Novel nanostructure-based electrochemical sensor for simultaneous determination of dopamine and acetaminophen

A carbon-paste electrode modified with a novel molybdenum (VI) complex and carbon nanotubes have been applied to the electrocatalytic oxidation of dopamine (DA) which reduced the overpotential by about 125 mV with obviously increase the current response. Due to its strong electrocatalytic activity towards DA, the modified carbon-paste electrode can resolve the overlapped voltammetric waves of DA and acetaminophen (AC) into two well-defined voltammetric peaks with peak-to-peak separation in potentials of about 230 mV. This property allows to selective determination of DA in the presence of AC. The transfer coefficient (a) for the electrocatalytic oxidation of DA and diffusion coefficient of this substance under the experimental conditions were also investigated. In phosphate buffer solution of pH 7.0, the oxidation current increased linearly with two concentration intervals of DA, one is 0.1 to 40.0 μM and, the other is 40.0 to 800.0 μM. The detection limit (3σ) obtained by DPV was 76.0 nM. The proposed method was successfully applied to the determination of DA, and AC in some commercial pharmaceutical samples.     

Carbon-Pt nanoparticles modified TiO2 nanotubes for simultaneous detection of dopamine and uric acid

The present work describes sensing application of modified TiO2 nanotubes having carbon-Pt nanoparticles for simultaneous detection of dopamine and uric acid. The TiO2 nanotubes electrode was prepared using anodizing method, followed by electrodeposition of Pt nanoparticles onto the tubes. Carbon was deposited by decomposition of polyethylene glycol in a tube furnace to improve the conductivity. The C-Pt-TiO2 nanotubes modified electrode was characterized by cyclic voltammetry and differential pulse voltammetry methods. The modified electrode displayed high sensitivity towards the oxidation of dopamine and uric acid in a phosphate buffer solution (pH 7.00). The electro-oxidation currents of dopamine and uric acid were linearly related to the concentration over a wide range of 3.5 x 10(-8) M to 1 x 10(-5) M and 1 x 10(-7) M to 3 x 10(-5) M respectively. The limit of detection was determined as 2 x 10(-10) M for dopamine at signal-to-noise ratio of 3. The interference of uric acid was also investigated. Electro-oxidation currents of dopamine in the presence of fix amount of uric acid represented a linear behaviour towards successive addition of dopamine in range of 1 x 10(-7) M to 1 x 10(-5) M. Furthermore, in a solution containing dopamine, uric acid and ascorbic acid the overlapped oxidation peaks of dopamine and ascorbic acid could be easily separated by using C-Pt-TiO2 nanotubes modified electrode.     

An electrochemical sensor based on Pt/g-C3N4/polyaniline nanocomposite for detection of Hg2+

The synthesis of Pt/g-C₃N₄/polyaniline nanocomposites (Pt/g-C₃N₄/PAn NCs) via the direct reduction of Pt (II) in the presence of L-cysteine as the reducing agent is presented in this study. X-ray diffraction analysis showed that the Pt cations were reduced to metallic Pt in the presence of L-cysteine. Field emission scanning electron microscope images confirmed a low agglomeration of metallic Pt when synthesized in the presence of g-C₃N₄. Electrochemical impedance spectroscopy results showed that the low conductivity of g-C₃N₄ is compensated with the presence of polyaniline (PAn). A glassy carbon electrode modified with the Pt/g-C₃N₄/PAn NCs showed high selectivity and sensitivity for the detection of Hg²⁺. The presence of active sites in the g-C₃N₄ and PAn enhanced the adsorption of Hg²⁺. The voltammetric response was linear in the concentration range of 1–500 nM Hg²⁺, with the detection limit of 0.014 nM (at S/N = 3).     

