bacteria were thiols, alcohols and short-chain fatty acid esters. The production of alkanes, cycloheptatriene and, paradoxically, increased butyrate production, was observed in the cultures grown in aerobiosis with the 3 antioxidant molecules. The qualitative shift suggests specific molecular mechanisms that remain to be elucidated. The increased production of butyrate, but also isobutyrate and isovalerate in vitro suggests that these 3 antioxidant molecules contributed to the maintenance and active resilience of host-bacterial mutualism against mucosal oxygen and uncontrolled oxidative stress in vivo. [ABSTRACT FROM AUTHOR]

A glassy carbon electrode has been modified by electrochemical polymerization of dianix yellow along with multi-walled carbon nanotubes (MWCNTs) and utilized for the selective determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA). Atomic force microscopy and scanning electron microscopy images were obtained to compare the surface morphology and topography of the bare and modified electrodes. Also, the electrochemical activities of DA, AA, and UA on the bare and modified electrodes were evaluated with the use of cyclic, linear sweep and differential pulse voltammetry (DPV). Large peak separation, good sensitivity, and stability allow to apply the poly-dianix yellow/MWCNTs modified electrode for the determination of DA individually and in the presence of AA and UA. The DPV data showed the linearity of DA, AA, and UA peak currents in the concentrations ranges of 7–2500 nM, 5–110 µM, and 0.100–7.500 µM with the detection limits of 6.1, 99 and 8.9 nM, respectively. The proposed electrode was applied for the quantification of dopamine in human blood serum samples. [ABSTRACT FROM AUTHOR]

A non-enzymatic glucose sensor based on the use of CuO-Cu nanospheres placed on a TiO2 nanotube (TNT) array with excellent performance is described. The electrode was fabricated by coating the CuO-Cu nanospheres onto the TNT array through electrochemical deposition. The CuO-Cu nanospheres with a diameter of ~200 nm are well dispersed on the TNT surface, which warrants smooth interaction and a 3D nanostructure with high uniformity. The modified electrode was then used for amperometric determination of glucose in 0.1 M NaOH solution. Figures of merit include (a) a typical working voltage of 0.65 V (vs. Ag/AgCl). (b) a linear range as wide as from 0.2–90 mM, (c) good sensitivity (234 μA mM−1 cm−2), and a 19 nM lower detection limit. The sensor is selective over ascorbic acid (AA), dopamine (DA), uric acid (UA), lactose, sucrose, and fructose. [ABSTRACT FROM AUTHOR]

Two-dimensional porous graphitic carbon nitride (g-C3N4) nanosheets were synthesized by low-cost and direct thermal oxidation. Porous g-C3N4 assembled with graphene oxide (GO) was immobilized on a glassy carbon electrode. The sensor was applied to simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) with high performance. Cyclic voltammetry and differential pulse voltammetry were used to investigate electrochemical and electrocatalytic properties. The results indicate that the electrochemical sensor possesses high specific surface area, hierarchical pore structure and excellent signal response to AA, DA and UA. The oxidation potentials are well separated at around 0.15, 0.34 and 0.46 V for AA, DA and UA respectively. The determination limits for AA, DA and UA are 3.7 μM, 0.07 μM and 0.43 μM, respectively. The sensor was applied to tracking the three analytes in spiked serum samples with recovery 95.1~105.5% and relation standard deviations of less than 5%. [ABSTRACT FROM AUTHOR]

