We report two novel biomedical applications of Au/Ag alloy nanoparticles called nanocages. In the first case, composite nanoparticles consisting of a nanocage core and a mesoporous silica shell doped with a photodynamic sensitizer Yb-2,4-hematoporphyrin were fabricated, characterized, and tested in vitro and ex vivo. In the second part of the study, Ag nanocubes and Au/Ag nanocages bioconjugates were applied to a multiplexed dot immunoassay.