A facile sonochemical approach based on graphene carbon nitride doped silver molybdate immobilized nafion for selective and sensitive electrochemical detection of chromium (VI) in real sample

The hexavalent Chromium (Chromium (VI) (or) Cr⁶⁺) is considered as the most toxic element that directly affects the environment and the human cycle adversely. Therefore, in the present study we proposed a sensitive and selective electrochemical sensor for the detection of Cr⁶⁺ in various water samples using graphene carbon nitride decorated with silver molybdate immobilized with nafion (g-C₃N₄/AgM/Nf) modified glassy carbon electrode (GCE). The nanocomposite was synthesized by sonochemical method and characterized by various analytical and spectroscopic techniques. The g-C₃N₄/AgM/Nf/GCE was exceptional and showed massive electrocatalytic change via the appearance of peaks in amperometric i-t technique. Cr⁶⁺ has a reduction peak appearing at 0.1–0.7 μM, with a low limit of detection of 0.0016 μM, and sensitivity of 65.8 µAµM⁻¹cm⁻². The g-C₃N₄/AgM/Nf/GCE sensor for Cr⁶⁺ exhibited a good selectivity, stability, sensitivity, and reproducibility, which certified that the g-C₃N₄/AgM/Nf/GCE is a promising electrode. The electrochemical sensing method also accessed for the recognition of Cr⁶⁺ in different water samples and showed good feasibility with superior recovery.     

A novel preparation of water-dispersed graphene and their application to electrochemical detection of dopamine

In the paper, water-dispersed graphene-GQDs composites were prepared by electrochemical exfoliation under alternating voltage combining ultrasonic treatment. The effects of alternating voltage, alternating frequency and the distance between electrodes were carefully explored. The results showed that the quality of composites prepared by alternating voltage was higher than that by direct voltage. The existence of graphene quantum dots (GQDs) hindered the agglomeration of graphene and facilitated dispersion of graphene in water. The sensor based on the obtained graphene-GQDs composites was used to detect dopamine (DA). The electrochemical investigation showed that the sensor had good selectivity and wide linear ranges for the detection of DA (0.1–100 µM). The detection limit could be down to 3 × 10^?8 M (S/N = 3) with a sensitivity of 14.25 µA µM^?1 cm^?2.     

Impedimetric biosensor based on magnetic nanoparticles for electrochemical detection of dopamine

One of the difficulties which limit the use of electrochemical sensors for detection of dopamine is the interference from ascorbic acid. We have sought to address this problem through the synthesis and characterization of a suitable electrode material based on magnetic nanoparticles. The interference from the ascorbic acid was overcome by fabricating a negatively charged electrode surface using PEGylated arginine functionalized magnetic nanoparticles (PA-MNPs). The nanoparticles were characterized by various techniques viz., X-ray diffraction, FT-Infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometer. The electrochemical behavior of the proposed sensor was investigated by cyclic voltammetry and the sensor showed high sensitivity and selectivity for dopamine. The response mechanism of the modified electrode is based on the interaction between the negatively charged electrode and the positively charged dopamine. Under optimized conditions, linear calibration plots were obtained for amperometric detection of dopamine (DA) over the concentration range of 1–9 mM dopamine, with a linear correlation coefficient of 0.9836, sensitivity of 121 μA/mM and a detection limit of 7.25 μM. Electrochemical impedance spectroscopy (EIS) has been used to study the interface properties of modified electrodes. The value of the polarization resistance (R_p) increases linearly with dopamine concentration in the range of 10 μM to 1 mM and the limit of detection (LOD) was calculated to be 14.1 μM. High sensitivity and selectivity, micromolar detection limit, high reproducibility, along with ease of preparation of the electrode surface make this system suitable for the determination of DA in pharmaceutical and clinical preparations.     

