Dopamine amperometric detection

FIGURE 3-27 Three-dimensional chromatogram for oxidizable biological compounds at a multichannel amperometric detection system, consisting of an array of 16 carbon-paste electrodes held at different potentials. AA = ascorbic acid NE = norepinephrine DOPAC = 3,4-dihydroxyphenylacetic acid 5-HIAA = 5-hydroxyindole-3-acetic acid DA = dopamine HVA = homovanillic acid. (Reproduced with permission from reference 68.)... 

To date, electrochemical (amperometric) detection of NO is the only available technique sensitive enough to detect relevant concentrations of NO in real time and in vivo and suffers minimally from potential interfering species such as nitrite, nitrate, dopamine, ascorbate, and L-arginine. Also, because electrodes can be made on the micro- and nano-scale these techniques also have the benefit of being able to measure NO concentrations in living systems without any significant effects from electrode insertion. 

A Pd film decoupler has also been constructed for amperometric detection of catecholamines. The Pd film has been thermally evaporated onto a plastic chip (without the use of the Cr or Ti adhesion underlayers). Owing to the fast diffusion of H2 on a Pd surface, gas bubbles will not form. Pd is able to absorb H2 produced at the cathode up to a Pd/H ratio of 0.6. This reduces one of the interferences to the EC signal, leading to an improvement of LOD to 0.29 pM dopamine [205,375]. With an optimal decoupler size of 500 pm, up to 6 h of operation was achieved with an electric field of 600 V/cm [375]. 

Neurotransmitters have also been detected on microchips using electrochemical detection, eliminating the need for on-chip reactions or derivitization. Amperometric detection, a current change when an analyte passes the detection electrodes, was demonstrated on a microchip for the determination of dopamine concentrations in standard solutions [10], The microdevice developed in this... 

Fig. 8-100. Gradient elution of catecholamines with amperometric detection. — Separator column Zorbax ODS eluent (A) 0.005 mol/L triethylamine / methanol, (B) 0.07 mol/L KH2P04 + 0.005 mol/L triethylamine + 0.001 mol/L sodium butanesulfonate (pH 3) gradient linear, 5% A in 20 min to 56% A flow rate 1 mL/min detection amperometry at a GC working electrode oxidation potential +0.8 V injection volume 50 pL solute concentrations 4 ppm each of norepinephrine (1), epinephrine (2), 3,4-dihydroxybenzyl-amine (3), dopamine (4), seratonine (5), 5-hydroxy-3-indolylacetic acid (6), and homovanillic acid (7).

The current response of a GCE used for AMD was greatly improved after modification with polyhistidine. LOD was 6 nM for dopamine (10a), 8 nM for epinephrine (15a) and 20 nM for catechol (42). The modified electrode has also been applied for AMD after CE37. PVC membranes were designed to serve as selective barriers for the amperometric detection of phenols and elimination of thiocyanate interference . 

Njagi, J., Chernov, M.M., Leiter, J.C., and Andreescu, S. (2010) Amperometric detection of dopamine in vivo with an enzyme based carbon fiber... 

Figure 11.6.8 Liquid chromatographic separation of tryptophan and tyrosine metabolites using amperometric detection with a glassy carbon working electrode at 0.65 V vs. Ag/AgCl in a thin-layer cell. NE, norepinephrine EPI, epinephrine DOPAC, 3,4-hydroxyphenylacetic acid DA, dopamine 5-HIAA,...

Wallenborg, S. R., Nyhohn, L., and Lunte, C. E. End-column amperometric detection in capillary electrophoresis Influence of separation-related parameters on the observed half-wave potential for dopamine and catechol. AnoZ. Chem. 71,544, 1999. 

Electrochemical detection is less widely used than UV absorbance or LIE detection, but has been used successfully by Ewing and coworkers to detect neurotransmitters within subcellular structures. " Electrochemical detection is attractive because it provides a lower LOD than UV absorbance, does not require sample derivatization, and in the case of amperometric detection, can be tuned to specific classes of compounds. Furthermore, unlike UV absorbance in which the sensitivity is dependent on the sample volume (i.e., the pathlength), the LOD of electrochemical detection improves when applied to miniaturized CE systems, since in this case sensitivity is related to contact between the analyte and the electrode surface. In fact, as described above, LODs in the zepto-mole range for the subcellular quantification of dopamine have been reported, with the sensitivity of these results making electrochemical detection the rival of many LIE detectors. However, the... 

Tu, X., Xie, Q., Jiang, S., and Yao, S. [2007]. Electrochemical quartz crystal impedance study on the overoxidation of polypyrrole-carbon nanotubes composite film for amperometric detection of dopamine. Biosens. Bioelectron., 22, pp. 2819-2826. 

Amperometric Techniques, Fig. 1 Typical electrophe-rogram for catechol and dopamine using amperometric detection on a microchip platform... 

Gordito MP, Kotsis DH, Minteer SD, Spence DM (2003) Flow-based amperometric detection of dopamine in an immobilized cell reactor. J Neurosci Methods 124 129-134... 

Figure 17.1.6 Amperometric monitoring of repeated exocytosis events at artificial cells and cells. (A) Amperometric detection of continuous exocytosis of three vesicles from an artificial cell (scale bars are 40 pA and 3000 msec). (B) Amperometric detection of dopamine exocytosis from a PC12 cell (scale bars are 10 pA and 40 msec). (C) Plot of half-width vs. vesicle radius for vesicles fusing from an artificial cell where the vesicle radius has been the only parameter varied in the experiment. Reproduced with permission from (79).

