  We propose two-dimensional organic poly(heptazine imide) (PHI) carbon nitride
microparticles as light-driven microswimmers in various ionic and biological
media. Their demonstrated high-speed (15-23 $\mu$m/s) swimming in
multi-component ionic solutions with concentrations up to 1 M and without
dedicated fuels is unprecedented, overcoming one of the bottlenecks of previous
light-driven microswimmers. Such high ion tolerance is attributed to a
favorable interplay between the particle's textural and structural nanoporosity
and optoionic properties, facilitating ionic interactions in solutions with
high salinity. Biocompatibility of the microswimmers is validated by cell
viability tests with three different cell types and primary cells. The
nanopores of the swimmers are loaded with a model cancer drug, doxorubicin
(DOX), in high (185%) loading efficiency without passive release. Controlled
drug release is reported in different pH conditions and can be triggered
on-demand also by illumination. Light-triggered, boosted release of DOX and its
active degradation products is demonstrated in oxygen-poor conditions using the
intrinsic, environmentally sensitive and light-induced charge storage
properties of PHI, which could enable future theranostic applications in
oxygen-deprived tumor regions. These organic PHI microswimmers simultaneously
solve the current light-driven microswimmer challenges of high ion tolerance,
fuel-free high-speed propulsion in biological media, biocompatibility and
controlled on-demand cargo release towards their biomedical, environmental and
other potential future applications.