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were electrodeposited by cyclic voltammetry on a glassy carbon electrode (GCE) in aqueous solution. Three kinds of supporting electrolytes were used, viz. graphene oxide (GO), phosphate buffered saline (PBS), and GO in PBS, respectively. The surface morphology of the modified electrodes was characterized by scanning electron microscopy. The electrochemical performance of the modified electrodes was investigated by cyclic voltammetry and electrochemical impedance spectroscopy by using the hexacyanoferrate redox system. The results demonstrate that the PEDOT-GO/GCE, which was electropolymerized in aqueous solutions containing EDOT and GO, shows the best electrochemical activities compared with other modified electrodes. The electrochemical behaviors of ascorbic acid (AA), dopamine (DA) and uric acid (UA) were investigated by cyclic voltammetry. The PEDOT-GO/GCE exhibits enhanced electrocatalytic activities towards these important biomolecules. Under physiological pH conditions and in the mixed system of AA, DA and UA, the modified GCE exhibits the following figures of merit: (a) a linear voltammetric response in the concentration ranges of 100–1000 μM for AA, 6.0–200 μM for DA, and 40–240 μM for UA; (b) well separated oxidation peaks near 31, 213 and 342 mV (vs. saturated Ag/AgCl) for AA, DA and UA, respectively; and (c) detection of limits (at S/N = 3) of 20, 2.0 and 10 μM. The results demonstrate that GO, based on its relatively large number of anionic sites, can be used as the sole weak electrolyte and charge balance dopant for the preparation of functionally doped conducting polymers by electrodeposition. [ABSTRACT FROM AUTHOR]

An electrochemical sensor is described for the simultaneous voltammetric determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). An indium-tin oxide (ITO) electrode was modified with a hierarchical core−shell metal-organic framework and Ag-doped mesoporous metal-oxide based hybrid nanocomposites on g-C3N4 nanosheets. The morphology, structural and chemical composition of the hybrid nanocomposite was characterized using different analytical methods. The modified ITO showed superior electrocatalytic performance towards the oxidation of AA, DA and UA due to the enhanced surface area, synergistic effects and well-organized porous assembly. Figures of merit, include (a) linear responses from 0.1 to 200 μM, 2.5 to 100 μM and 2.5 to 625 μM; (b) detection limits (at S/N = 3) of 0.02, 0.01 and 0.06 μM, and (c) well separated oxidation peaks near −50, 186 and 390 mV (vs. Ag/AgCl) for simultaneous sensing AA, DA and UA, respectively. The sensor was evaluated by analysing spiked serum samples and gave data with precision, with recoveries of >98%. [ABSTRACT FROM AUTHOR]

A glassy carbon electrode (GCE) was modified with nitrogen-enriched carbon frameworks decorated with palladium nanoparticles (Pd@NCF/GCEs). The modified GCE is shown to be a viable tool for determination of uric acid (UA) and dopamine (DA) in the presence of ascorbic acid (AA). The Pd@NCF was fabricated though one-step pyrolysis and characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and nitrogen-adsorption/desorption analysis. The Pd@NCF/GCE was characterized by differential pulse voltammetry (DPV). Both UA and DA have pronounced oxidation peaks (at 360 mV for UA and 180 mV for DA, all vs. Ag/AgCl) in the presence of AA. Response is linear in the 0.5-100 μM UA concentration range and in the 0.5-230 μM DA concentration range. The detection limits are 76 and 107 nM, respectively (at S/N = 3). This electrode is stable, reproducible and highly selective. It was used for UA and DA determination in spiked serum samples. [ABSTRACT FROM AUTHOR]

This work reports an enzyme-less glutamate sensor based on nickel oxide modified glassy carbon electrode. The nanoparticles of NiO were synthesized by sol-gel method, and showed high electro-catalytic activity towards glutamate oxidation in 0.1 M NaOH solution. The sensor displays a fast response time of < 5 s and a linear dependency of R2 0.997 for glutamate concentration of up to 8 mM at an applied potential of + 0.55 V with a sensitivity of 11 µA mM−1 cm−2 and a detection limit of 272 μM (S/N = 3). The interference studies of NiO/GC electrode showed a significant current response for glutamate in the presence of uric acid and ascorbic acid. Thereby, this simple NiO nanoparticle based sensor can be promising platform for the development of a robust enzymeless glutamate sensor. [ABSTRACT FROM AUTHOR]

