Ruthenium complex-modified carbon nanodots for lysosome-targeted one- and two-photon imaging and photodynamic therapy

Nanohybrids can in most cases kill cancer cells more efficiently as compared with free photosensitizers. In this work, we constructed nanohybrid Ru1@CDs composed of carbon nanodots (CDs) and a phosphorescent Ru(II) complex (Ru1) for one- and two-photon photodynamic therapy of cancer. The photosensitizer and imaging agent Ru1 is decorated onto the nanocarrier CDs covalently. Ru1 and Ru1@CDs can penetrate into cancer cells through an energy-dependent mechanism and endocytosis, respectively. Both Ru1 and Ru1@CDs are capable of lysosome-targeted phosphorescence imaging and photodamage under either 450 nm (one-photon) or 810 nm (two-photon) excitation. Conjugation with CDs can increase the cellular uptake efficacy of Ru1. Mechanism investigations show that both Ru1 and Ru1@CDs can induce apoptosis through generation of reactive oxygen species and cathepsin-initiated apoptotic signaling pathways. Upon two-photon excitation, Ru1@CDs show better penetrability, as well as higher inhibitory effects on cancer cell growth in both 2D cell and 3D multicellular tumor spheroid models. Our work provides an effective strategy for the construction of multifunctional imaging and phototherapeutic nanohybrids for the treatment of cancer.