Electrophoretic Migration
and Axial Diffusion of Individual
Nanoparticles in Cylindrical Nanopores
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Abstract
Membranes with straight, vertical nanopores have found
widespread
applications in chemical and biological sciences, including separation,
detection, catalysis, and drug delivery. They can also serve as a
model system to understand molecular behavior and fundamental mechanisms
of separation, bridging the gap between conventional model systems
such as flat surfaces and real chromatographic stationary phases such
as micrometer-sized porous particles. We recently found that the axial
motion of individual biomolecules inside nanopores can be significantly
slower than in bulk solution. This suggests that either chromatographic
adsorption was present and/or the viscosity inside the nanopores was
unusually high. In this study, we measured the electrophoretic motion
as well as the axial diffusion of individual nanoparticles in cylindrical
alumina nanopores. We found that the electrophoretic mobilities and
the diffusion coefficients of polystyrene nanoparticles were both
substantially smaller compared to bulk solution independent of particle
size or pore diameter. The results imply that the apparent solution
viscosity in nanodomains is anomalous