A novel electrochemical biosensor for the simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA), guanine (GUA), and adenine (ADE) was fabricated by the electrochemical deposition of Au nanoparticles onto a horizontal-graphene-modified tantalum wire (Au/HG) electrode. The graphene layer was grown using hot-filament chemical vapor deposition and shows high potential as a novel biosensor. The incorporation of Au nanoparticles and graphene was confirmed by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The electrochemical performance of the electrodes was characterized by electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). DPV reveals that AA, DA, UA, GUA, and ADE are detected simultaneously using the Au/HG electrode, exhibiting peaks at − 0.101, 0.112, 0.252, 0.608, and 0.874 V, respectively. In a system containing these five analytes, linear calibration plots for AA, DA, UA, GUA, and ADE were obtained over the 4-600, 0.4-20, 0.6-40, 6-500, and 0.6-40 μM ranges, respectively, with corresponding detection limits of 1.76, 0.02, 0.57, 2.5, and 0.42 μM, respectively. The Au/HG layer shows good electrocatalytic activities toward the redox reactions of AA, DA, UA, GUA, and ADE. This sensing electrode exhibited good selectivities, excellent sensitivities, high stabilities, and low detection limits. [ABSTRACT FROM AUTHOR]

Normetanephrine is a marker for pheochromocytoma, a rare catecholamine-secreting and neuroendocrine tumor, that arises from sympathetic and parasympathetic paraganglia. In this work, a novel carbon/chitosan electrode paste was used for sensitive voltammetric determination of normetanephrine and dopamine in the presence of ascorbic acid and uric acid. The modified electrode has shown an increase in the effective area of up to 68%, well-separated oxidation peaks, and an excellent electrocatalytic activity. The electrochemical response characteristics were investigated by cyclic and differential pulse voltammetry. Interestingly, high sensitivity and selectivity in the linear range of normetanephrine, dopamine, ascorbic acid, and uric acid concentrations were observed. The present method was applied in the urine sample and satisfactory results were obtained showing that this electrode is very suitable in pharmaceutical and clinical preparations. [ABSTRACT FROM AUTHOR]

Abstract: Active electrocatalytic electrode designs are needed for the sensitive and selective detection of a single or multi-active biomolecule among biological components. We report the design of hierarchical NiO catalyst (HNC) for one-step monitoring of bioactive molecules such as ascorbic acid (AA), dopamine (DA), and uric acid (UA). The novel mesostructured geometries, active surface sites, and multi-diffused spaces for easy electron movement through gaps provide highly active electrocatalytic electrode designing surface. Controlled HNC architecture along electrode-design surface domains having double-head branches spread out along both sides of the dipole-like rod may lead to the vital electron transfer and fast response signaling of multi-bioactive molecules in one-shot triggering individually or simultaneously. Electrochemical analyses showed evidence that the proposed electrode design can detect each component up to 0.02 µM. Sensitive detection up to 1.127, 0.02, and 0.978 µM and wide-range responses of 25-800, 2-60, and 10-000 µM for AA, DA, and UA, respectively, were observed. The simultaneous monitoring and selective signaling of AA, DA, and UA in real urine samples in one step under different potentials were realized. Thus, the HNC-modified electrode can monitor and evaluate the coexistence of biomolecules simultaneously in multi-components.Graphical Abstract: The electrochemical oxidation of AA, DA, and UA at the HNC-modified electrode and the corresponding DPV peaks with losing of 2e−/2H+. [ABSTRACT FROM AUTHOR]

A highly sensitive sensor based on Ni nanoparticles/poly (1,2-diaminoanthraquinone) modified electrode was fabricated at glassy carbon (GC) electrode (Ni/PDAAQ@GC ME) using cyclic voltammetry technique. The incorporation of nickel (II) ions nanoparticles (Ni NPs) followed by anodic polarization process was achieved. Surface morphologies of both PDAAQ@GC ME and Ni/PDAAQ@GC MEs were studied by scanning electron microscope. Ni/PDAAQ@GC ME was tested for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) by square wave voltammetry technique. The ME showed excellent electrocatalytic activity toward electrooxidation of these biomolecules in their single, binary and ternary systems in alkaline 0.1 M NaOH solutions. Experiment revealed that the low detection limits (LOD) for AA, DA and UA were 0.11, 0.072 and 1.2 µM in single system, respectively, and 0.069, 0.29 and 0.12 µM in ternary system, respectively. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

