Interactions of Hg(ii) with oligonucleotides having thymine-thymine mispairs. Optimization of an impedimetric Hg(ii) sensor.

The present work describes the effect of the number of thymine-thymine mispairs in single strand DNA probes on Hg(ii) interactions and further to develop a highly sensitive DNA based impedimetric sensor for Hg(ii) detection. To achieve this goal, the influence of the number of T-T mispairs on the signal response prompted by DNA-Hg(ii) binding interactions was examined on three designed DNA probes: 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCACACGTTCCTTACGC-3', 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCACATTTTCCTTTTGC-3', 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCATTTTTTCCTTTTTT-3' having 2T-T, 4T-T and 6T-T mispairs with identical length, respectively. This study revealed that the number of T-T mispairs plays a critical role in maximizing the signal intensity of DNA-Hg(ii) binding interactions. Based on these results, DNA comprising maximum number of T-T mispairs was further utilized for construction of the Hg(ii) sensor, which exhibited a linear correlation between the change in charge transfer resistance (ΔRCT) and the concentration of Hg(ii) over the range of 1.0 × 10-5 M to 1.0 × 10-10 M with a lower detection limit of 3.2 × 10-11 M. The selectivity was tested against 12 different metal ions including Hg(ii). The ΔRCT response from Hg(ii) is 3 times higher than the nearest competitor Pb(ii) and approximately 10 times than other ions. The potential application of such a robust and label-free DNA sensor was demonstrated by analyzing environmental samples collected from Lake Ontario.