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

• A signal amplification strategy was developed for Cu2+ by combining HCR with FRET.
• Cu2+-dependent DNAzyme enhanced the specificity of the biosensor for Cu2+ ion.
• The cleaved substrate strands were used as the initiator for HCR.
• Ratiometric measurement was used to detect Cu2+ ion with a LOD of 0.5 nmol L-1. .

A novel signal amplification strategy based on Cu2+-dependent DNAzyme was developed for sensing Cu2+ ion by combining hybridization chain reaction (HCR) with fluorescence resonance energy transfer (FRET) technique. In the presence of Cu2+ ion, the substrate strands of Cu2+-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 Cu2+ ion with a limit of detection of 0.5 nmol L−1. This proposed biosensor was applied to detect Cu2+ ion in tap water with satisfactory results.

Cu2+-dependent DNAzyme was immobilized on the magnetic beads via the biotin-streptavidin interaction. At the presence of target Cu2+ ion, the substrate strand was irreversibly cleaved at the cleavage site (the guanine base). The cleaved substrate strand as the initiator triggered the HCR process to form the nicked double-helix structure. In this state, FAM and TAMRA were brought into close proximity, resulting in the occurrence of FRET. By means of ratiometric measurement, Cu2+ ion could be quantitatively detected.Figure optionsDownload as PowerPoint slide