Poly( p-aminobenzene sulfonic acid) [poly( p-ABSA)] modified glassy carbon electrode (GCE) was used for the simultaneous determination of ascorbic acid (AA), 3,4-dihydroxyphenylacetic acid (DOPAC) and uric acid (UA). The polymer film was grown on GCE by the cyclic voltammetry method in the potential range from −1.5 to +2.5 V at a scan rate of 50 mV s for 14 cycles in 0.1 M KCl solution containing 5 mM p-ABSA. The anodic peaks for AA, DOPAC and UA at the poly( p-ABSA)/GCE were resolved in phosphate buffer solution (pH 7.0). On the other hand, the electro-oxidation peak current of AA, DOPAC and UA showed linear dynamic range, good stability and sensitivity. The linear range of DOPAC is over four orders of magnitude ( R = 0.998). The detection limit of DOPAC is 2.96 × 10 mol L. The proposed method and electrode have been successfully applied for the determination of DOPAC in urine and blood serum samples and pharmaceutical tablets, demonstrating the stability and reliability of the proposed method and electrode. [ABSTRACT FROM AUTHOR]

The authors describe a disposable non-enzymatic sensor for ascorbic acid (AA) that was obtained by modifying a screen printed electrode (SPE) with Cu(OH) nanorods (NRs). The NRs were synthesized by a wet chemical process which involves sequential addition of NH and NaOH to CuSO solution. NR formation was confirmed by thermogravimetric, spectroscopic, microscopic, and diffraction studies. The Cu(OH) NRs were mixed with carbon ink and printed onto an SPE. Electrochemical detection of AA was carried out at pH 7.4, at a typical voltage as low as 0 mV versus saturated calomel electrode with a scan rate of 100 mV/s, and is assumed to involve the chemical reduction of Cu(II) by AA followed by electrochemical oxidation of Cu(I). The sensor has a linear response in the 0.0125 to 10 mΜ AA concentration range. Response to AA is free from interference by urea, glucose, uric acid, dopamine, metal ions such as Fe, Zn and Ni, NaCl, KCl and ethanol. It was applied to the determination of AA in a vitamin C tablet and in urine. [ABSTRACT FROM AUTHOR]

A novel modified electrode was fabricated by a mixed-valent nickel hexacyanoferrate (NiHCF) and poly 1,5-diaminonaphthalene (PDAN) hybrid at glassy carbon (GC) electrode. The obtained NiHCF/PDAN/GC modified electrode was characterized using cyclic voltammetry (CV) technique and scanning electron microscope (SEM). This electrode showed excellent catalytic properties toward the electrooxidation of ascorbic acid (A.A), dopamine (D.A) and uric acid (U.A) in 0.1 M NaCl solution using CV and square wave voltammetry (SWV) techniques. The NiHCF/PDAN/GC modified electrode exhibits high sensitivity, selectivity and stability making it a suitable sensor for the simultaneous detection of A.A, U.A and D.A in single and ternary mixture solutions. Different analytical parameters such as low detection limit (LOD), low quantification limit, correlation coefficient ( R) and linear dynamic range were reported and discussed. The NiHCF/PDAN/GC modified electrode exhibits linear responses to A.A, D.A and U.A in the range 600-1000, 600-1000 and 600-1000 µM, respectively. The LOD for A.A, D.A and U.A were 0.036, 0.034 and 0.037 µM, respectively. The analytical behavior of this sensor had been evaluated for the detection of A.A and U.A in human serum and urine samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A voltammetric sensor for both the individual and the simultaneous determination of ascorbic acid (AA), uric acid (UA) and folic acid (FA) is described. It is based on a glassy carbon electrode (GCE) that was modified with bentonite (Bnt) that was first functionalized with cysteine (Cys) to which gold nanoparticles were linked. The resulting material (referred to as Au-Cys-Bnt) and the other materials were characterized by UV-vis spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray analysis and electrochemical methods. The XRD peak positions of bentonite and Cys-functionalized bentonite prove the incorporation of Cys into bentonite. The XPS spectrum of Au-Cys-Bnt confirms the interaction of gold nanoparticles with the thiol group of Cys. The modified GCE displays high electrocatalytic activity for the oxidation of AA, UA and FA, typically at 0.19, 0.41, and 0.73 V (vs. SCE), respectively. Differential pulse voltammetric data show a linear response that covers the 1 μM to 25 mM concentration range for AA, the 1 to 200 μM concentration range for UA, and two linear ranges for FA, one from 5 to 100 μM and one from 100 μM to 1.5 mM. The sensor was applied to the determination of AA, UA and FA in (spiked) multi-vitamin syrup, bird serum and milk samples. [ABSTRACT FROM AUTHOR]

