Abstract: BACKGROUND: Near-infrared luminescent carbon dots have tissue penetration that blue-green luminescent carbon dots do not have. They are ideal imaging agents. However, they are easily degraded in the body and cannot reach target tissues. This experiment combines them with nanoparticles, and it can reach the target through the circulatory system to achieve the purpose of real-time imaging. 
OBJECTIVE: To prepare mesoporous organosilica nanocapsules-carbon nanodots (MON-CDs) with imaging capability and high safety.
METHODS:  Utilizing the micelle/precursor co-template assembly strategy, using traditional tetraethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide) as the material, cetyltrimethylammonium chloride as the stencil agent, and triethanolamine as the alkaline catalyst, mesoporous organosilica nanoparticle (MON) was successfully prepared and carbon dots were added to the entire system to prepare MON-CDs. Transmission electron microscope and fluorescence spectrometer were applied to detect the structure, morphology and fluorescence intensity of nanoparticles. Photoacoustic image system and scanning laser confocal microscope were utilized to verify imaging ability, and in vivo photoacoustic imaging in mice was proven. CCK-8 was used to test the biosafety of MON-CDs solutions of different mass concentrations.  
RESULTS AND CONCLUSION: (1) The transmission electron microscope showed that the particle size of MON-CDs was (50.0±4.6) nm, which was spherical, uniform in size, and had good dispersibility. The pores were clearly visible and the carbon dots were mixed in it. Fluorescence detection showed that the carbon dots and mesoporous organic-inorganic hybrid silica nanoparticles were successfully connected. (2) CCK-8 detection showed that when the mass concentration of MON-CDs solution was within 200 mg/L, there was no obvious cytotoxicity. (3) Scanning laser confocal microscope showed that when MON-CDs were incubated with MCF-7 cells for 1 hour, the nanoparticles had already been taken up by cells, and most of them were concentrated near the cell membrane. When the CDs were incubated for 2 hours, the amount of nanoparticles accumulated into the cells increased, and the nanoparticles were mainly distributed in the cytoplasm. In addition, the uptake of nanoparticles occurred in most of the cells. (4) Photoacoustic imaging showed that with the proliferation of MON-CDs solution mass concentration, the in vitro photoacoustic signal intensity increased. At 6 hours after MON-CDs solution injection via tail vein, photoacoustic signals were observed at the tumor tissues of breast cancer mice. (5) The results showed that MON-CDs have good biosafety and possess near-infrared luminescence, and demonstrate good imaging capabilities under photoacoustic imager and laser confocal microscope.

Key words: materials, nanoparticles, silica, tracers, near-infrared materials, safety, bioimaging, safe degradation