Surface functionalization of poly(d,l-lactic acid) nanoparticles with poly(ethylenimine) and plasmid DNA by the layer-by-layer approach

Poly(d,l-lactic acid) (PLA) particles, obtained by the emulsification–diffusion process, were surface modified by electrostatic interactions with cationic poly(ethylenimine) (PEI). The charge inversion was evidenced by zeta potential measurements and the adsorption isotherms of PEI were established. No flocculation was observed by Quasi-Elastic Light Scattering (QELS) or Scanning Electron Microscopy (SEM) so long as the PEI amount in the adsorption medium was close to the surface saturation. With water as an adsorption medium, low PEI loading levels were achieved but, when salt was added, higher amounts of polymer were immobilized at the surface of the PLA particles, as proved by the positive value of the zeta potentials (+20–30 mV). Highly cationized latex particles complexed plasmid DNA under a compacted conformation, as evidenced by the ethidium bromide displacement results, similar to the PEI free in solution. With particles obtained by PEI adsorption from water, low amounts of DNA were loaded on the surface and the level of compaction was low.