Fluorescent Carbon Dots-Based Multifunctional Nonviral Gene Vectors

Carbon dot (C-dot, CD), a fluorescent carbon nanomaterial, has drawntremendous attention owing to its advantages in stable photoluminescence (PL), broadexcitation spectra, tunable emission spectra and low cytotoxicity.In this work, the surface passivated CDs (CD-TTDDA and CD-PEI) werefabricated by one-step microwave assisted pyrolysis of glycerol in the presence of4,7,10-trioxa-1,13-tridecanediamine (TTDDA) or branched polyethylenimine (PEI)serving as the surface passivation agent. FTIR, EA, TGA, HRTEM, XRD, UV-Vis andfluorescent microscopy were used to confirm the successful synthesis of CD and toilluminate its mechanism of photoluminescence (PL). According to the resultsobtained by above characterizations, the process of CD formation was supposed toundergo dehydration, polymerization, carbonization and surface passivation, whichhad no well-defined boundarys and might occur simultaneously. There were differentorganic groups on the surface of CD, endowing CD with hydrophilicity andphotostability. The origins of PL in CD mainly came from emissive traps on thesurface of CD, so the formation of surface passivation was the main factorcontributing to the enhanced fluorescence of CD. Agarose electrophoresis, TEM andZeta potential measturements indicated that CD-PEI was capable of condensing DNAinto nanocomplexes with diameters less than200nm. Beside above, it was revealedthat microwave time had great influence on the surface density of positive charge ofCD, which determined the zeta potential and capability of binding DNA.Further studies demonstrated that the CD-PEI could not only efficiently deliverplasmids into COS-7and HepG-2cells, but also mediate higher gene expression thanPEI25k with lower cytotoxicity. To optimize the performance of CD-PEI vectors,proper pyrolysis time was essential to balance formation of CD and destruction of PEI.The multicolor fluorescence of CD-PEI entrapped in cells could also be detected bylaser scanning confocal microscopy, making the PEI-functionalized carbon dot ahigh-efficient gene vector with gene delivery and bioimaging dual functions, whichhas great potential in biomedical applications.