  Janus particles have flourished as subject of intensive research due to their
synergetic properties and their promising use in different fields, especially
in biomedicine. The combination of materials with radically different physical
properties in the same nanostructure gives rise to the so-called Janus effects,
allowing phenomena of a contrasting nature to occur in the same architecture.
In particular, interesting advantages can be taken from a thermal Janus effect
for photoinduced hyperthermia cancer therapies. Such therapies still have
limitations associated to the heating control in terms of temperature stability
and energy management. While previous studies have shown that some plasmonic
single-material nanoparticles are somehow effective at killing cancer cells, it
is necessary to investigate alternative plasmonic Janus nanoheaters to improve
the heating efficiency and thermal control, mainly because the widespread
single-material nanoheaters are highly homogeneous sources of heat, which
implies that the surrounding biological medium is isotropically heated, equally
affecting cancerous and healthy cells. A detailed thermoplasmonic study of the
thermal Janus effect is still missing. Here we perform such study and
demonstrate that doughnut-based Janus nanoparticles exhibit an outstanding
photothermal control under practical illumination conditions, i.e., unpolarized
light. Furthermore, we present novel and effective Janus nanoparticle designs
that possess superior photothermal conversion features and unique directional
heating capacity, being able to channel up to 91% of the total thermal energy
onto a target. We discuss the implications of these innovative nanoparticles
with regards to thermoplasmonics hyperthermia cancer therapy.
