Colorimetric Detection of Copper Ion Based on Click Chemistry

Two colorimetric assays, lateral flow biosensor (LFB) and hemin/G-Quadruplex DNAzyme-based colorimetric assay, were developed for the detection of copper ion based on click chemistry. Two single-strand DNA (ssDNA) with azide- and alkyne- modified at 3′ and 5′ separately can be linked by the Cu + -catalyzed click chemistry. For hemin/G-Quadruplex DNAzyme-based assay, the two ssDNA fragments linked by Cu + catalyzed click chemistry could form a complete G-rich sequence that severed as a horse- radish peroxidase. In the presence of hemin and K + , the colorless substrate tetramethyl benzidine (TMB) is catalyzed into a colored product by the G-rich sequence. The con- centration of Cu 2+ can then be quantitatively analyzed by measuring the color density. For the LFB assay, the two ligated ssDNA fragments could form a sandwich complex between an ssDNA fragment immobilized on gold nanoparticles and another ssDNA fragment on test zone of a biosensor, respectively. The biosensor enables visual detection of copper ion with excellent specificity. In comparison with conventional methods, the present assays are simpler to operate and more cost-effective to use, and so have great potential in point-of-care diagnosis and environmental monitoring.