Vesicle capture on patterned surfaces coated with amphiphilic biopolymers

We describe a simple way to create patterns of ‘‘soft’’ biomolecular nanostructures such as vesicles on ‘‘hard’’ surfaces such as gold. The key to our approach is the use of an amphiphilic biopolymer as an ‘‘interconnect’’ or tether. The polymer is hydrophobically modified chitosan (hm-chitosan), which is obtained by covalently attaching alkyl tails to the backbone of chitosan. We electrodeposit films of hmchitosan onto microscale gold cathodes formed by lithography on a silicon wafer. Subsequently, the hm-chitosan films are used to spontaneously capture vesicles from solution; this is demonstrated both for surfactant as well as lipid vesicles (liposomes). Vesicles remain strongly bound to the hm-chitosan to a much greater extent than to native chitosan. This suggests that the mechanism for vesicle capture involves non-covalent binding of hydrophobes from hm-chitosan chains to the hydrophobic portions of vesicle bilayers. Importantly, the vesicles captured by hm-chitosan films are intact—this is shown both by direct visualization of captured vesicles (via optical and cryo-transmission electron microscopy) as well as through the capture and subsequent disruption of dye-filled vesicles. Various microscale patterns of immobilized vesicles are created and the vesicles are demonstrated to be capable of sensing a reporter molecule from the external solution.