The Role of Pore Geometry in Single Nanoparticle Detection

Abstract

We observe single nanoparticle translocation events via resistive pulse sensing using silicon nitride pores described by a range of lengths and diameters. Pores are prepared by focused ion beam milling in 50 nm-, 100 nm-, and 500 nm-thick silicon nitride membranes with diameters fabricated to accommodate spherical silica nanoparticles with sizes chosen to mimic that of virus particles. In this manner, we are able to characterize the role of pore geometry in three key components of the detection scheme, namely, event magnitude, event duration, and event frequency. We find that the electric field created by the applied voltage and the pore's geometry is a critical factor. We develop approximations to describe this field, which are verified with computer simulations, and interactions between particles and this field. In so doing, we formulate what we believe to be the first approximation for the magnitude of ionic current blockage that explicitly addresses the invariance of access resistance of solid-state pores during particle translocation. These approximations also provide a suitable foundation for estimating the zeta potential of the particles and/or pore surface when studied in conjunction with event durations. We also verify that translocation achieved by electro-osmostic transport is an effective means of slowing translocation velocities of highly charged particles without compromising particle capture rate as compared to more traditional approaches based on electrophoretic transport.

Effects of access resistance on the resistive-pulse caused by translocating of a nanoparticle through a nanopore

“…They found that a constant AR assumption tted their experimental measurements well. Under the hypothesis of invariant AR and a, Davenport et al 22 systematically investigated the role of nanopore geometry in nanoparticle experiments using different aspect ratio nanopores. However, constant AR might not be able to predict the current change correctly in some cases, especially when particle's diameter is larger than pore's length.…”

“…We then compared our numerical results with the experimental data of Bacri et al 36 and Davenport et al, 22 as shown in Table 1. This table also lists the results of two other analytical models: (i) the model without AR, which only considers the resistance change inside the pore, is used in the work of Bacri et al, 36 and (ii) the model with constant AR, which is the results of the no AR model divided by (1 + a o ), is similar to the approximate formula used in the work of Davenport et al 22 Our numerical results give more accurate values than the model without AR.…”

“…The detection of nanoparticles with nanopores is usually performed at high bulk concentrations (e.g., 100 mM or higher), [7][8][9]22,33,34 where the Laplace model with no surface charges and the PNP-NS model with typical surface charges give almost identical results. Therefore, we used Laplace model to simulate the cases at high salt concentrations.…”

Nanoparticle-induced rectification in a single cylindrical nanopore: Net currents from zero time-average potentials

“…1(a), partial pore blocking (V > 0) and unblocking (V < 0) occur when the migration (MIG) flow resulting from the particle surface charge and the electro-osmotic (EOF) flow resulting from the pore surface charge act in concert, reinforcing the rectification effect. 14,15,25 This mechanism is also shown in Fig. 1(b), with the trivial change in the sign of the blocking (V < 0) and unblocking (V > 0) voltages with respect to Fig.…”

“…Note that models for blocking predict high electric fields in the solution close to the pore mouth. 14,19,25 Single, approximately cylindrical pores are obtained in 12 lm thick polyethylene terephthalate membranes using track-etching procedures. Fig.…”