Performance improvement of macroporous polypyrrole sensor for detection of ammonia by incorporation of magnetite nanoparticles

In this work, polystyrene spheres were employed as templates to prepare polypyrrole inverse opal films on the surface of platinum electrodes. The facilitated access for both outer and inner active sites, as well as the exhibited electrochemical behaviour, turned macroporous PPy into a material more suitable than bulk PPy for electrochemically determining ammonium in samples. However, independently of employing bulk or macroporous polypyrrole, the loss of conductivity suffered by the polymer during the mediating process led to an irreversible increase of the electrical resistance that compromised the sensor's analytical performance. Here, it is shown that the incorporation of magnetite nanoparticles into the walls of the polypyrrole inverse opal films generated a protective effect. This increased the stability of the macroporous mediator due to the preservation of the polaron state, as shown by Raman spectroscopy experiments. Finally, the interaction between polypyrrole and magnetite also positively affected the observed analytical parameters, improving linear range, detection limit and sensitivity of the ammonium sensor.