EB1 is a penetratin analogue that was synthesised to be an endosomolytic cell penetrating peptide (CPP). Certain amino acids in the penetratin sequence were replaced with histidine to encourage formation of an alpha helix upon protonation in the acidic endosomes. As a CPP, EB1 has been shown to form a strong interaction with the phospholipid bilayer during insertion with rapid cellular uptake, there is a moderate amount of cell leakage and no significant cytotoxicity. EB1 is provided here as a C-terminal amide with a N-terminal 5-carboxyfluorescein (5-FAM), a widely used green fluorescent tag often preferred due to its high stability; absorbance 492 (nm), 518 emission (nm).