Optofluidic Chromatography: Label-Free Sorting of Exosomes with Plasmonic Microlenses

We introduce a subwavelength thick (similar to 200 nm) plasmofluidic microlens that effortlessly achieves objective-free focusing and self-alignment of opposing optical scattering and fluidic drag forces for selective separation of exosome size bioparticles. Our optofluidic microlens provides a self-collimating mechanism for particle trajectories with a spatial dispersion that is inherently minimized by the optical gradient and radial fluidic drag forces. We demonstrate that this facile platform facilitates complete separation of small size bioparticles (i.e., exosomes) from a heterogenous mixture through negative depletion and provides a robust selective separation capability based on differences in chemical composition (refractive index). Unlike existing optical chromatography techniques that require complicated instrumentation (lasers, objectives and precise alignment stages), our platform open up the possibility of multiplexed and high-throughput sorting of nanoparticles on a chip.