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Designing the size, morphology and interfacial charge of catalyst particles at the nanometer scale can enhance their performance. We demonstrate this with nanoceria which is a functional mimic of haloperoxidases, a group of enzymes that halogenates organic substrates in the presence of hydrogen peroxide. These reactions in aqueous solution require the presence of H 2 O 2 . We demonstrate in situ generation of H 2 O 2 from a CaO 2 reservoir in polyether sulfone (PES) and poly(vinylidene fluoride) (PVDF) polymer beads, which circumvents the external addition of H 2 O 2 and expands the scope of applications for haloperoxidase reactions. The catalytic activity of nanoceria was enhanced significantly by Bi 3+ substitution. Bi-doped mesoporous ceria nanoparticles with tunable surface properties were prepared by changing the reaction time. Increasing reaction time increases the surface area S BET of the mesoporous Bi 0.2 Ce 0.8 O 1.9 nanoparticles and the Ce 3+ /Ce 4+ ratio, which is associated with the ζ -potential. In this way, the catalytic activity of nanoceria could be tuned in a straightforward manner. H 2 O 2 required for the reaction was released steadily over a long period of time from a CaO 2 storage depot incorporated in polyether sulfone (PES) and poly(vinylidene fluoride) (PVDF) beads together with Bi 0.2 Ce 0.8 O 1.9 particles, which may be used as precision fillers and templates for biological applications. The spheres are prepared as a dry powder with no surface functionalization or coatings. They are inert, chemically stable, and safe for handling. The feasibility of this approach was demonstrated using a haloperoxidase assay.

Bacterial biofilm formation is a huge problem in industry and medicine. Therefore, the discovery of anti-biofilm agents may hold great promise. Biofilm formation is usually a consequence of bacterial cell-cell communication, a process called quorum sensing (QS). CeO 2 nanocrystals (NCs) have been established as haloperoxidase (HPO) mimics and ecologically beneficial biofilm inhibitors. They were suggested to interfere with QS, a mechanism termed quorum quenching (QQ), but their molecular mechanism remained elusive. We show that CeO 2 NCs are effective QQ agents, inactivating QS signals by bromination. Catalytic bromination of 3-oxo-C 12 -AHL a QS signaling compound used by Pseudomonas aeruginosa , was detected in the presence of CeO 2 NCs, bromide ions, and hydrogen peroxide. Brominated acyl-homoserine lactones (AHLs) no longer act as QS signals but were not detected in the bacterial cultures. Externally added brominated AHLs also disappeared in P. aeruginosa cultures within minutes of their addition, indicating that they are rapidly degraded by the bacteria. Moreover, we detected the catalytic bromination of 2-heptyl-1-hydroxyquinolin-4(1 H )-one (HQNO), a multifunctional non-AHL QS signal from P. aeruginosa with antibacterial and algicidal properties controlling the expression of many virulence genes. Brominated HQNO was not degraded by the bacteria in vivo. The repression of the Pseudomonas quinolone signal (PQS) production and biofilm formation in P. aeruginosa through the catalytic formation of Br-HQNO on surfaces with coatings containing CeO 2 enzyme mimics validates the non-toxic strategy for the development of anti-infectives.

Highly transparent CeO 2 /polycarbonate surfaces were fabricated that prevent adhesion, proliferation, and the spread of bacteria. CeO 2 nanoparticles with diameters of 10-15 nm and lengths of 100-200 nm for this application were prepared by oxidizing aqueous dispersions of Ce(OH) 3 with H 2 O 2 in the presence of nitrilotriacetic acid (NTA) as the capping agent. The surface-functionalized water-dispersible CeO 2 nanorods showed high catalytic activity in the halogenation reactions, which makes them highly efficient functional mimics of haloperoxidases. These enzymes are used in nature to prevent the formation of biofilms through the halogenation of signaling compounds that interfere with bacterial cell-cell communication ("quorum sensing"). Bacteria-repellent CeO 2 /polycarbonate plates were prepared by dip-coating plasma-treated polycarbonate plates in aqueous CeO 2 particle dispersions. The quasi-enzymatic activity of the CeO 2 coating was demonstrated using phenol red enzyme assays. The monolayer coating of CeO 2 nanorods (1.6 μg cm -2 ) and the bacteria repellent properties were demonstrated by atomic force microscopy, biofilm assays, and fluorescence measurements. The engineered polymer surfaces have the ability to repel biofilms as green antimicrobials on plastics, where H 2 O 2 is present in humid environments such as automotive parts, greenhouses, or plastic containers for rainwater.