Encapsulation of DNA by Cationic Copolymer Vesicles for Gene Delivery and Micro-arraying Techniques

The encapsulation of double-stranded DNA (dsDNA) fragments (158 base pairs, contour length L = 54 nm) by the cationic diblock copolymer poly-(butadiene-b-N-methyl-4-vinyl pyridinium) [PBd-b-P4VPQ] was studied using phase contrast microscopy. The DNA copolymer vesicles were prepared using a single emulsion technique. In this procedure, an aqueous solution containing the short fragment DNA is emulsified in toluene and stabilized by the amphiphilic diblock copolymer. The hydrophobic PBd block forms an interfacial brush, while the hydrophilic, cationic P4VPQ block complexes with the negatively charged DNA. When the emulsion droplets are transferred into ethyl acetate, which is a non-solvent for polybutadiene, the PBd brush collapses resulting in the formation of DNA capsules. Two different but related methods were used to produce DNA vesicles, which were stabilized in an aqueous polyethylene glycol (PEG) solution. The first method of preparation resulted in DNA vesicles which were adhered to the surface of a glass slide. This method is useful for in vitro gene delivery. The second method of preparation resulted in mobile DNA vesicles which were suspended in aqueous PEG solution. This method has potential application in the construction of DNA microarrays using multiple-spot optical tweezers.