Amperometric biosensor for choline based on layer-by-layer assembled functionalized carbon nanotube and polyaniline multilayer film

Conducting polymer film was prepared by electrochemical polymerization of aniline. Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. By using the layer-by-layer method, homogeneous and stable MWNTs and polyaniline (PANI) multilayer films were alternately assembled on glassy carbon (GC) electrodes. Conducting polymer of PANI had three main functions: (i) excellent antiinterference ability, (ii) protection ability in favor of increasing the amount of the MWNTs immobilized on GC electrodes, and (iii) superior transducing ability. The protection effect of PANI film and the electrostatic interaction between positively charged PANI and negatively charged MWNTs both attributed to immobilizing abundant MWNTs stably, thereby enhancing the catalytic activity. The layer-by-layer assembled MWNTs and PANI-modified GC electrodes offered a significant decrease in the overvoltage for the H2O2 and were shown to be excellent amperometric sensors for H2O2 from +0.2V over a wide range of concentrations. As an application example, by linking choline oxidase (CHOD), an amplified biosensor toward choline was prepared. The choline biosensor exhibited a linear response range of 1x10(-6) to 2x10(-3) M with a correlation coefficient of 0.997, and the response time and detection limit (S/N=3) were determined to be 3 s and 0.3 microM, respectively. The antiinterference biosensor displays a rapid response and an expanded linear response range as well as excellent reproducibility and stability.