Analysis of Single entity Anisotropy with a Solid-state Nanopore

Solid-state nanopore has emerging as a promising tool for detection and analysis of single molecules due to its advantages of high stability, easy control of diameter and channel length, and the potential for integration into devices and arrays. Therefore, there are intensive studies regarding nanopore-based detection of DNAs, proteins, polymers and other small molecules. The electrochemical confined space of nanopore could efficiently convert the information in single biological molecules with anisotropy characters into measurable electrochemical signatures with high temporal resolution. The anisotropy characters of each analyte, due to its featured physical and chemical properties in different directions, strongly affects the translocation behavior of each single entity (single molecule, single nanoparticle, etc.). To analyze the single-entity anisotropy effects on nanopore translocation, here, we employed gold nanorods (GNRs) as a model for single entities with anisotropy to investigate its translocation behavior through a solid-state nanopore. We performed the GNRs translocation experiments in 10 mmol.L-1 KCI (pH 8) electrolyte solution with a 100 nm SiNx solid-state nanopore. The current trace of GNRs translocation through nanopores had been recorded with an ultra-sensitive current amplifier at a sampling rate of 100 kHz filtered at 5 kHz via a low-pass Besse! filter. At applied voltage of -600 mV, two types of characteristic current blockades were observed when single GNRs translocate through the pore. We found this two types of blockades are mainly related to two translocation orientation of GNRs due to its anisotropy. The smaller current blockades are due to the GNR passing through the pore vertically while the larger current blockades are due to the GNR passing through the pore horizontally. To verify our observation of this two types of GNRs translocation events, we employed a simple model which is based on the relationship between the blockade magnitude and the exclude ion volume. The calculated current blockades of two types of GNRs translocation events agree well with the experimental values. These results illustrate that the anisotropy of single entity is an important factor that should be taken into consideration in nanopore translocation. This work will lead to a better understanding of the translocation behavior of single entity with anisotropy in the electrochemical confined space of nanopore. Such understanding is vital to the development of the solid-state nanopore system as a useful single molecule analytical device.