The tendency of poly-G oligonucleotides to undergo self-assembly into helical nucleic acid tetramers have been termed G-quartets. Also known as G-wires, these structures retain their crystallographic determined dimensions better than duplex DNA when imaged with the atomic force microscope (AFM). Relative humidity has been known to affect both the resolution and measured height DNA strands on mica. The results below aim to develop a model that can be used to define the mechanical properties of G-wires by scanning probe microscopy investigations. G-wires were examined under a wide range of relative humidity to determine their tolerance to shear forces under the AFM, and to establish imaging conditions for hydration scanning tunneling microscopy (HSTM).

The relative humidity dependence of G-wires were taken with 125 μm long, 20 μm wide silicon nitride cantilevers in contact AFM mode (spring constant ∼ 0.4 N/m) (Fig. 1).