The present invention discloses a new modality of photodynamic therapy (PDT) through the design of the present invention's truly dual-functional&mdash；PDT and imaging&mdash；gadolinium complex (Gd-N) with a molecular formula of: which can target cancer, cells specifically. The present invention provides a PDT drug that can specifically localize on the anionic cell membrane of cancer cells in which its laser-excited photoemission signal can be monitored without triggering the phototoxic generation of reactive oxygen species&mdash；singlet oxygen&mdash；prior to due excitation. The present invention also provides the use of Gd-N as a tumor selective PDT photosensitizer modality.
