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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 micron-sized porous particles.We recently found that the axial motion of individual biomolecules inside nanopores can be significantly slower than in bulk solution, even for surface-modified nanopores that are resistant to molecular adsorption.This suggests that the viscosity inside the nanopores was unusually high.In this study, we measured the electrophoretic motion as well as the diffusion of individual nanoparticles in alumina cylindrical nanopores.We found that both electrophoretic mobilities and diffusion coefficients of 85 nm and 50 nm polystyrene particles were reduced by a factor of 20~25 inside 200 nm nanopores.This confirms that the microenvironment in nanoscopic dimensions is anomalous, yielding an apparent viscosity 20~25 times larger than that of bulk solutions.