Electrooxidation Of Dopamine Research Articles

A Cerium Hexacyanoferrate (III) Nanoparticle‐modified Carbon Paste Electrode: Voltammetric Characterization and Behavior in the Presence of Dopamine

AbstractThis study describes a fast and simple methodology for the preparation of Cerium (III) Hexacyanoferrate (II) (CeHCF) nanoparticles (NPs). The NPs were characterized by fourier transform infrared (FTIR), x‐ray diffraction (XRD), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The CeHCF cyclic voltammogram indicate a well‐defined redox pair assigned as Fe2+/Fe3+ in the presence of cerium (III), with a formal potential of Eθ′=0.29 V (v=100 mV s−1, KNO3; 1.0 mol/L, pH 7.0). The carbon paste electrode modified with CeHCF (CeHCF‐CPE) was applied to the catalytic electrooxidation of dopamine applying Differential Pulse Voltammetry (DPV). DPV showed linear response at two concentration ranges, from 9.0×10−7 to 8.0×10−6 and 9.0×10−6 to 1.0×10−4 mol/L, with an LOD of 1.9×10−7 and 1.0×10−5 mol/L, respectively. The CeHCF‐CPE exhibited selectivity against substances commonly found in biological samples, with redox potentials close to that of dopamine, such as urea and ascorbic acid (AA). Subsequently the CeHCF‐CPE was successfully applied to the detection of dopamine in simulated urine samples, with recovery percentages ranging between 99 and 103%.

Morphology-dependent MnO2/nitrogen-doped graphene nanocomposites for simultaneous detection of trace dopamine and uric acid.

Four nanostructured MnO2 with various controllable morphologies, including nanowires, nanorods, nanotubes and nanoflowers were synthesized, and then further composited with nitrogen-doped graphene (NG) with the assistance of ultrasonication. The surface morphologies, phase structures, and electrochemical performances of the proposed MnO2/NG nanohybrids were investigated by various techniques, and their catalytic activities on the electrooxidation of dopamine (DA) and uric acid (UA) were compared systematically. The sensing performances were found to be highly correlated with their morphologies. Among these morphologies, the nanoflower-like MnO2, composited with NG, displayed the most sensitive response signals for DA and UA. The boosted electrocatalytic activity was ascribed to the unique porous structure, large electroactive area, and low charge transfer resistance (Rct), which facilitated the electron transfer between electrode and analytes. Two linear response ranges (0.1μM-10μM and 10μM-100μM) were accompanied with very low detection limits of 34nM and 39nM for DA and UA, respectively. Moreover, the successful application of the MnO2NFs/NG composites for the simultaneous detection of DA and UA in human serum was realized using second-derivative linear sweep voltammetry (SDLSV). These findings give valuable insights for understanding the morphology-dependent sensing properties of MnO2 based nanomaterials, which is conducive to the rapid development of ubiquitous MnO2-based electrochemical sensors.

Facile synthesis of hierarchical microsphere-like layered double hydroxide for non-enzymatic selective detection of dopamine

Layered double hydroxides (LDHs) are layered materials belonging to anionic clay family, have attracted attention for surface modification of electrodes for the electrochemical applications. Herein, we synthesized stable microsphere-like hierarchical structures of Mg–Al LDH using one-step surfactant free solvothermal method. The XRD pattern confirms the hydrotalcite-like LDH structure. The SEM images showed the 3D microspheres with flower-like structures with highly porous features visible at higher magnification. TEM images also confirmed the network of nanosheets interconnected with each other. Electrochemical studies showed that the microsphere like LDH material modified electrode exhibited enhanced electrochemical performance towards electrooxidation of dopamine with a linear response range from 2–100 μM and high sensitivity with low detection limit of 0.216 μM. The better results are due to its peculiar hierarchical structures with more exposure of active sites and fast electron transfer pathway. Therefore, this work provides a simple and feasible method for synthesizing Mg–Al LDH structures as a material for modifying electrodes for the electrochemical sensing application

