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pBS+ plasmid deoxyribonucleic acid (DNA) was imaged by scanning tunneling microscopy (STM) after mounting microdroplets by aerosol deposition onto heated epitaxial gold surfaces. However, the instability of the adsorbate to forces exerted by the tunneling tip points out the need for more aggressive bonding of molecules to surfaces. We describe a sensitive assay for the qualitative and quantitative evaluation of chemical agents to influence binding of DNA to surfaces using 32P-labeled pBS+ plasmid DNA. We propose that such an assay can make an important contribution to immobilization techniques prior to STM imaging.

We have investigated electrostatic spraying of DNA onto gold surfaces as an alternative sample-preparation technique for STM studies. Preliminary results show that a higher distribution of isolated strands as well as well ordered aggregates can be obtained with this technique when compared with electrodeposition or drop evaporation. In many places, the well ordered aggregates were found to cleave in a direction perpendicular to their length after repeated scanning in the same direction.