The work employs carbon dot (CD) which has been emerging as a fluorescent nanomaterial with excellent biocompatibility and perceived as a promising alternative to quantum dot (QD), to monitor the association/dissociation of polymeric carrier/plasmid DNA (pDNA) complex during transfection. To shed light on the underlying post-endosomal events and provide the insight to design rational and efficient gene delivery vector, the adopted strategy exploited the quenching of the fluorescence of CD by Au nanoparticles. The surface of CD and Au was modified with highly cationic polymer, polyethylenimine (PEI) and subsequent treatment with non-labeled pDNA gave rise to quenched delivery complex. High salt concentration triggered the dissociation of the complex with accompanied fluorescence recovery arising due to the increase in distance between CD and Au. The studies revealed the potential of the developed CD-PEI/Au-PEI/pDNA ternary nano-assembly as a highly efficient hybrid transfecting agent with high cell viability under the optimum condition. The changes occurred at the intracellular level during transfection especially post-endosomal step were monitored by fluorescence measurement using fluorescence microscope. This nano-assembly system was found to be very effective at monitoring the carrier/pDNA dissociation in a non-labeled manner, thus provides efficient strategy to study the mechanistic aspect of polymer-mediated pDNA delivery.
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