Nanovortex‐Driven All‐Dielectric Optical Diffusion Boosting and Sorting Concept for Lab‐on‐a‐Chip Platforms

Abstract The ever‐growing field of microfluidics requires precise and flexible control over fluid flows at reduced scales. Current constraints demand a variety of controllable components to carry out several operations inside microchambers and microreactors. In this context, brand‐new nanophotonic approaches can significantly enhance existing capabilities providing unique functionalities via finely tuned light−matter interactions. A concept is proposed, featuring dual on‐chip functionality: boosted optically driven diffusion and nanoparticle sorting. High‐index dielectric nanoantennae is specially designed to ensure strongly enhanced spin−orbit angular momentum transfer from a laser beam to the scattered field. Hence, subwavelength optical nanovortices emerge driving spiral motion of plasmonic nanoparticles via the interplay between curl−spin optical forces and radiation pressure. The nanovortex size is an order of magnitude smaller than that provided by conventional beam‐based approaches. The nanoparticles mediate nanoconfined fluid motion enabling moving‐part‐free nanomixing inside a microchamber. Moreover, exploiting the nontrivial size dependence of the curled optical forces makes it possible to achieve precise nanoscale sorting of gold nanoparticles, demanded for on‐chip separation and filtering. Altogether, a versatile platform is introduced for further miniaturization of moving‐part‐free, optically driven microfluidic chips for fast chemical analysis, emulsion preparation, or chemical gradient generation with light‐controlled navigation of nanoparticles, viruses or biomolecules.