Mixture Of Dopamine Research Articles

Electrodeposited reduced graphene oxide-PEDOT:PSS/Nafion hybrid interface for the simultaneous determination of dopamine and serotonin

The electrochemically deposited reduced graphene oxide-PEDOT:PSS/Nafion (rGO-PP/NF) hybrid material has provided a favorable interface for the simultaneous detection of dopamine (DA) and serotonin (5-HT). The rGO-PP/NF onto the Au seed layer of the flexible substrate was simple, and it was followed by the sequential electrophoretic deposition of GO, reduction at the optimal pH buffer media, electropolymerization of EDOT:PSS, and Nafion coating. The strong electron-transport capacity between rGO-PEDOT:PSS and the negatively charged Nafion matrix might allow the highly sensitive, simultaneous, and selective detection of DA and 5-HT due to its high affinity for cations. In the results of the electrochemical response, well-separated oxidation peaks were observed in a mixture that contained various concentrations of DA and 5-HT. It showed the dynamic sensing of DA and 5-HT in the ranges of 0.5–75 μM and 0.05–50 μM, respectively, and the detection limits of 0.17 and 0.16 μM, respectively. In the mixture of DA and 5-HT, the sensor had a detection limit of 0.1 μM for 5-HT and DA, and its sensitivities of DA and 5-HT were 99.3 and 86 µA/µMcm2. Furthermore, it demonstrated high selectivity, reproducibility, stability, and a recovery property in the human serum spike test that was good enough for the practical use.

Improved Sensitivity and Selectivity for the Redox Potentiometric Measurement of Biological Redox Molecules Using Nafion-Coated Platinum Decorated Nanoporous Gold Electrodes

Sensitivity and selectivity are two important figures of merit in analytical measurements, but in redox potentiometry, they are often limited. In this study, we describe how the potentiometric sensitivity and selectivity can be improved using nanoporous gold (NPG) electrodes with hydrogen peroxide, dopamine, ascorbic acid, and a mixture of dopamine and ascorbic acid as the test analytes. The results show that the addition of platinum (Pt) to the nanoporous framework significantly improves electrode sensitivity for the analytes studied. Furthermore, it was only possible to potentiometrically detect hydrogen peroxide at the NPG-Pt electrodes. To further improve sensitivity and also impart some selectivity, the electrodes were spin-coated with Nafion. The addition of Nafion shifts the open-circuit potential to more positive values, increases sensitivity by almost a factor of 2, and imparts selectivity to the surface for the analysis of mixtures. Collectively, this works shows the promise of Pt-decorated nanoporous electrodes coupled with a Nafion film to improve the overall performance of redox potentiometry in analytical science.

Different Electrochemical Behavior of Cationic Dopamine from Anionic Ascorbic Acid and DOPAC at CNT Yarn Microelectrodes

Carbon nanotube yarn microelectrodes (CNTYMEs) have micron-scale surface crevices that momentarily trap molecules. CNTYMEs improve selectivity among cationic catecholamines because secondary reactions are enhanced, but no anions have been studied. Here, we compared fast-scan cyclic voltammetry (FSCV) of dopamine and anionic interferents 3,4 dihydroxyphenylacetic acid (DOPAC) and L-ascorbic acid (AA) at CNTYMEs and carbon fiber microelectrodes (CFMEs). At CFMEs, dopamine current decreases with increasing FSCV repetition frequency at pH 7.4, whereas DOPAC and AA have increasing currents with increasing frequency, because of less repulsion at the negative holding potential. Both DOPAC and AA have side reactions after being oxidized, which are enhanced by trapping. At pH 4, the current increases for DOPAC and AA because they are not repelled. In addition, AA has a different oxidation pathway at pH 4, and an extra peak in the CV is enhanced by trapping effects at CNTYMEs. At pH 8.5, co-detection of dopamine in the presence of DOPAC and AA is enhanced at 100 Hz frequency because of differences in secondary peaks. Thus, the trapping effects at CNTYMEs affects anions differently than cations and secondary peaks can be used to identify dopamine in mixture of AA and DOPAC with FSCV.

