Plasmonic Nanopores: Optofluidic Separation of Nano-Bioparticles via Negative Depletion

In this chapter, we review a novel “optofluidic” nanopore device enabling label-free sorting of nano-bioparticles [e.g., exosomes, viruses] based-on size or chemical composition. By employing a broadband objective-free light focusing mechanism through extraordinary light transmission effect, our plasmonic nanopore device eliminates sophisticated instrumentation requirements for precise alignment of optical scattering and fluidic drag forces, a fundamental shortcoming of the conventional optical chromatography techniques. Using concurrent optical gradient and radial fluidic drag forces, it achieves self-collimation of nano-bioparticles with inherently minimized spatial dispersion against the fluidic flow. This scheme enables size-based fractionation through negative depletion and refractive-index based separation of nano-bioparticles from similar size particles that have different chemical composition. Most remarkably, its small (4 μm × 4 μm) footprint facilitates on-chip, multiplexed, high-throughput nano-bioparticle sorting using low-cost incoherent light sources.