Properties of polyaniline/carbon nanotube multilayer films in neutral solution and their application for stable low-potential detection of reduced beta-nicotinamide adenine dinucleotide.

A conducting polymer, polyaniline (PANI), was successfully assembled with commercially available poly(aminobenzenesulfonic acid)-modified single-walled carbon nanotubes (PABS-SWNTs) via the simple layer-by-layer method. PABS-SWNTs inside the multilayer film can dope PANI effectively and shift its electroactivity to a neutral pH environment, pointing to their potential biological applications. The obtained PANI/PABS-SWNTs multilayer films are very stable and show a high electrocatalytic ability toward the oxidation of reduced beta-nicotinamide adenine dinucleotide (NADH) at a much lower potential (about +50 mV vs Ag/AgCl), which makes it an ideal substrate for NADH detection and offers great promise for developing dehydrogenase-based biosensors depending on NADH as a cofactor. For a six-bilayer sample, the detection limit can go down to 1 x 10(-6) M as detected by the simple cyclic voltammetry method, with a linear detection range for NADH at concentrations between 5 x 10(-6) and 1 x 10(-3) M. The substrate can be used repeatedly for consecutive detection cycles of NADH with a very stable signal.