Multifunctional CuInS Quantum Dots Based Nanoprobes Used For Tumor Targeted In Vivo Imaging

With the growing development of nano-science and molecular imaging technology, quantum dots(QDs) based multifunctional nanoprobes have gained intense interests and been widely used for bio-imaging as versatile contrast agents. Due to the near infrared fluorescence and no toxicity elements containing, CuInS-based QDs are considered as one of the promising candidates for in vivo fluorescence imaging. However, the previous prepared QDs-based imaging nanoprobes are hampered with some drawbacks, including uncontrollable fluorescence properties, poor structural and colloidal stability, serious toxicity and unknown surface properties. Aimed at addressing the above issues, herein we tried to establish some multifunctional CuInS QDs-based nanoprobes with tunable fluorescence, good structural and colloidal stability and uncompromised highly fluorescent quality when combined with other functional moieties. The as-prepared Cu InS QDs-based nanoprobes were able to be used for tumor targeted in vivo multimodal imaging.Firstly, a facile strategy is reported for synthesis of Zn-Cu-In-S/ZnS(ZCIS/ZnS) core/shell QDs to address the synthetic issues that the unexpected blue-shift of CuInS2-based nanocrystals. In this strategy, Zn2+ ions are intentionally employed for the synthesis of alloyed ZCIS core QDs before ZnS shell coating, which contributes to the reduced blue-shift in photoluminescence(PL) emission. The experimental results demonstrate this elaborate facile strategy is effective for the reduction of blue-shift during shell growth. Particularly, a hypothesis is proposed and proved for explanation of this effective strategy. Namely, both cation exchange inhibition and ions accumulation are involved during the synthesis of ZCIS/ZnS QDs. Furthermore, the obtained near infrared(NIR) ZCIS/ZnS QDs are transferred into aqueous phase by a polymer coating technique and coupled with cyclic Arg-Gly-Asp peptide(cRGD) peptides. After confirmation of biocompability by cytotoxicity test on normal 3T3 cells, these QDs are injected via tail vein into nude mice bearing U87 MG tumor. The result indicates that the signals detected in the tumor region are much more distinguishing injected with ZCIS/ZnS-cRGD QDs than that injected with ZCIS/ZnS QDs.Secondly, although synthesis of Cu InS-based quantum dots(QDs) in organic phase has been currently one of the fastest growing points of nanotechnology, most of the reported Cu InS-based QDs are hydrophobic and could not be directly used for biomedical application without phase transfer. We put forward a one-pot synthetic strategy aimed at fabricating hydrophilic Zn-Cu-In-S/ZnS(ZCIS/ZnS) QDs directly used for in vivo imaging without surface treatment. This strategy is based on the use of a hydrophilic ligand(6-sulfanyl-1-hexanol, MPH) and noncoordinating solvents such as a low molecular weight polyethylene glycols(PEG, MW=400 Da). The capping ligand MPH endows the obtained ZCIS/ZnS QDs with good hydrophilicity and therefore offers great opportunity for direct bioimaging application without phase transfer. Experiment results have indicated that these so-called hydrophilic ZCIS/ZnS QDs show low cytotoxicity and are successfully utilized for in vivo imaging. Furthermore, here reported strategy doesn’t only present a synthetic idea, but also might stimulate other innovative ideas on fabricating hydrophilic or water-soluble ZCIS/ZnS QDs directly used for biological applications.Thirdly, inorganic nanoparticles have been introduced into biological systems as useful probes for in vitro diagnosis and in vivo imaging, due to their relatively small size and exceptional physical and chemical properties. A new kind of color tunable Gd-Zn-Cu-In-S/ZnS(GZCIS/ZnS) QDs with stable crystal structure was successfully synthesized and utilized for magnetic resonance(MR) and fluorescence dual modality imaging. This strategy allows successful fabrication of GZCIS/ZnS QDs by incorporating Gd into ZCIS/ZnS QDs to achieve great MR enhancement without compromising the fluorescence properties of the initial ZCIS/ZnS QDs. The as-prepared GZCIS/ZnS QDs show high T1 MR contrast as well as ―color-tunable‖ fluorescence in the range of 550-725 nm by adjusting the Zn/Cu feeding ratio with high PL quantum yield(QY). The GZCIS/ZnS QDs were transferred into water via a bovine serum albumin(BSA) coating strategy. The resulting Cd-free GZCIS/ZnS QDs reveal negligible cytotoxicity on both He La and A549 cells. Both fluorescence and MR imaging studies were successfully performed in vitro and in vivo. The results demonstrated that GZCIS/ZnS QDs could be a dual-modal contrast agent to simultaneously produce strong MR contrast enhancement as well as fluorescence emission for in vivo imagingFinally, functionalized QDs have been widely explored for multi-modality bioimaging and proven to be versatile agents. Attaching positron-emitting radioisotopes onto QDs not only endows their positron emission tomography(PET) functionality but also results in self-illuminating QDs, with no need for an external light source, by Cerenkov resonance energy transfer(CRET). Traditional chelation methods have been used to incorporate the radionuclide, but these methods are compromised by the potential for loss of radionuclide due to cleavage of the linker between particle and chelator, decomplexation of the metal, and possible altered pharmacokinetics of nanomaterials. Herein, we described a straightforward synthesis of intrinsically radioactive [64Cu]CuInS/ZnS QDs by directly incorporating 64 Cu into CuInS/ZnS nanostructure with 64CuCl2 as synthesis precursor. The [64Cu]Cu InS/ZnS QDs demonstrated excellent radiochemical stability with less than 3% free 64 Cu detected even after exposure to serum containing EDTA(5 mM) for 24 h. PEGylation can be achieved in situ during synthesis, and the PEGylated radioactive QDs showed high tumor uptake(10.8% ID/g) in a U87 MG mouse xenograft model. CRET efficiency was studied as a function of concentration and 64 Cu radioactivity concentration. These [64Cu]CuInS/ZnS QDs were successfully applied as an efficient PET/self-illuminating luminescence in vivo imaging agents.