Preparation Of PEI Modified Carbon Dots And Their Cell-labeling And Cytotoxicity

Cell-labeling is one of the most important technologies in biological research, which growing trends are to strengthen the bio-compatibility, to enhance the ability for trace and to achieve in vivo imaging. Therefore, it is still one of the important steps to develop biomarkers materials with good biocompatibility and excellent labeling performance. Carbon dots (CDs) were a new type of fluorescent nanoparticles, with many unique advantages such as small size, strong penetrability, adjustable emission spectrum, easy for functionalization and high chemical and optical stability. The main component element of CDs was carbon which was similar the constituent of organism. Consequently, CDs showed obvious superiority in biocompatibility comparing to traditional flourescent materials. As a result, the research on the synthesis and bio-applications of CDs has become a hot-point area.Firstly, bare CDs were synthesized solvothermaly in ethylene glycol solution and then modified with branched polyethyleneimine (PEI) to improve their fluorescence property and functionalize them with amino-group. The as-prepared CDs were characterized by transmission electron microcopy (TEM), laser particle size analyzer (LPSA), infrared spectrum (IR) and fluorescence spectrum (FL). The results indicated that the synthesized CDs have small size of7.5nm, good monodispersity and uniform size distribution. After modification with PEI, the quantum yield of as-prepared CDs was3.5%, showing about300-fold enhancement in fluorescence emission. The PEI-modified CDs showed multicolor emissions from blue to green under diffirent excitation wavelength meanwhile it were stable within the wider pH range of3-8.And then, in the presence of activator (NHS and EDC), the PEI-modified CDs were conjected with rabbit anti-CEA8antibody and then used as the biolabels for immunolabelling and imaging of HeLa cells, which was achieved by the specific recognization and binding between the CEA8antibody and CEA antigen. In addition, owing to small diameter and excellent biocompatibility, the as-prepared CDs were used successful to label yeast by endocytosis.Finally, the cytotoxicity of as-prepared CDs and CdTe QDs were compared by using bath MTT method and trypan blue dye exclusion assay and HeLa cells were employed as model organisms. Experimental results from the two methods indicated that the cytotoxicity of as-prepared CDs was markedly less than that of CdTe QDs. The cell viability of HeLa cells, which were incubated with as-prepared CDs, could reach99.3%under the condition of cell-labelling (the concentration was0.75mg/mL; incubating time was1.5h). In conclusion, the cytotoxicity of as-prepared CDs is ignorable.