A gold bare template modified with self-assembled layers (SAMs) composed of gold nanoparticles and organic S-containing compound: cysteamine and dihydrolipoic acid were prepared. The electrode with SAMs endowed with gold nanoparticles gave a high catalytic effect for dopamine electrooxidation alone and in the presence of biogenic interfering compounds: ascorbic acid and uric acid in solution at pH 7. For this novel sensor, a linear relationship between the current response of dopamine at the potential of peak maximum ( j ) and the concentration of this compound in solution ( c ) was found over the range 0.1 μM to 0.85 mM with the detection limit of 0.023 μM. [ABSTRACT FROM AUTHOR]

This paper describes the development of a simple and efficient nanostructured platform based on multi-walled carbon nanotubes (MWCNT) functionalized with an in situ generated vanillic acid (VA) polymer. It was used as an analytical sensor for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electropolymerization process of VA, performed on MWCNT-modified glassy carbon electrode, produces three redox systems based on quinone/hydroquinone functionality, as observed by cyclic voltammetry. The amperometric sensor has as figures of merit for the simultaneous determination of AA, DA, and UA the following values: for AA, a linear range of 5-120 μM and detection limit of 3.5 μM; for DA, a linear range of 5-120 μM and detection limit of 4.5 μM; and for UA, a linear range of 5-120 μM and a detection limit of 1.5 μM. From the obtained performance, the development of the platform based on MWCNT/poly-VA is justified for the simultaneous determination of AA, DA, and UA. [ABSTRACT FROM AUTHOR]

