A sensitive biosensor for mercury ions detection based on hairpin hindrance by thymine-Hg(II)-thymine structure

The exploitation of a dual-signal amplificatory electrochemical DNA biosensor was provided in this article, which can be used to detect Hg(II). One of the signal amplification units is nanocomposite modified electrode and the other is DNA-functionalized Au nanoparticle (DFNP), which include two types of DNA - a hairpin probe DNA with biotin at the 3′ terminal and thiol at the 5′ terminal, and a linear signal DNA with methylene blue (MB)-labeled. Because of the Hg(II) mediated thymine-Hg(II)-thymine (T-Hg(II)-T) structure, when Hg(II) appears, the T-Hg(II)-T that existed between the probe DNA (PD) and helper DNA (HD) can open the hairpin structure of PD and make biotin to be capable of being recognized by avidin, which results in DFNP being brought onto an electrode surface. However, without Hg(II), the distinction between biotin and avidin would not be found. Under optimum conditions, the resultant biosensor brought out a high sensitivity and selectivity for the determination of Hg(II). It has wide linearity from 0.35 pM to 3500 pM (R = 0.9981), and the lower limit of detection is 0.21 pM (S/N = 3). Moreover, the proposed biosensor has been used to its advantage in the test of Hg(II), which was carried out in an environmental water specimen with satisfactory results.