Multifunctional up-converting nanocomposites with multimodal imaging and photosensitization at near-infrared excitation

Abstract

Here we report the synthesis of silica coated NaYF₄:Yb/Tm nanocomposites, with a covalent coating of 1,8-dihydroxy-3-methylanthraquinone (DHMA), which has high ability to produce reactive oxygen species (ROS) and fluorescein isothiocyanate (FITC) for downconverting imaging. Upon excitation by near-infrared light, the nanocomposites convert lower-energy light to higher-energy light, which will trigger DHMA to generate ROS and consequently kill the folate receptor (FR) (+) tumor cells. The apoptosis effect of tumor cells induced by the as-prepared nanocomposites [UCNP@(DHMA/FITC)@SiO₂–FA] was proven by fluorescence microscope imaging after staining with Annexin V-FITC/PI, Caspase-3 Western blotting, flow cytometry assay and cell viability assay. The results indicated that the as-prepared nanocomposites can effectively induce apoptosis in HeLa and HepG2 cells and the percentage of early apoptosis in tumor cells is as high as 42.75%. In addition, the photosensitive efficiency of DHMA covalent coating nanocomposites [UCNP@(DHMA/FITC)@SiO₂–FA] is higher than that of DHMA simply deposited nanocomposites [UCNP@SiO₂(DHMA/FITC)–FA]. As a result, high photosensitivity and selectivity are achieved in tumor cells upon incubation with the nanocomposites and exposure to an NIR laser. Furthermore, multimodal fluorescence labelling is also achieved with good photostability and no background noise. Therefore, they will potentially be useful either as PDT drugs or multimodal luminescent probes in bioimaging.