(Foreground) Doxorubicin molecule, detected using the van der Waals vertical heterostructure biosensor. (Background) Actual nanoscale optical image (sSNOM) of the heterostructure: large triangle is a single-layer MoS2 island (ca. 3.7 micron wide); smaller triangle is a partially oxidized MoOS island; whole sample is covered with the monolayer graphene, with several wrinkles clearly seen in the map; darker graphene area corresponds to the region of extra charge doping.