In situ lipid dip-pen nanolithography under water.

Lipids form the structural and functional basis of biological membranes, and methods for studying their self-organization in well-defined nano- and micro-scale model systems can provide insights into biology. Using lipids as an ink for dip-pen nanolithography (lipid DPN) permits the rapid nanostructuring of multicomponent model lipid membrane systems, but this technique has so far been limited to air. Here we demonstrate that lipid DPN can be carried out under water with single tips or parallel arrays. Using the same tip for deposition and imaging in aqueous solution permits imaging of self-spreading lipid bilayer spots in situ and quantification of the nanoscale spreading kinetics in real time by means of lateral-force microscopy. Furthermore, using fluorophore-labeled phospholipids, we directly observed, by confocal laser scanning microscopy, a two-phase (oil in water) meniscus formed around the contact point between the DPN tip and surface, gaining insights into the mechanisms of the ink transport. The methods described here provide a new tool and environment for high-resolution studies of lipid nanodynamics and molecular printing processes in general.