Activated charcoal as a capture material for dopamine, paracetamol and salicylic acid in human blood and pharmaceutical formulations

In this work, the authors present an activated carbon modified carbon paste electrode that has superior electrocatalytic activity for the electro-oxidation of dopamine (DA), paracetamol (PCT) and salicylic acid (SA). This excellent electrochemical performance was referred to the porous structure of activated carbon, surface functional groups existing in activated carbon surface and the electron donor–acceptor complex mechanism assumes that the aromatic rings of the drugs act as the electron acceptors. However, the reaction mechanisms of the corresponding electrode were studied in detail in this article. Additionally, under the optimized experimental conditions, DA, SA and PCT exhibit a linear response over the range of 0.1–1000.0 μmol L−1, with the low detection limits of 0.0313 μmol L−1, 0.0282 μmol L−1 and 0.0487 μmol L−1 for DA, PCT and SA, respectively. Furthermore, the AC-CPE showed a high sensitivity, good reproducibility and high stability. The proposed method was applied successfully for the detection of DA, PCT and SA in human blood and pharmaceutical formulations with satisfactory recovery.

Nanoporous gold-based dopamine sensor with sensitivity boosted by interferant ascorbic acid

Tuning electrochemical reactivity of nanoporous gold (NPG) by controlling its fabrication parameters is a convenient strategy to realize a selective electroanalytical platform for dopamine (DA), whose detection in real biological samples is hampered by the presence of structurally similar ascorbic acid (AA) typically in 1000-fold excess. Accordingly, a simple strategy was devised to overcome such a problem by exploiting the electrocatalytic properties associated with higher surface energy (220), (200) and (311) Au planes, which are formed in larger amounts as a function of the thickness of the NPG films prepared by an electrodeposition method. Such selectivity in DA electrooxidation could only be retained at thicker NPG films and this was attributed to the higher density of reactive electrocatalytic sites, which enhance the rate of the electron transfer reaction associated to the AA anodic process. Such proposition was confirmed by a comprehensive electron transfer kinetics study by Scanning Electrochemical Microscopy. The current response due to DA oxidation was enhanced by the follow-up chemical reaction between dopamine-o-quinone (the oxidation product of DA) and AA present in large excess, converting a potential interferant into a partner. In this way, detection limit as low as 60 nmol L−1 allied to sensitivity as high as 6.7 μA/μmol L−1 were achieved under up to 10000 times excess of that interferant, demonstrating the high potentiality of such NPG3 modified electrode as a sensor for analyses of DA in real biological samples.

Correlative Voltammetric Microscopy: Structure-Activity Relationships in the Microscopic Electrochemical Behavior of Screen Printed Carbon Electrodes.

Screen-printed carbon electrodes (SPCEs) are widely used for electrochemical sensors. However, little is known about their electrochemical behavior at the microscopic level. In this work, we use voltammetric scanning electrochemical cell microscopy (SECCM), with dual-channel probes, to determine the microscopic factors governing the electrochemical response of SPCEs. SECCM cyclic voltammetry (CV) measurements are performed directly in hundreds of different locations of SPCEs, with high spatial resolution, using a submicrometer sized probe. Further, the localized electrode activity is spatially correlated to colocated surface structure information from scanning electron microscopy and micro-Raman spectroscopy. This approach is applied to two model electrochemical processes: hexaammineruthenium(III/II) ([Ru(NH3)6]3+/2+), a well-known outer-sphere redox couple, and dopamine (DA), which undergoes a more complex electron-proton coupled electro-oxidation, with complications from adsorption of both DA and side-products. The electrochemical reduction of [Ru(NH3)6]3+ proceeds fairly uniformly across the surface of SPCEs on the submicrometer scale. In contrast, DA electro-oxidation shows a strong dependence on the microstructure of the SPCE. By studying this process at different concentrations of DA, the relative contributions of (i) intrinsic electrode kinetics and (ii) adsorption of DA are elucidated in detail, as a function of local electrode character and surface structure. These studies provide major new insights on the electrochemical activity of SPCEs and further position voltammetric SECCM as a powerful technique for the electrochemical imaging of complex, heterogeneous, and topographically rough electrode surfaces.

