Study of DNA immobilization on mica surface by atomic force microscopy

Abstract

Since its discovery, atomic force microscopy (AFM) is widely used to study biological objects and materials, including cells, proteins, and nucleic acids. AFM measurements are carried out in the air as well as in liquid with a very high resolution, even more complex bioprocesses can be monitored in situ under physiological conditions. Successful imaging of DNA molecules on the flat supporting surface typically requires appropriate treatment of mica. The original surface charge of mica is the same as of DNA, i.e. negative. Accordingly, immobilization using bivalent cations (Mg²⁺, Ni²⁺, and Co²⁺), deposition of ethanolamine, and mica surface silanization with alkoxysiloxane derivatives were reported to achieve an optimal concentration and surface arrangement of DNA molecules. Vapours of alkoxysiloxane derivatives led to uniform negatively charged mica surface and it was found that higher ionic radius causes a weaker bond. A better quality and sharper images of DNA molecules were achieved by adjusting the correct real amplitude of the cantilever. This amplitude should correspond with the expected size of the target objects—DNA molecules in the x–y plane of the image. The length of the observed DNA molecules was 1000 bp and the planar width of DNA was 7.8 nm (in reality 3 nm). The AFM spectroscopic mode was particularly useful.

Graphical abstract