Low-pH synthesis of colloidal conducting polymers for antibacterial applications

Colloidal conducting polymers (CPs) such as polyaniline (PANI) and polypyrrole (PPy) are typically synthesised using ammonium persulfate (APS), the IUPAC‑recommended oxidant. High conductivity and protonation levels in colloidal CPs are associated with antibacterial activity, and this requires strongly acidic polymerisation media. Iron (III) chloride (FeCl 3 ) as an oxidiser is only effective under weakly acidic or neutral conditions. This study evaluates oxidants capable of supporting colloidal CP formation in low‑pH media, focusing on APS and potassium iodate (KIO 3 ). PANI and PPy colloids were synthesised in 1.25 M aqueous hydrochloric acid (HCl) using polyvinylpyrrolidone (PVP) as a stabiliser. PVP stabilised PANI more effectively than PPy, with PPy dispersions exhibiting greater agglomeration and polydispersity. Morphological analysis revealed fibrous PANI structures and granular or crystalline PPy structures, while dynamic light scattering indicated significant secondary aggregation in both systems. Electrochemical impedance spectroscopy further differentiated the materials: PANI PVP colloids exhibited a semicircular charge‑transfer arc, whereas PPy PVP colloids showed a Warburg‑type diffusion response dominated by ion transport. All CP PVP samples displayed antibacterial activity against Escherichia coli and Staphylococcus aureus. PPy PVP KIO₃ showed the strongest effect, with a minimum bactericidal concentration (MBC) of 0.25 wt%, likely due to enhanced protonation, improved electron transfer, and increased reactive oxygen species generation. These findings demonstrates both APS and KIO 3 can produce antibacterial PPy and PANI colloids under strongly acidic synthesis conditions, with the oxidant choice influencing colloidal stability, morphology, electrochemical behaviour, and antibacterial performance. Future work will assess synthesis scalability and oxidant suitability.