Particle to particle and particle to cell interactions in physiologic fluids using Atomic Force Microscopy (AFM)

 Georgios Pyrgiotakis, Christoph Blattman, Joel Cohen, Philip Demokritou

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The formation of protein corona has emerged as a key mechanism in the particle-cell and particle-particle interactions in physiological fluids. While the particle corona formation was studied using proteomics and another analytical techniques, there is a lack of data in terms of atomic forces at the molecular level and their link to bio-interactions. In this novel bottom-up approach we investigate the interactions between particles and between particles and cells in physiological fluids, utilizing the state of the art Atomic Force Microscopy (AFM). Industry relevant ENMs (SiO2, F2O3 and CeO2) were synthesized with the Harvard VENGES flame spray pyrolysis platform and were deposited on pristine Si substrate in the flame. The same ENMS were collected and characterized off-line regarding their size, crystal structure and surface area using state of the art analytical methods. The collected ENMs were also used to modify AFM tips by attaching them on the tip from an ethanol or water suspension under an inverted microscope and the use of micromanipulators. The surfaces and the tips were characterized with SEM before and after each experiment to ensure that the particles did not detach during the experiment. The interaction (adhesion) force between the surface and the tip (particle-particle interaction) was measured in various media (air, water, RPMI and RPMI with FBS) as a function of the particle material and size. Iron oxide particles were found to experience less adhesion between them compared to ceria, in water, while both of them experience the same adhesion in physiological fluid (RPMI and FBS). The measured adhesion is in accordance with the DLVO theory and was verified with the DLS particle size. In addition, the atomic level forces between the particle functionalized tip and lung epithelial cells (A549) adhered on a slide glass and immersed in physiological media were measured.