Preparation And Biological Application Of Near-Infrared Fluorescent Ag₂Se Quantum Dots

The rapid development of nanotechnology has promoted the explosive progress of Physics, Chemistry, Biology, Medicine, and other disciplines in recent years. Nanomaterials, as the essential foundation of nanotechnology, have gained much attention of researchers. Semiconductor quantum dots ?QDs? with many excellent optical properties have been extensively applied in biomedicine fields, which contain biolabeling, biodetection, and bioimaging. Near-infrared fluorescence ?FL? could penetrate deep into the tissue, and is less absorbed and scattered by the tissue and less influenced by the tissue autofluorescence, which facilitates in vivo imaging with high signal-to-background ratios. Hence, near-infrared fluorescent QDs have more advantages on bioimaging in vivo, and are playing a propelling role in the research on cancer, anti-cancer drugs, clinical surgery, and so on. Moreover, constructing multifunctional nanotheranostic biodevices by integrating imaging and therapy on one single object, could realize simultaneous imaging and therapy, which might contribute to the early diagnosis, precise treatment, and prognosis assessment of cancer and is of great significance for "simultaneous diagnosis and therapy" and "personalized medicine" for cancer research.Ag2Se QDs are a kind of low-toxicity near-infrared fluorescent quantum dots. Many researchers have been working on the preparation and application of Ag2Se QDs. Currently, the controlled preparation of Ag2Se QDs still remains to be a great challenge in this field. In addition, the biosafety issues and in vivo imaging of Ag2Se QDs are not well understood. This thesis aims to prepare high-quality near-infrared fluorescent Ag2Se QDs, systematically evaluate their biological effect, and apply them in in vivo tumor research. The main work has been summarized as follows:?1? Ag2Se QDs with tunable FL emission in the second near-infrared window ?NIR-II, 1000-1400 nm? have been synthesized. The influence of three typical ligands ?oleylamine, tetradecylphosphonic acid, and 1-octanethiol? on the property of Ag2Se nanocrystals has been investigated to select the suitable ligand for preparing high-quality Ag2Se QDs. As a soft Lewis base,1-octanethiol could effectively stabilize the Ag precursor and balance nucleation and growth to realize controlled preparation of Ag2Se QDs. By varying the reaction time, the FL wavelength of Ag2Se QDs could be tuned in the range from 1080 nm to 1330 nm. The prepared Ag2Se QDs could be conveniently transferred to the aqueous phase by ligand exchange, retaining good dispersibility and FL properties. This work sets up a firm foundation for multicolor NIR-II FL imaging in vivo.?2? Near-infrared Ag2Se QDs have been synthesized, and their biotoxicities and in vivo behavior have been systematically studied. Ag2Se QDs emitting at 930 nm have been synthesized by using highly reactive ?TMS?2Se as Se precursor. The surfaces of Ag2Se QDs were modified by hydrophobic encapsulation with amphiphilic polymers and subsequent conjugation with NH2-PEG-NH2. The PEGlyated Ag2Se QDs exhibited low cytotoxicity. When intravenously administrated into the Balb/c mouse, Ag2Se QDs have no significant influence on the increase of the body weight, and more than 60% of Ag2Se QDs could be cleared from the body after 61 days, and very few were remained in main organs. Also, the near-infrared FL of Ag2Se QDs could penetrate through the back of nude mice. This work has demonstrated the great potential of low-toxicity near-infrared Ag2Se QDs for imaging in vivo.?3? An Ag₂Se QDs-based multifunctional nanotheranostic biodevice has been constructed by skillfully combining near-infrared Ag2Se QDs with cetuximab, a clinical anti-cancer drug, through simple bioconjugation. The nanotheranostic biodevice has integrated three functions of tumor targeting, tumor imaging, and tumor therapy. Compared with unbioconjugated Ag2Se QDs, the nanotheranostic biodevice exhibited quicker and more enrichment at tumor tissue. The FL of Ag2Se QDs in tumor still could be clearly observed at 24 h post-injection. Moreover, the nanotheranostic biodevice has significantly increased the survival rate of orthotopic tongue tumor-bearing Balb/c nude mice and inhibited the tumor growth. The treatment mechanism was also proved to be consistent with that of cetuximab by immunohistochemistry analyses. This work provided a facile strategy for constructing a nanotheranostic biodevice, offering a new perspective to realize "simultaneous diagnosis and therapy" and "personalized medicine" for cancer research.