The initial electrochemical studies on PC 12 cells have focused on quantitation of catecholamine release. Zeptomole levels of catecholamine have been observed for a single-release event using amperometric detection with carbon fiber microelectrodes [15]. To measure the time course of these release events the electrode, held at a potential where dopamine is readily oxidized, is gently placed against the cell surface. Catecholamines are released from individual vesicles following perfusion of the cell with a solution containing nicotine, elevated potassium chloride, or other chemical stimulants. Such agents serve to directly depolarize the... 

Wallenberg, S.R. Nyholm, L. Lunte, C.E. End-Column Amperometric Detection in Capillary Electrophoresis Influence of Separation-Related Parameters on the Observed Half-Wave Potential for Dopamine and Catechol. Anal. Chem. 1999 71, 544-549. 

Amperometry can be used in conjunction with capillary electrophoresis (CE). On chip the CE system uses an electric held for separation of analyte molecules in a narrow channel or capillary on the basis of electrophoretic mobilities of molecules. The CE system usually consists of a sample injection channel, a separation channel, and electrodes for application of electric held, as well as measurement of current signals. There are quite a few instances of such development [56-58]. For example, Wang et al. integrated micromachined capillary electrophoresis with amperometric detection for dopamine detection [59]. The glass chips consist of a separation channel, a sample injection channel, and a thin layer of sputtered An (acting as working electrode) at the outlet of the separahon channel (Fig. 5.11). Dopamine was delected with LOD of 1 pM and linear response from 20 to 200 pM. 

Besides the permselective properties, the electrocatalytic properties of ECP films can be also used for the amperometric detection of some target molecules. Accordingly, electrodes modified with PPy, polythiophene (PTh), PAni, and their derivatives were found to catalyze the electrochemical oxidation of ascorbic acid [127-129], NADH [115, 116,130], dopamine [128], pyrrolo-quinoline quinone [131] as a coenzyme of some oxidoreductases, and quinone and derivatives [132, 133]. Selectivity exhibited by these materials could be enhanced by the introduction of an appropriate substituent onto the polymer backbone. So, a facilitated electron transfer between cytochrome c and carboxylic acid or carboxylate-substituted PPy [134] or polyindole [135] has been observed. As such an effect was not obtained with unsubstituted polymer films, the cytochrome c-polymer interaction was e lained on the basis of binding between the polymer substituents and the lysine residues on the redox protein. 

Warsh J J, Chiu A, Godse D D 1982 Simultaneous determination of norepinephrine, dopamine and seratonin in rat brain regions by ion-pair liquid chromatography on octy silane columns and amperometric detection. J Chromatogr 228 131-141... 

The enzymatic method described above has two disadvantages (1) trapping of CO2 is a cumbersome procedure, and (2) the use of a radioactive substrate requires special precautions for use and disposal of reagents. Measurement of the primary amine formed by decarboxylation of the amino acid can also be exploited to monitor the PLP-dependent, enzyme-catalyzed reaction. This principle has been applied by Allenmark et al. (106), who used L-3,4-dihydroxyphenyl-alanine (L-DOPA) as substrate for tyrosine decarboxylase the dopamine produced by the decarboxylation reaction was determined by HPLC followed by amperometric detection. Both Hamfelt (107) and Lequeu et al. (108) utilized apo-tyrosine decarboxylase with tyrosine as substrate. The tyramine produced by the decarboxylation reaction was separated from the substrate (tyrosine) by HPLC and quantitated by either amperometric (108) or fluorometric (107) detection. The procedures discussed above are still subject to the main disadvantage of enzymatic methods possible interference by other materials present in the PLP containing extract which could either inhibit reconstitution of the holoenzyme or alter the reaction rate of enzyme catalysis. Moreover, HPLC with amperometric detection can hardly be described as less cumbersome than CO2 trapping difficulties in baseline-stabilization encountered with these detectors are well known. 

Nien, P. C., P. Y. Chen, and K. C. Ho. 2009. On the amperometric detection and electrocatalytic analysis of ascorbic acid and dopamine using a poly(acriflavine)-modified electrode. Sens. Actuat. B 140 58-64. 

C. Xue, Q. Han, Y. Wang, J.H. Wu, T.T. Wen, R.Y. Wang, J.L. Hong, X.M. Zhou and H.J. Jiang, Amperometric detection of dopamine in human serum by electrochemical sensor based on gold nanoparticles doped molecularly imprinted polymers. Biosens. Bioelectron., 49 199-203, 2013. 

Cheng, H., Huang, W.-H., Chen, R.-S. et al. 2007. Carbon fiber nanoelectrodes apphed to microchip electrophoresis amperometric detection of neurotransmitter dopamine in rat pheochromocytoma (PC 12) cells. Electrophoresis 28 1579-1586. 

M.J. Schoning, M. Jacobs, A. Muck, D.-T. Knobbe, J. Wang, M. Chatrathi and S. Spillmann, Amperometric PDMS/glass capillary electrophoresis-based biosensor microchip for catechol and dopamine detection, Sens. Actuator B, 108 (2005) 688-694. 

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