Role of nanomaterial physicochemical properties on fate and toxicity in bacteria and plants

Nanomaterials, defined as those having at least one dimension <100 nm, are ubiquitous in nature. However, engineered nanomaterials have gained increasing attention for use in drug-delivery applications and consumer goods. Examination of nanomaterial toxicity, both beneficial (e.g., drug delivery to bacterial pathogens) and detrimental (e.g., death of terrestrial plants), thus warranted. Herein, I present the evaluation of nitric oxide-releasing nanomaterial toxicity to bacteria and silica particle toxicity to plants as a function of nanomaterial physicochemical properties.;Nanomaterial toxicity toward planktonic (i.e., free-floating) Pseudomonas aeruginosa and Staphylococcus aureus bacteria was evaluated as a function of scaffold size, shape, and exterior functionality using nitric oxide-releasing (NO) silica particles, dendrimers, and chitosan oligosaccharides. Improved bactericidal efficacy was observed for silica particles with decreased size and increased aspect ratio (i.e., rod-like) due to improved particle-cell interactions. Likewise, better nanomaterial-bacteria association and biocidal action was noted for more hydrophobic NO-releasing dendrimers and chitosan oligosaccharides. Planktonic bacterial killing was not dependent on chitosan molecular weight due to rapid association between the cationic scaffolds and negatively-charged bacterial cell membranes.;Given the importance of nanomaterial physicochemical properties in planktonic bacterial killing, the NO-releasing scaffolds were also evaluated against clinically-relevant bacterial biofilms. Similar to planktonic studies, smaller particle sizes proved more efficient in delivering NO throughout the biofilm. Particles with rod-like shape also eradicated biofilms more effectively. The role of NO-releasing dendrimer and chitosan oligosaccharide hydrophobicity was prominent in scaffold diffusion through the biofilm and subsequent NO delivery, with hydrophobic functionalities generally exhibiting better bacterial association. Lastly, biofilm eradication was more effective for NO-releasing dendrimers exhibiting sustained NO-release compared to delivery of NO via an intial burst.;Phytotoxicity and uptake of silica nanoparticles was evaluated for the plant, Arabidopsis thaliana, as a function of particle size, surface composition, and shape (i.e., spherical versus rod-like particles). Overall, the silica nanoparticles examined were found to be relatively non-toxic to A. thaliana plants when pH effects were mitigated. Size-dependent uptake of the silica particles was observed; however no shape-dependent uptake was noted at the low exposure concentration examined.