The validity of GO-based DNA biosensor for the amplification detection of target ATP: fluorescence spectrum of (a) GO-based DNA biosensor system consisting of target, polymerase and nicking enzyme in the absence of CPDNA; (b) GO-based DNA biosensor system consisting of CPDNA, polymerase and nicking enzyme in the absence of target; (c) GO-based DNA biosensor system consisting of target, CPDNA, nicking enzyme in the absence of polymerase; (d) same as (c), but it contains polymerase instead of nicking enzyme; (e) only contain GO-based DNA biosensor system; and (f) same as (b), but in the presence of target. The concentration of target ATP involved is 500 μM.