Examination of nano-C60 aggregates through dialysis membranes as surrogates for cell membrane diffusion

Kelly Lookabill Stump

Nanoparticles in the environment are naturally ubiquitous but the increased introduction of nanoscale materials may have unintended ecotoxicological effects. One nanoparticle produced in large quantities is buckminsterfullerene or C60. Studies confirmed the formation of C60 aggregates (nano-C60) as C60 come into contact with water. Suspensions of nano-C60 may also have ecotoxicological properties. Studies have shown that C60 and nano-C60 cause cellular membrane stress, lipid peroxidation of the phospholipid bilayer, and readily move into the cell. Conversely, another study showed that C60‟s do not penetrate into the lipid bilayer because they adsorb to the hydrophilic functional groups. Whether nano-C60 has potential for toxicological effects depends on whether nano-C60 can diffuse through membranes. Because of the conflicting observations of nano-C60 interactions with a phospholipid bilayer, this study proposed using dialysis membranes as surrogates for cellular membranes. Use of dialysis membranes reduces the question of cellular toxicity interaction to one aspect of toxicological properties, what size nanoparticles can diffuse through pores in cells. A bulk suspension of nano-C60 was produced and dialysis cells of variable pore size were used to determine if nano-C60 was diffusing into the interior water. UV/Visible spectrophotometry, atomic force microscopy, and transmission electron microscopy techniques examined the aggregate formation in the bulk solution and within the dialysis membranes. Particle sizes tended to increase in direct proportion to dialysis membrane pore size. The particles were larger than expected based on pore size, but C60 aggregation may have continued inside the cells. Some AFM images unexpectedly contained lines swirled around the particles recovered from dialysis cells but not surrounding particles in the bulk suspension. TEM images did not show any line formation but the TEM does not have the resolution of the AFM due to the grid it is prepared upon. The experiment showed the smallest dialysis pores effectively reduced diffusion of nano-C60. This observation suggests that environmental exposures to nano-C60 won't necessarily lead to bioavailability because plasma membrane pore diameters are likely smaller than the dialysis pores that effectively excluded buckyball diffusion. But if increased pore size is occurring due to cellular rupture, diffusion rate would then become important.

Examination of nano-C60 aggregates through dialysis membranes as surrogates for cell membrane diffusion

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