Biotinylated liposomes can be conjugated non-covalently with (strept)avidin through either direct interaction with the protein/antibody conjugated to (strept)avidin or by coupling with other biotinylated proteins using (strept)avidin as a bridging molecule. Both avidin and (strept)avidin form strong non-covalent bond with biotin. The high resistance to breakdown makes them very useful in bioconjugate chemistry. However, (strept)avidin has replaced avidin in most bioconjugation applications due to its enhanced properties. NeutrAvidin (ThermoFisher) is a modified avidin without negative properties. It performs much better than original avidin and sometimes (strept)avidin.

In order to exploit the high-affinity interaction of biotin with (strept)avidin, a two-step “sandwich” protocol (Method A) has been developed for the preparation of targeted immunoliposomes. In this methodology, (strept)avidin is first attached to biotinylated liposomes, then a biotin-modified protein/antibody is introduced into the biotinylated (strept)avidin-labeled liposomes. This noncovalent approach is rapid, extremely versatile and applicable to numerous targeting ligands of interest with respect to in vitro and in vivo applications. Alternatively, instead of forming a (strept)avidin bridge, (strept)avidin molecule can also be covalently conjugated to antibody or ligand (Method B) and non-covalently bound to liposomes containing biotin on surface in order to form immunoliposomes.

ImmunoFluor™-Biotin is a PEGylated product. For other amine reactive (PEGylated and non-PEGyalated products) and also ImmunoFluor™ products suitable for other types conjugation methods see here.