Acid-assisted polymerization: the novel synthetic route of sensing layers based on PANI films and chelating agents protected by non-biofouling layer for Fe 2+ or Fe 3+ potentiometric detection.

A new synthetic method for the fabrication of a sensing layer is presented. PANI films as an ion-to-electron transducer were prepared via acid-assisted polymerization in concentrated formic acid (HCOOH) in the presence of ethanol and ammonium persulfate (APS, as the initiator). The ratio of monomer to ammonium persulfate was 1 : 0.1. 2,2-Bipyridyl, 1,10-phenanthrolin-5-amine, and 8-hydroxyquinoline were used as chelating agents that can complex Fe 2+ or Fe 3+ ions. The proposed sensors demonstrated an appropriate reproducibility with a rapid response to the presence of Fe 2+ or Fe 3+ ions, even at T ∼ 37 °C. It was revealed that the method of deposition of a chelating molecule affects the response of sensors. The in situ deposition during acid-assisted polymerization leads to a fast response compared to the layer-by-layer deposition. PMeOx/X 1 -PANI@FTO and PMeOx/Z 1 -PANI@FTO sensors exhibit rapid response and are considered a promising detection layer for Fe 2+ or Fe 3+ ions respectively. We envision that this system can contribute to the next generation of advanced bio-sensors for the potentiometric detection of iron.