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 theGstock 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 Gnanostructures 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 Gmolecules are changed significantly by tuning the assembly conditions, which show that it is indeed possible to grow complex 2D nanostructures from simple nucleoside molecules.