  Deposits from evaporating drops have shown to take a variety of shapes,
depending on the physicochemical properties of both solute and solvent.
Classically, the evaporation of drops of colloidal suspensions leads to the
so-called coffee ring effect, caused by radially outward flows. Here we
investigate deposits from evaporating drops containing living motile microalgae
(Chlamydomonas reinhardtii), which are capable of resisting these flows. We
show that utilizing their light-sensitivity allows to control the final
pattern: adjusting the wavelength and incident angle of the light source
enables to force the formation, completely suppress and even direct the spatial
structure of algal coffee rings.
