Analysis of the surface structure of DNA/polycation/hyaluronic acid ternary complex by Raman microscopy

We have developed a new type of ternary gene transfection system comprising plasmid, polyethyleneimine, and hyaluronic acid (HA). HA recharged the positively charged DNA complexes into negative, and diminished the adverse interactions with bio-components. HA also improved the transcription efficiency, stabilized the dispersion, and protected the particles against lyophilizing induced inactivation. It enabled the preparation of very small complex particles, which showed high in vivo gene expression. In spite of the many attractive properties of the ternary complex systems, their detailed structure is still not clear. In this study, surface structures of the complexes were analyzed by non-confocal laser Raman microscopy. The correlation between the zeta-potential and the Raman spectrum is discussed. The DNA complex that showed the highest gene-expression level was prepared at the mixing ratio of COOH/NH=0.5. At this ratio, all the amino groups were just protonated, and the surface was completely covered by HA attributed to the reduced nonspecific interaction of the complex in which all the amino groups have already interacted with carboxyls of HA, but not too much HA on the surface taken up by the cells.