Effect of processable polyindole and nanostructured domain on the selective sensing of dopamine

The effect of carboxylic acid functionality present in polymer backbone is reported on electrochemical sensing of dopamine (DA). The electropolymerized conducting polymers made from carboxylic acid substituted indole at positions − 5 and − 6 are found processable in aqueous medium and are compatible with suitable additives/precursors for fabricating polymer modified electrodes (PMEs). The modified electrodes are fabricated following two methods, i.e.: (1) the processable polymers are cast over glassy carbon electrode (GCE) using Nafion® followed by chemical modification using hydrophobic organic redox mediators and (2) the processable polymers are encapsulated within organically modified silicate (Ormosil) matrix along with the hydrophilic redox mediator followed by incorporation of silver and gold nanoparticles. The electrochemical performances of these modified electrodes show selective sensing of DA with major findings: (i) both polymers introduced selectivity in electrochemical sensing of DA with analogous sensitivity, (ii) sensitivity is enhanced when hydrophobic organic redox mediators are coupled with modified electrode matrix involving Nafion®, (iii) the polymers are suitable for encapsulation within ormosil matrix thus introducing nanostructured network for further improvement in sensitivity of DA analysis, (iv) the presence of gold and silver nanoparticles within ormosil matrix along with polymers caused > 100 fold increase in sensitivity of DA sensing with lowest detection limit to the order of 100 nM.     

Microfabricated electrophoresis chips for simultaneous bioassays of glucose, uric acid, ascorbic acid, and acetaminophen

A micromachined capillary electrophoresis chip is described for simultaneous measurements of glucose, ascorbic acid, acetaminophen, and uric acid. Fluid control is used to mix the sample and enzyme glucose oxidase (GOx). The enzymatic reaction, a catalyzed aerobic oxidation of glucose to gluconic acid and hydrogen peroxide, occurs along the separation channel. The enzymatically liberated neutral peroxide species is separated electrophoretically from the anionic uric and ascorbic acids in the separation/reaction channel. The three oxidizable species are detected at the downstream gold-coated thick-film amperometric detector at different migration times. Glucose can be detected within less than 100 s, and detection of all electroactive constituents is carried out within 4 min. Measurements of glucose in the presence of acetaminophen, a neutral compound, are accomplished by comparing the responses in the presence and absence of GOx in the running buffer. The reproducibility of the on-chip glucose measurements is improved greatly by using uric acid as an internal standard. Factors influencing the performance, including the GOx concentration, field strength, and detection potential, are optimized. Such coupling of enzymatic assays with electrophoretic separations on a microchip platform holds great promise for rapid testing of metabolites (such as glucose or lactate), as well as for the introduction of high-speed clinical microanalyzers based on multichannel chips.     

Development of two-dimensional titanium tin carbide (Ti2SnC) plates based on the electronic structure investigation

Titanium tin carbide (Ti₂SnC) is a novel layered ternary compound. The ab initio calculations on the electronic structure and bonding properties indicated that Ti₂SnC exhibit anisotropy of chemical bonding and properties. The electrical conductivity parallel to the basal plane is metallic and is much higher than that in c-axis. Thus Ti₂SnC material in two-dimensional quasi-infinite form with the sheet surface parallel to the basal plane will show superior properties and have diverse device applications. Based on the theoretical predicted anisotropic electronic structure and properties, two-dimensional Ti₂SnC plates were synthesized through a solid–liquid reaction process utilizing elemental Ti, Sn and C as starting materials. X-ray diffraction and scanning electron microscopy demonstrated that the morphology of the as-prepared plates were two-dimensional sheets. And the sheet surface was parallel to the (001) plane of Ti₂SnC. Received: 4 April 2000 / Reviewed and accepted: 1 July 2000     

Highly selective and sensitive voltammetric sensor based on modified multiwall carbon nanotube paste electrode for simultaneous determination of ascorbic acid,acetaminophen and tryptophan

A carbon-paste electrode modified with multiwall carbon nanotubes (MWCNTs) was used for the sensitive and selective voltammetric determination of ascorbic acid (AA) in the presence of 3,4-dihydroxycinnamic acid (3,4-DHCA) as mediator. The mediated oxidation of AA at the modified electrode was investigated by cyclic voltammetry (CV), chronoamperommetry and electrochemical impedance spectroscopy (EIS). Also, the values of catalytic rate constant (k), and diffusion coefficient (D) for AA were calculated. Using square wave voltammetry (SWV), a highly selective and simultaneous determination of AA, acetaminophen (AC) and tryptophan (Trp) has been explored at the modified electrode. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of AA, AC and Trp into three well-defined voltammetric peaks. In the mixture containing AA, AC and Trp, the three compounds can well separate from each other with potential differences of 200, 330 and 530 mV between AA and AC, AC and Trp and AA and Trp, respectively, which was large enough to determine AA, AC and Trp individually and simultaneously.     

