This manuscript describes the result of a series of electrochemical, spectroscopic and thermodynamic studies into oligonucleotide hairpin structures equipped with T-T mispairs and investigates their interaction with Hg(II). For this purpose, three hairpin DNAs were designed, in which the stem-region remains constant and loop region contains increasing T-T mispairs (5'-Ho-(CH2)(6)-S-S-(CH2)(6)TGTAGITCCTTCTACA-3', 5'-HO-(CH2)(6)-S-S-(CH2)(6)-TGTAGTTTTCCTTTTCTACA-3'; 5'-HO-(CH2)(6)-S-S(CH2)(6)-TGTAGTTTTTTCTACA-3'). Various techniques such as electrochemical impedance spectroscopy (EIS), circular dichroism (CD), UV-visible and isothermal titration calorimetry (ITC) were employed to get a systematic evaluation of the need for multiple T-T mispairs for enhanced Hg(II) binding. EIS shows an increase in charge transfer resistance (Delta R-CT) due to structural changes within the thin film caused by Hg(II) binding. The CD studies indicate the Hg(11) induced changes in CD signals of hairpin DNAs from right-handed to left handed structures. Highest cooperative binding was observed with DNA having maximum T-T mispairs which was supplemented by detailed UV-visible thermal analysis of DNA-Hg(II) structures. These findings were further supported by detailed measurements of the thermochemistry of the interaction by ITC. Our studies show that the number of T-T mispairs are critical for maximizing nucleobase-Hg(II) interactions. (C) 2017 Elsevier Ltd. All rights reserved.