Lyophilization enabled disentanglement of polyethylenimine on rambutan-like silica nanoparticles for enhanced plasmid DNA delivery

Polyethylenimine (PEI) functionalization onto nanoparticles is a widely used strategy for constructing particulate vectors for gene delivery. However, how to control the conformation of PEI chains and the resultant impact on gene transfection efficiency remains largely unexplored. Herein, we report that drying methods dramatically affect the conformation of PEI chains modified on the surface of silica nanoparticles and consequently the plasmid DNA transfection performance. Specifically, lyophilization renders less entangled PEI compared to commonly used vacuum drying as evidenced by an elevated glass transition temperature. The lyophilization induced disentangled conformation is likely associated with the solid-to-gas phase transition drying mechanism, which removes the bound crystal water content and thus reduces hydrogen bonding between amines. Moreover, we find that the stretched PEI chains on the surface of rambutan-like silica nanoparticles promote their binding capacity towards plasmid DNA molecules and thereby enhanced gene delivery and transfection efficiency. Our findings have provided new understanding about amine based polymers modified on nanoparticles, and have significant implications on the design of efficient particulate vectors for gene delivery.

Polyethyleneimine as a novel desorbent for anionic organic dyes on layered double hydroxide surface

Polyethyleneimine (PEI) is a positively charged polymer with hydrogen-bonding sites and hydrophobic chains. Therefore, it has been clearly established as an efficient adsorbent by means of these native properties in the literatures. However, there is apparently no good reason to disregard the use of PEI as a desired desorbent. Herein, using methyl orange as a model anionic dye, we investigated the desorption performances of PEI toward anionic dyes adsorbed on the surface of CO3-layered double hydroxides (LDHs) in a wide range of pH values. The experiment results showed that the positively charged PEI had very strong desorption capacity for anionic dyes at low pH values (<9.5) through electrostatic attraction between PEI and methyl orange because of the high degree of protonation of PEI. At high pH values (>9.5), PEI existed as neutral molecule, it could desorb methyl orange via hydrogen bonding between the amino groups of it and sulfonate group of methyl orange; simultaneously, the anion-exchange process occurred between abundant hydroxyl anions and anionic methyl orange. The adsorption capacity of the used LDH adsorbent was about 80% after five cycles of adsorption-desorption-regeneration, which was much higher than that conducted by 0.1M NaOH solution. These findings suggested that PEI could be regarded as a promising desorbent for enriching anionic dyes in wastewater and regenerating LDHs through surface adsorption-desorption cycles.