Methods, structures, devices and systems are disclosed for rapid enrichment and mass transport of biomolecules (e.g., such as proteins) or other small molecules and particles using electrodeless dielectrophoresis (eDEP). In one aspect, a device to aggregate molecules includes a substrate that is electrically insulating, an electrically insulative material formed on the substrate and structured to form a channel to carry an electrically conducting fluid containing particles, a constriction structure formed of the electrically insulative material and located in the channel to narrow a channel dimension and forming an opening with a size in the nanometer range, and a circuit coupled to the substrate to apply an ac electric field and a dc bias electric field along the channel, in which the constriction structure is structured to magnify the applied ac electric field to produce forces that operate collectively to aggregate the particles.