Enhancement of dopamine sensing by layer-by-layer assembly of PVI-dmeOs and Nafion on carbon nanotubes

In this study, carbon nanotubes (CNTs) were modified to further improve their performance in electrochemical sensing of dopamine (DA) levels. After a redox polymer, poly(vinylimidazole) complexed with Os(4,4'-dimethyl-2,2-bipyridine)(2)Cl (termed PVI-dmeOs) was electrodeposited on multi-wall CNTs (MWCNTs), Nafion and PVI-dmeOs films were successfully layer-by-layer (LBL) assembled on the hydrophilic surface of the as-prepared PVI-dmeOs/CNTs nanocomposites through electrostatic interactions. The LBL assembly was proved by scanning electron microscopy (SEM), electrochemistry and UV-vis spectroscopy measurements. LBL assembly of Nafion/PVI-dmeOs films on CNTs significantly enhanced their linear sweep voltammetry (LSV) response sensitivity to DA, with a maximum enhancement for three Nafion/PVI-dmeOs film-modified MWCNTs. The LSV peak current density of (Nafion/PVI-dmeOs)(3)/CNT electrodes in response to 10 and 50 mu M DA solutions was about 7.3 and 3.9 times those for bare CNTs. At the (Nafion/PVI-dmeOs) 3/CNT electrodes, the limit of detection (LOD) (signal-to-noise ratio: 3) was 0.05 mu M DA, the linear range was 0.1-10 mu M DA (with a linear regression coefficient of 0.97) and the DA-sensing sensitivity was 8.15 mu A cm(-2) mu M(-1). The newly fabricated (Nafion/PVI-dmeOs) 3/CNT electrodes may be developed as an ideal biosensor for direct and in situ measurement of DA levels.