A new type of pH biosensor was developed for biological applications. This biosensor was fabricated using silicon microsystem technology and consists in two platinum microelectrodes. The first microelectrode was coated by an electrosynthesized polymer and acted as the pH sensitive electrode when the second one was coated by a silver layer and was used as the reference electrode. Then, this potentiometric pH miniaturized biosensor based on electrosynthesized polypyrrole or electrosynthesized linear polyethylenimine films was tested. The potentiometric responses appeared reversible and linear to pH changes in the range from pH 4 to 9. More, the responses were fast (less than 1 min for all sensors), they were stable in time since PPy/PEI films were stable during more than 30 days, and no interference was observed. The influence of the polymer thickness was also studied.

In recent years, there has been a growing interest in electrodes chemically modified with electropolymerized films and in their application as potentiometric pH sensors since the protonation of nitrogen or oxygen atoms in the polymers are expected to impart a pH response to the modified electrode. If glass membrane electrodes are still the most often used pH sensors, the polymer-based pH electrodes have many advantages compared with traditional glass membrane pH electrodes. For example they can be miniaturized and so be useful for clinical or biological applications such as in vivo analysis.