Energy transfer facilitated near infrared fluorescence imaging and photodynamic therapy of tumors.

Near infrared (NIR) light activated fluorescence imaging and photodynamic therapy hold great potential for tumor treatment in deep tissues. Development of effective theranostic nanosystems to integrate both functions is becoming an attractive route for tumor diagnosis and therapy. Herein, nitrogen (N), sulfur (S) co-doped graphene quantum dots (GQDs) were engineered on the surface of upconversion nanoparticles (UCNPs) to form GUCNP nanosystems, where fluorescence resonance energy transfer (FRET) from UCNPs to GQDs could significantly facilitate the NIR fluorescence enhancement and NIR light activated singlet oxygen (1O2) generation. Under 980 nm laser irradiation, UCNPs could emit green and NIR fluorescence, where the wavelength of green fluorescence matched the excitation band of GQDs to activate 1O2 generation and produce additional NIR fluorescence. Both NIR fluorescence from UCNPs and GQDs could be used for cell and animal fluorescence imaging, and the generated 1O2 enhanced ROS production, phase II enzyme expression, apoptosis and cell death in 4T1 cells, as a result of tumor growth inhibition in 4T1 tumor-bearing mice. GUCNP nanosystems may pave a new way for cancer therapy.