High-throughput nanoparticle manipulation <i>via</i> controlled electro-elasticity and Joule heating in microchannels

Effective nanoparticle (NP) manipulation is crucial for diverse nanotechnology applications, including biomolecule sorting, drug delivery optimization, and metallic material synthesis. However, continuous enrichment and focusing of NPs remain challenging. Here, we introduce a microfluidic method that leverages controlled electro-elasticity and Joule heating to achieve high-throughput, precise manipulation of NPs. This approach synergistically combines the advantages of microfluidics (high throughput, precision, and continuous operation) with the real-time control of electric fields, while mitigating adverse thermal effects. We demonstrate high-throughput focusing of 100 nm particles in a large, straight rectangular microchannel. The underlying mechanism, driven by slip velocity induced by the interplay of electric fields and viscoelastic flow, is investigated using nearly electrically neutral, surface-modified particles. We quantitatively determine optimal control parameters, including electric field strength, flow velocity, and polymer concentration. Furthermore, a simple dry-ice-based temperature control system enables focusing of NPs as small as 20 nm under high electric fields, effectively mitigating Joule heating. This method balances the need for high-energy input for NP control with the elimination of detrimental thermal energy. By controlling electro-elasticity and Joule heating, our approach overcomes limitations of existing NP manipulation techniques, providing a route towards rapid and gentle enrichment of diverse NP types.