RGDC Peptide Modified Quantum Dots Targeting Tumor Cells And Biotoxicity Analysis

Quantum dots (QDs) have been widely used in various fields of bioimaging and biosensing detection for their exceptional fluorescent properties. The basic rationale is that these nanometer-sized particles have unique functional and structural properties, such as size and composition tunable fluorescence emission, large absorption cross sections, and exceptional brightness and photostability compared with organic dyes and fluorescent proteins. Recent research has achieved considerable success in using QDs for labeling fixed cells and tissue specimens and for imaging cell membrane acceptors. Many labeling methods have been developed to target chemical probes site-specifically to proteins in the cellular environment. In most of these methods, peptide recognition sequences are more desirable than protein-based recognition sequences because they minimize perturbation to the target protein. On the other hand, peptide-mediated transfection has attracted more and more attention for the efficient cellular transmembrane delivery and labeling. Though the mechanism of peptide-mediated membrane translocation remains unclear, increasing evidence indicates the involvement of several types of endocytosis.The tripeptide sequence Arg-Gly-Asp (RGD) was identified as a minimal essential cell-adhesion peptide sequence and often used to stimulate cell adhesion process. Herein, the RGD motif was employed to modify the surface of QDs, which was covalently attached to QDs via the cross-linking reagent. Moreover, considering the cytotoxicity of QDs in the biological system, QDs have been investigated for core-shell nanocrystals with surface modification which coating with polymaletic acid aliphatic alcohol (PMAA). Thus, in our work, PMAA was selected to coat QDs with carboxyl groups as functional groups for further covalent bonding to the amino terminal of RGDC peptide.First of all, the optical properties of quantum dots have been studied and confirmed the CdSe / ZnS quantum dots with good luminescent properties. Its strong absorption to ultraviolet light, can use a wide range of excitation light for their excitation, which emits strong fluorescence. Change the size of quantum dots, the fluorescence emission peak position is also changed to different colors of fluorescence. Then we detected the UV absorption spectra and fluorescence emission spectra of fluorescent dye Ru-coated SiO2 shell before and after. Found the fluorescence peak position of SiO2-coated dye remains unchanged, but peak intensity enhanced.Then, RGDC peptide on the use of CdSe / ZnS quantum dots for the surface modification. This small peptide can binding specificity with integrin receptor on tumor cell surface. So that quantum dots have a better biological histocompatibility and tumor-specific. By comparing the UV and fluorescence spectroscopy of the quantum dots before and after modified, that the binding of functional peptide RGDC and quantum dots is a successful.Then RGDC modified quantum dot labeling of tumor cells, after 2 hours the modified quantum dots are mainly distributed in the cell membrane, but unmodified quantum dots is not specific on the membrane. As time was extended to six hours to observe the modified quantum dots gathered inside cells. At the same time, the use of quantum dots to nematodes for biological markers, quantum dots can better labeled nematodes body.Subsequent we used the coated and uncoated dye labeled cells. The dye is not marked the boundary of cells clearly, and the coated dye can be clearly seen after the particle. With the time extended to 24 hours, the particles turn into cells. Dye significantly reduced the fluorescence intensity, after coated the situation has improved. Through the use of dye markers on tumor cells, found that it has a certain impact on cells, after coated, this impact has improved.Compared quantum dots with the fluorescent dye markers in tumor cells, found fluorescent dyes labeled tumor cells showed strong fluorescence, can not be distinguished, and quantum dots can be seen clearly. It seems likely that the quantum dot attached to the cell membrane or into cells.Then use of the method of MTT of several quantum dots, fluorescent dyes, gold nanoparticles and Fe3O4 nanoparticles for the detection of cell toxicity. We found that the use of several quantum dots is not toxic to cells; gold nanoparticles and Fe3O4 nanoparticles are not toxic to cells; CdTe quantum dots with strong cell toxicity; dyes the most toxic of the cells. And then use of nematodes for the biological toxicity of quantum dots were tested. Quantum dots was found to have a certain impact on nematodes. The impact depends on the concentration of quantum dots.These results indicate that quantum dots are suitable for biological fluorescence labeling. In addition to their better luminescent properties, easy to carry out surface modification, but also the ability to connect a number of biological molecules. Modify fewer impact on the fluorescence intensity of quantum-dot ,they will not be weakened, and have specific biological functions, such as specific with organisms or cells. This makes quantum dots has good prospects in the application of biomarkers. However, its components often contain toxic materials, it will have a certain impact on cells and organisms, so to reduce the toxicity of quantum dots or develop new non-toxic and excellent luminescent properties of quantum dots is the direction of future research. Although the red fluorescent dye Ru have a strong fluorescence, but with regard to cell markers, they can not show a clear cell outline. And, after cell toxicity test revealed that the toxicity of dyes is the largest on cell, morphology change is also larger, so it is not suitable for label cells. The silica shell-coated fluorescent dyes can also be sent a strong fluorescence. The fluorescence peak even more intensity than fluorescent dyes. Because the silicon-coated shell structure, its toxicity may be reduced, therefore, it is expected to be new biomarkers material.