Layer-by-layer assembly of biologically inert inorganic ions/DNA multilayer films for tunable DNA release by chelation.

In this work, we illustrate a simple chelation-based strategy to trigger DNA release from DNA-incorporated multilayer films, which were fabricated through the layer-by-layer (LbL) assembly of DNA and inorganic zirconium (IV) ion (Zr(4+)). After being incubated in several kinds of chelator solutions, the DNA multilayer films disassembled and released the incorporated DNA. This was most probably due to the cleavage of coordination/electrostatic interactions between Zr(4+) and phosphate groups of DNA. Surface plasmon resonance (SPR), UV-vis spectrometry and atomic force microscopy (AFM) were used to characterize the assembly and the disassembly of the films. By incorporating plasmid DNA (pDNA) into this controllable disassembly system, the multilayer films sustained the consecutive DNA release. The released pDNA retained its integrity and transcriptional activity, and also expressed enhanced green fluorescent protein (EGFP) after being transfected into HEK 293 cells. Besides the simplicity and cost efficiency of this method, the most advantage of this route was that the release of DNA from the films could be modulated by various external conditions, such as the chelator and ionic strength. The Zr(4+)/DNA multilayer films with the ability to precisely control the release rate of DNA might serve as an alternative localized gene delivery system in the perspective of biomedical applications.