Ag+ and cysteine detection by Ag+-guanine interaction based on graphene oxide and G-quadruplex DNA

Sensitive and selective techniques for both Ag+ and Cys detection have been designed based on graphene oxide (GO) and G-quadruplex DNA. The G-quadruplex structure can capture the fluorescent molecule acridine orange (AO) from the surface of graphene oxide (GO), which will recover the fluorescence of AO that was initially quenched by GO. Then the addition of Ag+ will release AO back to GO, because Ag+ can destroy the G-quadruplex structure, giving a fluorescence quenching process again. Based on this "turn off" principle, a highly sensitive and selective Ag+ detection method was developed. In addition, cysteine (Cys) can capture Ag+ from the guanine base of DNA which will result in the regeneration of the G-quadruplex DNA structure and thus the regeneration of the fluorescence signal. This "turn on" principle can be used for the development of a highly selective and sensitive detection method for Cys.