Porous cuprous oxide nanospheres were deposited on reduced graphene oxide (pCuO NS-rGO) by a solvothermal approach that uses hexadecyltrimethylammonium bromide as the capping agent and L-glutamic acid as the reducing agent. The nanomaterial was characterized by transmission electron microscopy, Raman spectroscopy, thermogravimetry, and electrochemical methods. A glassy carbon electrode was modified with pCuO NS-rGO, and the respective electrode displays a well expressed oxidation peak for dopamine (DA) located at 160 mV (vs. SCE). It also gives a strong peak for uric acid (UA) which is separated from the DA peak by 130 mV (vs. SCE). No signals can be detected for ascorbic acid (AA) in concentrations up to 2.0 mM. The findings are exploited in a method for simultaneous determination of UA and DA. The linear ranges are from 1.0 to 138 μM for UA, and from 0.05 to 109 μM for DA even in the presence of relatively high concentrations of AA. The detection limits are 112 nM for UA and 15 nM for DA (at an S/N ratio of 3). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The authors report that a glassy carbon electrode modified with the [Ni(phen)] complex and single-walled carbon nanotubes represents a useful sensor for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The material was characterized by scanning electron microscopy, and the electrode by cyclic voltammetry and electrochemical impedance spectroscopy. The experiments showed that this electrode responds to AA, DA and UA, best at working potentials of 0.130 V, 0.334 V, 0.486 V (vs. SCE), over the wide linear ranges from 30 to 1546 μM (for AA), 1 to 780 μM (for DA), and 1 to 1407 μM (for UA). The respective detection limits are 12 μM, 1 μM and 0.76 μM at an S/N ratio of 3. The modified electrode was successfully applied to the determination of AA, DA and UA in real samples. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A hierarchical nanoporous PtCu alloy was fabricated by two-step dealloying of a PtCuAl precursor alloy followed by annealing. The new alloy possesses interconnected hierarchical network architecture with bimodal distributions of ligaments and pores. It exhibits high electrochemical activity towards the oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA) at working potentials of 0.32, 0.47 and 0.61 V (vs. a mercury sulfate reference electrode), respectively. The new alloy was placed on a glassy carbon electrode and then displayed a wide linear response to AA, DA, and UA in the concentration ranges from 25 to 800 μM, 4 to 20 μM, and 10 to 70 μM, respectively. The lower detection limits are 17.5 μM, 2.8 µM and 5.7 μM at an S/N ratio of 3. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This paper describes the construction, evaluation, and application of an electrochemical sensor for the determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). Satisfactory results were achieved for the simultaneous determination of DA and UA, it was verified that it is possible to detect AA in the presence of DA, but high concentrations of AA interfere in detection of DA. The sensor was constructed using the layer-by-layer (LbL) technique with the modification of the surface of indium tin oxide coated glass (ITO) substrate with nanostructured films comprising a 3- n-propylpyridinium silsesquioxane polymer (SiPyCl) and nickel(II) tetrasulfophthalocyanine (NiTsPc). Using the square wave voltammetry technique (SWV), the LbL modified electrodes produced at different pHs (pH 2 and 8) were used to determine DA in the presence UA, and the electrochemical responses of the electrodes were compared. It was observed that the electrodes with the highest concentration of monomeric species showed the highest current intensity and the lowest peak potential for the DA and UA analytes in analysis of DA and UA, individually and simultaneously, with peak potential separation of 460 mV versus Ag/AgCl. Applying SWV, a linear dynamic range of 10-99 μmol L and 100-900 μmol L with detection limit of 16.8 μmol L and 58.3 μmol L was obtained for DA and UA, respectively. The method has good selectivity and sensitivity, and it was successfully applied to the simultaneous determination of DA and UA in spiked human urine sample. [ABSTRACT FROM AUTHOR]

We report on a nonenzymatic method for the determination of glucose using an electrode covered with graphene nanosheets (GNs) modified with Pt-Pd nanocubes (PtPdNCs). The latter were prepared on GNs by using N,N-dimethylformamide as a bifunctional solvent for the reduction of both metallic precursors and graphene oxide, and for confining the growth of PtPdNCs on the surface. The modified electrode displays strong and sensitive current response to the electrooxidation of glucose, notably at pH 7. The sensitivities increase in the order of PtPdNCs< PtPdNCs< PtPdNCs< PtPdNCs< PtPdNCs. At an applied potential of +0.25 V, the electrode responds linearly ( R = 0.9987) to glucose in up to 24.5 mM concentration, with a sensitivity of 1.4 μA cm M. The sensor is not poisoned by chloride, and not interfered by ascorbic acid, uric acid and p-acetamidophenol under normal physiological conditions. The modified electrode also displays a wide linear range, good stability and fast amperometric response, thereby indicating the potential of the bimetallic materials for nonenzymatic sensing of glucose. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A selective determination of levodopa (LD) in the presence of ascorbic acid (AA) and uric acid (UA) has been investigated at a glassy carbon electrode modified with reduced graphene oxide (rGO). The graphene oxide was synthesized chemically by Hummers method and characterized by energy-filtered transmission electron microscopy (EF-TEM). The reduced graphene oxide modified glassy carbon electrode (rGO/GCE) showed excellent electrochemical performance in the simultaneous electrochemical detection of LD, AA, and UA due to the unique properties of graphene, such as large surface area, facile electronic transport and high electrocatalytic activity. The redox characteristics of rGO/GCE were investigated with cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Well-resolved oxidation peak potentials, corresponding to the oxidation of AA, LD, and UA, were observed from their mixture solution at 0.098, 0.285, and 0.423 V, respectively. The rGO/GCE showed that LD can be detected without the interference of AA and UA. Under the optimized conditions, the oxidation peak current of LD is linear with the concentration of LD from 2.0 to 100 μM with the detection limit of 1.13 μM (S/N = 3). The present electrode system was also successfully applied to direct determination of LD in commercially available tablets and urine samples. [ABSTRACT FROM AUTHOR]

