Complexes prepared from cationic, dichain lipid (L) vesicles and negatively charged siRNA (R), with and without positively chargely targeting peptides (P) known as LR or LPR complexes respectively have emerged as major non-viral gene delivery vehicles. Despite the wide spread interest in LR and LPR complexes as delivery vehicles, very little is understood about their mechanism by which they deliver their payload and in particular overcome many of the barriers they encounter on their passage to their target cell. Yet such an understanding is essential for the development of improved gene delivery. Among the barriers the delivery vehicles encounter on their passage to the target cell is serum proteins. The present proposal aims to study the differential effect of serum proteins on the detailed nanostructure of LR and LPR vehicles using SANS with contrast variation.