Ag-Deposited Porous Silicon as a SERS-Active Substrate for the Sensitive Detection of Catecholamine Neurotransmitters

The sensitive detection of various neurotransmitters is very useful in diagnosing diseases related to the dysfunction of the neurotransmitter system. Surface-enhanced Raman scattering (SERS) is one of the best methods for bio-analyte detection as it provides a molecular fingerprint at a trace concentration level. In this study, Ag-deposited porous silicon (Ag@pSi) was fabricated as a SERS-active substrate via metal-assisted chemical etching and electroless plating methods. Dopamine (DA) and norepinephrine (NE) neurotransmitters were tested as probing analytes. The Ag@pSi substrate demonstrated the sensitive detection of the neurotransmitters (DA and NE) over the wide concentration range (from 10‒6 to 10‒10 M), with a good linearity between the intensity of specific Raman peak and the log-scale concentration. The Ag@pSi substrate also distinguished the individual analytes in a mixture of DA and NE at 10‒8 M, confirming the efficacy of the developed SERS substrate for the selective detection of neurotransmitters.

A Fast and Validated HPLC Method for Simultaneous Determination of Dopamine, Dobutamine, Phentolamine, Furosemide, and Aminophylline in Infusion Samples and Injection Formulations.

A simple, fast, and validated HPLC method was developed for the simultaneous quantization of five cardiovascular agents: dopamine (DPM), dobutamine (DBM), phentolamine (PTM), furosemide (FSM), and aminophylline (APL) either in infusion samples or in an injection dosage form. The proposed method was achieved with a 150 mm × 4.6 mm, 5.0 μm C18 column, by using a simple linear gradient. Mobile phase A was buffer (50 mM KH2PO4) and mobile Phase B was acetonitrile at a flow rate of 1.0 mL/min. The column temperature was kept at 30°C, and the injection volume was 20 μL. All analytes were separated simultaneously at a retention time (tr) of 3.93, 5.84, 7.06, 8.76, and 9.67 min for DPM, DBM, PTM, FSM, and APL, respectively, with a total run time of less than 15.0 min. The proposed method was validated according to ICH guidelines with respect to accuracy, precision, linearity, limit of detection, limit of quantitation, and robustness. Linearity was obtained over a concentration range of 12.0–240.0, 12.0–240.0, 20.0–200.0, 6.0–240.0, and 10.0–200.0 μg/mL DPM, DBM, PTM, FSM, and APL, respectively. Interday and intraday accuracy and precision data were recorded in the acceptable limits. The new method has successfully been applied for quantification of all five drugs in their injection dosage form, infusion samples, and for evaluation of the stability of investigated drugs in mixtures for endovenous use. The results of the stability study showed that mixtures of DPM, DBM, PTM, FSM, and APL in 5% glucose or 0.9% sodium chloride injection were stable for 48 hours when stored in polypropylene syringes at 25°C.

Anaerobic wastewater treatment and reuse enabled by thermophilic bioprocessing integrated with a bioelectrochemical/ultrafiltration module

The current study aimed to develop an anaerobic wastewater treatment and reuse module enabled by thermophilic bioprocessing, a microbial fuel cell (MFC) and ultrafiltration (UF) treatment. A previously unexplored consortium based on Thermoanaerobacterium thermosaccharolyticum and Arcobacter sp. was used to remove ~73% of chemical oxygen demand (COD) from wastewater under anaerobic conditions (CODi = 200 mg/L). The subsequent MFC and UF treatment removed the COD remnants to meet the secondary treatment standards and reuse criteria. The energy efficiency of polyethersulfone UF membranes was improved by modifying their surfaces with coatings based on self-polymerized dopamine, mixtures of dopamine and poly(2-dimethylamino) ethyl methacrylate methyl, and dopamine analog norepinephrine. The resulting hydrophilic, anti-fouling layers were found to reduce interactions between rejected species and the membrane surface. Finally, this study presents a comparative treatment performance and energy efficiency of the wastewater treatment and reuse modules arranged in six different configurations.

Noradrenaline enhances the excitatory effects of dopamine on medial prefrontal cortex pyramidal neurons in rats.

