Langmuir-Blodgett film and carbon paste electrodes based on phthalocyanines as sensing units for taste

In this work, the possibility of using voltammetric electrodes based on phthalocyanine compounds as the sensing units of an electronic tongue has been investigated. Sensors based on monophthalocyanines (including cobalt and copper phthalocyanines) and lanthanide bisphthalocyanines (comprising europium, gadolinium and lutetium bisphthalocyanines and the octa-tertbutyl substituted praseodymium bisphthalocyanine) have been prepared using two different methods: the Langmuir-Blodgett (LB) technique and the carbon paste electrode (CPE) technique. The sensors have been used to evaluate the five types of basic tastes (sweet, bitter, salty, acid and umami). Each phthalocyanine shows a characteristic electrochemical response for the solutions investigated. The electrochemical response towards the five basic types of flavours is particularly rich in the case of the bisphthalocyanine compounds. The responses of the sensors prepared using the LB technique has been compared with that of the sensing units prepared by the CPE technique. The response of both types of electrodes is similar, but in the case of the LB films the peaks are better resolved, and the electrodes show a very good repeatability. Nevertheless, their reproducibility is lower than for the CPE electrodes. The electrochemical studies indicate that the charge transport in both types of electrodes is diffusion controlled. A multichannel taste sensor has been constructed using those sensors with the best performances. The array of sensors has been exposed to solutions of the five basic flavours. The principal component analysis (PCA) of the obtained signals has allowed the discrimination of basic tastes.