We have developed an enzymatic glucose biosensor that is based on a flat platinum electrode which was covered with electrophoretically deposited rhodium (Rh) nanoparticles and then sintered to form a large surface area. The biosensor was obtained by depositing glucose oxidase (GOx), Nafion, and gold nanoparticles (AuNPs) on the Rh electrode. The electrical potential and the fractions of Nafion and GOx were optimized. The resulting biosensor has a very high sensitivity (68.1 μA mM cm) and good linearity in the range from 0.05 to 15 mM ( r = 0.989). The limit of detection is as low as 0.03 mM (at an SNR of 3). The glucose biosensor also is quite selective and is not interfered by electroactive substances including ascorbic acid, uric acid and acetaminophen. The lifespan is up to 90 days. It was applied to the determination of glucose in blood serum, and the results compare very well with those obtained with a clinical analyzer. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We have fabricated, in a single step, carbon ceramic electrodes modified with a poly(acridine orange) film containing reduced graphene oxide. They display electrocatalytic activity to ascorbic acid (AA) and uric acid (UA) at pH 4.5. The anodic peak potentials of AA and UA are separated by 276 mV so that they can be well resolved in cyclic voltammetry. UA and AA were simultaneously determined in a mixture at working potentials of 170 and 400 mV, respectively. Under optimized conditions, the calibration curves for AA and UA cover the 0.8-5,000 μM and 0.6-900 μM concentration range, respectively, while detection limits are 0.3 μM and 0.2 μM. The electrode was applied to determine AA and UA in urine samples. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Composites of Nafion, COOH-capped CdSe, and self-doped polyaniline (SPAN) were used to prepare novel chemical modified glassy carbon electrodes (Nafion/CdSe/SPAN/GCE). The electrocatalytic activities of the modified GCE to the redox reactions of dopamine (DA), uric acid (UA), and ascorbic acid (AA) were investigated by cyclic voltammetry (CV). CV curves revealed that the electrocatalytic activities of Nafion/CdSe/SPAN/GCE to oxidations of the analytes in solution of pH 7 were in the order of DA > UA > AA. This order was consistent with the strong-to-low extent of interactions between the modified GCE and the analytes. These interactions were consistent with the observations that the oxidation rate of DA followed a diffusion-controlled process whereas that of UA followed a surface adsorption-controlled process. The composites of casting at higher pH levels were found to exhibit better CdSe and SPAN dispersions in films and higher electrocatalytic activities. CdSe and SPAN exhibited insignificant synergistic effects on the oxidations of DA when cast from Nafion solutions of both low and high pHs whereas CdSe and SPAN exhibited much synergistic effects on the oxidations of UA when cast from the Nafion solution of high pH at 12. [ABSTRACT FROM AUTHOR]

