Simultaneous measurement of dopamine and ascorbate at their physiological levels using voltammetric microprobe based on overoxidized poly(1,2-phenylenediamine)-coated carbon fiber

Sodium dodecyl sulfate-modified electrochemical paper-based analytical device for determination of dopamine levels in biological samples

We report the development of an electrochemical paper-based analytical device (ePAD) for the selective determination of dopamine (DA) in model serum sample. The ePAD device consists of three layers. In the top layer, SU-8 photoresist defines a hydrophilic sample application spot on the filter paper. The middle layer was made from transparency film and contained two holes, one for sample preconcentration and the other for the surfactant to allow transfer to the third layer. A screen-printed carbon electrode formed the bottom layer and was used for electrochemical measurements. In the absence of the anionic surfactant, sodium dodecyl sulfate (SDS), the oxidation peaks of DA, ascorbic acid (AA) and uric acid (UA) overlapped. With the addition of SDS, the DA oxidation peak shifted to more negative values and was clearly distinguishable from AA and UA. The oxidation potential shift was presumably due to preferential electrostatic interactions between the cationic DA and the anionic SDS. Indeed, whilst the SDS-modified paper improved the DA current five-fold, the non-ionic Tween-20 and cationic tetradecyltrimethylammonium bromide surfactants had no effect or reduced the current, respectively. Furthermore, only the SDS-modified paper showed the selective shift in oxidation potential for DA. DA determination was carried out using square-wave voltammetry between -0.2 and 0.8 V vs. Ag/AgCl, and this ePAD was able to detect DA over a linear range of 1-100 μM with a detection limit (S/N=3) of 0.37 μM. The ePAD seems suitable as a low cost, easy-to-use, portable device for the selective quantitation of DA in human serum samples.

Simultaneous determination of ascorbic acid, dopamine, uric acid and tryptophan on gold nanoparticles/overoxidized-polyimidazole composite modified glassy carbon electrode

A novel electrode was developed through electrodepositing gold nanoparticles (GNPs) on overoxidized-polyimidazole (PImox) film modified glassy carbon electrode (GCE). The combination of GNPs and the PImox film endowed the GNPs/PImox/GCE with good biological compatibility, high selectivity and sensitivity and excellent electrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). In the fourfold co-existence system, the peak separations between AA-DA, DA-UA and UA-Trp were large up to 186, 165 and 285 mV, respectively. The calibration curves for AA, DA and UA were obtained in the range of 210.0-1010.0 μM, 5.0-268.0 μM and 6.0-486.0 μM with detection limits (S/N=3) of 2.0 μM, 0.08 μM and 0.5 μM, respectively. Two linear calibrations for Trp were obtained over ranges of 3.0-34.0 μM and 84.0-464.0 μM with detection limit (S/N=3) of 0.7 μM. In addition, the modified electrode was applied to detect AA, DA, UA and Trp in samples using standard addition method with satisfactory results.

Au/TiO2 NANOTUBES FOR SELECTIVE DETECTION OF DOPAMINE

A novel biosensor for dopamine (DA) detection was fabricated using TiO2 nanotube and Au/TiO2 nanotube films on glassy carbon electrode (GCE). The Au/TiO2 nanotubes on electrode showed better electrocatalytic activity towards the detection of DA which was attributed to its excellent electron conductive network. The biosensor elicited sensitivity of 22 nA/μM with a linearity of detection localized in the concentration range from 5–120 μM with correlation coefficient of 0.99. The detection limit of DA for the Au/TiO2 nanotube biosensor was found to be ~3 μM (S/N = 3). In addition, the fabricated sensor showed good anti-interference capability towards biological compounds such as ascorbic acid and uric acid. In conclusion, Au/TiO2 nanotube biosensor exhibits excellent catalytic activity, selectivity and simplicity for the detection of dopamine.

Simultaneous electrochemical determination of dopamine and ascorbic acid using AuNPs@polyaniline core-shell nanocomposites modified electrode

A simple and effective strategy was proposed for synthesis of AuNPs@polyaniline (AuNPs@PANI) core-shell nanocomposites. AuNPs@PANI nanocomposites were prepared by one-step chemical oxidative polymerization of aniline using chloroaurate acid as the oxidant and AuNPs as the seeds. The synthesized AuNPs@PANI nanocomposites were characterized with transmission electron microscope and UV-vis absorption spectra. Cyclic voltammetric experiments indicated that AuNPs@PANI nanocomposites showed excellent electroactivity in neutral and even alkaline solution. The obtained AuNPs@PANI nanocomposites-modified electrode was fabricated to simultaneously determine dopamine (DA) and ascorbic acid (AA) by differential pulse voltammetry. The separation between the two peak potentials of DA and AA oxidation is 236 mV. The catalytic peak currents were linearly with the concentrations of DA and AA in the range of 10-1700 and 20-1600 μM with correlation coefficients of 0.9997 and 0.9998, respectively. The detection limits for DA and AA were 5 and 8 μM, respectively.

