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.