The role of pramipexole functionalized MWCNTs to the fabrication of Pd nanoparticles modified GCE for electrochemical detection of dopamine.

Interest in functionalized carbon nanotubes for many applications arises from a variety on the kind of modification atoms or molecules that are attached to it. Dopamine, the feel-good hormone, release by neurons and playing an important role in body systems. Abnormal dopamine levels cause nerve disorders such as Parkinson's disease and schizophrenia. The aim of this study was the design and fabrication of electrochemical sensor based on MWCNTs and Pd nanoparticles for detection and determination of dopamine in biological samples. For this purpose, we report the synthesis of pramipexole-functionalized MWCNTs (pp-MWCNTs) for efficient capture of palladium nanoparticles and fabrication of Pd/pp-MWCNTs nanocomposite. Morphological and structural characteristics of the nanocomposites were characterized using various techniques including field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FT-IR). This newly synthesized nanocomposite may have numerous applications in nanotechnology and sensing. We show that the synthesized nanocomposite reported here will be applicable for modifications of bare glassy carbon electrode (Pd/pp-MWCNTs/GCE) to sense of dopamine electrochemically. Two linear calibrations for dopamine are obtained over ranges of 0.01 to 10μM and 10 to 200μM with a detection limit of 1.4nM. The Pd/pp-MWCNTs/GCE shows high stability and sensitivity, and an acceptable decrease of over-potential for the electrooxidation of dopamine that decreases interference in the analysis. The proposed Pd/pp-MWCNTs nanocomposite can be used as a voltammetric detector for dopamine monitoring in routine real sample analysis. The proposed sensor showed high sensitivity and selectivity in sensing dopamine in biological samples. Graphical abstract Preparation of Pd/pp-MWCNTs/GCE for detection of dopamine.

NdFeO3 as a new electrocatalytic material for the electrochemical monitoring of dopamine

A new electrochemical sensor, based on NdFeO3 nanoparticles as electrocatalytic material, was proposed here for the detection of dopamine (DA). NdFeO3 nanoparticles were first synthesized by a simple thermal treatment method and subsequent annealing at high temperature (700°C). The prepared electrocatalytic material has been characterized in detail by SEM-EDX, XRD, and Raman techniques. Characterization results display its sheet-like morphology, constituted by a porous network of very small orthorhombic NdFeO3 nanoparticles. NdFeO3 electrocatalytic material was then used to modify the working electrode of screen-printed carbon electrodes (SPCEs). Electrochemical tests demonstrated that NdFeO3- modified screen-printed carbon electrode (NdFeO3/SPCE) exhibited a remarkable enhancement of the dopamine electrooxidation, compared to the bare SPCE one. The analytical performance of the developed sensor has been evaluated for the detection of this analyte by means of the square-wave voltammetry (SWV) technique. The modified electrode showed two linear concentration ranges, from 0.5 to 100μM and 150 to 400μM, respectively, a limit of detection (LOD) of 0.27μM (at S/N = 3), and good reproducibility, stability, and selectivity. Additionally, we also report an attempt made to propose the modified sensor for the simultaneous detection of dopamine and uric acid (UA). The procedure was also applied for the determination of dopamine in spiked real samples. So, this paper reports for the first time the use of a modified NdFeO3 screen-printed electrode for developing an electrochemical sensor for the quantification of important biomolecules. Graphical abstract.

