Fluorescence Detection of Potassium Ion Using the G-Quadruplex Structure

Oligonucleotides with sequences of human telomere DNA or thrombin binding aptamer (TBA) are known to form tetraplex structures upon binding the K(+) ion. Structural changes associated with the formation of tetraplex assemblies led to the development of potassium-sensing oligonucleotide (PSO) probes, in which two fluorescent dyes were attached to both termini of particular oligonucleotide. The combination of dyes included fluorescence resonance energy transfer (FRET) and excimer emission approaches, and the structural changes upon binding K(+) ion could be monitored by a fluorescence technique. These systems showed a very high preference for K(+) over Na(+) ion, which was suitable for fluorescence imaging of the potassium concentration gradient in a living cell. In the case of human telomere DNA, it was also possible to follow the polymorphism of its tetraplex structures.