Detection of metal ions (Cu²⁺, Hg²⁺) and cocaine by using ligation DNAzyme machinery

The Cu²⁺-dependent ligation DNAzyme is implemented as a biocatalyst for the colorimetric or chemiluminescence detection of Cu ²⁺ ions, Hg²⁺ ions, or cocaine. These sensing platforms are based on the structural tailoring of the sequence of the Cu ²⁺-dependent ligation DNAzyme for specific analytes. The tethering of a subunit of the hemin/G-quadruplex DNAzyme to the ligation DNAzyme sequence, and the incorporation of an imidazole-functionalized nucleic-acid sequence, which acts as a co-substrate for the ligation DNAzyme that is tethered to the complementary hemin/G-quadruplex subunit. In the presence of different analytes, Cu²⁺ ions, Hg²⁺ ions, or cocaine, the pretailored Cu ²⁺-dependent ligation DNAzyme sequence stimulates the respective ligation process by combining the imidazole-functionalized co-substrate with the ligation DNAzyme sequence. These reactions lead to the self-assembly of stable hemin/G-quadruplex DNAzyme nanostructures that enable the colorimetric analysis of the substrate through the DNAzyme-catalyzed oxidation of 2,2'-azinobis(3- ethylbenzothiazoline-6-sulfonic acid), ABTS^2-, by H₂O ₂ into the colored product ABTS^.-, or the chemiluminescence detection of the substrate through the DNAzyme-catalyzed oxidation of luminol by H₂O₂. The detection limits for the sensing of Cu²⁺ ions, Hg²⁺ ions, and cocaine correspond to 1 nM, 10 nM and 2.5 μM, respectively. These different sensing platforms also reveal impressive selectivities.