Hydrothermal synthesis of ZnO flower-reduced graphene oxide composite for electrochemical determination of ascorbic acid

In this work, reduced graphene oxide coated zinc oxide flower (ZnO–RGO) nanocomposite has been prepared via a simple one-pot hydrothermal synthesis method. The morphology and properties of the proposed ZnO–RGO were characterized using SEM, Raman and UV–VIS spectroscopy. Then, an ascorbic acid (AA) electrochemical sensor was prepared based on a glassy carbon electrode (GCE) modified with the ZnO–RGO nanocomposite. An advanced performance was recorded on the ZnO–RGO/GCE compared with that of the bare GCE, ZnO/GCE, and RGO/GCE. The proposed electrochemical sensor exhibited a wide linear detection from 5 μM to 2 mM with a low detection limit of 1.2 μM. Further, the proposed AA electrochemical sensor showed a good repeatability, reproducibility and stability.     

Multi-walled carbon nanotube modified carbon paste electrode as an electrochemical sensor for the determination of epinephrine in the presence of ascorbic acid and uric acid

A biocompatible electrochemical sensor for selective detection of epinephrine (EP) in the presence of 1000-fold excess of ascorbic acid (AA) and uric acid (UA) was fabricated by modifying the carbon paste electrode (CPE) with multi-walled carbon nanotubes (MWCNTs) using a casting method. The electro-catalytic activity of the modified electrode for the oxidation of EP was investigated. The current sensitivity of EP was enhanced to about five times upon modification. A very minimum amount of modifier was used for modification. The voltammetric response of EP was well resolved from the responses of AA and UA. The electrochemical impedance spectroscopic (EIS) studies reveal the least charge transfer resistance for the modified electrode. The AA peak that is completely resolved from that of EP at higher concentrations of AA and the inability of the sensor to give an electrochemical response for AA below a concentration of 3.0 × 10^? 4 M makes it a unique electrochemical sensor for the detection of EP which is 100% free from the interference of AA. Two linear dynamic ranges of 1.0 × 10^? 4–1.0 × 10^? 5 and 1.0 × 10^? 5–5.0 × 10^? 7 M with a detection limit of 2.9 × 10^? 8 M were observed for EP at modified electrode. The practical utility of this modified electrode was demonstrated by detecting EP in spiked human blood serum and EP injection. The modified electrode is highly reproducible and stable with anti fouling effects.     

Sensitive and selective imprinted electrochemical sensor for p-nitrophenol based on ZnO nanoparticles/carbon nanotubes doped chitosan film

A sensitive and selective molecularly imprinted electrochemical sensor for p-nitrophenol detection has been developed based on ZnO nanoparticles/multiwall carbon nanotubes (MWNTs)-chitosan (CTS) nanocomposite. This nanocomposite was dripped onto an indium tin oxide electrode and then imprinted sol-gel solution was electrodeposited onto the modified electrode to construct the proposed sensor. The morphologies and electrochemical behaviors of the imprinted sensor were characterized by scanning electron microscope, X-ray diffraction, electrochemical impedance spectroscopy, square wave voltammetry and cyclic voltammetry. The imprinted sensor displayed excellent selectivity towards the target molecule p-nitrophenol. Meanwhile, the introduced nanocomposite increased surface area and active sites for electron transfer, thus remarkably enhancing the sensitivity of the imprinted sensor. Under optimal conditions, the peak current was linear to p-nitrophenol concentration ranging from 1.0 × 10^− 8 to 2.0 × 10^− 4 mol·L^− 1 with a detection limits of 1.0 × 10^− 9 mol·L^− 1 (S/N = 3). This proposed sensor was applied to the detection of p-nitrophenol in various water samples successfully.     