Nitrogen-doped 3D hierarchical ordered mesoporous carbon supported palladium electrocatalyst for the simultaneous detection of ascorbic acid, dopamine, and glucose

In the present work, nitrogen-doped three-dimensional (3D) hierarchical ordered mesoporous carbon supported palladium (Pd 20 wt%/N-3D) electrocatalyst was successfully synthesized with the nanocasting method. The as-prepared material was physicochemically and electrochemically characterized. It is found that the as-prepared electrocatalyst exhibits a hierarchically porous structure with interconnected walls, which permits the exposure of more active sites to the respective reactant. Due to its special structure, the electrocatalyst (i) is highly poison-tolerant to the intermediates of glucose electrooxidation reaction, (ii) presents high activity for ascorbic acid electrooxidation, and (iii) exhibits a moderate activity to dopamine electrooxidation reaction. The as-prepared electrocatalyst displayed a relatively good stability behavior. Its sensitivity range is reported to be 0.990 μA μM−1 cm−2, 0.38 μA μM−1 cm−2, and 0.09 μA μM−1 cm−2 for ascorbic acid, dopamine, and glucose, respectively.

Facile Synthesis of MnO2 Nanoflowers/N-Doped Reduced Graphene Oxide Composite and Its Application for Simultaneous Determination of Dopamine and Uric Acid.

This study reports facile synthesis of MnO2 nanoflowers/N-doped reduced graphene oxide (MnO2NFs/NrGO) composite and its application on the simultaneous determination of dopamine (DA) and uric acid (UA). The microstructures, morphologies, and electrochemical performances of MnO2NFs/NrGO were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), respectively. The electrochemical experiments showed that the MnO2NFs/NrGO composites have the largest effective electroactive area and lowest charge transfer resistance. MnO2NFs/NrGO nanocomposites displayed superior catalytic capacity toward the electro-oxidation of DA and UA due to the synergistic effect from MnO2NFs and NrGO. The anodic peak currents of DA and UA increase linearly with their concentrations varying from 0.2 μM to 6.0 μM. However, the anodic peak currents of DA and UA are highly correlated to the Napierian logarithm of their concentrations ranging from 6.0 μM to 100 μM. The detection limits are 0.036 μM and 0.029 μM for DA and UA, respectively. Furthermore, the DA and UA levels of human serum samples were accurately detected by the proposed sensor. Combining with prominent advantages such as facile preparation, good sensitivity, and high selectivity, the proposed MnO2NFs/NrGO nanocomposites have become the most promising candidates for the simultaneous determination of DA and UA from various actual samples.

A Highly Sensitive and Stable Dopamine Sensor Using Shuttle-Like α-Fe2O3 Nanoparticles/Electro-Reduced Graphene Oxide Composites

The development of sensitive and stable electrochemical sensors toward dopamine is highly desirable. Herein, a novel voltammetric sensor was developed for the detection of dopamine using shuttle-like α-Fe2O3 nanoparticles/electro-reduced graphene oxide nanocomposites (S-Fe2O3/ErGO). The surface morphology, microstructure, and chemical composition of S-Fe2O3/ErGO nanocomposites were investigated by SEM, XRD and Raman spectra, respectively. The electrochemical behavior of Fe2O3/ErGO nanocomposite modified glass carbon electrode (S-Fe2O3/ErGO/GCE) was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the results show that S-Fe2O3/ErGO nanocomposites have large electrochemical active area and low charge transfer resistance. The anodic peak current of S-Fe2O3/ErGO/GCE increases 1-fold and 37-fold compared to that of ErGO/GCE and S-Fe2O3/GCE, respectively, suggesting the remarkably synergistic enhancement effect on the electrooxidation of dopamine. The anodic peak current is proportional to the concentration of dopamine over the range of 0.01 μM–2 μM. However, the logarithm of anodic peak current versus logarithm of dopamine concentration is linearly related in the range of 2 μM–80 μM. The detection limit (3σ/s) and sensitivity are estimated to be 1.15 nM and 95.57 μA μM−1 cm−1, respectively. Moreover, S-Fe2O3/ErGO/GCE also showed good anti-interference, reproducibility and stability. Finally, the proposed S-Fe2O3/ErGO/GCE was successfully employed to determinate dopamine in the human serum samples with satisfactory results.

