The Tetrahymena telomeric repeat sequence d(TG4T) contains only guanine (G) and thymine (T) bases and has medical and nanotechnological applications because of its ability to self-assemble into stiff tetra-molecular parallel-stranded G-quadruplexes. The hexadeoxynucleotide d(TG4T) was studied using atomic force microscopy (AFM) on the highly oriented pyrolytic graphite surface and differential pulse (DP) voltammetry at a glassy carbon electrode. The d(TG4T) single-strands self-assembled into G-quadruplex structures, very fast in K(+) ions solution and slowly in Na(+) ions containing solution. The G-quadruplex structures were detected in AFM by the adsorption of small spherical aggregates and by DP voltammetry by the G oxidation peak decrease and G-quartets oxidation peak occurrence, in a time and K(+) ions concentration dependent manner. In the presence of Na(+) ions, the d(TG4T) single-strands also slowly self-assembled into higher-order nanostructures, detected by AFM as short nanowires and nanostructured films that were never observed in K(+) ions containing solution.