Generation of Nanostructures of Mica Supported Lysozyme and Lysozyme-Nanogold Conjugates by Diving Tip Nanowriting

Nanostructures of lysozyme molecules and lysozyme-nanogold conjugates were generated by atomic force microscopy in contact-, tapping- and force-distance-mode on mica in aqueous solution. In contact mode at high ionic strength, adjusted lysozyme concentration and lower loading force a monolayer of defined structure and orientation of lysozyme can be formed by the scan process of the tip. A lateral resolution of the monolayer of about 80 nm could be achieved. At larger loading forces besides a lysozyme monolayer also 3D-aggregates could be generated in parallel. In force-distance mode the volume of 3D-aggregates was studied as function of lysozyme concentration, loading force and number or frequency of up- and down-movement of the tip. Also in tapping mode 3D-aggregates were generated at the selected incubation conditions. Application of the linescan mode for solutions of nanogold or lysozyme-nanogold conjugates allowed the formation of monolayers of linear shape with lateral resolution of about 35 nm on mica. Nanogold line-structures could be connected to macroscopic gold contacts. It is postulated that adjustment of electrostatic interaction between lysozyme and substrate and the applied loading force is critical for monolayer formation. Different to the underlying mechanism of the well-established dip-pen nanolithography (DPN) (Piner et al., 1999) for the presented method of diving tip nanowriting (DTN) adsorption of the molecules from the aqueous bulk phase to the tip and thereafter the flow to the mica surface is discussed. DTN could be used to either contact proteins electrically or to form preaggregates for protein crystallization (Wiechmann et al., 2000)