| Gold nanoparticles(GNP) refer to the particles composed of Au whose sizes were between 1 nm-100 nm. Due to their good nature of optics, chemistry and physics, GNPs have been regarded as an ideal nano-platform for imaging, treatment and targeted delivery. “PEG dilemma” of the hydrophilic nanomaterials, which might have long circulation time in blood, but difficult to be internalized by tumor cells, makes them difficult to take effect. In this paper, we designed a CT/fluorescence dual-mode tomography nanoparticles, using pH responsive hydrophilic/hydrophobic reversal polymer poly N-isopropylacrylamide-acrylic acid(PNA) to modify GNP, then conjugating the near-infrared fluorescent molecules Cy5.5 at the end of PNA. We also studied and evaluated their capacity of overcoming “PEG dilemma” and imaging. The main works are as follows:(1) Preparation and characterization of GNP-PNA-Cy5.5 nanoparticles: Using trifluoroacetic acid to hydrolyze p(NIPAM-b-tBA) polymers for different time courses, we got the pH-responsive hydrophilic/hydrophobic reversal PNA polymers and then animated at the end. We prepared GNPs by REDOX method whose diameter is about 30 nm. Then PNA was modified on GNPs' surface and Cy5.5 was modified at the end of PNA. The size, zeta potential, pH responsive and surface morphology of GNP-PNA-Cy5.5 were further determined. The results showed that GNP-PNA-Cy5.5 nanoparticles are about 100 nm in size and-15 mV in zeta potential. They appeared to exhibit pH-responsive hydrophilicity/hydrophobicity reversal property between pH 7.4 and 6.5.(2) Ability of GNP-PNA30%-Cy5.5 nanoparticles to overcome the PEG dilemma: We studied BSA/FBS adsorption by GNP-PNA30%-Cy5.5 nanoparticles and phagocytosis by Raw264.7 macrophages in different pH. Then we studied the long circulation ability of nanoparticles in SD rats. What's more, the cellular uptake of GNP-PNA-Cy5.5 by HepG2 human liver cancer cells in different pH, their endocytic pathways and intracellular localization were further studied. The results showed that, in the pH of blood environment(pH= 7.4), the GNP-PNA-Cy5.5 nanoparticles absorbed a small amount of BSA/FBS, and were rarely phagocytosed by Raw264.7 macrophages. As expected, the modification of PNA can significantly improve GNPs' circulation time in blood. In pH of tumor environment(pH=6.5), the cellular uptake of the nanoparticles by HepG2 cells was more than that in pH 7.4. The cells were internalized mainly by macropinocytosis and caveolin-mediated endocytic pathways. GNP-PNA-Cy5.5 nanoparticles were mainly located in membranes and endoplasmic reticulum, but not in the nucleus.(3) Evaluation of the imaging capability of GNP-PNA30%-Cy5.5 nanoparticles: We studied the ability of GNP-PNA30%-Cy5.5 nanoparticles for CT/ fluorescent dual-mode tomography in vitro and in tumor-bearing mice. The biodistribution of GNP-PNA30%-Cy5.5 nanoparticles in different organs and tumor were further evaluated. The results showed that the GNP-PNA-Cy5.5 nanoparticles have a higher X-ray absorption ability than Iohexol in vitro. Fluorescence of tumor was brightest at 12 h after injection. The nanoparticles were mainly distributed in liver, spleen and tumor 24 h after injection.In short, we successfully prepared GNP-PNA-Cy5.5 nanoparticles which can overcome the PEG dilemma and had dual-mode imaging capability of CT. The results in this paper might provide experimental and theoretical basis for further study of the GNP-PNA-Cy5.5 dual-mode imaging nanoparticles. |
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