Electrochemically selective determination of dopamine in the presence of ascorbic and uric acids on the surface of the modified Nafion/single wall carbon nanotube/poly(3-methylthiophene) glassy carbon electrodes

A voltammetric method based on a combination of incorporated Nafion, single-walled carbon nanotubes and poly(3-methylthiophene) film-modified glassy carbon electrode (NF/SWCNT/PMT/GCE) has been successfully developed for selective determination of dopamine (DA) in the ternary mixture of dopamine, ascorbic acid (AA) and uric acid (UA) in 0.1M phosphate buffer solution (PBS) pH 4. It was shown that to detect DA from binary DA-AA mixture, the use of NF/PMT/GCE was sufficient, but to detect DA from ternary DA-AA-UA mixture NF/SWCNT/PMT/GCE was required. The later modified electrode exhibits superior electrocatalytic activity towards AA, DA and UA thanks to synergic effect of NF/SWCNT (combining unique properties of SWCNT such as high specific surface area, electrocatalytic and adsorptive properties, with the cation selectivity of NF). On the surface of NF/SWCNT/PMT/GCE AA, DA, UA were oxidized respectively at distinguishable potentials of 0.15, 0.37 and 0.53 V (vs. Ag/AgCl), to form well-defined and sharp peaks, making possible simultaneous determination of each compound. Also, it has several advantages, such as simple preparation method, high sensitivity, low detection limit and excellent reproducibility. Thus, the proposed NF/SWCNT/PMT/GCE could be advantageously employed for the determination of DA in real pharmaceutical formulations.

Enhancement of dopamine sensing by layer-by-layer assembly of PVI-dmeOs and Nafion on carbon nanotubes

In this study, carbon nanotubes (CNTs) were modified to further improve their performance in electrochemical sensing of dopamine (DA) levels. After a redox polymer, poly(vinylimidazole) complexed with Os(4, 4'-dimethyl- 2, 2-bipyridine)(2)Cl (termed PVI-dmeOs) was electrodeposited on multi-wall CNTs (MWCNTs), Nafion and PVI-dmeOs films were successfully layer-by-layer (LBL) assembled on the hydrophilic surface of the as-prepared PVI-dmeOs/CNTs nanocomposites through electrostatic interactions. The LBL assembly was proved by scanning electron microscopy (SEM), electrochemistry and UV-vis spectroscopy measurements. LBL assembly of Nafion/PVI-dmeOs films on CNTs significantly enhanced their linear sweep voltammetry (LSV) response sensitivity to DA, with a maximum enhancement for three Nafion/PVI-dmeOs film-modified MWCNTs. The LSV peak current density of (Nafion/PV I-dmeOs)(3)/CNT electrodes in response to 10 and 50 microM DA solutions was about 7.3 and 3.9 times those for bare CNTs. At the (Nafion/PV I-dmeOs)(3)/CNT electrodes, the limit of detection (LOD) (signal-to-noise ratio: 3) was 0.05 microM DA, the linear range was 0.1-10 microM DA (with a linear regression coefficient of 0.97) and the DA-sensing sensitivity was 8.15 microA cm( - 2) microM( - 1). The newly fabricated (Nafion/PV I-dmeOs)(3)/CNT electrodes may be developed as an ideal biosensor for direct and in situ measurement of DA levels.

Voltammetric determination of dopamine in the presence of uric acid using a 2-hydroxy-1-(1-hydroxynaphthyl-2-azo)- naphthalin-4-sulfonic acid modified glassy carbon electrode

A polymerized film of 2-hydroxy-1-(1-hydroxynaphthyl-2-azo)- naphthalin-4-sulfonic acid (HHNANSA) was prepared at the surface of a glassy carbon electrode by electropolymerization. The modified electrode was used for the simultaneous determination of dopamine (DA) and uric acid (UA). The electrochemical behaviors of the compounds at the surface of the modified electrode were studied using cyclic voltammetry, chronoamperometry, and square wave voltammetry (SWV). The experimental results indicated that the modified electrode exhibited an efficient electrocatalytic activity towards the oxidation of DA and UA, with a peak separation of about 140 mV at pH 5.0. Using chronoamperometry, the catalytic reaction rate constant was measured and found to equal to 1.23 ? 104 mol-1 L s-1. At pH 5.0, the catalytic peak currents linearly depended on the DA and/or UA concentrations in the range of 1.0 - 300 ?mol L-1 DA (two linear segments with different slopes) and 6.7 - 20 ?mol L-1 UA, using SWV. The detection limits for DA and UA were 0.25 ?mol L-1 and 1.17 ?mol L-1, respectively. The RSD % for 40.0 and 140.0 ?mol L-1 DA were 1.9 % and 2.2 %, respectively, whereas for 10.0 and 20.0 ?mol L-1 UA, they were 1.8 % and 1.2 %, respectively. The modified electrode showed good sensitivity, selectivity, and stability. It was successfully applied for the determination of DA and UA in real samples, such as drugs and urine.