Fabrication and characterization of platinum black and mesoporous platinum electrodes for in-vivo and continuously monitoring electrochemical sensor applications

Most electrochemical biosensors are disposable due to enzymes that are living creatures. Thus, these are limited to use in in-vivo and continuously monitoring biosensor system applications. The mesoporous (pores with a size of 2-50 nm) platinum (Pt) structure formed on a rod-shaped Pt microelectrode was reported for developments glucose sensors without any enzymes. In this paper, plane Pt electrode (non-treated), Pt black electrode, and mesoporous Pt electrode are fabricated and characterized on a silicon substrate in order to check their usability as enzymeless sensing electrodes for in-vivo and continuously monitoring electrochemical biosensors integrated with silicon CMOS read-out circuitry. The Pt black electrode with rough surface was fabricated by using an electrodeposition technique with hexachloroplatinic acid hydrate (HCPA) solutions. The proposed mesoporous Pt electrode with approximately 3 nm in pore diameter was fabricated by using an electrodeposition technique with nonionic surfactant octaethylene glycol monohexadecyl ether (C₁₆EO₈) and HCPA. The measured current responses at 40 mM glucose solution of the fabricated plane Pt, Pt black, and mesoporous Pt electrodes are approximately 12.4 nA/mm², 2.1 μA/mm², and 2.8 μA/mm², respectively. These data indicate that the mesoporous Pt electrode is much more sensitive than the other Pt electrodes and has strong potential for enzymeless electrochemical sensor applications.     

Simple and selective extraction process for chromium (VI) in industrial wastewater

A simple and relatively green method has been developed for the determination of chromium based on the extraction of chromium (VI) as its ion-association complex with tetrabutylammoniumiodide (TBAI) in acidic medium. The ion-pair is extracted using isobutylmethylketone (MIBK) as the solvent. The concentration of the extracted chromium (VI) in the organic layer was measured spectrophotometrically at a wavelength maximum of 366 nm and the organic layer was characterized using FT-IR spectroscopy. The influence of various analytical parameters such as pH, aqueous phase volume, equilibration time, interfering ions etc. has been studied in detail. The extracted chromium (VI) was back extracted into the aqueous phase to the non-toxic chromium (III) using ascorbic acid. The calibration graph was linear in the range of 0–2 μg mL⁻¹ chromium (VI) with a relative standard deviation of 2.4%. A detection limit of 0.25 μg in 25 mL aqueous phase volume could be achieved and the validity of the proposed method has been checked by applying it to synthetic mixtures, spiked water sample, electroplating wastewater and certified reference material BCR^®-715.     

Comparison of different methodologies for integration of molecularly imprinted polymer and electrochemical transducer in order to develop a paraoxon voltammetric sensor

In this work a paraoxon voltammetric sensor was introduced. Different methods for integration of molecularly imprinted polymer (MIP) and electrochemical transducer were investigated. Three techniques including MIP particles embedding in the carbon paste (CP) (MIP-CP), coupling of MIP with the glassy carbon electrode (GC) surface by using poly epychloro hydrine (PECH) (MIP/PECH-GC) and MIP/graphite mixture thin layer attachment onto the glassy carbon electrode (MIP/Graphite-PECH-GC) were tested. The prepared electrodes were applied for paraoxon measurement by using a three-step procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of paraoxon. The washing of electrodes, after paraoxon extraction, led to high selectivity of electrode for paraoxon. It was found that MIP-CP electrode had higher response to paraoxon in comparison to other tested electrodes. Besides, the washing process decreased response magnitude of MIP/PECH-GC and MIP/Graphite-PECH-GC but, the response of MIP-CP was not affected considerably by the washing. Parathion was chosen to evaluate the selectivity of MIP based sensors. It was proved that the MIP-CP had better selectivity, wider linear range and lower detection limit in comparison to other tested electrodes. The developed MIP-CP electrode was used as a high selective sensor for paraoxon determination in water and vegetable samples.     

