Some cell-permeable peptides can carry cargo across the cell membrane even without any covalent links. Biotinylated peptides, including L—and D-TAT peptides made by LifeTein, were used in this study to show that two types of cell surface receptors, heparan sulfate proteoglycans, and Neuropilin-1, play critical roles in the delivery of silver-based nanoparticles into cells by cell-permeable peptides.

Nano Particles & Cell-Permeable Peptides

Science Advances 06 Nov 2015: Vol. 1, no. 10, e1500821 DOI: 10.1126/sciadv.1500821.  Neuropilin-1 and heparan sulfate proteoglycans cooperate in cellular uptake of nanoparticles functionalized by cationic CPP peptides.