DNAzyme-based biosensor for Cu2+ ion by combining hybridization chain reaction with fluorescence resonance energy transfer technique

A novel signal amplification strategy based on Cu 2+ -dependent DNAzyme was developed for sensing Cu 2+ ion by combining hybridization chain reaction (HCR) with fluorescence resonance energy transfer (FRET) technique. In the presence of Cu 2+ ion, the substrate strands of Cu 2+ -dependent DNAzyme immobilized on magnetic beads were specifically cleaved and released. The released strands initiated the HCR process of hairpin H1 and H2 labeled with FAM as the donor and TAMRA as the acceptor, respectively. Long nicked dsDNA structures were self-assembled to bring the donor and the acceptor in close proximity, resulting in a FRET process. The relative ratio of fluorescent intensities of the acceptor and donor was used to quantitatively detect Cu 2+ ion with a limit of detection of 0.5   nmol   L −1 . This proposed biosensor was applied to detect Cu 2+ ion in tap water with satisfactory results.