A nonoxidative sensor based on a self-doped polyaniline/carbon nanotube composite for sensitive and selective detection of the neurotransmitter dopamine

Most of the current techniques for detection of dopamine exploit its ease of oxidation. However, the oxidative approaches suffer from a common problem. The products of dopamine oxidation can react with ascorbic acid present in samples and regenerate dopamine again, which severely limits the accuracy of detection. In this paper, we report a nonoxidative approach to electrochemically detect dopamine with high sensitivity and selectivity. This approach takes advantage of the high performance of our newly developed poly(anilineboronic acid)/carbon nanotube composite and the excellent permselectivity of the ion-exchange polymer Nafion. The binding of dopamine to the boronic acid groups of the polymer with large affinity affects the electrochemical properties of the polyaniline backbone, which act as the transduction mechanism of this nonoxidative dopamine sensor. The unique reduction capability and high conductivity of single-stranded DNA functionalized, single-walled carbon nanotubes greatly improved the electrochemical activity of the polymer in physiological buffer, and the large surface area of the carbon nanotubes largely increased the density of the boronic acid receptors. The high sensitivity along with the improved selectivity of this sensing approach is a significant step forward toward molecular diagnosis of Parkinson's disease.     

Zinc oxide-decorated multiwalled carbon nanotubes: a selective electrochemical sensor for the detection of Pb(II) ion in aqueous media

Journal of Materials Science: Materials in Electronics - Multiwalled carbon nanotubes, due to high conductivity, stability, and large specific surface area, have a potential ability to promote...     

Comparative study on the electrochemical synthesis of polyaniline in the presence of mono- and poly(2-acrylamido-2-methyl-1-propanesulfonic) acid

The electrochemical synthesis of polyaniline (PANI) layers was studied in mixed inorganic/organic acid solutions containing poly(2-acrylamido-2-methyl-1-propane-sulfonic) acid (PAMPSA) or the corresponding monomeric acid, AMPSA, under both potentiostatic and potentiodynamic conditions. Electrosynthesis in the presence of a small amount of PAMPSA in the mixed solutions resulted in accelerated polymerization in both growth modes whereas the AMPS anions slowed down the process. Scanning electron microscopic studies indicated a marked influence of the PAMPS and AMPS anions on the surface morphology of potentiostatically synthesized PANI. The electrochemical stability of PANI layers was studied by continuous potentiodynamic cycling. The PANI layers degradation behaviour was found to follow two different patterns depending on the mode of synthesis and not on the anions present in the polymerization solution.     

Simultaneous electrochemical determination of dopamine and tryptophan using a TiO2-graphene/poly(4-aminobenzenesulfonic acid) composite film based platform

TiO₂-graphene/4-aminobenzenesulfonic acid composite film modified glassy carbon electrode (TiO₂-GR/4-ABSA/GCE) was first employed for the simultaneous determination of dopamine (DA) and tryptophan (Trp). TiO₂-GR/4-ABSA/GCE displayed excellent electrochemical catalytic activities toward the redox of DA and Trp. The cathodic peaks potentials of DA and Trp decreased significantly and their cathodic current peaks increased dramatically at TiO₂-GR/4-ABSA/GCE. Differential pulse voltammograms (DPV) was used for the simultaneous determination of DA and Trp in their dualistic mixture. The peak separation between DA and Trp was large up to 177 mV. The calibration curves for simultaneous determination of DA and Trp were obtained in the range of 1–400 μM. The detection limits (S/N = 3) were 0.1 μM and 0.3 μM for DA and Trp, respectively. The present method was applied to the determination of DA and Trp in human serum samples.