In this study, a simple paper-based aptasensor has been developed for the ultrasensitive detection of lead -Pb2+- ion within about 10 min. The aptasensor has been successfully designed by taking advantages of the Förster Resonance Energy Transfer -FRET- process and the super fluorescence quenching property of graphene oxide -GO- sheet. The sensing mechanism of the aptasensor is based on the conformational switch of the Pb2+-specific aptamer from a random coil to a G-quadruplex structure. An injection of Pb2+ on the paper-based platform induces the release of the specific aptamer from the GO surface that recovers the fluorescence emission. Under the optimal experimental conditions, there is a good linear relationship between the fluorescence recovery and the Pb2+concentration in the ranges of 5–70 pM and 0.07–20nM. Moreover, the aptasensing array exhibits a high sensitivity to Pb2+ with an ultra-low detection limit of 0.5 pM. The developed aptasensor has been successfully applied to determine Pb2+ in tap water, lake water, milk, and human blood serum. The paper-based aptasensor can be efficiently utilized to detect other metal ions and biological molecules by substituting target specific aptamer

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