Microstructuring of solid-supported lipid layers using SAM pattern generation by scanning electrochemical microscopy and the chemical lens.
To prepare patterns of adsorption sites for alkanethiols with high lateral resolution, we used the scanning electrochemical microscopy (SECM) to etch masks into uniform layers of nickel coated on gold surfaces. The patterning of the nickel mask was accomplished in aqueous solutions by electrogenerating nitric acid out of nitrite at an ultramicroelectrode. Due to the sluggish kinetics of nickel etching in acidic media, the pattern generated by a 10-microm tip was about 50-microm wide, depending on the duration of the etching. As an alternative, applying the principle of the chemical lens by adding potassium hydroxide as a scavenger, the size of the adsorption sites had been reduced to 4 microm, independent of the duration of etching. In a follow-up step, monolayers of 11-mercaptoundecanoic acid were formed on the exposed gold areas of the surface by self-assembly. Fluorescent liposomes containing tetramethylrhodamine-labeled phospholipids were used to create solid-supported lipid layers (SSLLs). These fluorescent liposomes showed a selective binding affinity to the self-assembled monolayers (SAMs) modified areas, but not to the nickel surface. The patterns generated were imaged by the SECM itself, as well as by optical and fluorescence microscopy.