A new way to deposit Carbon Nanotubes: application to o-toluidine determination

Pyrolized Photoresist Carbon Electrodes (PPCEs) are fabricated by photolithographic micro-fabrication and pyrolysis of an epoxy-based photoresist named SU-8 [1]. After the electrochemical characterization of these electrodes as a function of the pyrolysis time and SU-8 film thickness, the modification of the PPCE with carbon nanotubes (CNT) is proposed in order to enhance the analytical potentialities of PPCE, improving sensitivity and lowering detection limits, as well as permitting the production of disposable and low cost sensors. Carbon nanotubes are usually dispersed through ultrasonication and diluted in an organic solvent, such as DMF. Cast coating is the most commonly used deposition technique due to its fast and simple procedure, however it lacks in reproducibility and uniformity. A new technique based on two-steps approach has been developed. CNT are first dispersed in a liquid medium and then deposited onto the surface by spray-coating technique. These devices have been completely characterized and employed for the development of a sensor for the detection of o-toluidine, an organic carcinogenic synthetic pollutant, mainly used as an intermediate in production of azo-dyes. In particular, using the optimized electrode configuration, o-toluidine was detected by Linear Sweep Voltammetry in the range 0.5-5 ppm, obtaining a limit of detection of 89 ppb. The new devices are competitive with respect to other carbon-based electrodes, which present problems of fouling. [1] S. Ranganathan, R. McCreery, S. M. Majji, M. Madou, J. Electrochem. Soc. 147 (2000) 277.