Formation Of Receptor-targeted Fluorescent Carbon Dots And Its Application In The Diagnosis Of Tumor Imaging

Bioactive small molecules have the effect of regulating cell function and are closely related to the occurrence and development of some major diseases.Fluorescence imaging technology has the advantages of high space-time resolution and high sensitivity.It is a powerful tool for accurate detection of cells and active small molecules in vivo,which provides new technology support for the fluorescence imaging diagnosis of cancer.Carbon Dots?CDs?is a new type of"zero-dimensional"fluorescent carbon nanomaterial because of its perfect water-solubility,photostability,favourable biocompatibility,low biological toxicity,and adjustable emission.It has potential application in the field of targeted imaging and drug delivery of tumor cells.Based on EDC/NHS and addition reaction,ligands and fluorescent carbon dots as carriers were assembled into receptor-targeted fluorescent carbon dots which were successfully applied in targeted recognition of cancer cells for visual detection.Chapter 1:We briefly described the methods of cancer diagnosis and tumor-related biomarkers,and reviewed receptor-targeted fluorescent carbon dots for cancer imaging diagnosis.Chapter 2:The green fluorescent CDs with active-NH₂ were prepared by a facile hydrothermal treatment of dandelion and ethanediamine as carbon precursors.The active-NH₂ on the surface of the CDs was covalently bonded to the-COOH on the folic acid?FA?to generate receptor-targeted fluorescent carbon dots?FA-CDs?.The uptake of FA-CDs into HepG-2 cells occurs via receptor-mediated endocytosis;this was confirmed by a comparative experiment using FR-negative?FR?PC-12 cells as revealed by confocal laser scanning microscopy.Intracellular experiments demonstrated that the FA-CDs could accurately recognize positive FR?FR++/FR+?cancer cells in different cell mixtures of MCF-7/HepG-2 cells and HepG-2/PC-12 cells and could distinctly indicate the expression level of FR on the membranes of the cancer cells.The FA-CDs show excellent biocompatibility and low toxicity and may have great potential as an effective tool for accurately differentiating cancer cells from normal cells,in addition to cancer detection,prognosis,and individualized treatment.Chapter 3:The yellow-green fluorescent carbon dots?CDs?,with easy-modification functional groups and perfect fluorescent performance,were prepared by one-step hydrothermal method using D-?+?-glucosamine hydrochloride and L-aspartic acid as carbon precursors.Based on the high-expression FR and CD44 receptors,the FA and hyaluronic acid?HA?were successively grafted onto the polyethyleneimine?PEI?via amide bond.Then,a dual receptor-targeted fluorescent CDs?FA-PEI-HA-CDs?was constructed by covalently bonding the-COOH of CDs to the residual–NH₂of PEI,due to the high specific affinity with FA,HA for FR and CD44receptors,respectively.By the competitive contrast imaging experiments:FA and HA as highly-affinitive targeting ligands can specifically bind to tumor cells,and FA-PEI-HA-CDs can take into tumor cells in a short time and almost do not into normal cells,may be achieve rapid,efficient and accurate identification of tumor cells.Chapter 4:The NH₂-modified yellow fluorescent CDs were prepared by one-step hydrothermal method using natural-source jujube as carbon source and polyethyleneimine?PEI?as nitrogen source.An epidermal growth factor receptor?EGFR?-targeted fluorescent CDs?thiourea-CDs?was constructed by the addition reaction of isothiocyanate groups on sulforaphane and-NH₂ on CDs.The cytotoxicity of thiourea-CDs on lung cancer epithelial cells?A549?and normal lung epithelial?BEAS-2B?cells as well as active EGFR mediated targeting performance were evaluated by MTT cytotoxicity assay and laser confocal imaging.Thiourea-CDs not only exhibited the optical properties of CDs but also the specific recognition and inhibition of EGFR kinase activity on the surface of A549 cell membrane by thiourea ligands,giving it the dual function of cancer cell diagnosis and activity inhibition.This novel receptor-targeted fluorescent carbon dots thiourea-CDs integrates targeting and treatment,which provides a new foundation for the integration of diagnosis and treatment of early cancer.Chapter 5:We summarized the results of the research on the receptor-targeted fluorescent carbon dots as fluorescent probes for applications in targeted imaging diagnosis and treatment cancer,and the future work was prospected.