A simple route to fabricate controllable and stable multilayered all-MWNTs films and their applications for the detection of NADH at low potentials

This study demonstrates a polyelectrolyte-free method to fabricate controllable and stable all-MWNTs films via a covalent layer-by-layer (LBL) deposition. Aminated MWNTs and carboxylated MWNTs were prepared by surface functionalization, allowing the incorporation of MWNTs into highly tunable thin films through the formation of covalent amide bonds. Fourier transform infrared spectroscopy (FTIR) analysis demonstrated the formation of covalent linkages between MWNTs layers. Scanning electron microscopy (SEM) and ultraviolet–visible spectroscopy (UV–vis) were used to characterize the assembly process. Electrochemical studies indicated that the all-MWNTs film possessed a remarkable electrocatalytic activity toward dihydronicotinamide adenine dinucleotide (NADH) at relatively low potentials, without the need for redox mediators. The film thickness and the amount of assembled MWNTs were readily adjusted by simply changing the number of cycles in the LBL assembly process, which also effectively tuned the electrocatalytic activity of the film toward NADH. The film constructed with four bilayers showed a high sensitivity of 223.8μAmM−1cm−2 and a detection limit of 1.5μM, with a fast response of less than 3s. Furthermore, the all-MWNTs film also showed good selectivity and excellent stability for the determination of NADH. ► A covalent layer-by-layer self-assembly strategy to prepare all-MWNTs films is reported. ►The resulting film was uniform with a large accessible surface area. ► We applied this all-MWNTs film for the highly sensitive detection of NADH. ► The electrocatalytic activity was adjusted by simply changing the number of cycles in the LBL assembly process. ► The low applied potential minimized the interference, which improved the selectivity of the biosensor.