Facile in situ Electrosynthesis and High Electrocatalytic Performance of Interconnected Layered Double Hydroxides/Graphene Hybrids for Dopamine Oxidation: A Comparative Study

AbstractWe are reporting a facile in situ electrodeposition approach to prepare a rational design of M−Al (M: Ni, Co) layered double hydroxide (LDH)/reduced graphene oxide (G) hybrids and its superior electrocatalytic activity towards the electrooxidation of dopamine. Comparatively, the worm like interconnected nano‐chain networks of as‐prepared NiAl‐LDH/G hybrid modified electrode exhibits better performance than the CoAl‐LDH/G hybrid modified electrode. The enhanced electrocatalytic activity is because of its morphological evolution, which is due to its enhanced reduction rate, attachment pathway and incorporation or heterogeneous combination of Al3+ in the bimetallic LDHs/G hybrid. The satisfactory results are obtained for modified electrodes for the real‐time quantitative detection of dopamine in the real injectable medicine as well as human blood serum samples and it has also shown good reproducibility, stability and anti‐interference. This cost‐effective and facile in situ electrodeposition approach will give insights to design high performing hybrid materials and its application to non‐invasive electrochemical sensing which will be useful for daily diagnosis of neurological disorder.

Interference of ascorbic and uric acids on dopamine behavior at graphene composite surface: An electrochemical, spectroscopic and theoretical approach

Graphene materials are widely used in the area of dopamine (DA) detection, but, in spite of the extensive work and the good reported results, the development of commercial graphene-based sensors for DA detection is still challenging. Actually, a lot of studies related to dopamine detection are conducted only for the development of new graphene materials, but the processes and transformations occurred at graphene electrode surface are not considered. In this work, the capacity of a nanocomposite, based on graphene and gold, platinum nanoparticles, to adsorb dopamine and the changes occurred during the DA electrooxidation process were investigated by electrochemistry, Raman spectroscopy and DFT methods. These studies were realized in the absence and the presence of two interfering agents, ascorbic (AA) and uric (UA) acids. Different molecular structures have been found for the species adsorbed on the graphene surface, before and after the electrooxidation process. The DA current density increased in the presence of AA even if neither the diffusion process nor the homogeneous catalysis were involved. The DA detection in the presence of UA appears to be influenced by larger adducts formed at the graphene surface. The DQ presence on the graphene surface was revealed when the procedure involved an electrochemical treatment with DA free in solution, more than five DPVs measurements and higher levels of DA concentration. The Raman investigations of the graphene-based electrodes indicated that the shifts of D frequency from graphene can be easily correlated with the electronic properties of adducts that have been adsorbed to the graphene surface (red shift for a graphene - electron-rich system interaction and a blue shift for graphene – electron-deficient adduct interaction). These results should be taken into consideration in the DA detection procedures or to the stategies to minimise the electrochemical fouling of DA when the graphene composites are used for electrode preparation.

A voltammetric biosensor based on poly(o-methoxyaniline)-gold nanocomposite modified electrode for the simultaneous determination of dopamine and folic acid

Dopamine (DA) and Folic acid (FA) are co-existing compounds in biological fluids that plays a vital role in central nervous system and human metabolism. DA is an important neurotransmitter in the brain's neural circuits and its diminution often results in Parkinson's disease. Folate is another form of folic acid, which is known as one of the B vitamins. It is utilized as an additive by women during pregnancy in order to prevent the neural tube defects. The present study reports on the fabrication of electrochemical sensor for the simultaneous determination of DA and FA using poly(o-methoxyaniline)-gold (POMA-Au) nanocomposite. The POMA-Au nanocomposite was prepared via insitu chemical oxidative polymerization method and characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The suitability of POMA-Au nanocomposite as a modifier for the electrocatalytic detection of DA and FA in aqueous solution was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) techniques. The fabricated POMA-Au/GCE sensor exhibited sharp and intense peaks towards the electro-oxidation of DA and FA as compared to bare electrode. The sensor exhibited the promising electron mediating behavior with well separated oxidation peaks with a potential difference of about 350.0 mV. The linear calibration plots of DA and FA were obtained from 10.0 to 300.0 μM and 0.5 to 900.0 μM with the detection limits of 0.062 μM and 0.090 μM, respectively. The reliability of this sensor was verified to be precise as well as sensitive for the determination of DA and FA in pharmaceutical samples and human urine samples.

