Visible-light-driven antibacterial activity of poly(3-hexylthiophene-2,5-diyl) nanoparticles

Sterilisation using photocatalysts does not lead to the development of drug-resistant bacteria and has therefore attracted significant attention. Particularly, organic semiconductors typically comprise earth-abundant elements and allow facile tuning of their material properties through organic synthesis. A representative organic semiconductor, poly(3-hexylthiophene-2,5-diyl) (P3HT), exhibits visible-light absorption and efficient charge-transport properties owing to its π-conjugated structure, emphasising its potential for visible-light-driven photocatalysis. However, the hydrophobic nature of P3HT makes it difficult to employ in aqueous environments conducive to bacterial growth while maintaining its chemical structure. In this work, to investigate the antibacterial activity of hydrophobic organic semiconductors in aqueous environments, P3HT nanoparticles (NPs) with diameters ranging approximately 40-100 nm were prepared via reprecipitation, enabling stable dispersion in aqueous solution while maintaining the molecular structure of P3HT. P3HTNPs with higher regioregularity and larger specific surface areas generate greater amounts of reactive oxygen species and exhibit an enhanced antibacterial activity. P3HTNPs with 99% regioregularity and an average particle diameter of 42 nm achieved a sterilisation rate of 99% against E. coli after 6 h of visible-light irradiation. This work demonstrates that predominantly hydrophobic organic semiconductors can be developed as photocatalysts capable of sterilisation in aqueous environments through NP formation.