This paper describes the simultaneous determination of ascorbic acid (AA), norepinephrine (NE) and uric acid (UA) using a graphene modified glassy carbon electrode (GME) in pH 4.0 phosphate buffer solution. The electrochemical behaviors of AA, NE and UA at a bare glassy carbon electrode (GCE) and the GME were studied by cyclic voltammetry. Bare GCE failed to resolve the voltammetric signals of AA, NE and UA in a mixture, whereas the GME not only resolved their voltammetric signals, but also exhibited excellent electrocatalytic activity towards their electrochemical oxidation. The oxidation peak currents of AA, NE and UA were linearly proportional to their concentrations over the range of 1.0.0-1000.0, 0.6-45.0 and 1.0-100.0 μM, respectively, and their detection limits were 1.2, 0.10 and 0.60 μM, respectively, The modified electrode is of excellent sensitivity and selectivity, and has been satisfactorily used for the simultaneous determination of AA, NE and UA in their ternary mixture. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper describes a rapid and reliable method for dopamine (DA), ascorbic acid (AA), and uric acid (UA) determination in human urine using a cathodically pretreated poly(1-aminoanthraquinone) (PAAQ)-modified electrode. By applying a simple cathodic pretreatment to the PAAQ electrode well-defined voltammetric peaks for AA, DA, and UA were obtained. The pretreated PAAQ showed good selectivity, sensitivity, and repeatability for measuring AA, DA, and UA with detection limits of 2.50 × 10, 3.05 × 10, and 1.15 × 10 M, respectively. The practical applicability of the modified electrode is illustrated by selective measurements of AA and UA in human urine without any preliminary treatment. Recovery values between 94.8 and 102 % for AA and between 77.8 and 100 % for UA were obtained with a relative standard deviation of 2.74 and 2.98 %, respectively. [ABSTRACT FROM AUTHOR]

Poly( N-isopropylacrylamide)(PNIPAAm) with a lower critical solution temperature of about 32 °C was used as matrix to prepare temperature responsive carbon nanotubes (CNT) and functionalized CNT (fCNT) composites to modify glassy carbon electrode (GCE) as working electrode for electrochemical selective detection of dopamine, uric acid, and ascorbic acid. The GCE modification temperature (25 and 37 °C, denoted as 25f and 37f), working temperature (25 and 37 °C, denoted as 25aq and 37aq), and the type of CNT (CNT and fCNT) were found to significantly affect the electrocatalytic activity of the composites toward redox reactions of Fe(CN) as a probe and the selective detection ability for the three analytes. The fCNT/PNIPAAm composite with the 25f-37aq temperature combination exhibited strong electrocatalytic activity and highly selective detection ability for the three analytes. In contrast, the same composite with the other three combinations (25f-25aq, 37f-25aq, and 37f-37aq) and the CNT/PNIPAAm composite with all four combinations exhibited insignificant electrocatalytic activity and no selective detection ability. [ABSTRACT FROM AUTHOR]

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 SiO/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 SiO/MPTS/Au electrode was proven to be an efficient tool in the simultaneous determination of ascorbic acid (HAA), 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 HAA, DA, and UA was observed. The separations of the anodic peak potentials between DA/HAA and UA/HAA were 310 and 442 mV, respectively. The results obtained show that the SiO/MPTS/Au electrode can be used in the simultaneous determination of HAA, DA, and UA. [ABSTRACT FROM AUTHOR]

A non-enzymatic amperometric sensor is developed based on the graphite electrode modified with functionalized graphene for the determination of β, d (+)-glucose. Cyclic voltammetry and electrochemical impedance spectroscopy techniques are used to study the behavior. Atomic force microscopy was used to study the surface topography of the working electrode before and after its modification. The sensor enabled the direct electrochemical oxidation of β, d (+)-glucose in alkaline medium and responded linearly to the analyte over the range from 0.5 × 10 to 7.5 × 10 M with a limit of detection of 10 μM. The sensor is found to exhibit a better sensitivity of 28.4 μA mM cm, good stability, and shelf life. The sensitivity of the sensor to β, d (+)-glucose was not affected by the commonly co-existing interfering substances such as l-ascorbic acid, dopamine, uric acid, and acetaminophen. [ABSTRACT FROM AUTHOR]