Preparation and analytical application of pyrolized photoresist carbon electrodes modified with carbon nanotubes

Pyrolized Photoresist Carbon Electrodes (PPCEs) are fabricated by photolithographic micro-fabrication and pyrolysis of an epoxy-based photoresist named SU-8 [1]. SU-8 derived carbon tends to be glassy in nature however, based on the fabrication and pyrolysis strategies one can obtain a range of electrical, electrochemical and thermal properties related to the tuning of the graphitic content of the thus obtained carbon. To this aim, the electrochemical behaviour of PPCEs is examined as a function of the pyrolysis time and SU-8 film thickness. The results of the electrical, spectroscopic and diffractometric characterization of the PPCEs are reported and discussed with reference to the observed voltammetric performances. 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. The surface is heated at a temperature higher than the boiling point of the solvent, allowing an efficient dry of the electrode. Changing the number of spray treatments it is possible to find the best electrode modification. These devices have been completely characterized by Cyclic Voltammetry and Impedance Spectroscopy and finally 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, as well as excellent apparent recovery factors (99%) and repeatability. 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.