  Catalytically active particles suspended in a liquid can move due to
self-phoresis by generating solute gradients via chemical reactions of the
solvent occurring at parts of their surface. Such particles can be used as
carriers at the micro-scale. As a simple model for a carrier-cargo system we
consider a catalytically active particle connected by a thin rigid rod to a
catalytically inert cargo particle. We show that the velocity of the composite
strongly depends on the relative orientation of the carrier-cargo link.
Accordingly, there is an optimal configuration for the linkage. The subtlety of
such carriers is underscored by the observation that a spherical particle
completely covered by catalyst, which is motionless when isolated, acts as a
carrier once attached to a cargo.
