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 H2O2-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 mM. Through this facile approach, K+ can be detected down to 2 mu M, 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.