Recovery of submicron particles using high-throughput dielectrophoretically switchable filtration

Conventional methods for separation of submicron particles, e.g., filtration or centrifugation, suffer from severe problems, such as loss of particles during resuspension and high energy demands due to fouling of separating membranes. Here we present the novel concept of dielectrophoretically switchable filtration using pore sizes that are two to three orders of magnitude larger than the particles. We used layer-by-layer (LbL) assembled nanocapsules of 340 nm diameter that were to be separated and recovered from polyelectrolyte solution. The filter being an insulating porous structure is placed in between two electrodes generating an electric field which is bend at the solid–liquid interface and is thus highly inhomogeneous. Dielectrophoresis (DEP) is used as a driving force to trap particles in the filter. The filtration is based on electric effects and could thus be easily turned off by switching off the electric field allowing safe and easy resuspension of the trapped nanocapsules. A parametric study has been conducted to investigate the influence of voltage, pore size, flux and membrane thickness on the separation efficiency. Maximum separation and recovery efficiencies in a semi-continuous run reached almost 65% when working with a specific flow rate of 4.12 mL s−1 m−2, a voltage of 200 V, frequency of 210 kHz and a filter with thickness of 1.5 mm and pore sizes in the range of 20–60 μm. The results demonstrate that electrically switchable retardation of nanoparticles is possible even in large flow systems. This finding paves the way for preparative DEP chromatography of nanoparticles. Its ease makes this switchable filtration attractive for nanoparticle separation and purification in general.