AimOur previous studies showed that exposure to acute restraint stress enhanced cocaine‐induced conditioned place preference (cocaine‐CPP) and suggested the possibility that co‐activation of adrenergic transmission boosts the increase in medial prefrontal cortex (mPFC) neuronal activity by the activation of dopaminergic transmission. To examine this possibility, the effects of the co‐treatment with dopamine (DA) and noradrenaline (NA) on mPFC neurons were compared with those of treatment with DA alone using whole‐cell patch‐clamp recordings.MethodsThe effects of DA alone and a mixture of DA and NA on the membrane potentials and spontaneous excitatory postsynaptic currents (sEPSCs) were examined by electrophysiological recordings of mPFC pyramidal neurons in brain slices of male Sprague Dawley rats. Extracellular DA and NA levels in the mPFC during and after restraint stress exposure were also examined by in vivo microdialysis.ResultsDopamine significantly produced depolarizing effects on mPFC neurons and tended to increase sEPSC frequency. Co‐administration of NA with DA produced stronger depolarizing effects and significantly increased sEPSC frequency. The findings suggest that the additional depolarizing effect of NA on DA‐responsive neurons, rather than the excitation of DA‐nonresponsive neurons by NA, contributes to the stronger effect of co‐treatment of NA with DA.ConclusionThe present study suggests that NA released by restraint stress exposure cooperates with DA to stimulate DA‐responsive neurons in the mPFC, thereby causing the stress‐induced enhancement of cocaine‐CPP.

Simultaneous determination of dopamine, uric acid and estriol in maternal urine samples based on the synergetic effect of reduced graphene oxide, silver nanowires and silver nanoparticles in their ternary 3D nanocomposite

A facile and efficient electrochemical biosensing platform based on screen printed carbon electrode (SPCE) modified with three-dimensional (3D) nanocomposite consists of reduced graphene oxide (RGO) with the insertion of silver nanowires (AgNWs) followed by the anchoring of silver nanoparticles (AgNPs) is constructed as RGO/AgNWs/AgNPs/SPCE for the simultaneous determination of dopamine (DA), uric acid (UA) and estriol (EST). The morphology characteristic and surface elemental composition of RGO/AgNWs/AgNPs nanocomposite are investigated by field-emission scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscope. Cyclic voltammetry, electrochemical impedance spectroscopy, linear sweep voltammetry and differential pulse voltammetry are utilized to explore the electrochemical performances of the constructed electrodes. Due to abundant active sites and excellent electrocatalytic activity of the nanocomposite, the RGO/AgNWs/AgNPs/SPCE sensor exhibits well-resolved oxidation peaks and enhanced oxidation peak currents in the ternary mixture of DA, UA and EST with respective linear response ranges of 0.6 to 50 μM, 1 to 100 μM and 1 to 90 μM and detection limits (S/N = 3) of 0.16 μM, 0.58 μM and 0.58 μM, respectively. Moreover, the constructed biosensor exhibits good selectivity, reproducibility and stability, and excellent performance in determining DA, UA and EST in synthetic urine samples with excellent recovery. The results reveal that the RGO/AgNWs/AgNPs nanocomposite is a promising candidate for advanced electrode material in electrochemical sensing field and possesses great application prospects in further sensing researches.

Simultaneous electrochemical investigations of dopamine and uric acid by in situ amino functionalized reduced grahene oxide

We have synthesized amino functionalized reduced graphene oxide (NH2-rGO) composite. Bucherer reaction was used for the in situ modification of graphene oxide into the (NH2-rGO). A simple hydrothermal method was utilized for proposed synthesis. Electrochemical sensor was fabricated by drop coating NH2-rGO nanocomposite onto the glassy carbon electrode (GCE) for individual and the simultaneous detection of dopamine (DA) and uric acid (UA). The NH2-rGO materials formation was confirmed by X-ray diffraction, IR, UV and FE-SEM. The electrochemical sensing of DA and UA was examined by cyclic voltammetry and differential pulse voltammetry. For individual detection of DA, the linear responses of current concentration plot was found in the concentration range of 2.04 × 10−4– 2.04 × 10−3 M with detection limit 1.4 × 10−4 M (S/N = 3) and for UA, 1.8 × 10−3– 1.8 × 10−4 M with detection limit 1.67 × 10−4 M (S/N = 3). The NH2-rGO/GCE electrochemical sensor further tested for the simultaneous detection of binary mixtures of DA and UA and found to be high sensitive compared to individual detection of DA and UA at pH 3. Sensor selectivity is demonstrated in the presence of 2 × 10−4 M concentrations of potentially active interfering compounds including dopamine, uric acid and glucose isomers.

