Dandelion-like CuO microspheres decorated with Au nanoparticle modified biosensor for Hg detection using a T-Hg-T triggered hybridization chain reaction amplification strategy.

We fabricate a novel electrochemical biosensor based on the specific thymine-Hg-thymine (T-Hg-T) base pair for the highly sensitive detection of mercury ions (Hg) and utilize toluidine blue (TB) as a redox indicator that is combined with a hybridization chain reaction (HCR) for signal amplification. The dandelion-like CuO (D-CuO) microspheres that were assembled using Au nanoparticles were first introduced as support materials, which produced more active sites for the thiolated probe (P1) combination. Then, the presence of Hg induced P1 to hybridize with the other oligonucleotide (P2) through Hg-mediated T-Hg-T complexes. In addition, the partial sequence of P2 acted as an initiator sequence, which led the two hairpin DNA (H1 and H2) strands to collectively form the extended double-strand DNA through the HCR process on the electrode surface. TB was employed to interact with the double strands and produce an efficient electrochemical signal. The proposed strategy combined the amplification of the HCR and the inherent redox activity of TB and utilized D-CuO/Au composites, which exhibited high sensitivity for Hg determination. Under the optimum conditions, the proposed biosensor showed a prominent response for Hg, including a linear range from 1 pM to 100 nM and a detection limit of 0.2 pM (S/N = 3). Moreover, the new biosensor proved its potential application for trace Hg determination in environmental water samples.