Computational and experimental study of AC measurements performed by a double-nanohole plasmonic nanopore sensor on 20 nm silica nanoparticles

A novel method of AC sensing is presented that uses a double nanohole (DNH) nanoaperture atop a solid-state nanopore (ssNP) to trap analytes and measure their optical and electrical properties. In this method analytes are propelled by an external applied voltage towards the sensor until they are trapped at the DNH-ssNP interface via a self-induced back action (SIBA) plasmonic force. We have previously named this method SIBA Actuated Nanopore Electrophoresis (SANE) sensing and have shown its ability to perform concurrent optical and DC electrical measurements. Here, we extend this method to AC sensing of 20 nm SiO₂ (silica) nanoparticles, using voltage modulation over a wide range of frequencies applied on top of a baseline DC bias. The sensor was constructed using two-beam GFIS Focused Ion Beam (FIB) lithography, incorporating Ne FIB to mill the DNH and He FIB to drill a central 30 nm ssNP. We utilized COMSOL Multiphysics simulations to explore the multi-frequency AC current conductance properties of the silica nanoparticles trapped at the SANE sensor. These simulations computed conductance changes and phase shifts induced by the presence of the nanoparticle over an AC frequency range of 20 Hz to 100 kHz. Experimental measurements confirmed the trends seen in the computational data. Additional computational studies were then performed to dissect the underlying mechanisms driving the observed AC measurements. Looking forward, we aim to adapt this technology for probing therapeutic nanoparticles non-invasively, offering a promising tool for enhancing quality control of nanoparticle-mediated drug and gene delivery systems.