Effects of surface heterogeneity on the colloidal stability, protein adsorption and bacterial interaction of nanoparticles.
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Interfacial processes like aggregation and deposition control the transport and fate of natural and engineering nanoparticles (NPs) in the environment, which are relevant to important environmental processes, applications, and effects of NPs. These processes are controlled by a wide range of NP properties. Depending on the time frame and nature of the interfacial processes, a combination of different techniques (including dynamic light scattering, isothermal titration calorimetry, batch adsorption and spectroscopic techniques) were used to systematically investigate the effects of surface heterogeneity on the colloidal stability, protein adsorption and bacterial interaction of self-assembled monolayer coated gold nanoparticles (AuNPs). These AuNPs have similar size and shape but quantitative difference in the ligand composition and distribution on their surface, therefore serve as ideal models for heterogeneous surfaces that are ubiquitous in the environment and engineering system. Key findings of this work include: 1) In addition to surface chemical composition, the organization of different functional groups on NP surface was also found to influence the electrical double layer structure and the relative contribution of different interfacial forces. Therefore, direct comparison of zeta potential of different particles and the prediction using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory should be made with cautions; 2) The effects of surface heterogeneity were found to be scale-dependent in NP-protein interactions. The size of proteins and surface features of NPs together determined the interaction mechanism (e.g., binding stoichoimetry and forces involved). The interaction mechanism subsequently affects the protein corona structure; 3) When these AuNPs adsorb onto bacterial cells, the adsorption kinetics is in agreement with the DLVO prediction, where the magnitude of electrostatic repulsion determines the diffusion of NPs onto bacterial cell. The adsorption capacity reflects the influence of surface heterogeneity on the association of bacterial surface components with these AuNPs. Overall, these findings improve our understanding on the effects of surface heterogeneity on representative interfacial processes that control the transport and fate of NPs. This work also provided new insights into better design of surfaces for various applications.