Nanocomposite antimicrobials prevent bacterial growth through the enzyme-like activity of Bi-doped cerium dioxide (Ce1−xBixO2−δ)

Abstract

Preventing bacterial adhesion on materials surfaces is an important problem in marine, industrial, medical and environmental fields and a topic of major medical and societal importance. A defense strategy of marine organisms against bacterial colonization relies on the biohalogenation of signaling compounds that interfere with bacterial communication. These reactions are catalyzed by haloperoxidases, a class of metal-dependent enzymes, whose activity can be emulated by ceria nanoparticles. The enzyme-like activity of ceria was enhanced by a factor of 3 through bismuth substitution (Ce_1−xBi_xO_2−δ). The solubility of Bi³⁺ in CeO₂ is confined to the range 0 < x < 0.25 under quasi-hydrothermal conditions. The Bi³⁺ cations are located close to the nanoparticle surface because their ionic radii are larger than those of the tetravalent Ce⁴⁺ ions. The synthesis of Ce_1−xBi_xO_2−δ (0 < x < 0.25) nanoparticles was upscaled to yields of ∼50 g. The halogenation activity of Ce_1−xBi_xO_2−δ was demonstrated with phenol red assays. The maximum activity for x ≈ 0.2 is related to the interplay of the ζ-potential of surface-engineered Ce_1−xBi_xO_2−δ nanoparticles and their BET surface area. Ce_0.80Bi_0.20O_1.9 nanoparticles with optimized activity were incorporated in polyethersulfone beads, which are typical constituents of water filter membrane supports. Although Ce_1−xBi_xO_2−δ nanoparticles are not bactericidal on their own, naked Ce_1−xBi_xO_2−δ nanoparticles and polyethersulfone/Ce_1−xBi_xO_2−δ nanocomposites showed a strongly reduced bacterial coverage. We attribute the decreased adhesion of the Gram-negative soil bacterium Pseudomonas aeruginosa and of Phaeobacter gallaeciensis, a primary bacterial colonizer in marine biofilms, to the formation of halogenated signaling compounds. No biocides are needed, H₂O₂ (formed in daylight) and halide are the only substrates required. The haloperoxidase-like activity of Ce_1−xBi_xO_2−δ may be a promising starting point for the development of environmentally friendly, “green” nanocomposites, when the use of conventional biocides is prohibited.