Simultaneous voltammetric detection of dopamine and uric acid at their physiological level in the presence of ascorbic acid using poly(acrylic acid)-multiwalled carbon-nanotube composite-covered glassy-carbon electrode

The use of poly(acrylic acid) (PAA)-multiwalled carbon-nanotubes (MWNTs) composite-coated glassy-carbon disk electrode (GCE) (PAA-MWNTs/GCE) for the simultaneous determination of physiological level dopamine (DA) and uric acid (UA) in the presence of an excess of ascorbic acid (AA) in a pH 7.4 phosphate-buffered solution was proposed. PAA-MWNTs composite was prepared by mixing of MWNTs powder into 1 mg/ml PAA aqueous solution under sonication. GCE surface was modified with PAA-MWNTs film by casting. AA demonstrates no voltammetric peak at PAA-MWNTs/GCE. The PAA-MWNTs composite is of a high surface area and of affinity for DA and UA adsorption. DA exhibits greatly improved electron-transfer rate and is electro-catalyzed at PAA-MWNTs/GCE. Moreover, the electro-catalytic oxidation of UA at PAA-MWNTs/GCE is observed, which makes it possible to detect lower level UA. Therefore, the enhanced electrocatalytic currents for DA and UA were observed. The anodic peak currents at ∼0.18 V and 0.35 V increase with the increasing concentrations of DA and UA, respectively, which correspond to the voltammetric peaks of DA and UA, respectively. The linear ranges are 40 nM to 3 μM DA and 0.3 μM to 10 μM UA in the presence of 0.3 mM AA. The lowest detection limits (S/N = 3) were 20 nM DA and 110 nM UA.