Fabrication Of Near-infrared Fluorescent Quantum Dots-based Probes For Bioimaging

Molecular imaging is a new frontier of biomedical research for visualizing, characterizing andmonitoring biological processes at the molecular and cellular levels in humans and other living systems using sensitive instrumentation and contrast mechanisms. Consequently, cancer molecular imaging has created unique opportunities to study and noninvasively monitor tumor genesis, development and metastasis in vivo. Design of the molecular probe is the key for molecular imaging. Near-infrared (NIR) fluorescence imaging (650-900nm) displays properties of low absorption and relatively low autofluorescence, it offers several advantages over other modalities for imaging living organisms. Moreover, it is cost-efficient intermsof preparation of molecular probes and the detection hardware is relatively simple to operate. Compared with organic dyes, quantum dots (QDs) possess several distinct advantageous optic properties, such as greater brightness, better stability with respect to photobleaching, and narrow spectral line-width. The available NIR QDs offer a wide range of emission wavelengths spanning the optical window for deep tissue imaging, compositions presenting limited toxicity. Recently, the progress in controlled synthesis of high-quality NIR QDs without toxic elements and the effective surface modifications for NIR QDs has explored as promising molecular probes for bioimaging. This dissertation aims at developing available NIR QDs-based molecular probes for selective and sensitive bioimaging. The following is the main content and innovation point.(1) We report a one-pot fabrication of mercapto polyethyleneimine (SH-PEI) stabilized ultrasmall NIR fluorescent silver nanoclusters (PEI-AgNCs), and the bioconjugation of the PEI-AgNCs with folate (FA) for targeted cancer imaging in vitro and in vivo. Firstly, mercapto polyethyleneimine was prepared through an amide condensation reaction. PEI-AgNCs are synthesized in aqueous solution via a simple synthetic route. The resulting PEI-AgNCs exhibit intense NIR fluorescence, ultrasmall size and low in vitro toxicity, which is favorable for bioimaging. SH-PEI not only acts as a stabilizer, but also facilitates post-surface modifications with functional biomolecules. Compared with the existing methods, the PEI-AgNCs have an excellent stability. Further bioconjugation of PEI-AgNCs with FA allows targeted imaging of the folate receptor positive tumor MCF-7-bearing mice.(2) We report the fabrication of transferrin functionalized gold nanoclusters (Tf-AuNCs)/graphene oxide (GO) nanocomposite (Tf-AuNCs/GO) as a turn-on NIR fluorescent probe for bioimaging cancer cells and small animals. Tf was used not only as stabilizer and reducer, but also as a functional ligand for targeting TfR to prepare Tf-AuNCs via a one-step approach. The resulting Tf-AuNCs exhibited intense NIR fluorescence that could avoid interference from biological media such as tissue auto-fluorescence and scattering light. To achieve a fluorescent signal activation process, GO, an efficient fluorescence quencher, was employed to fabricate a turn-on NIR fluorescent probe of Tf-AuNCs/GO composite with negligible fluorescence background. The prepared probe was successfully applied for turn-on NIR fluorescent imaging TfR over-expressed cancer cells and Hela tumor sites in mice. To our knowledge, no AuNCs based fluorescent turn-on probes have been reported for bioimaging small animals so far.(3) We report a one-pot fabrication of bovine serum albumin (BSA) stabilized ultrasmall NIR fluorescent Ag2S QDs, and the bioconjugation of the BSA-stabilized Ag2S QDs with vascular endothelial growth factor (VEGF) antibody (antiVEGF) for targeted cancer imaging in vivo. BSA stabilized Ag2S QDs are firstly synthesized in aqueous solution via a simple and mild synthetic route without the need for high temperature and inert gas protection. The resulting Ag2S QDs exhibit intense NIR fluorescence, ultrasmall size and low in vivo toxicity, which is favorable for bioimaging. BSA not only acts as a stabilizer, but also facilitates post-surface modifications with functional biomolecules. Further bioconjugation of BSA-stabilized Ag2S QDs with antiVEGF allows targeted imaging of the VEGF positive U-87MG human glioblastoma tumor-bearing mice. To our knowledge, no functionalized Ag2S QDs fluorescent probes have been reported for targeted cancer imaging in vivo so far.(4) We report an efficient synthesis of CuInS2QDs with strong photoluminescence in the near-infrared. This method can produce gram quantities of material with a chemical yield in excess of90%with minimal solvent waste. The overgrowth of as-prepared nanocrystals with a few monolayers of ZnS increases the photoluminescence quantum efficiency to>60%. Furthermore, the obtained NIR CuInS2/ZnS QDs are transferred into aqueous phase by a simple method. The CuInS2/ZnS QDs phase transfer technique utilized a low molecular weight amphiphilic polymer that is formed via maleic anhydride coupling of poly(styreneco-maleic anhydride) with6-aminocaproic acid. The polymer encapsulated water-soluble CuInS2/ZnS QDs exhibit the same optical spectra and colloidally stable over a wide pH range.