posted on 2018-02-05, 00:00authored byChristopher G. Gunderson, Zhuoyu Peng, Bo Zhang
We
describe the use of a quartz pipet nanopore to study the collision
and coalescence of individual emulsion oil droplets and their subsequent
nanopore translocation. Collision and coalescence of single toluene
droplets at a nanopore orifice are driven primarily by electroosmosis
and electrophoresis and lead to the fast growth of a trapped oil droplet.
This results in a stepwise current response due to the coalesced oil
droplet increasing its volume and its ability to partially block the
nanopore’s ionic current, allowing us to use the resistive-pulse
method to resolve single droplet collisions. Further growth of the
trapped oil droplet leads to a complete blockage of the nanopore and
a nearly 100% current decay. The trapped oil droplet shows enormous mechanical
stability at lower voltages and stays in its trapped status for hundreds
of seconds. An increased voltage can be used to drive the trapped
droplet into the pipet pore within several milliseconds. Simultaneous
fluorescence imaging and amperometry were performed to examine droplet
collision, coalescence, and translocation, further confirming the
proposed mechanism of droplet–nanopore interaction. Moreover,
we demonstrate the unique ability to perform fast voltammetric measurements
on a nanopore-supported attoliter oil droplet and study its voltage-driven
ion transfer processes.