Potassium-sensitive G-quadruplex DNA for sensitive visible potassium detection.

A novel visual method for K(+) detection is developed utilizing a K(+)-sensitive G-quadruplex DNA named PS5.M as the sensing element. In the absence of K(+), PS5.M is in a random coil state and does not bind hemin. Upon addition of K(+), PS5.M folds into the quadruplex structure stabilized by K(+). Such quadruplex structure is able to bind hemin to form the hemin-G-quadruplex DNAzyme that catalyzes the H(2)O(2)-mediated oxidation of colorless 3,3',5,5'-tetramethylbenzidine to the blue product. Under the optimal conditions, the color change can be clearly observed with the naked eye in the concentration range from 2 to 1000 microM. Through this facile approach, K(+) can be detected down to 2 microM, with high selectivity against other cations. In view of its simplicity, sensitivity and specificity, our developed visual method for K(+) detection would potentially be utilized for bioassays and K(+)-sensitive test paper.