Self-induced back action actuated nanopore electrophoresis (SANE)

Abstract

We present a novel method to trap nanoparticles in double nanohole (DNH) nanoapertures integrated on top of solid-state nanopores (ssNP). The nanoparticles were propelled by an electrophoretic force from the cis towards the trans side of the nanopore but were trapped in the process when they reached the vicinity of the DNH-ssNP interface. The self-induced back action (SIBA) plasmonic force existing between the tips of the DNH opposed the electrophoretic force and enabled simultaneous optical and electrical sensing of a single nanoparticle for seconds. The novel SIBA actuated nanopore electrophoresis (SANE) sensor was fabricated using two-beam GFIS FIB. Firstly, Ne FIB milling was used to create the DNH features and was combined with end pointing to stop milling at the metal-dielectric interface. Subsequently, He FIB was used to drill a 25 nm nanopore through the center of the DNH. Proof of principle experiments to demonstrate the potential utility of the SANE sensor were performed with 20 nm silica and Au nanoparticles. The addition of optical trapping to electrical sensing extended translocation times by four orders of magnitude. The extended electrical measurement times revealed newly observed high frequency charge transients that were attributed to bobbing of the nanoparticle driven by the competing optical and electrical forces. Frequency analysis of this bobbing behavior hinted at the possibility of distinguishing single from multi-particle trapping events. We also discuss how SANE sensor measurement characteristics differ between silica and Au nanoparticles due to differences in their physical properties and how to estimate the charge around a nanoparticle. These measurements show promise for the SANE sensor as an enabling tool for selective detection of biomolecules and quantification of their interactions.