Development of highly sensitive IgA immunosensors based on co-electropolymerized L-DOPA/dopamine carbon nano-onion modified electrodes

The development of versatile platforms to construct novel and sensitive immunosensors is nowadays an intense research field. Nanomaterials and polymers are often combined to fabricate new platforms to immobilize capture antibodies. Here we evaluate for the first time the co-electropolymerization of dopamine (DA) and L-3,4-dihydroxyphenylalanine (L-DOPA) on carbon nano-onion (CNO) modified electrodes as versatile platform to develop electrochemical immunosensors. Mixtures of DA and L-DOPA at different molar rations were co-electropolymerized on CNO-modified glassy carbon electrodes to form a poly(L-DOPA/DA) film. Immobilization of aminoferrocene was used to estimate the number of accessible carboxylic acid groups on the surface (11.3 nmol/cm2), a value comparable to three-dimensional matrices. This platform was applied to the electrochemical detection of IgA antibodies using both a HRP-based sandwich type assay and label-free detection based on [Fe(CN)6]3-/4- signal blocking. The sandwich and the label-free assays showed a wide linear response with LOD of 19 and 48 ng/mL, respectively, allowing the detection of serum IgA deficiency. Most remarkably, the incorporation of CNO layer led to a significant improvement (three-orders of magnitude) of the analytical performance of these immunosensors due to a combination of high surface area and increased electron transfer rates provided by the CNO layer.

Dopamine enhancement of dextrorphan-induced skin antinociception in response to needle pinpricks in rats.

Dextrorphan with long-acting local anesthetic effects did not cause system toxicity as fast as bupivacaine, while catecholamines (i.e., epinephrine) with the vasoconstrictive characteristics enhanced the effects of local anesthetic drugs. The objective of the experiment was to examine the synergistic effect of local dopamine (a catecholamine) injection on cutaneous antinociception of dextrorphan. The panniculus reflex in response to skin stimulation with a needle was used as the primary endpoint when dextrorphan (1.50, 2.61, 5.46, 10.20 and 20.40 μmol) alone, dopamine (16.20, 32.40, 51.60, 60.00 and 81.60 μmol) alone, or dopamine + dextrorphan (a ratio of ED50vs. ED50) was injected subcutaneously on the rat's back. We used an isobolographic modelling approach to determine whether a synergistic effect would be observed. We showed that dextrorphan, dopamine, or the mixture of dopamine and dextrorphan produced dose-related skin antinociception. The potency (ED50, 50% effective dose) for cutaneous antinociception was dextrorphan [6.02 (5.93-6.14) μmol] greater than dopamine [48.91 (48.80-49.06) μmol] (p < 0.01). The duration of nociceptive inhibition induced by dopamine was longer than that induced by dextrorphan (p < 0.01) based on their equipotent doses (ED25, ED50, and ED75). Enhancement and prolongation of skin antinociception occurred after co-administration of dopamine with dextrorphan. When compared to dopamine, dextrorphan was more potent and had a shorter duration of skin nociceptive block. Dopamine produced a synergistic effect on dextrorphan-mediated antinociception, and prolonged dextrorphan's antinociceptive duration.

Durable superhydrophobic and superoleophilic electrospun nanofibrous membrane for oil-water emulsion separation

Marinepollution andindustrial wastewater have caused serious environmental pollution, thereby resulting into an alarming damage to public health in the past decades, hence the high demand for, cost effective, energy-efficient oil-water separation technologies for the removal of oil contaminants from such water. Herein, we report a facile method to fabricate superhydrophobic/superoleophilic membrane by immersing a polyimide (PI)-based nanofibrous membrane into a water/ethanol/ammonia/dopamine mixture, followed by modification with 1H, 1H, 2H, 2H-perfluorodecanethiol (PFDT). The PI-based membrane exhibited water contact angle (WCA) above 153°, while the oil contact angle (OCA) approached 0°, thereby promoting an outstanding chemical stability which sustained its superhydrophobicity when immersed in aqueous solutions at different pH values. Additionally, the PI-based membrane possesses ultrahigh flux, high separation efficiency and good reusability in oil-water separation. The aforementioned properties, as well as the easily scale-up preparation process ensure that this promising as-fabricated membrane can be applied for practical environmental applications including treatment of oily wastewater and oil spillage clean-up.

