Reversible size-tuning of self-assembled silver nanoparticles in phospholipid membranes via humidity control.

A monolayer of 5-nm-sized Ag nanoparticles embedded in a liquid-crystalline lipid membrane undergoes a reversible morphological change during hydration and dehydration of the lipid membrane. High mobility of the encapsulating lipid molecules, chemically bound to the Ag atoms, induces redistribution of metal particles to produce significant and optically detectable changes in nanoparticle morphology. The morphological change occurs on a time scale that enables the Ag-nanoparticle-embedded membrane to be used as a convenient visual sensor for moisture and other organic solvents, as well as for biosensing by virtue of the biocompatibility of the lipid molecules. The mechanism demonstrated here can also be extended to construct guided nanostructures based on self-assembled nanoparticles.