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Resistive pulse asymmetry for nanospheres passing through tunable submicron pores

Geoff R. Willmott and Beth E. T. Parry
J. Appl. Phys. 109, 094307 (2011)

Asymmetric resistive pulses caused by nanoparticles passing through tunable nanopores have been recorded and studied using a semianalytic physical model. Experiments used 220 nm diameter carboxylate-modified polystyrene spheres, electrophoretically driven through two elastomeric nanopore specimens. Asymmetry is evident both within the pulse full-width half-maximum and over a longer 5 ms window. This asymmetry is consistent with the near-conical pore geometry, and is greater for both large and slow-moving particles. Particle mobility did not increase with size, and was unexpectedly enhanced when the electrolytepH was reduced from 8.0 to 7.0. In the model, an on-axis insulating particle with an effective electrophoretic charge is suspended in an electrolyte of homogeneous resistivity. End effects, particle transport, and any azimuthally symmetric pore geometry are supported. When a linear cone geometry was fitted to experiments, values for the pore opening radii and the particle effective charge were obtained. More complicated geometries can better reproduce experimental pulse asymmetry and absolute sizes of pore openings. Nanopore-based resistive pulse measurement is being applied to sensing and analysis of many submicron particle types, including viruses, synthetic nanoparticles, and single molecules.

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