Fig. 7. (A) Two-photon excitation fluorescence (TPEF) emission spectra for TPE-TETRAD@biotin NPs in water. (B) Two-photon absorption (2PA) cross-section of AIE NPs (red), Rhodamine B (black) and DCM (blue). (C) TPEF images of HeLa cervical cancer cells after incubation with 6 μg mL–1 AIE NPs for 1 h at 37 °C, using a multiphoton excitation wavelength of 980 nm. (D) Simultaneous three-photon luminescence and third harmonic generation (THG) emission spectra for AIE NPs excited by a femtosecond laser at 1560 nm. (E) Diagram showing the proposed excitation mechanism of THG and THG-induced photoluminescence.