Graphene oxide reinforced core–shell structured Ag@Cu2O with tunable hierarchical morphologies and their morphology–dependent electrocatalytic properties for bio-sensing applications

In this study, a facile solution approach was developed for the synthesis of a series of core–shell structured Ag@Cu2O nanocrystals of various shapes including triangles, spheres, and cubes with well–defined stable heterojunctions. The electrooxidation of dopamine (DA), uric acid (UA), guanine (G), and adenine (A) using these hybrids revealed morphology–dependent sensing properties, with activities and accumulation ability following the order, triangular Ag@Cu2O > spherical Ag@Cu2O > cubic Ag@Cu2O. Further, we constructed a novel graphene oxide (GO) nanosheet–reinforced triangular Ag@Cu2O ternary hetero–nanostructure. Such a hybrid with a three–dimensional interconnected hierarchical architecture is suitable for catalysis, since it not only leads to improved interfacial electron transfer, but also readily exposes the highly catalytic Ag@Cu2O to the reactants. Therefore, more enhanced electrochemical activities were observed for the oxidation of DA, UA, G, and A. This study provides an efficient way to synthesize morphology–controlled Ag@Cu2O heterogeneous catalysts for the fabrication of potential biosensors, and also opens up attractive avenues in the design of multifunctional ternary noble metal–semiconductor–carbon hybrids.

Fabrication of TiO2 Hollow Spheres and its Application in Modification of Carbon Paste Electrode For Simultaneous Determination of Dopamine and Piroxicam in the Presence of Ascorbic acid

In this work we report preparation TiO2 hollow spheres and its application as an electrochemical sensor. Therefore the novel carbon paste electrode modified with TiO2 hollow spheres (TOHS), multi-walled carbon nanotubes (MWCNTs) and poly-glutamic acid (PGA) film (PGA/TOHS/MWCNTs/CPE) was used for simultaneous determination of dopamine (DA) and piroxicam (PRX) in the presence of ascorbic acid (AA). The electro-oxidation of dopamine(DA) and piroxicam (PRX) has been investigated by application of the modified electrode using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) methods. The modified electrode accelerates the electron transfer reactions of DA and PRX. In addition it shows no significant interference of AA as the electroactive coexistent compounds with DA and PRX in biological systems. The fabricated sensor revealed some advantages such as excellent selectivity, good stability and high sensitivity toward DA and PRX determination. Under the optimum conditions the electrode provides a linear response versus DA and PRX concentrations in the range of 0.3–60 and 0.4–80 µM and with a detection limit of 0.2µM and 0.3µM(S/N=3) respectively using the DPV method. The modified electrode was used for determination of DA and PRX in human urine with satisfactory results.

$$\mathrm{NiFe}_{2}\mathrm{O}_{4 }$$ NiFe 2 O 4 nanoparticles-decorated activated carbon nanocomposite based electrochemical sensor for selective detection of dopamine in presence of uric acid and ascorbic acid

