Growing a Nucleotide/Lanthanide Coordination Polymer Shell on Liposomes.

Coating liposomes with a shell is a useful strategy to increase membrane stability and prevent leakage or fusion. Nucleotide/lanthanide coordination nanoparticles (NPs) are formed by a simple mixing at ambient conditions. Because some lipid headgroups contain lanthanide binding ligands, they may direct the growth of such coordination NPs. Herein, a gadolinium/adenosine monophosphate (Gd3+/AMP) shell was formed on liposomes (liposome@Gd3+/AMP) using lipids containing phosphoserine (PS) or cholinephosphate (CP) headgroups, while phosphocholine liposomes did not support the shell. Liposome binding Gd3+ is confirmed by transmission electron microscopy (TEM). The negatively charged CP and PS liposomes reversed to positive upon Gd3+ binding, while other metals such as Ca2+ and Zn2+ did not reverse the charge. Binding of Gd3+ did not leak the PS liposomes. Then, AMP was further added to cross-link Gd3+ on the liposome surface. A shell was formed as indicated by TEM, and the content inside the liposome remained for the PS liposomes. While adding Triton X-100 still induced leakage of the encapsulated liposomes, the shell protected the liposomes from leakage induced by ZnO NPs, suggesting a porous structure of the Gd3+/AMP shell which allowed penetration of Triton X-100 but not the larger ZnO NPs. This work provides a simple method to coat liposomes, and also offers a fundamental understanding of liposome adsorption of lanthanide ions.