Electrocatalytic Discrimination between Dopamine and Norepinephrine at Graphite and Basal Plane HOPG Electrodes

AbstractUnderstanding the regulatory mechanisms of neurotransmission is impossible without in vivo monitoring of neurotransmitters’ (NTs) transformation in the brain, and that can be performed by a variety of electrochemical methods. Close redox potentials of such NTs as catecholamines, however, impede their specific analysis in systems where they do co‐exist. Here, we studied the kinetics of dopamine and norepinephrine redox transformations on glassy carbon, micro‐structured spectroscopic graphite, and basal plane HOPG electrodes. We showed that in contrast to the “positive electrocatalysis” on porous microstructured graphite electrodes, “negative electrocatalysis” at the HOPG electrodes, displayed through slowing down of the reaction rate, allowed a ca. 0.1 V separation between dopamine and norepinephrine oxidations and individual detection of dopamine in the artificial cerebrospinal fluid. Dopamine could be detected within the 50 nM to 4 μM range with no interference from excesses of norepinephrine and ascorbic acid. The results suggest a new approach for design of the electrodes for specific analysis of dopamine in mixtures of structurally related NTs.

One-step selective screening of bioactive molecules in living cells using sulfur-doped microporous carbon

A metal-free electrode using heteroatom-doped microporous carbon was fabricated for the ultrasensitive monitoring of mono-bioactive molecules and the selective signaling of dopamine (DA) secreted by living cells. The constructed electrode based on sulfur-doped microporous carbon (S-MC) shows a high surface area, a spherical construction, numerous carbon chain defects, and microporous structures, which are the key factors of the interactive signaling transducer, fast response, and active interfacial surfaces. The intrinsic features of S-MC with different %S-doping (S-MC-1, and S-MC-2) through the sp2-carbon chain create abundant catalytic active sites, facilitate molecular diffusion through the microporous structure, promote strong binding with the targeted molecules, and induce interactions at electrolyte–electrode interfaces. The S-MC-1 provides selective signaling in a tertiary mixture of DA, ascorbic acid (AA), and uric acid (UA) with a high sensitivity and a wide linear range of 0.01–5, 10–4000, and 1–2000 µM, respectively. The detection limits were set at 3 nM, 1.26 µM, and 0.23 µM for DA, AA, and UA respectively. The S-MC-1 demonstrated a selective screening of DA released from PC12 cells under a K+ ion- stimulator with high sensitivity and promoted high biocompatibility, low cytotoxicity, high stability, and reliable reproducibility (%RSD ranged from 1 to 2.7). Our findings indicated that the S-MC-1 can be utilized as an in-vitro model for simultaneously monitoring extracellular-DA secreted from living cells and sensing mono-bioactive molecules in biological samples.

Removal of nitrophenols from water using cellulose derived nitrogen doped graphitic carbon material containing titanium dioxide

ABSTRACTNitrophenols (NPs) and their derivatives are highly toxic, mutagenic and bio-refractory pollutants commonly present in natural water resources and industrial wastewater. To remove NPs from water, N-doped graphitic carbon (NGC) and NGC adsorbent containing titanium dioxide (NGC–TiO2) were synthesized by pyrolysis of microcrystalline cellulose and dopamine mixture, and the mixture along with TiO2 at 500°C, respectively. NCG-TiO2 was thoroughly characterized using various analytical techniques. NP adsorption on the NGC–TiO2 adsorbent surface was studied by varying the pH, initial concentration of NP, and adsorbent dose. The results showed that the most efficient adsorption was achieved at pH 3. After 4 h sonication at pH 3, 80% 4-NP adsorption was achieved using NGC–TiO2 compared to 74% with NGC adsorbent. The percentage removal of 4-NP was higher than 3-NP which was also higher than 2,4-DNP using NGC–TiO2. 4-NP adsorption best fitted to the Langmuir isotherm plot with R2 value of 0.9981 and adsorption capacity of 52.91 mg g−1. The adsorption process of NP was found to follow a pseudo-second-order kinetic model. The rate constant value for the adsorption of 10−4 M 4-NP at pH 3 using 10 mg of NGC–TiO2 adsorbent was found to be 3.76 × 10−5 g.mg−1.min−1

