Emerging investigator series: enhanced peroxidase-like activity and improved antibacterial performance of palladium nanosheets by an alginate-corona

Once released into the natural environment, ecological macromolecules can rapidly form a coronal architecture on the surface of engineered nanomaterials, altering their intrinsic physicochemical properties as well as nano-bio interactions. Palladium (Pd)-based nanomaterials attract an increasing attention in the fields of environmental science, due to their remarkable catalytic activity. However, the current understanding of the interplay between Pd-based nanomaterials and ecological macromolecules remains limited. In this study, taking two-dimensional Pd nanosheets (Pd NSs) as a representative, we characterized the corona formation of four ecological substances (i.e. humic acid, fulvic acid, alginate and Suwannee River natural organic matter) on the Pd NS surface, and assessed their influence on the peroxidase-like activity of Pd NSs. Our findings showed that the overcoating of alginate-corona on Pd NS surface could significantly enhance the peroxidase-like activity of Pd NSs, but not the other three, thus leading to the fast generation of hydroxyl radicals (HO). Moreover, the antibacterial activity of the pristine and alginate-coronated Pd NSs was respectively examined with both Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa). The growth inhibition assay yielded the half maximal inhibitory concentration (IC50) values of the pristine Pd NSs ranging from 4.6 to 12.1 mu g mL(-1) and the alginate-coronated Pd NSs ranging from 2.0 to 6.7 mu g mL(-1), respectively. The higher toxicity of the alginate-coronated Pd NSs was demonstrated to be attributed to the formation of alginate-corona and enhanced HO radical production ability, giving rise to bacterial membrane damage, oxidative stress, biofilm inhibition and cell death. Our findings may facilitate an in-depth understanding of the crucial role of environmental corona in the exotoxicological risks and antibacterial performance of engineered nanomaterials.