The Dynamics of Concentrated Polycations and DNA Based Polyelectrolyte Complexes

Gene therapy solutions to communicable and developed pathologies have long been limited by a lack of molecular insight into the delivery process. While previous literature has demonstrated the effectiveness of polycations at shielding DNA in cellular environments, there is yet no work explicitly probing the mechanistic workings of this as a diffusive process. In this single particle tracking (SPT) study, we used microscopy to track individual molecules of fluorescently labeled polymer. We found unique diffusive behavior in concentrated polycationic solutions, as well as interesting phase behavior and ensemble statistics when examining DNA containing polyelectrolyte complexes. Our work with aqueous poly-lysine (PL) demonstrates a high dependence of the apparent diffusion coefficient on solution concentration, independent of salinity. This previously unobserved degree of correlation points to a unique mechanism of diffusion that is strongly governed by the prevalence of interactions between polymer chains. Moreover, in PL and DNA complexes, variation in charge ratio and preparation technique result in multiple mechanically distinct phases. These range from liquid coacervates to stiff solid complexes but remained imageable via SPT microscopy. This level of phase variation is not typical for coacervitic systems and adds to a burgeoning field of work on the nature of DNA-Polycation interactions. Ensemble statistics show that within these mechanically distinct phases, there is a salinity independent level of molecular heterogeneity that makes this system impossible to properly describe using bulk measurements. The results also suggest that assumptions of phase, molecular homogeneity, and deshielding mechanisms in this field may need adjustment; almost all current thought presents polyplexes as monopopulational, ionically destabilizable liquid droplets, when this may only rarely be true. We find this shift in paradigm to be an exciting step forward, as it has greatly multiplied the avenues of study for the system and has shown great potential for this advanced material to reach beyond the initial scope of gene delivery.