Array of recessed gold nanoelectrodes formed with polymethylmethacrylate for individual detection of ascorbic acid, dopamine and uric acid

A series of recessed gold nanoelectrode arrays with different array densities are patterned on polymethylmethacrylate (PMMA) coated gold substrate by precisely controlled patterning through electron beam lithography. The influence of the nanoelectrode density of the arrays and scan rate on the diffusion regimes and hence electrochemical behaviors are systematically investigated. It is demonstrated that the electrostatic interaction exists between the oxygen-containing groups of the PMMA nanocylinder and the charged analytes in solution. The difference in the electrostatic interaction of dopamine (DA), ascorbic acid (AA), and uric acid (UA) with PMMA nanocylinders leads to differentiation of the oxidation of the three species. Thus, an electrochemical sensing platform for the detection of individual components in a mixture of DA, AA, and UA is developed. The linear ranges and detection limits of individual components in the mixture are 3.5–125μM and 0.66μM for DA, 30–190μM and 7.5μM for AA, 20–170μM and 6.38μM for UA, respectively, on the array electrode.

Clay Composite Modified Electrodes II: Voltammetric Method for Simultaneous Detection of Dopamine and Serotonin

Dopamine (DA) and serotonin (SN) are important catecholamine neurotransmitters in the central nervous system that play key roles in muscle stimulation and transmission of signals. DA release in the brain plays a key role in the regulations of pleasure and pain while SN helps to relay messages from one area of the brain to another. Abnormal DA levels are associated with serious diseases such as Schizophrenia and Parkinson’s. Imbalance in SN levels affects the muscles and cardiovascular system. Thus developing methods for detection of DA and SN in the presence of interfering species is an important area of research. Electrochemical methods for DA and SN detection have been developed since there is increasing demand for more reliable and rapid methods. Excess levels of interfering species such as ascorbic acid (AA) and uric acid (UA) co-exist in biological samples. These pose problems for DA and SN detection during electrochemical measurements since they all oxidize around the same potential region. Several types of electrode modifications have been reported for selective detection of DA and SN, but each one has its own advantages and limitations. The use of clay-composite modified electrodes have not been exploited. This work aims to employ clay composite modified glassy carbon electrodes for selective detection of DA and SN. The goal is to use clay composites to exclude AA and UA while enhancing DA and SN detection. Clay film serves as the polymeric membrane as clays are able to form membrane-like films. Clays are naturally occurring and much more stable than synthetic membranes. Clay film on an electrode surface provides important functions such as charge-exclusion and catalysis of electrochemical reactions. The clay composite was prepared by incorporating methylene blue and xanthate into clay interlayers by simply mixing them with clay suspension and sonicating. Several voltammetric experiments were undertaken to investigate the behavior of DA, SN, AA, and UA at the bare electrode (BE), clay modified electrode (CME), glycerol-clay modified electrode (GCME), glycerol-methylene blue-clay modified electrode (GMBCME), glycerol-xanthate-clay modified electrode (GXTCME), and glycerol-methylene blue-xanthate-clay modified electrode (GMBXTCME). Voltammetric techniques used were Cyclic Voltammetry (CV), Square-Wave Voltammetry (SWV), and Differential-Pulse Voltammetry (DPV). Experiments were performed at the physiological pH of 7.4. Glycerol was added to prevent cracks in films. At GCME, calibration curves by CV show linear range of 0.0010 – 0.25 and 0.0010 – 0.10 mM for DA and SN, respectively. The DA and SN oxidation peak potentials are around 0.26 and 0.27 V versus Ag/AgCl, respectively. For a mixture of DA and SN, the CV shows an oxidation peak around 0.43 V (due to SN) with a small hump around 0.28 V (due to DA). The hump is more pronounced at the GCME than at the BE, indicating catalytic effect by the clay on DA. For a mixture of DA, SN, AA, and UA, one broad oxidation peak is observed. Oxidation currents for both AA and UA at GCME are much lower than those at BE. This is evidenced by the fact that at pH of 7.4, AA and UA exist in their anionic form while DA and SN exist in the cationic form. Most clay layer surfaces are negatively charged so readily attract the cationic DA/SN into the interlayers and repel the anionic AA/UA. This enhances DA/SN detection while diminishing AA/UA detection. Only clay does not efficiently exclude AA/UA, hence the incorporation of methylene blue and xanthate. At GMBCME, both DA and SN exhibit oxidation potential at 0.20 V. However, a mixture of DA and SN exhibits peak potentials at 0.22 (DA) and 0.32 V (SN). Hence, the GMBCME film is able to separate and distinguish between the two peaks. It is also observed that both DA and SN peak potentials shift slightly negative compared to the BE. The DA peak currents increased at GMBCME compared to BE, while those of SN decreased. This confirms the catalytic effect of clay on DA stated above, but little or insignificant catalytic effect on SN. Again, GMBCME is unable to efficiently exclude AA and UA. With the addition of xanthate to form GMBXTCME, no oxidation peaks for AA and UA are seen. This is true for all three voltammetric techniques. This implies that the glycerol-methylene blue-xanthate-clay composite film efficiently discriminates against AA and UA detection. GMBXTCME film stability was also investigated and was observed that all old films exhibited great stability, reproducible results, and efficiently exclude both AA and UA. REFERENCES 1. T. Selvaraju, R. Ramaraj, J. Appl. Electrochem., 33, 759 (2003). 2. J.-M. Zen, P.-J. Chen, Anal. Chem., 69, 5087 (1997).

