Size effects on adsorption of hematite nanoparticles on E. coli cells.

Adsorption of engineered nanoparticles (NPs) onto bacterial cells is critical for quantifying nanobio interactions as well as toxicokinetic properties of NPs. The purpose of this work was to study adsorption of hematite (α-Fe(2)O(3)) NPs onto Escherichia coli cells and to determine the particle size effects on the adsorption kinetics. Adsorption of large NPs (76 and 98 nm) on cells reached equilibrium faster (within 30-40 min) than small NPs (approximately 60-90 min). The adsorption rates in mg Fe/(L · s) decreased in the order of 98 nm > 76 nm > 53 nm > 26 nm. However, adsorption rates expressed as the number of adsorbed hematite NPs per unit cell surface area in #/(m2 · s) were faster for small NPs than those for large NPs. To interpret the size effects on adsorption kinetics, the Extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory was combined with interfacial force boundary layer (IFBL) theory. The computed adsorption rates for different sizes had excellent agreement with the experimental data, and they explained that that faster kinetics for smaller NPs could be attributed to faster particle mobility and lower energy barriers in the total interaction energy. This study lays the groundwork for quantifying the kinetic behavior of NPs interacting with microbial cells, and the results provide insight into adsorption processes at the nanoscale.