Nanosensors applied to water quality: developing a low-cost pH sensor for natural water, and application of other techniques

A low-cost optical sensor built-in strip has been developed from a composite obtained with application of in-situ chemical polymerisation, using polyaniline in the emeraldine oxidation state, doped with HCl onto poly(ethylene terephthalate) (PET) film, used to measured the pH of water. The absorption of UV-Vis spectra was used to evaluate the optical response to pH change of natural water. The strip showed a reversible colour change upon variation of the pH. The pH range used to calibrate the optical sensor was from 2.0 to 12.0. These kinds of sensors show the potential to investigate the pH of natural waters, with application to limnological studies, as well as to investigate the influence of the ionic strength. This paper describes new techniques that can be used to conduct research with pesticides in water using electrochemistry and biosensors, and an electronic tongue with conductive polymers for global quality evaluation.