Polyarginine peptides, which are very efficient CPPs have been used for siRNA delivery into cells.
Stearylated octaarginine (Stearyl-R8), are able to encapsulate and shuttle nucleic acids through cell membranes without the need to covalently attach the nucleic acid to the arginine-containing carrier peptide.
Case Study: EGFP-expressing hippocampal neurons
Efficiency: 16 nmol/l siRNA& → 50% reduction in EGFP activity
Reference: Tonges, L, Lingor, P, Egle, R, Dietz, GP, Fahr, A and Bahr, M (2006). Stearylated octaarginine and artificial virus-like particles for transfection of siRNA into primary rat neurons. RNA 12: 1431-1438.
See details about the cell penetrating peptides: http://lifetein.com/Cell_Penetrating_Peptides.html