A fluorescence turn-on detection of copper(II) based on the template-dependent click ligation of oligonucleotides

• A copper(II) detection method with good sensitivity and selectivity.
• The click reaction could be monitored in a real-time fashion.
• A molecular beacon was used as the template.
• A fluorescence turn-on strategy reduces the possibility of false positive signals.

In this work, a fluorescence turn-on method for copper(II) detection is reported. A molecular beacon (MB) was designed as a template. Cu2+ was reduced to Cu+ in the presence of a reductant (ascorbic acid). Two short single-stranded oligonucleotides one was labeled with a 5′-alkyne and the other with 3′-azide group, proceeded a template-dependent chemical ligation through the Cu(I)-catalyzed azide-alkyne cycloaddition. The newly generated click-ligated long chain oligonucleotide, which was complementary to the MB, opened the MB hairpin structure and resulted in a turn on fluorescence. The increase in fluorescence intensity is directly proportional to the amount of Cu2+ added to the assay solution. The present assay is quite sensitive and allows the detection of 2 nM Cu2+. The described assay also exhibits high selectivity over other metal ions.

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