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Porphyrins are promising materials for photodynamic therapy, but their low solubility and aggregation in biological environments are still obstacles to surpass. In order to overcome these limitations, the conjugation of porphyrins with graphene quantum dots (GQDs), here functioning as a vehicle to improve the internalization of porphyrins by cancer cells, was considered. The GQDs were conjugated with an aminoporphyrin via amide linkage using both thionyl chloride (SOCl2) and 1-ethyl-3-(3′-dimethylaminopropyl)-carbodiimide coupling methodologies. Based on structural characterization (Fourier transform infrared and X-ray photoelectron spectroscopy), the best porphyrin loading was observed with the SOCl2 procedure. The new hybrids were investigated as phototherapeutic agents in high incidence breast cancer (T-47D cell line) under white light, and a significant photocytotoxic effect was observed at 10 nM. The conjugation of GQDs to the aminoporphyrin promoted an efficient uptake by the T-47D cells when compared with the nonimmobilized porphyrin. These results point out the high potential of the new hybrids to be explored as theragnostic agents. [ABSTRACT FROM AUTHOR]