A highly sensitive and selective fluorescent probe without quencher for detection of Pb2+ ions based on aggregation-caused quenching phenomenon

Lead is a highly toxic heavy metal, and various functional nucleic acid (FNA)-based biosensors have been developed for the detection of Pb2+ in environmental monitoring. However, most fluorescence biosensors that have been reported were designed on the basis of a double-labeled (fluorophore and quencher group) DNA sequence, which not only involved an inconvenient organic synthesis but also restricted their wider use in practical applications. Here, we utilized a G-rich DNA sequence as a recognition probe and conjugated fluorene (CF) to develop a fluorescence sensor without a quencher based on the aggregation-caused quenching (ACQ) effect. In the presence of Pb2+, the degree of aggregation of CF was reduced because Pb2+ induced the formation of a G-quadruplex structure of the CF-DNA probe, and the fluorescence signal increased with the concentration of Pb2+ (0-1 M), with a limit of detection of 0.36 nM. This fluorescent probe without a quencher enables the sensitive and selective detection of Pb2+. On the basis of these advantages, the CF-DNA probe represents a promising analytical method for detecting Pb2+.