Electrical trapping mechanism of single-microparticles in a pore sensor

Abstract

Nanopore sensing via resistive pulse technique are utilized as a potent tool to characterize physical and chemical property of single –molecules and –particles. In this article, we studied the influence of particle trajectory to the ionic conductance through a pore. We performed the optical/electrical simultaneous sensing of electrophoretic capture dynamics of single-particles at a pore using a microchannel/nanopore system. We detected ionic current drops synchronous to a fluorescently dyed particle being electrophoretically drawn and become immobilized at a pore in the optical imaging. We also identified anomalous trapping events wherein particles were captured at nanoscale pin-holes formed unintentionally in a SiN membrane that gave rise to relatively small current drops. This method is expected to be a useful platform for testing novel nanopore sensor design wherein current behaves in unpredictable manner.

Volume discrimination of nanoparticles via electrical trapping using nanopores

“…Before trapping, the pore is fully open and the current values represent a constant ionic current I open . When a particle is captured, the flow of ions is suppressed and the drop to I trap is observed [ 16 , 17 , 29 ]. As complete sealing should lead I ion to zero, the non-zero I trap indicates a particle floating at the vicinity of the pore because of the drag force of electroosmotic back flow antagonizing to the electrophoretic forces of the negatively-charged particle.…”

“…To shed light on the relationship between I trap and positions of a particle, multiphysics simulation was conducted (Fig. 4 and see Additional file 1 ) [ 16 , 17 ]. We approximate the pore-particle distance ( Δd ) by comparisons between the experimental I trap with simulated ones.…”

“…The fabrication process of a nanopore is described elsewhere [8, 17]. Briefly, 20 mm × 20 mm sized silicon chips constructed with three layers, SiN/Si/SiN = 50 nm/0.5 mm/50 nm, were used as substrates.…”

“…On the other hand, nanopore trap method is a more simple and facile strategy for the target immobilization at a single-particle level (Fig. 1 a) [ 16 , 17 ]. This method utilizes a nanopore with a diameter smaller than that of analytes of interest.…”

Key Parameters That Determine the Magnitude of the Decrease in Current in Nanopore Blockade Sensors

“…The surface charge effect was disregarded as additional charges on MNPs were expected to bring counterions into nanopores and lead to increases in ionic current, while decreases in ionic current were observed for these PEI-MNPs. Therefore, the decrease in ionic current of 500–900 pA for PEI-MNPs, being greater than 0–170 pA as predicted by the volume exclusion effect from model 1, could be explained by increases in access resistance of nanopores, when nanoparticles occupied nanopores. − A variable access resistance is in contrast to translocation-based nanopore sensors where the access resistance is shown to remain constant. − Here, we suggest that the access resistance of the pore in nanopore blockade sensors increases when a MNP blockade occurs, and this increase plays a major role in determining the magnitude of the decrease in ionic current. Further evidence showing the importance of the access resistance in the system is given by the relationship between the nanopore diameter and the open pore resistance (Figure S14).…”