Using a simple method of mass production of green carbon nanotags (G-tags) from harmful cyanobacteria, we developed an advanced and efficient imaging platform for the purpose of anticancer therapy. Approximately 100 grams of G-tags per 100 kilograms of harmful cyanobacteria were prepared using our eco-friendly approach. The G-tags possess high solubility, excellent photostability, and low cytotoxicity (<1.5 mg/mL for 24 h). Moreover, doxorubicin-conjugated G-tags (T-tags; >0.1 mg/mL) induced death in cancer cells (HepG2 and MCF-7) in-vitro at a higher rate than that of only G-tags while in-vivo mice experiment showed enhanced anticancer efficacy by T-tags at 0.01 mg/mL, indicating that the loaded doxorubicin retains its pharmaceutical activity. The cancer cell uptake and intracellular location of the G- and T-tags were observed. The results indicate that these multifunctional T-tags can deliver doxorubicin to the targeted cancer cells and sense the delivery of doxorubicin by activating the fluorescence of G-tags.