In this work, we synthesized a type of compound, MWCNTs-CONH-(CH2)(2)-SH, via carboxylation, and investigated a thickness-tunable multilayer films DNA biosensor built by layer-by-layer (LBL) covalent attachment of gold nanoparticles (GNPs) and multi-walled carbon nanotubes (MWCNTs) on an Au electrode. Fourier transform infrared (FT-IR) spectra were used to identify the products formed in the step of carboxylation: scanning electron microscopy (SEM) and cyclic voltammetry (CV) were used to study the film assembly process. The hybridization events were monitored through measurement the signal of intercalated doxorubicin by differential pulse voltammetry (DPV), and the oxidation peak currents show a good linear relationship with the logarithm of the concentration of target DNA from 5.0 x 10(-10) to 1.0 x 10(-11) M with a detection limit of 6.2 pM. The improved DNA biosensor has a good stability and reproducibility. (C) 2008 Elsevier Ltd. All rights reserved.