Chemically modified solid state nanopores for high throughput nanoparticle separation

Abstract

The separation of biomolecules and other nanoparticles is a vital step in several analytical and diagnostic techniques. Towards this end we present a solid state nanopore-based set-up as an efficient separation platform. The translocation of charged particles through a nanopore was first modeled mathematically using the multi-ion model and the surface charge density of the nanopore membrane was identified as a critical parameter that determines the selectivity of the membrane and the throughput of the separation process. Drawing from these simulations a single 150 nm pore was fabricated in a 50 nm thick free-standing silicon nitride membrane by focused-ion-beam milling and was chemically modified with (3-aminopropyl)triethoxysilane to change its surface charge density. This chemically modified membrane was then used to separate 22 and 58 nm polystyrene nanoparticles in solution. Once optimized, this approach can readily be scaled up to nanopore arrays which would function as a key component of next-generation nanosieving systems.

Functional analysis of single Poly(methyl-methacrylate)-based submicron pore electrophoretic flow detectors via translocation of differently sized silica nanoparticles

“…These forces are governed by the charge of nanoparticles and membranes. As described in a recent study Prabhu et al [13], for a case like ours, with negatively charged nanoparticles and also a negatively charged membrane, the EOF at the nanoparticles as well as the membrane surface creates a drag force that opposes the electrophoretic pull experienced by nanoparticles, and hence in order for a nanoparticle to translocate the pore, the electrophoretic force must overcome the drag force created by EOF. As the potential difference across the pore is increased by increasing the voltage, a higher electrophoretic force will be created overcoming the existing EOF, and thus resulting in a higher number of particles passing through the pore.…”

“…This is likely happening because of aggregation of silica nanoparticles despite treatment with the surfactant Triton X-100. According to other studies [13], IIa and IIc could represent the presence of nanoparticles at the entrance of the pore near its top surface and at the exit of the pore near its bottom surface, respectively. IIb represents the presence of passing nanoparticles in the centre of the pore blocking a major portion of the baseline current flowing through the pore.…”

“…However, this could destabilise our analyte molecules and is hence not a feasible option. In any case, the preceding arguments stress the importance of finetuning the surface chemistry of the membranes in micro/ nanopore systems [13]. Another such way could be through chemical surface modification, which can be implemented relatively easy on polymer membranes; another huge advantage for our selected membrane material of PMMA.…”

Modeling and simulation of nanoparticle separation through a solid‐state nanopore

“…Firnkes et al [16] showed that electrokinetic transport of model proteins (avidin) through a silicon nitride (Si 3 N 4 ) nanopore can be controlled by modifying the z potential or surface charge density of pore. More recently, Prabhu et al [17] presented an electrokinetic-based nanopore device to control the permeability rate of different types of polysterene beads by chemically modifying the membrane surface.…”

Nonequilibrium Capture Rates Induce Protein Accumulation and Enhanced Adsorption to Solid-State Nanopores

“…This study provides additional evidence that nanopores do not measure bulk solution properties of an analyte which has otherwise been shown by previous experiments. 5,27,47,48 CONCLUSION In this report we show that the rate in which proteins translocate a solid-state pore is not constant with time. Instead, event frequency is enhanced over time through a process involving protein accumulation, which stems from unbalanced rate equations.…”