In this study we develop a sensor based on helical carbon nanotubes (HCNTs) for the simultaneous electrochemical determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). A water soluble cationic polymer, poly(diallyl dimethylammonium chloride) (PDDA), is used to functionalize the nanotubes' surface, aiming to improve the HCNTs dispersibility and adhesion to substrates. After electrochemical pre-treatment, the PDDA@HCNTs coated glassy carbon electrodes can separate the anodic oxidation potential of AA, DA and UA with well-defined peak separation in the presence of each other. The calibration curves were obtained in the range of 25-1045 mu M L-1 for AA, 2.5-10 mu M L-1 for DA, and 5.0-175 mu M L-1 for UA. Detection limits of 0.12 mu M L-1, 0.08 mu M L-1, and 0.22 mu M L-1 were obtained for AA, DA, and UA at pH 7.4, respectively. The analytical performance of this sensor has been evaluated for simultaneous detection of AA, DA, and CIA in the fetal bovine serum samples. (C) 2012 Elsevier Ltd. All rights reserved.