An electrochemical impedance biosensor for Hg²⁺ detection based on DNA hydrogel by coupling with DNAzyme-assisted...

In this work, an electrochemical impedance biosensor for high sensitive detection of Hg²⁺ was presented by coupling with Hg²⁺-induced activation of Mg²⁺-specific DNAzyme (Mg²⁺-DNAzyme) for target cycling and hybridization chain reaction (HCR) assembled DNA hydrogel for signal amplification. Firstly, we synthesized two different copolymer chains P1 and P2 by modifying hairpin DNA H3 and H4 with acrylamide polymer, respectively. Subsequently, Hg²⁺ was served as trigger to activate the Mg²⁺-DNAzyme for selectively cleavage ribonucleobase-modified substrate in the presence of Mg²⁺. The partial substrate strand could dissociate from DNAzyme structure, and hybridize with capture probe H1 to expose its concealed sequence for further hybridization. With the help of the exposed sequence, the HCR between hairpin DNA H3 and H4 in P1 and P2 was initiated, and assembled a layer of DNA cross-linked hydrogel on the electrode surface. The formed non-conductive DNA hydrogel film could greatly hinder the interfacial electronic transfer which provided a possibility for us to construct a high sensitive impedance biosensor for Hg²⁺ detection. Under the optimal conditions, the impedance biosensor showed an excellent sensitivity and selectivity toward Hg²⁺ in a concentration range of 0.1pM - 10nM with a detection limit of 0.042pM Moreover, the real sample analysis reveal that the proposed biosensor is capable of discriminating Hg²⁺ ions in reliable and quantitative manners, indicating this method has a promising potential for preliminary application in routine tests.