  The use of active colloids for cargo transport offers unique potential for
applications ranging from targeted drug delivery to lab-on-a-chip systems.
Previously, Janus particles (JPs), acting as mobile microelectrodes have been
shown to transport cargo which is trapped by a dielectrophoretic mechanism
[Boymelgreen et al. (2018)]. Herein, we aim to characterize the cargo loading
properties of mobile Janus carriers, across a broad range of frequencies and
voltages. In expanding the frequency range of the carrier, we are able to
compare the influence of different modes of carrier transport on the loading
capacity as well as highlight the differences between cargo trapped by positive
and negative dielectrophoresis. Specifically it is shown that cargo trapping
results in a reduction in carrier velocities with this effect more pronounced
at low frequencies where cargo is trapped close to the substrate.
Interestingly, we observe the existence of a maximum cargo loading capacity
which decreases at large voltages suggesting a strong interplay between
trapping and hydrodynamic shear. Finally, we demonstrate that control of the
frequency can enable different assemblies of binary colloidal solutions on the
JP. The resultant findings enable the optimization of electrokinetic cargo
transport and its selective application to a broad range of targets.