Selective detection of dopamine combining multilayers of conducting polymers with gold nanoparticles.

Electrodes based on the combination of three-layered films formed by two different conducting polymers and gold nanoparticles have been developed for the selective voltammetric determination of dopamine in mixtures with ascorbic acid and uric acid and human urine samples with real interferents. Voltammetric studies of solution mixtures indicate that electrodes formed by alternated layers of poly(3,4-ethylenedioxithiophene) (internal and external layer) and poly(N-methylpyrrole) (intermediate layer) show the best performance in terms of sensitivity and resolution. Furthermore, the sensitivity of such three-layered electrodes increases only slightly after coating its surface with gold nanoparticles (AuNPs), indicating that the catalytic effect typically played by AuNPs in the oxidation of dopamine is less effective in this case. Electrochemical pretreatments based on the application of consecutive oxidation-reduction cycles to electrodes before the detection process have been found to improve the selectivity without altering the sensitivity. On the other hand, the flux of dopamine to the three-layered surface increases linearly with the scan rate. The detection limit for these electrodes is around 10 μM DA in mixtures with uric acid, ascorbic acid, and cetaminophen, decreasing to 2-3 μM in the absence of such interferents. The utility of three-layered electrodes as sensors has also been demonstrated by determining DA in human samples with real interferents.

Clay Composite Modified Electrodes I: Voltammetric Method for Selective Analysis of Dopamine and Ascorbic Acid

Clay Composite Modified Electrodes I: Voltammetric Method for Selective Analysis of Dopamine and Ascorbic Acid

The use of a multichannel capillary for electrophoretic separations of mixtures of clinically important substances with contactless conductivity and UV photometric detection

A fused-silica capillary with a common outer diameter, 360 μm, but containing seven internal channels, each 28 μm in diameter (a multichannel capillary), has been tested on electrophoretic separations of mixtures of dopamine, adrenaline, and noradrenaline, using a contactless conductivity and UV photometric detection. It has been demonstrated that the sensitivity of the detection of these neurotransmitters in multichannel capillary, in comparison with those obtained for a standard singlechannel capillary with similar cross-sectional area, is comparable to that for the contactless conductivity and is about 50% higher for the UV photometry. The sensitivity is increased without loss of the separation efficiency, in contrast to UV detection with bubble cell. Further possibilities of using a multichannel capillary are demonstrated on separations of mixtures of inorganic cations (K⁺, Ba²⁺, Na⁺, Mg²⁺, and Li⁺) and mixtures of glucose and ribose. The main advantage of multi-channel capillary in comparison with a singlechannel capillary with the same cross-sectional area becomes apparent in separations in background electrolytes of high conductivity.