The enhancement of the oxidation current of DA was possible due to its diffusion through the cyclodextrin cavities and the facile contact with the dispersed MWCNTs. Moreover, Li et al. found that polypyrrole SWCNTs composite film can detect DA, AA, and UA simultaneously, and it showed the electrocatalytic activity towards the oxidation of nitrite. Zhou,s group reported that the modified electrode with poly and MWCNTs can suppress the oxidation peak of AA but enhance MP-470 the DA and UA signals. The application of poly functionalized MWCNTs was also reported by Yogeswaran and Chen for the simultaneous detection of AA, UA, and DA. The clear separation of peaks was attributed to the electrostatic and hydrophobic interaction between the three analytes and the fixed cationic sites on polymer backbone as well as the functionalized MWCNTs, which are negatively charged.
Another important catecholamine neurotransmitter is epinephrine, which . In biological fluids such as blood and urine, EP coexists with AA, and UA, so AA and UA may interfere during the electrochemical AB1010 detection of EP at an unmodified electrode. CNTs modified electrodes have been successfully used for the determination of EP. Chen,s group developed a method for simultaneous determination of AA, EP, and UA at physiologically relevant conditions by using the composite film composed of functionalized MWCNTs and Nafion incorporating platinum and gold nanoparticles. The oxidation peaks for AA, EP, and UA were separately observed and thus, the detections of these compounds did not interfere with each other. An EP sensor prepared by an in situ electropolymerization of brilliant cresol blue was reported by Yi et al.
In this work, the GCE modified by the film of polymeric BCB and functionalized MWCNTs composite were used to detect EP. A low detection limit of 10 nM was obtained by using the BCB and functionalized MWCNTs nanocomposite. However, the authors did not discuss the issue of interference from other biological compounds such as AA. Valentini et al. used functionalized SWCNTs instead of MWCNTs for the selective detection of EP in the presence of AA. They used the stainless steel microelectrodes modified by hydroxyl group functionalized SWCNTs, which were deposited electrophoretically. The presence of electron donating OH groups on SWCNTs repels AA and attracts the positively charged EP. It provided a relatively high electrochemical sensitivity for EP up to the detection limit of 2.
0 nM. Nicotinamide adenine dinucleotide is a coenzyme involved in a wide range of enzymatic reactions. The direct oxidation of NADH at a bare electrode needs a high overpotential. CNT modified electrode can be used for the stable low potential detection of NADH. Zhai et al. developed a multilayer film of MWCNTs and chitosan using the layer by layer method by taking advantage of the interaction between a positively charged CS and the negatively charged MWCNTs. They assembled nine layers of CS/MWCNTs successfully, which showed a very rapid and stable response of NADH oxidation at about 400 mV with the detection limit of 0.3 M. A layerby layer approach is an efficient way to increase the amount of catalyst or enzyme at the sensor surface. However, the thickness of the multilayer need to be optimized as the sensor response can be suppressed by the very thick multilayer.