  Manipulating fluids by light at the nanoscale has been a long-sought-after
goal for lab-on-a-chip applications. Plasmonic heating has been demonstrated to
control microfluidic dynamics due to the enhanced and confined light absorption
from the intrinsic losses of metals. Dielectrics, counterpart of metals, is
used to avoid undesired thermal effects due to its negligible light absorption.
Here, we report an innovative optofluidic system that leverages a quasi-BIC
driven all-dielectric metasurface to achieve nanoscale control of temperature
and fluid motion. Our experiments show that suspended particles down to 200
nanometers can be rapidly aggregated to the center of the illuminated
metasurface with a velocity of tens of micrometers per second, and up to
millimeter-scale particle transport is demonstrated. The strong electromagnetic
field enhancement of the quasi-BIC resonance can facilitate increasing the flow
velocity up to 3-times compared with the off-resonant situation. We also
experimentally investigate the dynamics of particle aggregation with respect to
laser wavelength and power. A physical model is presented to elucidate the
phenomena and surfactants are added to the particle colloid to validate the
model. Our study demonstrates the application of the recently emerged
all-dielectric thermonanophotonics in dealing with functional liquids and opens
new frontiers in harnessing non-plasmonic nanophotonics to manipulate
microfluidic dynamics. Moreover, the synergistic effects of optofluidics and
high-Q all-dielectric nanostructures can hold enormous potential in
high-sensitivity biosensing applications.
