Heavy metal detection by electrochemical electronic tongue with poly(thiophene)-metal oxide nanoparticle composite electrodes

Rapid monitoring methods of heavy metals in water are in great demand for industrial environmental managements. This work aims to develop a heavy metal sensing device based on an electrochemical electronic tongue using a hybrid composite of metal oxide nanoparticles and conductive polymer as the working electrodes. The electrodes were prepared by drop-casting colloidal mixtures of Regioregular poly(3-hexylthiophene) (P3HT) and metal oxide nanoparticles (ZnO or TiO₂) in chloroform onto a fluorine-doped tin oxide (FTO) glass. Optical microscopy measurements reveal some microstructural organization of the metal oxide-P3HT composite films on the electrodes, in comparison to a smooth P3HT film. Cyclic voltammetry (CV) measurements using bare FTO, P3HT, P3HT/ZnO and P3HT/TiO₂ electrodes were performed on aqueous solutions of various metal acetates at the concentration of 0.01M. The Principal Component Analysis (PCA) was applied to the CV results to obtain the classification of the data from the various metal salt solutions. The PCA score plot exhibits a clear separation of the data groups of different heavy metals, with the highest distinction between zinc and lead. The PCA loading plot confirms that the different electrochemical nature of the various electrodes is responsible for such distinctive classification. Further work is to examine the capability of the electrochemical electronic tongues for semi-quantitative analyses of the metal salt concentration.