Conformational switching of G-quadruplexes as a label-free platform for the fluorescence detection of Ag+ and biothiols

Abstract

G-rich DNA sequences could be promoted to form G-quadruplex structures in the presence of a water-soluble fluorogenic dye, thioflavin T (ThT), which is weakly fluorescent in the free state, but exhibits obvious fluorescence enhancement once it binds to G-quadruplex structures with high specificity. We developed a novel approach using G-quadruplex-specific fluorescence enhancement of ThT for the label-free detection of Ag⁺ and biothiols. This approach relies on the coordination of Ag⁺ with guanine, which inhibits the formation of the G-quadruplex structure and delivers a quenched fluorescence signal, and the stronger coordination of biothiols with Ag⁺, which releases Ag⁺ from guanine and restores the G-quadruplex with an activated fluorescence. This “turn-off/on” biosensor may provide a label-free, robust, yet sensitive platform for the detection of Ag⁺ and GSH.