We report a highly sensitive and selective strategy for Cd(II) assay using a singly labeled multifunctional probe consisting of a Cd(II)-specific aptamer (CAP), which acted as a recognition element for Cd(II) and a signal reporter. The presence of Cd(II) can induce the conformational switching of the CAP, accompanied by a change in fluorescence intensity. Thereby, a fluorescence strategy for Cd(II) assay was established. The proposed method has a detection limit of 2.15 nM, which is much lower than the detection limits reported in related literature. This strategy involves only an aptamer probe, and the use of such a G4-based quencher avoids the dual labeling of the CAP with fluorophore/quencher units. It is obviously more convenient and economical than the other aptamer-based biosensors for Cd(II) detection. The mechanism by which Cd(II) induces the CAP to change from a random coil sequence to a stem-loop structure was studied in a series of control experiments. This strategy would be helpful in the design of a sensitive analytical platform for various target assays in environmental and biomedical fields. Graphical Abstract The presence of Cd2+ leads to the conformational change of CAP from a random coil sequence to a stem-loop structure, resulting in a quenching in the fluorescence.
Keywords: Cadmium(II); Conformational switching; Fluorescence strategy; Mechanism certification; Multifunctional aptamer probe; Stem-loop structure.