A Pb2+-driven DNA molecular device which is constructed based on a DNA duplex quadruplex exchange is utilized for the highly selective and sensitive detection of Pb2+. The power of this DNA device originates from the excellent efficiency of Pb2+ for stabilizing G-quadruplexes, which makes the DNA duplex unwind thereby driving the device. This device can be reset to the original state by addition of a strong Pb2+ chelator DOTA, endowing the device with good reusability. In the whole process, the signal readout is modulated via a fluorescent probe binding to and being released from the G-quadruplex. Such a DNA device can serve as a novel turn-on fluorescent sensor for Pb2+ detection with high selectivity and sensitivity.