DNAzyme self-assembled gold nanorods-based FRET or polarization assay for ultrasensitive and selective detection of copper(II) ion

• An ultrasensitive method for the detection of Cu2+ has been developed.
• The FRET or fluorescence polarization between gold nanorods (AuNRs) and the 3'-TAMRA-labeled substrate strand of DNAzyme was used as signal readout.
• The method is a novel, ultrasensitive and rapid tool for sensitive and selective detection of Cu2+.

In the paper, we have constructed a very simple, sensitive and promising assay for fluorescence biosensor detection of Cu2+ in aqueous solutions based on FRET between gold nanorods (AuNRs) and the 3'-TAMRA-labeled substrate strand (Sub) of DNAzyme. The fluorescence of the Sub is quenched when the substrate strand-DNAzyme strand (Sub-Enz) duplex is adsorbed on AuNRs surface through electrostatic interaction. In the presence of Cu2+, the fluorescence is restored due to the decrease of FRET efficiency caused by the specific cleavage of the Sub by the DNAzyme (Enz), which weakens the electrostatic interaction between the AuNRs and short 3'-TAMRA-labeled DNA fragment. This method shows a high sensitivity for Cu2+ with a detection limit of 9.83 pM (S/N=3) and a linear range from 0.016 nM to 40 nM. At the same time, Cu2+ can be detected sensitively based on the significantly decreased Fluorescent polarization (FP). The detection limit of 8.40 pM is experimentally achieved for Cu2+.