Optimization of the structural parameters of new potentiometric pH and urea sensors based on polyaniline and a polysaccharide coupling layer

Screen-printed carbon electrodes were modified with polyaniline by electrochemical oxidation to produce a potentiometric pH transducer. The resulting pH sensor exhibited a fast, reproducible and sensitive potentiometric response of approximately 59 mV per pH unit from pH 4 to 8. The pH sensor response was found to be stable in time for up to one month. Such potentiometric response was obtained for thick polyaniline films. Thinner polymer films exhibited less sensitive responses and were found to have a smaller lifetime. The sensitivity of polyaniline to pH variations was then used to design an enzymatic biosensor. For that purpose, urease was immobilized on a polyelectrolyte multilayer film (PEM), obtained by the alternate deposition of charged polysaccharides (layer-by-layer assembly, LbL), over the polyaniline film. Covalent grafting of the urease enzyme to the PEM film was also tested using carbodiimide coupling reaction. The potentiometric response of this assembly to pH variations was similar to the one of polyaniline films, and its response to urea, from 10−4 to 10−1 mol L−1, exhibited a very high sensitivity combined to fast response, good lifetime and reproducibility. The number of polyelectrolyte layers composing the PEM film was also found to affect the response of the urea sensors.