Ultralow-aspect-ratio micropore sensor for a particle translocation: Critical role of the access region

In this paper, we analyze particle translocation through micropores with low aspect ratios. Micropores with diameters of 11.6 μm and various lengths (1000 nm, 500 nm, 100 nm, and 50 nm) are fabricated on a silicon nitride membrane via laser machining at a low aspect ratio. After measuring the translocation signals of a 5.4- μm particle, we find that the effects of the access region become more significant than those of the pore region for detecting signals at low aspect ratios. To clarify this mechanism, finite element method simulation and mathematical analysis are performed and we describe the relationship between an inhomogeneous electric field and the critical role of the access region. Additionally, we detect the translocation signal of a double particle. As a result, we achieve a decrease in translocation speed and improve signal detection at an ultralow aspect ratio, demonstrating the potential to detect the shapes of small particles directly.