  We experimentally investigate the chiral optical response of an individual
nanostructure consisting of three equally sized spherical nanoparticles made of
different materials and arranged in \ang{90} bent geometry. Placing the
nanostructure on a substrate converts its morphology from achiral to chiral.
Chirality leads to pronounced differential extinction, i.e., circular dichroism
and optical rotation, or equivalently, circular birefringence, which would be
strictly forbidden in the absence of a substrate or heterogeneity. This first
experimental observation of the substrate-induced break of symmetry in an
individual heterogeneous nanostructure sheds new light on chiral light-matter
interactions at substrate-nanostructure interfaces.
