Objective(s): Carbon nanotube (CNT) has been widely applied at molecular and cellular levels due to its exceptional properties. Studies based on conjugation of CNTs with biological molecules indicated that biological activity is preserved. Polyethylenimine (PEI) is explored in designing novel gene delivery vectors due to its ability to condense plasmid DNA through electrostatic attraction. In this study functionalization and grafting polyethylenimine onto the surface of carbon nanotube was used

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... to improve the solubility and biocompatibility. Materials and Methods: The effect of molecular weight of polymer on final efficacy of vectors has been investigated using three different molecular weights of polymer. In this study no linker was used and both segments (PEI and CNT) were directly attached resulted in the synthesis of three different vectors. Synthesized vectors were tested for their ability to condense plasmid DNA and cellular toxicity using ethidium bromide and MTT assays. Size and Zeta potential of nanoparticles was determined using Malvern zeta sizer. Evaluation of transfection efficiency of vectors was carried out on N2A cell line by different methods including qualitative fluorescence imaging, flow cytometry and luciferase assay. Results: All three synthesized vectors bear positive surface charges with sizes in the range of 85-190 nm. More than 80 percent of treated cells were viable and in the case of V25 significant improvement in reducing cytotoxicity compared to unmodified polymer was observed. Obtained results indicated that vector containing PEI 1.8 kDa has the greatest improvement in terms of its transfection efficiency compared to unmodified polymer. Conclusion: Conjugation of PEI with carbon nanotube les to new vectors with lowered cytotoxicity and higher transfection efficiency. The highest transfection efficiency was obtained with the lowest molecular weight PEI.