Influence of tunable external stimuli on the self-assembly of guanosine supramolecular nanostructures studied by atomic force microscope.

The self-assembly of guanosine (G) molecules on solid surfaces is investigated by tapping-mode atomic force microscopy (AFM) upon controlling and introducing external factors (stimuli) to the G stock solution such as incubation time, presence/absence of metal cations, and mechanical shaking. Surprisingly, at different stages of incubation time at room temperature and in the absence of any metal cations in the G stock solution, which are known to be one of the governing factors in forming G-nanostructures, two assembly pathways resulting into two distinct supramolecular nanostructures were revealed. Astonishingly, by introducing a mechanical shaking of the tube containing the G stock solution, one-dimensional (1D) wires of G molecules are observed by AFM, and very interestingly, novel "branched" supramolecular nanostructures are formed. We have also observed that the later branched G nanostructures can grow further into a two-dimensional (2D) thin film by increasing the incubation time of the G stock solution at room temperature after it is exposed to the external mechanical stimuli. The self-assembled nanostructures of G molecules are changed significantly by tuning the assembly conditions, which show that it is indeed possible to grow complex 2D nanostructures from simple nucleoside molecules.