We propose an electrochemical sensor using $$\hbox {NiFe}_{2}\hbox {O}_{4}$$ nanoparticles-decorated activated carbon (AC) nanocomposite for selective detection of dopamine (DA) in the presence of uric acid (UA) and ascorbic acid (AA). The nanocomposite was prepared by a simple hydrothermal method and the characterization was done using transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectroscopy. The $$\hbox {NiFe}_{2}\hbox {O}_{4}$$ -AC-modified glassy carbon electrode (GCE) showed excellent electrocatalytic activity towards DA compared to $$\hbox {NiFe}_{2}\hbox {O}_{4}$$ /GCE and AC/GCE. This is attributed to the synergistic action and the large surface area of the nanocomposite. Differential pulse voltammetry (DPV) was employed for the detection of DA wherein the detection limit of $$0.4\,\upmu \hbox {M}$$ along with a linear range of $$5\,\upmu \hbox {M}$$ to $$100\,\upmu \hbox {M}$$ was deduced. The selective detection of DA in presence of AA and UA was demonstrated. The advantages of the present sensor include the ease of preparation of the nanocomposite, low detection limit, remarkable selectivity, good reproducibility and stability. $$\hbox {NiFe}_{2}\hbox {O}{4}$$ -AC nanocomposite was prepared by a simple hydrothermal method. The nanocomposite exhibited enhanced activity towards electro-oxidation of dopamine and excellent selectivity in the presence of uric acid (UA) and ascorbic acid (AA).

Communication—Electrooxidation of Dopamine at CoNP-pAHNSA Modified Electrode: A Sensitive Approach to Its Determination

A voltammetric sensor for the simple and rapid determination of dopamine (DA) has been developed using a glassy carbon electrode modified with cobalt nano/poly (4-amino-3-hyroxy-1-naphthalenesulfonic acid) composite. On square wave voltammetric mode, the modified electrode was found to efficiently catalyse the electrochemical oxidation of DA in 0.1 M PBS (pH 7). Response of DA increased linearly with its concentration in the range 5 × 10−5 M to 5 × 10−7 M with a limit of detection (LOD) 1.75 × 10−8 M. Reliability of the developed sensor in real sample analysis was ascertained successfully by determining DA in artificial blood serum, urine and cerebrospinal fluid (CSF).

P.1.h.046 - A novel method to study behavioral strategy in probabilistic learning in group housed mice

Graphene materials are widely used in the area of dopamine (DA) detection, but, in spite of the extensive work and the good reported results, the development of commercial graphene-based sensors for DA detection is still challenging. Actually, a lot of studies related to dopamine detection are conducted only for the development of new graphene materials, but the processes and transformations occurred at graphene electrode surface are not considered. In this work, the capacity of a nanocomposite, based on graphene and gold, platinum nanoparticles, to adsorb dopamine and the changes occurred during the DA electrooxidation process were investigated by electrochemistry, Raman spectroscopy and DFT methods. These studies were realized in the absence and the presence of two interfering agents, ascorbic (AA) and uric (UA) acids. Different molecular structures have been found for the species adsorbed on the graphene surface, before and after the electrooxidation process. The DA current density increased in the presence of AA even if neither the diffusion process nor the homogeneous catalysis were involved. The DA detection in the presence of UA appears to be influenced by larger adducts formed at the graphene surface. The DQ presence on the graphene surface was revealed when the procedure involved an electrochemical treatment with DA free in solution, more than five DPVs measurements and higher levels of DA concentration. The Raman investigations of the graphene-based electrodes indicated that the shifts of D frequency from graphene can be easily correlated with the electronic properties of adducts that have been adsorbed to the graphene surface (red shift for a graphene - electron-rich system interaction and a blue shift for graphene – electron-deficient adduct interaction). These results should be taken into consideration in the DA detection procedures or to the stategies to minimise the electrochemical fouling of DA when the graphene composites are used for electrode preparation.

A descrição matemática da eletrooxidação de dopamina, acompanhada por sua eletropolimerização

An interesting case for dopamine electrooxidation, in which either a monomer, or a polymer may be oxidized to the correspondent quinonic form, has been investigated from the theoretical point of view. The analysis o the correspondent mathematical model has shown that in this system the steady-state is easy to maintain stable, despite of the more narrow extension of the topological zone, correspondent to this stability. Yet the oscillatory and monotonic instabilities may be more probable in this cast, than in the similar ones.